The Harmonies of Spacetime — GW150914

by Shane L. Larson

I have a good friend, Tyson, whom I don’t get to see nearly often enough. We are both privileged to be among the first generation of scientists who will know the Universe by observing the faint whisper of spacetime, bending under the influence of massive astrophysical systems. We are “gravitational wave astronomers.”

Picking crab with Tyson (far right) and family. [Image: Sabrina Savage]

Picking crab with Tyson (far right) and family. [Image: Sabrina Savage]

A while back we were sitting on his back porch late into the evening, picking crab and talking about everything. It was the kind of common, easy conversation among friends that ranges over movies, politics, family, childhood memories, inside jokes, and so on. But at one point, the conversation drifted back to science and to the near future. Tyson said something that really just kind of made us all stop in shocked silence: “If we’re really going to detect gravitational waves in the next 3 or 4 years, they are already closer than Alpha Centauri and heading right for us.”


Little did we know then how prescient that observation was. We are both part of a project called LIGO — the Laser Interferometer Gravitational-wave Observatory. And this morning our collaboration made the big announcement.

Frame from a visualization of the binary black hole merger seen by LIGO [Visualization by "Simulating Extreme Spacetime" (SXS) Collaboratoin]

Frame from a visualization of the binary black hole merger seen by LIGO [Visualization by “Simulating Extreme Spacetime” (SXS) Collaboration]

On 14 September 2015, the two LIGO observatories detected a very loud gravitational wave event. Our analysis since that day has told us that it was the merger of two black holes — one 29 times the mass of the Sun, the other 36 times the mass of the Sun. The two black holes merged, forming a new, bigger black hole 62 times the mass of the Sun. We named the event after the date: GW150914.

All of this happened about 400 Megaparsecs from Earth (1.3 billion lightyears). If you are adding up the numbers, you see that there are 3 solar masses missing. That is the equivalent mass that was radiating away from the system in the energy of the gravitational waves.

Make no doubt about it — this is one of the most momentous discoveries in the history of astronomy. It will be up to historians of science to place this within context, but I would rank it right up there with the discovery of the nature of the spiral nebulae and the discovery of the Cosmic Microwave Background.

There are many important and stunning parts of this story. Let’s me tell you just a small slice of how we got to today.

LIGO: LIGO is two gravitational wave observatories that work together as a single experiment. The are located 3002 kilometers apart, with one in Hanford, Washington and the other in Livingston, Louisiana. They are enormous, 4 kilometers to a side — so large, they can be seen in satellite photos.

(L) Aerial view of LIGO-Hanford Observatory [top] and in Google Maps [Bottom]. (R) Aerial view of LIGO-Livingston Observatory [top] and in Google Maps [Bottom].

(L) Aerial view of LIGO-Hanford Observatory [top] and in Google Maps [Bottom]. (R) Aerial view of LIGO-Livingston Observatory [top] and in Google Maps [Bottom].

The observatories are “laser interferometers” — laser light is injected into the the detector, and split so it flies up and down each of the two arms. When the light returns back to the splitter, it is recombined. When you combine laser light in this way, it can be combined such that the beams cancel out (making what we call a “dark fringe”) or they combine to make a bright spot (making what we call a “bright fringe”); in between combinations have a full range between bright and dark. We sit on a “dark fringe.”

Schematic of the LIGO interferometers, showing the basic layout of the lasers and optics locations. [Image: S. Larson & LIGO Collaboration]

Schematic of the LIGO interferometers, showing the basic layout of the lasers and optics locations. The lasers travel up and down the two 4 kilometer long arms, and are recombined and detected at the photodetector. [Image: S. Larson & LIGO Collaboration]

When a gravitational wave hits LIGO, it stretches and compresses the arms. The result is that it changes how long it takes the lasers to travel from the splitter to the end mirror and back. If that happens, when the lasers are recombined the brightness of the fringe changes.

What Happened? Both the LIGO detectors run more or less continuously, and we get our primary science data when they are on at the same time. In the early morning hours of 14 September 2015, at 4:50:45am Central Daylight Time, a signal was detected in the Livingston detector. 7 milliseconds later, a signal was also detected in the Hanford detector. These detections are sensed automatically by sophisticated software that looks for things that are “out of the ordinary.” Notable events are logged, and then humans can take a look at them. In this case, we knew almost immediately it was significant because it was in BOTH detectors, and it was a strong signal (we use words like “loud” and “bright” to mean strong, but we don’t really “hear” or “see” the signals in the usual sense; these are descriptive adjectives that are helpful because of the analogy they make with our normal senses).

Spectrograms of the event at Hanford and Livingston. The darker areas are what a "typical" spectrogram might look like; the bright swoops are the (very noticeable) signal! [Image: LIGO Collaboration]

Spectrograms of the event at Hanford and Livingston. The darker areas are what a “typical” spectrogram might look like; the bright swoops are the (very noticeable) signal! [Image: LIGO Collaboration]

One of the easiest ways to see the signal is in a diagram called a “spectrogram” which shows how the signal in the detector changes in time. Once we had the first spectrograms, the emails began to fly.

Finding Out: We all get LOTS of email, so it took a while before everyone in the collaboration actually realized what was going on. I didn’t hear until the night of September 15. AT 9:35pm CST I got an email from Vicky Kalogera, the leader of our group, that said “have you caught any of what’s going on within LIGO?” We had a round of email with unbearably long delays between them, but by 11:35pm, I had our initial understanding/guesses in my hands. That was enough to do what we all do in science — we make some calculations and extrapolations to understand what we have seen, and to plan what we should do next. We want to figure out what the new result might mean! Here’s the page out of my Moleskine, where I started to compute what a detector in space, like LISA, might be able to see from a source like this.

My journal page from the hour after I first found out about the event. [Image: S. Larson]

My journal page from the hour after I first found out about the event. [Image: S. Larson]

The Importance: There are all kinds of reasons why this discovery is important. If you take your favorite gravitational physicist out for pizza, they’ll talk your ear off for hours about exactly why this is important. But let me tell you the two I think the most about.

First, this is the first direct detection of gravitational waves. It is the first time we have built an experiment (LIGO) and that experiment has responded because a gravitational wave passed through it. This is the beginning of gravitational wave astronomy — the study of the Cosmos using gravity, not light.

Second, this is the first time that we have directly detected black holes, not observed their effects on other objects in the Universe (stars or gas).

The Astrophysics: The two black holes, caught in a mutual gravitational embrace, had spent perhaps a million years slowing sliding ever closer together, a long and lonely inspiral that ended with their merger into a single, bigger black hole. This is the first time we know conclusively of the existence of black holes that are tens of solar masses in size. Such black holes have been predicted in theoretical calculations, but never seen in the Cosmos before.

A more technical simulation of the binary black hole merger; gravitational physicsists and astronomers will be comparing the data to their simulations to examine how well we understand "real" black holes. [Image: SXS Collaboration]

A more technical simulation of the binary black hole merger; gravitational physicsists and astronomers will be comparing the data to their simulations to examine how well we understand “real” black holes. [Image: SXS Collaboration]

Our next big question is “how often does this happen?” If it happens a lot, that is a potential clue pointing to where such black holes come from. If it is a rare event, that also tells us something. So now, we wait — this is just the beginning of LIGO observations, and after a few years of listening for more, we’ll know how common these are.

The People: Science is a way of thinking about the Universe, and so often when we talk about science we talk about Nature — all the wonder, all the mystery, the rules of the Cosmos. But science is a uniquely human endeavour and every momentous discovery is the culmination of countless hours of sweat, uncountable failures, and equally uncountable tiny moments of success that culminate at a profound moment of knowing something new. It would not be possible without the dedication of enormous numbers of people. The world gravitational wave community has been working toward this day for decades. More than 1000 authors appear on the discovery paper, and there are thousands of others who have worked and are working on the project, who are not in that list of authors. It has been a heroic effort on the part of physicists, astronomers, optical engineers, data and computer scientists, technical and support staff, professors and students.

Just some of the thousands of people who have made LIGO a reality and the detection of GW150914 possible. [Images from the LIGO Collaboration]

Just some of the thousands of people who have made LIGO a reality and the detection of GW150914 possible. [Images from the LIGO Collaboration]

Teasing out the secrets of Nature is hard. Since before recorded history began, our distant ancestors  have plumbed the mysteries of the Cosmos using tools that Nature gave us — our five senses. Astronomer Edwin Hubble once opined “Equipped with his five senses, man [sic] explores the universe around him and calls the adventure Science.” (Harper’s Magazine 158: 737 [May, 1929]).

Today, we add a new sense to our quest to understand the Cosmos. TODAY the Era of Gravitational Wave Astronomy opens. Within the next few years, we will no longer live in a world where our view of the Cosmos is limited to what light alone can tell us. TODAY, we see the Cosmos anew, with senses attuned to the fabric of space and time itself!


I’ve written about gravitational waves here at WriteScience before. In many of those I’ve explored what the physical description and meaning of gravitational waves are, and what the endeavour to detect them is all about. If you’d like to take a stroll down memory lane, here are links to those old posts:

Many of my colleagues in LIGO are also blogging about this momentous discovery. I will add their links here as they appear, so you can read their accounts as well:


The Red Sands of Mars

by Shane L. Larson


My grandfather and me, when I was in middle school.

I had the good fortune of knowing all my grandparents. My maternal grandfather, Robert Steele Kelher, Sr., was a chemist. I have vivid memories of spending time with him when I was young, but I don’t recall much of what we talked about. Now that I’m all grown up and a physicist, I often wish I could chat science with him. But one conversation I do remember vividly, was about Ford Thunderbirds. My grandfather once told me he had always dreamed of owning a Thunderbird. But in those later days of his life, when we would walk around the backyard together just chatting, he said he was glad he never got one; he was sure it would never have been as great as he imagined. He preferred the simple joy of savoring the idea of owning a Thunderbird.

I stumble across this memory now and then, and think about my own longings. This week, I am reminded that I often dream of Mars. I imagine an alternate reality where I get up in the morning and don a spacesuit instead of Levi’s, and walk the cold red deserts looking for clues to where we came from, clues to how Mars has changed over the aeons, and clues to what its future fate may be. But interspersed with those idle scientific longings and ponderings of an “other career” are daydreams about living and playing on Mars. What I wouldn’t give to spend a week, camping on Mars near the abandoned hulk of Spirit, once our faithful emissary on the Red Planet. Spirit was one of two Mars Exploration Rovers that landed on Mars in 2004, the ’57 Thunderbirds of their time. It spent a more than 2000 days roving across Mars, covering a total of 7.7 kilometers. Sprit has a twin, called Opportunity that is still roving, and this week we celebrated its 12th birthday on Mars.


I often dream of camping on Mars, maybe next to the Spirit rover.

I’m not yet as old as my grandfather was when we talked about Thunderbirds, but as I get older, I’m beginning to think that my future will forever be confined to the surface of the Earth. My wonderful daughter fears that she is preventing me from becoming an astronaut (an idea she is firmly against, especially after seeing “The Martian”). She has repeatedly seen us throw space probes and rovers at Mars, but she doesn’t have the perspective to know that while sending humans into space is possible, it is not easy.

Despite my fear that I was born a bit too early to be part of the generations that live and work in space, I feel fortunate that I have lived through the first age of Mars exploration. I’ve been witness to the years when our species obtained its first up close views of the red sands of Mars, and found the landscapes to be not as alien as we might have expected. Pick up any picture, any panorama from Mars and take a good look. Looking across the rubble strewn plains, across the shifting dunes of sand toward soaring mountains rising in the distance, you could easily believe you are looking at a picture of the American Southwest.


The “Rocknest Panorama” taken by the Curiosity rover in 2012. It does not look unlike places you might find on Earth. [Image: NASA, PIA16453]

But this is not Earth. This world is Mars. It does look like Earth, in many ways, and that is part of the reason it captures our imagination. Like people, every world is unique — they have their own individual characters, their own long histories, their own destinies to fulfill in the Cosmos.  But also like people, they are similar as well — the laws of Nature that govern the Earth govern Mars. We can take what we know about Earth, and what we don’t know, and use it to learn about Mars.  Mars has its own remarkable moons, atmosphere, climate, and orbit; it has a long history of physical processes that shaped the evolution of its surface. Understanding the similarities and differences between Mars and Earth is one part of the long quest to understand our own planetary home.  Understanding the similarities and differences is one of the principle reasons we send our robotic emissaries to other worlds.


The Hubble Space Telescope view of Mars, centered on the dark plain known as Syrtis Major [Image: Hubble Space Telescope]

Why does Mars fascinate us so? More than any other world (except perhaps the Moon), Mars has captured the imagination of humans.  It is the only planet whose surface can be studied telescopically, and even from Earth there are tantalizing views of a dynamic and changing world.  The polar ice caps grow and receed with the seasons, visible even in a small backyard telescope. The vast dark plain of Syrtis Major darkens and fades with the Martian seasons. The planet clearly rotates when viewed from afar, and every so often, globe girdling dust storms blanket the planet, a doleful display that other worlds have dramatic weather patterns of their own. We can see much, and what we can see itches our curiosity and engenders questions.

The Martian atmosphere is thin (only about 1% as thick as Earth’s), but it is still strong enough to toss dust around the planet in globe-girdling dust storms that envelop the world for months on end. Our spacecraft have watched (and encountered!) swirling dust devils meandering across the plains, and rimes of frost condense out of the cold winter air. Once, long ago, we think the atmosphere was thicker, thick enough to move liquid water around the planet in a vast hydrological cycle like ours on Earth.  What happened to Mars’ atmosphere? Why and how did it change, and what does that mean about our long term future? The Martian poles are studded by brilliant white ice caps that grow and shrink with the Martian seasons. As the poles grow and shrink, does the ice entomb a layered record of Mars’ storied past, like the Earth’s ice does?


We see familiar atmospheric and hydrological phenomena on Mars, similar but not identical, to what we see on Earth. L to R: Dust devils (seen by Mars Reconnaissance Orbiter), frost (at the Viking 2 site in Utopia Planitia), south polar ice cap (seen by Mars Global Surveyor).

One side of Mars is bulged out in a geologic area known as the Tharsis Bulge. It is a vast volcanic plateau dominated by four massive shield volcanoes, the largest of which is three times higher than Mount Everest as as wide as the state of Washington — it is the largest mountain in the solar system.  We call it Olympus Mons.  How did this massive volcanic landscape form? Why is it higher than the rest of Mars?  Was it created in some astronomical cataclysmic event, or is there something about Mars’ geologic past that made it prone to massive mountain building?


Topographic map of Mars. Hellas (dark blue, right center) is lowest point on Mars; Olympus Mons (white peak, farthest left center) is highest point on Mars.

Since the 1960’s we’ve been sending spacecraft to Mars, and they’ve been dutifully sending back pictures and discoveries that lead to more questions. Mars, more than any other world, is the objet du désir. So as the Space Age unfolded, it was the target of many “firsts.”

Mars was the first planet to ever be visited by interplanetary spacecraft. On 15 July 1965, Mariner 4 flew past Mars, returning the first up close pictures of that distant shore. The very first picture was returned to Earth, but with some anomalous housekeeping data that suggested something might be wrong with the spacecraft’s tape recorder. While the issues were being sorted out and the computer was processing the data, the flight team had enough time to hand draw the first image directly from the data, pixel-by-pixel in true paint-by-number style. The first picture we saw was hand drawn (the computer later caught up and confirmed it could draw just as well as the Mariner 4 flight team). In all, Mariner 4 returned only 22 pictures, but those pictures showed us a barren, rocky world pock marked by craters, not (we thought) unlike the Moon.


The hand drawn image of the first Mariner 4 image (left) and the final computer generated image (right). [Images: NASA]

In November 1971, the Mariner 9 spacecraft successfully inserted itself into Martian orbit, becoming the first spacecraft to orbit another planet. Orbiting mars for 349 days, it returned more than 7000 pictures. Hidden among that treasure trove of images were amazing discoveries, including enormous volcanoes larger than any we have ever seen on Earth, and a vast chasm that girdled the planet, now called Valles Marineris — the Valley of the Mariner Spacecraft.


Mariner 9 showed us the first close up images of the caldera atop Olympus Mons (left) and the Valles Marineris (right). We have far better pictures of both today, but these were the first time humans had ever seen either. [Images: NASA]

Mars was the first planet to ever be landed on. On 20 July 1976, Viking 1 settled down in a rock-strewn red desert called Chryse Planitia — Greek for the “Plains of Gold.” Viking 2 landed just 45 days later, 6475 kilometers away in an equally stunning Martian plain called Utopia Planitia. Together, the Viking landers worked on the surface for 3621 days, returning images, monitoring the atmosphere, and sifting the sands of Mars for indications of life.


Landscapes of Mars. Chryse Planitia seen by Viking 1 (L) and Utopia Planitia seen by Viking 2 (R). [Images: NASA]


The Curiosity rover was lowered onto Mars by a flying robotic sky crane. [Image: NASA]

Mars is, to date, the only planet ever visited by rovers. The first was Sojourner, a micro-rover the size of a toaster oven that travelled a grand total of 100 meters in 1997. It was followed in 2004 by two larger Mars Exploration Rovers called Spirit and Opportunity. Today we celebrate Opportunity‘s 12th birthday on Mars; Spirit roved for six years before it fell silent in 2010. And in 2012, and even larger rover named Curiosity was lowered to the red sands of Mars using an ambitious and daring landing technology called a sky crane. All told, the rovers have covered nearly 60 kilometers among them, and the total is still climbing as Opportunity and Curiosity continue to roll.

All these “firsts” are fun and amazing to be sure. They inspire a kind of astonishment and awe that goes hand in hand with the uncontrollable urge to blurt out, “I can’t believe they just did that!” But in the end, the things that speak to me the most about Mars, the tantalizing bits that draw the mind and the soul into pondering the shifting red sands, are the pictures. The pictures inspire an unrequited longing to walk where none have walked before.


My grandfather, R. S. Kelher, Sr.

As I myself have grown older, I’ve learned to appreciate my grandfather’s thinking about his dream Thunderbird, especially in a society that seems increasingly commercialized. But when I think about Mars, when I imagine even just a few moments of being able to shuffle around in the light gravity, to turn over a stone scoured by a billion years of Martian weather, to let the red, red sands sift through my outstretched fingers, the longing for that experience is almost overwhelming. Given the chance, I think I’d trade the daydream for the opportunity. But Grandpa? You should know I remembered what you said, and I thought hard about it first.

This is just the beginning

by Shane L. Larson

Each morning, I roll out of bed, dutifully feed the three cats that own me, help my fourth-grader get her backpack put together for the day and put my daily secret note in her lunch, enjoy a few brief moments over morning coffee with my spouse, and then it is off to work.

For my day job, I’m a scientist. My friends and I work in a completely new branch of astronomy called gravitational wave astronomy. Our express goal is to detect a phenomenon that was predicted almost a century ago by Einstein: the undulations and propagating ripples in the fabric of spacetime that signify the dynamic motion of matter in the Cosmos.


Gravitational waves are ripples in the fabric of spacetime; propagating disturbances caused by the dynamical motion of heavy masses, like black holes or neutron stars.

Gravitational waves are expected to be a phenomenal probe of the Cosmos because they are readily generated by objects that are otherwise hard to detect by other means. This includes objects of intense interest to astronomers, like neutron stars, stellar mass black holes, white dwarfs, cosmic strings, and supermassive black holes at the hearts of galaxies. Despite their apparent utility in astronomy, the are exceedingly hard to detect. When Einstein first deduced their existence, he famously showed that the waves were so weak he thought we might never be able to measure them. But as is often the case, the future is full of wonders, and with the advent of the Space Age, people began to question that judgement. Maybe, with some cleverness and awesome technology, we could gaze at the Universe with gravity rather than light.

As with many scientific endeavours, gravitational wave detection is a difficult task because we’ve never built machines to do this before. We are learning how to do everything for the first time. You try things out, making your best guess as to how it is all going to work, but when you finally flick the switch to “on” you can debug your experiment because it is right in front of you.  That’s all well and good when your lab is here on planet Earth, but when you shift your experiments to space, it becomes a bit more difficult.


LISA will be a constellation of 3 spacecraft, 5 million kilometers apart, shining lasers at each other. [Image: Astrium]

Someday we want to build a space observatory for measuring gravitational waves, called LISA — the Laser Interferometer Space Antenna. LISA consists of three spacecraft, each about 2 meters in diameter and 50cm deep. They fly in space, 5 million kilometers apart, and shine lasers back and forth between themselves. We time the flight of those lasers (nominally just over 16.6 seconds from one spacecraft to another) and if a gravitational wave blasts through LISA, we see the laser times change.

So how do we go about building new spacecraft for the first time? We take things in stages, just like you and I do when we try to learn something new. When I want to learn to play guitar, I don’t take the stage on Day One with Dr. Brian May; instead I get an old beater guitar out of the basement and I plunk out riffs of “Old Sussanah” until my fingers bleed. Then I work on the guitar solo in “Brighton Rock.”  Building spacecraft is kind of the same thing.


Artists conception of the LISA Pathfinder spacecraft. [Image: European Space Agency]

No space observatory like LISA has ever been built before, so we have to figure out how to do it. How do you build the laser timing system? How do you set up the spacecraft thrusters to respond to external influences like the solar wind? How do you get the whole thing into orbit in one piece, then set it up so it works? How do you control spacecraft temperature to the precision we need?  The best way to answer all of these questions, and to discover all the pitfalls we haven’t imagined, is to build one. This is one of the primary reasons we built a spacecraft called LISA Pathfinder.

LISA Pathfinder is an “almost LISA”. The spacecraft itself is roughly the size and shape of a LISA spacecraft, but it’s guts are slightly different. Deep down inside, it has a linked laser system that is easiest to think of as if it is just an entire LISA arm, shrunk down to fit on a single spacecraft. This is not ideal for doing astrophysical work, but it is perfect for understanding how the spacecraft are going to work in space.


The heart of LISA Pathfinder (the “payload” in spaceflight lingo). A laser system monitors two freely flying “test masses” (2 kg cubes of gold & platinum). [Image: European Space Agency]

Throwing a robot into space is hard. You have to get it to outer space, and get it there in one piece! The usual way you get things into space (so far) is with rockets. Putting aside the fact that they sometimes explode, a rocket ride to space is not the gentlest experience in the world. It’s loud — noise levels in proximity to a typical rocket engine are a million-billion times louder than sound you encounter at home every day. It shakes a LOT — rocket vibrations back and forth across the body of a rocket can be so strong they have led to catastrophic destruction of the rocket itself. The launch forces are enormous — human spaceflight engineers keep launch forces low for crew comfort (the maximum on space shuttle flights was about 3 times Earth gravity), but rockets without human crews regularly reach 5 to 10 times Earth gravity during launch. Add that all together, and the ride to space can be pretty rough. So how do you get a sensitive gravitational wave experiment into space, all in one piece and undamaged, on a rough and tumble rocket ride?

Hucking robots into space is hard, to be sure, but using a robot you threw into space to do science can be even harder. First, everything has to work. When your robot is tens of thousands of kilometers away from the closest space engineer, you can’t tinker with it — there’s no tightening up bolts, no replacing faulty lasers, no kicking stuck gear boxes, nor swapping out new battery packs. Second, the environment of space is harsh — there’s no air, the Sun is constantly blasting and heating one side of your spacecraft while the other side is turned toward the frigid chill darkness of deep space. And all the while, your dedicated space robot is bathing in a constant wash of hard cosmic radiation. Every ultra-sensitive space experiment has to weather through those hardships, while collecting data that would be hard to collect even under controlled laboratory conditions on Earth.

So you take a baby step, and you test everything first on Earth, then in space. This is the purpose of LISA Pathfinder. To teach us how to build a spaceborne gravitational wave detector, then to show we know how to get the thing safely to space, then once we’re in space, we turn it all on to show that we can do the actual experiment we want to do.

VV06 Lisa PathFinder Launch

LISA Pathfinder launch on a Vega rocket (VV06). [Image: European Space Agency]

On December 2, after many years of design and laboratory work, LISA Pathfinder was launched atop a Vega rocket from Kourou Space Center in French Guiana. It has gone through a series of orbital burns that are sending it to a neutral “Lagrange point” between the Earth and Sun, where it will enter a “halo orbit” to test its lasers, thrusters, and spacecraft guidance systems in the very same way that LISA will have to work. So far, the flight has been flawless.


Just a few of the people who worked on LISA Pathfinder, my colleagues Karsten Danzmann (L), Paul McNamara (C), and Stefano Vitale (R). [Image: Paul McNamara]

What constantly amazes me about the people who build these machines is their diligence and tenacious attention to detail. A robot that we huck into space is not just a dumb hunk of metal. It is an amazing complex machine that is capable of thinking and taking care of itself. It conducts experiments that we tell it to do, stores the results of those experiments and faithfully beams the information back to Earth. At the same time, it is surviving one of the most hostile environments known: the vacuum of space. The influence of the Sun produces drastic temperature shifts across your spacecraft. Cosmic radiation is constantly bathing the spacecraft in a wash of seething, energetic particles. And all the while it has to gather and store energy, and all the zillions of parts and components have to work together, flawlessly and seamlessly.

Your car is also an amazingly complex machine. But if some piece of it stops working and leaves you on the side of US Route 50 in Nevada (the Loneliest Highway in America), a passing motorist will still happen along to help you, or you can make a quick call to the motor club to come tow you. There are no such luxuries in the game of space exploration.

awesomeLISAThe scientists and engineers who contemplate these things every day are ingenious and clever. The delivery of LISA Pathfinder was the culmination of a decade long effort by an enormous team of scientists and engineers. And all the while they were designing and building LISA Pathfinder, they were teaching classes, and training new students and young scientists who will go on to do new and awesome things in the future. These are the people who make our modern world go ’round. I have nothing but admiration for my colleagues who have built and flown this marvelous machine.

So, at long last, the beginning has arrived. We are all simultaneously exhilarated, relieved, joyous, and eager for the next bit of news and the latest results to get here. Because this is only the beginning, the culmination of decades of hard work, difficult hardships, and anticipation. The BEST stuff — the detection of gravitational waves from the Cosmos — is yet to come.

Astronomy as Sherlockian Drama

by Shane L. Larson

The world, and social media in particular, was riveted this past week by the announcement of a strange optical signal from a star 1480 lightyears away in the constellation Cygnus, called KIC 8462852. Part of the suite of targets observed by the Kepler mission, the data shows the brightness of the star going up and down in odd ways, unusual when compared to typical stellar brightness records (what astronomers call a “light curve”) that we’ve ever seen.

The location of KIC 8462852 in the sky, 1480 lightyears from Earth, in the constellation of Cygnus.

The location of KIC 8462852 in the sky, 1480 lightyears from Earth, in the constellation of Cygnus.

In an of itself, the changing of a star’s brightness would not normally garner news around the world. Many stars fluctuate in brightness, and dips in brightness caused by a planet passing in front of a star is a common tool to search for worlds elsewhere (this is, in fact, what Kepler’s primary observational goal was).

No, what caused the stir is the somewhat speculative notion that the weird light curve could be artificial in origin, caused by mega-structures, built by some unimaginably advanced alien civilization, orbiting this star.

For a species that longs to know if we are alone in the universe or not, and for a civilization that is well versed in speculating on the existence of life elsewhere for entertainment purposes, the idea of alien mega-structures immediately conjures well imagined pictures and ideas in our heads, and generates tremendous excitement. Hence, the response of the world-girdling infoweb.

Alien mega-structures might slowly be built up to girdle the parent star, occasionally blocking the light. [Image by Kevin M. Gill]

Alien mega-structures might slowly be built up to girdle the parent star, occasionally blocking the light. [Image by Kevin M. Gill]

The idea has been met with tempered and cautious response from scientists (here, here, here, many more!). There are many competing psychological and sociological forces at work. First: we don’t want to squelch people’s enthusiasm for our work (“OMG! The world cares about light curves!”). We also don’t want to give the impression that we put much stock in an (obviously crazy) idea like “alien mega-structures.” But we also want to impress upon people that we entertain any and all ideas.

I’m a practicing scientist myself, and I’d like to take a slightly different view on this matter. We shouldn’t be tempering our response at all! There is nothing wrong with assuming from the get-go that this signal IS alien mega-structures — the analysis and  evolution in our thinking that follows will be the same either way.  So how will it all shake out?

Annual World Energy Demand. Note the constant and steady growth over time. [Wikimedia Commons]

Annual World Energy Demand. Note the constant and steady growth over time. [Wikimedia Commons]

To begin the story, it is useful to go back to the beginning — where did the idea of alien mega-structures come from? It is part of a very old observation that as our civilization grows, and our dependence on technology grows, our need for energy grows as well. Since the Industrial Revolution this growth has, more-or-less, been unchecked. Looking at a graph of the growth in energy use by the human race, we see that there will come a time when we will outgrow our ability to produce the energy we need by “simple” means (such as burning fossil fuels).

This idea of predicting the future is a large part of what science and engineering are all about: take some observations of the world today (“data”), look at what the evolution up to today has been (“historical record”), and using the Laws of Nature calculate what should happen tomorrow (“prediction”). When tomorrow gets here, you make a new observation and ask, “did things turn out like I expected?” If not, you refine your prediction method and try again. Over time, you get very good at predicting the future.

Scientists do it all the time — we know where Mars is will be when we shoot rockets towards it; we know how much water and waste dialysis removes from a kidney patient’s blood and can tell how often they have to dialyze; we know how much friction the cylinders in your car experience, so know how much heat your cooling system has to dissipate; and so on. Science is about predicting the future, and using that power to improve our lives.

Freeman Dyson

Freeman Dyson

So in 1960, physicist Freeman Dyson was thinking about the escalating energy needs of our civilization, and proposed that some day we would reach a point where the best possible source of energy was the Sun, and in order to maximize the use of that energy, we should completely surround the Sun by a solid sphere (now known as a “Dyson sphere”), so that every bit of sunlight was captured and could potentially be used. The idea has originally been proposed in a science fiction novel by Olaf Stapleton (“Star Maker” in 1937), and Dyson suggested one way to look for alien civilizations was to look for such a mega-structure in the Universe.

Find a quiet corner of your couch, grab a bowl of popcorn, and start thinking about building such a structure. You can imagine what an enormous engineering endeavour it would be — the sphere would have a surface area 550 million times larger than the Earth! Obviously it would have to be built by a civilization far more advanced than ours. Perhaps more obviously, it could not be built all at once — it would take generations to design, construct, and maintain! So one might imagine that it could be built up piecemeal, not as an entire sphere, but as a swarm of parts that if connected, would form a Dyson sphere. One famous realization of this is Larry Niven’s “Ringworld”, where a star was girdled by a single continuous ring, with the inhabitants living on the starward side of the ring.

A ringworld is one option for a civilization that does not want to invest in building an entire Dyson Sphere. Perhaps it is just an intermediate stage that will ultimately lead to a full sphere. [Wikimedia Commons]

A ringworld is one option for a civilization that does not want to invest in building an entire Dyson Sphere. Perhaps it is just an intermediate stage that will ultimately lead to a full sphere. [Wikimedia Commons]

This all sounds perfectly reasonable, provided you can imagine the construction endeavour needed to construct such an artifact.  So why all the skepticism toward the idea of the signal in KIC 8462852 being alien mega-structures? The simple fact of the matter is we can’t imagine humans building a mega-structure, so we find it hard to imagine any civilization building a mega-structure.

The cautious skepticism of the scientific community can be summarized by Marcello Truzzi’s observation that was popularized by Carl Sagan in Cosmos:Extraordinary claims require extraordinary evidence.” This is often regarded as a modern restatement of the Principle of Laplace: “The weight of the evidence should be proportioned to the strangeness of the facts.”

[L] Carl Sagan, [M] Marcelo Truzzi, [R] Pierre-Simon Laplace

[L] Carl Sagan, [M] Marcelo Truzzi, [R] Pierre-Simon Laplace

Laplace was highly cognizant of the fact that our knowledge of the world, and hence our understanding of the world, evolves over time. New discoveries and new observations necessarily make way for new ways of thinking. So what to do when you encounter something strange and unusual?  Laplace wrote in 1814 in his essay Essai philosophique sur les probabilités, “We are so far from knowing all the agents of nature and their diverse modes of action that it would not be philosophical to deny phenomena solely because they are inexplicable in the actual state of our knowledge. But we ought to examine them with an attention all the more scrupulous as it appears more difficult to admit them.”

So, at the outset, intellectual honesty insists that we cannot deny the weird signal from this star may be due to alien mega-structures. But we must examine such claims with extreme skepticism. Because it appears difficult to explain how it might be alien mega-structures.

Or is it? Why is it difficult to explain these as alien mega-structures? Any more-so than some other plausible explanation (many of which astronomers have already discounted)?

Astronomy is a Sherlockian drama, and as the famous detective observed to Watson (in “The Sign of the Four” [1890]), “When you have eliminated the impossible, whatever remains, however improbable, must be the truth.” Astronomers are starting at the top of their list of possible “natural” causes, and eliminating them one by one.  The data at hand is that we see the brightness of the star changing with time, and the pattern of brightness changes looks… weird.  What could it be?

Light curves for KIC 8462852. The top panel shows the full light curve. [C] Enlarged view of the dip around day 793; very typical shape for

Light curves for KIC 8462852 — the lines plot the brightness of the star, with time across the horizontal direction. If the line is high, the star is bright, and if the line dips, the star gets dimmer by some amount. The deeper the dip, the bigger the change in brightness. The top panel shows the full light curve. [C] Enlarged view of the dip around day 793; very typical shape for “common” dips used to detect planets, but BIG. [d-f] These enlargements of other dips are the mystery — they are BIG, but also show remarkably complex structure. What is causing this? [Figure adapted from Boyajian et al (2015)]

Perhaps it is just a variable star. We know of many different kinds of variable stars in the Cosmos. These stars, due to some process in their innards or due to some interaction with their environment, change in brightness in a steady and regular way. These variations seen in KIC 8462852 are not apparently regular in immediately obvious ways. More to the point, astronomers would not normally expect there to be intrinsic variations in the brightness of this star. Why? We know how big and how old it is, its temperature and composition — all of these bits of information define what astronomers call the “spectral type.” It’s a bit like classifying different breeds of cats — you know one cat is a different type than another based on gross, observational characteristics like fur color and length, tail and ear structure, and so on.

KIC 8462852 is a spectral type F3 V/IV (just in case you ever get that question in a round of Trivial Pursuit) — this means it is about 1.0-1.4 times the mass of our Sun, and has a surface temperature between 5700 and 6700 degrees Celsius. There are lots of F-type stars known to astronomers — they are yellow dwarf stars, in the middle of their lives, stably burning hydrogen on the main-sequence. To see an F-type star show tremendous strange variability would be a serious challenge to our understanding of stellar astrophysics, and the overwhelming data supporting the stable brightness of F-type stars in the galaxy. Astronomers think this is not what is causing the light curves.

Perhaps it is a debris disk of some sort. The Oort Cloud is a bubble of debris that surrounds the outermost fringes of stars like the Sun, the left-over icy detritus from the formation of the Sun and its attendant planets. We know of the Oort Cloud because periodically, it drops an icy rock into the inner solar system, which you and I call a comet. Maybe another star in the galaxy passed very close to KIC  8462852 (a rare, but not impossible occurrence) and disturbed its Oort Cloud. The gravitational tug of this passing star would have churned up the Cloud, and destabilized it so lots of comets dropped in toward the star. That doesn’t sound far fetched until you look at the light curve — fully 22% of the light from the star is blocked during some of the light curve dips. Comets are tiny, only 1/10,000th the diameter of a star. It would take an absurdly large number of comets to make the data look the way it looks.

There are many scenarios we can imagine that will generate vast debris fields around stars [NASA Image, PIA11375].

There are many scenarios we can imagine that will generate vast debris fields around stars [NASA Image, PIA11375].

Maybe there was an enormous collision between planetary sized objects, creating a debris disk or some kind of large asteroid field. This is not unheard of — the Earth’s Moon is thought to have formed by such an impact, early in the history of the solar system.  If there was such an event, there should be a lot of residual dust, which would glow brightly in infrared light. So far, astronomers have not noticed any extra infrared light from KIC  8462852, casting doubt on this idea.

And so on. We just keep working our way down the list of clever and plausible explanations.  But when we get to the bottom of the list, what if the one idea we have left is alien mega-structures? What will we do then?

I maintain that this should not bother us at all. The reason is simple: we have not looked for alien life long enough, nor the signatures of alien civilizations carefully enough, to know what their signatures are! When you’ve been doing zillions of experiments and making zillions of observations, it is easy to discount ideas in the face of overwhelming data, but in the case of alien civilizations, our experience in the search is so profoundly limited that scientific integrity demands we consider the possibility.  We haven’t searched for aliens enough to know whether they are improbable or not.

But science is not a game where you rest on your laurels either.  Everything we believe is subject to constant scrutiny no matter how confident we are in the results. That’s what science is about — not fooling yourself. As Feynman quipped, “The principle is that you must not fool yourself, and you are the easiest person to fool.” (Caltech Commencement Address [1974]).

So over the next many weeks, possibly months, maybe even years, we will observe and scrutinize and ponder KIC  8462852. Eventually someone will have a clever idea that suggests it is not alien mega-structures. When they do, astronomers will look at the idea and say, “if this is true, then this other thing should also be true” and they’ll go check.

If they are right, the idea of alien mega-structures will fade, and we will be no worse for wear. But if they are wrong, we won’t be able to discard the idea, and we’ll live with the notion of alien mega-structures a bit longer. And perhaps longer, and perhaps longer still.

My standard bet: a Dr. Pepper and a Boston Cream Donut. What have you got to lose?

My standard bet: a Dr. Pepper and a Boston Cream Donut. What have you got to lose?

But in the end, the Sherlockian drama will play itself out: whatever remains in the end, must be the truth. Alien mega-structures or not.

PS: In case you haven’t guessed: I don’t see any reason to favor or disfavor alien mega-structures. So I’ll bet you a Dr. Pepper and a Boston Cream donut it’s alien mega-structures… ;-)

Modus Operandi: The Last Planet for the First Time

by Shane L. Larson

July 2015 was a triumphant month in the annals of robotic space exploration — the long held dream of sending a space probe to explore worlds in the outer reaches of our solar system was realized. New Horizons, a robot the size and shape of a baby-grand piano, wrapped in golden mylar, shot past Pluto at 31,000 miles per hour. Semi-sentient and single-minded, New Horizons spent 22 hours on July 14 ignoring its masters on Earth, focusing all its attention on Pluto for the brief moment we call “Encounter Day.” New Horizons had been constructed with this single purpose in mind: to make a nine-and-a-half year voyage across 3 billion miles of the void — a voyage we humans could not make — and record everything it could about Pluto as it blazed by.

For most of the 85 years since Pluto’s discovery, we’ve seen little more of it than a fleck of light, even in our best telescopes. But New Horizons has been steadily crossing the gulf since its launch in 2006, carrying the promise that someday, it would send back pictures to replace the ones in our imaginations.

Before New Horizons made its daring flyby, we had no idea what Pluto looked like. Every image you ever saw was how we imagined it might look.

Before New Horizons made its daring flyby, we had no idea what Pluto looked like. Every image you ever saw was how we imagined it might look. [Image: NASA]

For a long while, the pictures sent back were still only spots of light, Pluto and Charon engaged in a slow and lazy dance around one another.  But each day carried our faithful robot 1.2 million kilometers closer, and Pluto grew inexorably larger.  For the month or so before Encounter Day, the details visible on Pluto and its attendant moons streamed back to Earth in tiny, tantalizing bits. The spacecraft carries only 16 GB of memory on board — tiny by the standards of the smartphone you have in your pocket, but huge by the standards of the early 2000’s when New Horizons was built.  The data link is a paltry 1000 bits per second, about 50 times slower than a dial-up modem (the dominant technology at the time New Horizons was built), and about 1000x slower than the modern high-speed internet you enjoy in your home today.

At those speeds, it takes about 2 hours to download a typical picture you might snap of your coffee or cat with your phone. But these pictures streaming back are from Pluto, 3 billion miles away, and are of things we have never seen before this summer. The past several months have been a veritable circus of emotional highs, punctuated by long waits to find out what secrets Pluto would reveal to us next. Every picture reveals something new, for the first time. This has always been the modus operandi in planetary space exploration.

I was little during the late 1970s, the years when the solar system was being seen up close for the first time. My first real memory of a space probe visiting another planet was of the Viking missions to Mars. On 20 July 1976, 7 years to the day after astronauts first walked on the Moon, Viking 1 became the first spacecraft to ever land on Mars. It touched down on a vast Martian plain that we had named Chryse Planitia — a Lyrical Greek name meaning “the Plains of Gold.”

The landing happened at 7:53pm EDT. At that time, Mars was high in the sky over the United States, east of the Sun and hidden in the blue velvet of daytime. 25 seconds after landing, Viking snapped its first image, a selfie of sorts. It took 4 minutes to transmit the entire image to Earth, but for NASA engineers breathlessly waiting for news from their space age hot rod, the wait was even longer — travelling at the speed of light, it took 19 minutes for the message to cross the gulf of space and reach Earth. The first picture it sent home was of its foot, firmly planted on Martian soil amid a tantalizing scatter of rocks on the surface of an alien world.

The first image ever returned from the surface of Mars -- the footpad of Viking 1, solidly planted on a rocket Martian plain. [NASA PIA00381].

The first image ever returned from the surface of Mars — the footpad of Viking 1, solidly planted on a rocky Martian plain. [NASA PIA00381].

The next day, Viking sent back the first picture of Mars in glorious living color, and it looks for all the world like a picture from some barren patch of the rocky deserts in the American southwest. Never again would the surface of Mars be unknown. Our imaginations are now forever supplanted by real pictures of the surface of Mars.

The first color image ever returned from the surface of Mars, showing the Chryse Planitia was a red, rocky desert.

The first color image ever returned from the surface of Mars, showing the Chryse Planitia is a red, rocky desert. [NASA PIA00563]

I don’t remember whether or not these images percolated into the news or not; I’m not cognizant of whether or not I watched the news.  But what I do remember is waiting breathlessly for National Geographic to arrive. After each magnificent encounter with another world, an issue would eventually arrive at our house, the cover splashed with images from NASA. The articles within were chock full of images from the missions, everything a young and curious mind with dreams of outer space could desire.

My childhood was punctuated by long waits for National Geographic to deliver the latest images from NASA's deep space probes to the planets.

My childhood was punctuated by long waits for National Geographic to deliver the latest images from NASA’s deep space probes to the planets.

But by the mid-1990’s, a new technology was slowly capturing the public’s attention, and it went hand in hand with the heady future of space exploration: the internet. NASA figured it was going to be big, and they started to figure out how to use it to deliver all the wonders of the Cosmos directly to me and you.

Fast forward to today, and we use the internet for everything. We check the weather. We look for the nearest veterinarian. We get customer reviews of cars. We play games with friends. We read blog posts. We order paper-clips from Amazon.

NASA has become the master of this new technology, delivering images of the Cosmos directly to me and you on our smartphones and computers. Every day, NASA gives us the latest pictures from Hubble: color renderings of delicately twirled galaxies millions of light years away, images of towering columns of stardust making new stars, and pictures of a tiny speck of light at the fringes of the neighborhood around the Sun. But this summer that fleck of light became so much more.

One vertical stripe, at full resolution, clipped from New Horizon's full disk image of Pluto. For the full imaged, visit this page (be sure to click on

One vertical stripe, at full resolution, clipped from New Horizon’s full disk image of Pluto. For the full image, visit this page (be sure to click on “Full Resolution“!).

New Horizons, after a 9.5 year journey out from Earth, flew by Pluto for the first time. It is the only spacecraft to ever visit that far away world. It passed within 7800 miles of the surface. At the speeds it was travelling, it sailed across the face of Pluto in just 3 minutes, snapping as many pictures as it could in that brief moment it was close.  After it had sailed past Pluto, New Horizons sent a short message home: a simple, “All is well, but I’ve still got work to do!” It then returned to observations, looking back toward Pluto and its family as it receded in the rear view mirror.

The next day, images began to be sifted out of the memory and beamed back to Earth, pixel by pixel. As the images arrived, they revealed a world of wonders and mystery.

Pluto has mountains:11,000 feet high, but apparently made of ice, not rock. How can mountains like that form, and why have they not been slowly eroded into oblivion by impacts and crater formation? Astronomers don’t know yet.

The bright, white heart of Pluto is a vast icy plain called Tombaugh Regio. Largely comprised of nitrogen ice, its vast expanse is divided up into polygonal cells, like irregular tiles on a kitchen floor. Near the fringes, the ice appears to be flowing, like glaciers do on Earth, pushing out into the surrounding valleys and mountains. Why is the ice so vast and smooth? Why are there no craters on it, and what is lifting it up so it can flow near the edges? Astronomers don’t know yet.

Charon, Pluto’s largest moon, is scarred by a rift canyon that is six miles deep and stretches across the entire face of the moon. It is so large that when viewed in profile on the limb of this world, it looks like someone took a cleaver to Charon. Nearby, we have spotted a “Mountain in a Moat” — a mountain sized rock sticking up out of the surface. Apparently its not part of Charon’s crust, but not surrounded by an impact crater either! How did these features form? How long have they been there and how long will they persist? Astronomers don’t know yet.

We’re not worried that we don’t understand these things yet. This is what astronomy is all about — uncovering mysteries, and finding out the explanation for them. Understanding how the Universe works, how things are put together and change over time, tells us about our own small, blue world. Pluto knows part of the story of the beginning of the solar system. Pluto is at the heart of our attempts to understand the nature of planets, and the evolution of the architecture of planetary systems. The knowledge we glean from Pluto will inform the way we think about planets for the next century and beyond.

All of the astronomers you know are still giddy about the information streaming back from New Horizons. It will take more than a year for all the images to get back, and even longer to understand them.

But right now — this moment — is one all of us should savor and enjoy, because as of today, every world in the solar system that has ever been considered a planet has now been visited by spacecraft from Earth.

This includes Pluto, and Ceres. Both were visited by spacecraft from Earth for the first time this year.

All of us witnessed, for the last time, the discovery of new worlds for the first time.

Never again will we see a planet up close for the first time. That sense of astonishment, of unfettered curiosity for a newly seen planet, is now a memory for the ages. It will be replaced by other moments of wonder and discovery, but never again for the surface of an unknown planet. Not in our lifetimes.

We will never again imagine what Pluto might look like. From here on out, you will not be able to open up a webpage and not see real pictures of this far away world.

The next humans to see new planets for the first time, will be those who live to see our species travel to other stars.

Feeling Small in a Big Cosmos 03: Proverbs

by Shane L. Larson

On 19 April 1610, Johannes Kepler wrote an open letter to Galileo Galilei, musing on possible future voyages that would allow explorers — human explorers — to see what Galileo’s telescope had shown.  He mused that some day inventors might “provide ship or sails adapted to the heavenly breezes, and there will be some who will not fear even that void.” Kepler called on Galileo to join him in preparing the way for those so0n to be travellers, and create a new science to light their way: astronomy.

Yuri Gagarin and the Vostok 1 launch on 12 April 1961.

Yuri Gagarin and the Vostok 1 launch on 12 April 1961.

It was almost exactly 351 years before Kepler’s speculations were realized — on 12 April 1961 the Soviet Union launched cosmonaut Yuri Gagarin into space. In a flight that lasted only 108 minutes, Gagarin orbited the Earth in a capsule bearing the callsign Kedr (“Cedar”), and initiated The Space Age.

Kepler’s poetic  words are a testament to our visceral desire to know the Cosmos. Gagarin was perhaps no less poetic when, in the middle of the launch, he belted out an exclamation of joy born from the same deep well of emotional longing — Gagarin’s hearty “Poyekhali!” (“Let’s go!”) ushered in a new era in the history of our species — the beginning of our quest to walk among the stars.

The Cosmos is vast, and nothing makes that point more abundantly clear than contemplating long journeys by humans into space. Trying to protect and sustain our fragile bodies for the duration of a long space voyage brings into sharp focus a single, glaring fact: we are designed for Earth, not for the void, not for alien landscapes, not for far-off icy moons. Despite all the tantalizing things we can see, it seems Nature never intended us to stray far from the small Blue Marble of Earth. We shouldn’t feel bad about that; it is also true for starfish, and seagulls, and housecats, and pine trees.

Every spaceprobe we have ever flung into space has returned remarkable pictures, and made new discoveries. Top to bottom: Mariner 4 was the first to flyby Mars, and returned the first pictures of the Red Planet's surface. The Soviet Venera 9 was the first to send pictures back from the surface of Venus; it survived for only 53 minutes. The Sojourner rover was the first spacecraft to move around Mars, in 1997. In November 2014, the lander Philae was the first spacecraft to land on a comet.

Every spaceprobe we have ever flung into space has returned remarkable pictures, and made new discoveries. Top to bottom: Mariner 4 was the first to flyby Mars, and returned the first pictures of the Red Planet’s surface. The Soviet Venera 9 was the first to send pictures back from the surface of Venus; it survived for only 53 minutes. The Sojourner rover was the first spacecraft to move around Mars, in 1997. In November 2014, the lander Philae was the first spacecraft to land on a comet.

But humans are a particularly stubborn and imaginative species. We could easily abandon the dream of travelling beyond Earth, but instead we designed and built machines to make the voyage for us. Our knowledge of the Cosmos today is largely populated by images collected by semi-intelligent robots built to be our eyes and ears. They have travelled where we cannot, and faithfully returned images which are arguably the most artistic, the most beautiful, the most stunning, the most confusing, the most awe-inspiring, and the most thought-provoking things humans have ever seen.

spacecraft_highresFor every space probe we have thrown into space, for every world they have visited, for every picture they have snapped, there is a tale to tell. All of them unique, all of them stirring. Let’s revisit the tale of one spacecraft that has been outbound now for almost 38 years; a spacecraft called Voyager 1.

Launched on a bright September morning in 1977, Voyager set sail for the outer solar system. Its mission was to visit Jupiter and Saturn and tell us what it discovered, and then to begin a long slow march into space, searching for the edge of the solar system. Voyager returned tens of thousands of pictures during its mission, but I find two particularly compelling.

In February of 1979, as Voyager was speeding toward its encounter with Jupiter, it snapped this photo: the most exquisite and detailed image of the iconic Great Red Spot ever taken. Voyager showed us the magnificent swirl and drift of the clouds on Jupiter, bands of colorful and dynamic gas driven by 600 kilometer per hour winds around the boundaries of a 400 year old hurricane twice the size of the Earth. This is a storm that,  before we turned our eyes to the skies, our species had never encountered nor imagined. But Voyager painted it for us, indelibly etching it into our memory, with a casual snap of a camera.

Voyager I view of the Great Red Spot as it approached Jupiter in 1979.

Voyager I view of the Great Red Spot as it approached Jupiter in 1979 [Image: NASA].

I like this picture because, to the unknowing eye, one might assume that it is a painting, made by an Earthbound artist, trying to capture or evoke some deep feeling or emotion about the human condition. But this was not painted by human hands. This is Nature painting, using a planet as its canvas.

After sailing past Jupiter, Voyager sped on to Saturn, where it took even more pictures and uncovered more mysteries, painting new pictures of a gentle giant bejeweled by a ring of ice. The encounter with Saturn ultimately propelled it on a course to carry it out of our solar system and into interstellar space. On Valentine’s Day in 1990, right after Voyager crossed the orbit of Neptune, we commanded it to turn its cameras inward and take one last series of pictures before they were turned off. In a sequence of 60 pictures, Voyager snapped a family portrait — a stitched panorama that contains every planet of the Solar System, the family of the Sun. This is the frame that contains the Earth. Like the Blue Marble, it is one of the most iconic images of Earth ever taken, dubbed The Pale Blue Dot.

The Pale Blue Dot -- the frame from the Voyager family portrait that includes the Earth [Image: NASA].

The Pale Blue Dot — the frame from the Voyager family portrait that includes the Earth [Image: NASA].

More than any other picture, this captures how small and tiny the Earth is. Voyager wasn’t even out of the solar system when it took this picture. In a Cosmic sense it was still close to home, and already the Earth was nothing bigger than a small fleck of light that if we weren’t looking for it, we may not have noticed.  Everything you’ve ever known is inside that dot.

This is the Earth. It’s tiny. And what I find most remarkable when I look at this image: there is nothing in this picture to indicate there is anything special about this planet. Nothing to indicate there is life there, nothing to indicate that we are there, nothing to indicate that this is where Voyager hails from. This one picture captures indelibly in a single frame the fact that we are small, in a Cosmic sense. Some days, we might feel despondent and overwhelmed by the immensity of it all.

The Voyager Golden Record.

The Voyager Golden Record.

But Voyager also carries a sign of our optimism about belonging to a much larger Cosmos. Bolted onto its side, is a Golden Record. It is a phonograph record, a message to anyone who might stumble on Voyager in the distant future, long after its electronics have died and it becomes little more than a fleck of space junk drifting aimlessly through the galaxy. Should someone find Voyager and its Golden Record,  they would find information about the record, and instructions for playing it. Included in those instructions is a map of the galaxy, pointing back to Voyager’s point of origin. On the reverse, etched in golden grooves that will survive a million year journey into the void, is a collection of data about us, and about our world. It includes greetings recorded in 55 languages of Earth. It includes 115 images from the planet Earth from the time when Voyager set sail into the Cosmos. It includes 90 minutes of music from our civilization. And engraved on the inner edge is a single sentence, in English, that reads “To the makers of music, all worlds, all times.”

This is not the kind of thing  you make and throw out into the vast sea of the Cosmos if you are hiding from the immensity of the Universe. Voyager will outlast every person alive on Earth today. It will outlast every one of us, every person who selected music or pictures to be included on this Golden Record. It will outlast our entire civilization. But some part of us can imagine — hopes — that Voyager will survive and be found, and tell the tale of who we are. Perhaps those listeners will be unimaginable alien intelligences; perhaps they will be our descendants who have utterly forgotten us and our civilization.

Voyager and all the other robotic spacecraft we have built are magnificent creations. We can look at them and be amazed that they have gone so far and seen so much. The very existence of pictures like those I have shown you, and literally millions of others like them, should convince you that we can do anything. We can solve any problem we face, we can uncover any mystery the Cosmos puts before us.

Which leads to one last, important thought. Let’s go back to where we started, thinking about the 10 billion billion grains of sand on Earth, and the 10,000 billion billion stars in the Cosmos.


Consider: in just ten drops of water, splashed on your window in a summer rainstorm, there are as many molecules of water as there are stars in the entire Universe. You have heard that every one of us is made of 50%-60% water. Which means there are 100,000 times more molecules of water in your body than there are stars in the entire Universe.

And every molecule of water has two atoms of hydrogen, which is what the stars are made of. And the other atom in every molecule of water is oxygen, which was made by stars, burning hydrogen. At the end of their lives, those stars exploded and threw all that they were back out into the Cosmos to eventually become all that you and I are.

In a very real way, you are atoms the Universe has assembled to look at itself. You are atoms that have been organized to look out into the Cosmos and ask the question, “What’s the deal with all those other atoms?

You are the Cosmos made manifest.

You are a way the Cosmos has organized itself to ask those questions that humans have always asked. Where did we come from? Where are we going? Why are we here? And what is our role to play in the enormous universe all around us?

We’re not different than all those other galaxies, than all those other stars, than all those other grains of sand. We’re all made of the same star stuff.

There is a meme that floats around the internet that is a purported Serbian proverb (1). “Be humble, you are made of the Earth. Be noble, you are made of the stars.

It’s okay to feel small. We are small, so we should be humble. We don’t know all there is to know about the Universe.  But be noble, because you are made of the stars. You and I are members of the only species we know that is capable of asking the questions we ask, of figuring things out and asking new questions. It’s very empowering and an important part of who we are. It’s something I think we tend to forget; we get caught up in our problems and in our concerns every single day. But just like artists, scientists, and clergy, we are all true seekers. We’re just trying to understand what our place in the Cosmos really is.

— (1) I have been unable to indeed verify that this is a proverb from Serbian culture! I would love it if someone actually knew where this came from!


This post is the last in a series of three that capture the discussion in a talk I had the great pleasure of giving for Illinois Humanities as part of their Elective Studies series, a program that seeks to mix artists with people far outside their normal community, to stimulate discussion and new ideas for everyone.  The first post can be found here:

Illinois Humanities taped this talk and you can watch it online;  many thanks to David Thomas for doing the videography!

Feeling Small in a Big Cosmos 02: Discovery

by Shane L. Larson

Suppose we wanted to imagine some very big numbers, to somehow develop an appreciation for how BIG the Cosmos truly is. Sitting on a the beach somewhere, one might idly wonder “how many grains of sand are there on all the beaches and in all the deserts of Earth?”  Counting is certainly out of the question, so how might you figure that out?

Bear Lake, Utah.

How many grains of sand, on all the beaches and in all the deserts of Earth?

You would do it the same way we “counted” the galaxies in the sky using the Hubble Extreme Deep Field. You count all the grains in some small amount, perhaps a handful of sand picked up off the shores of Lake Michigan. Then you figure out how long and wide all the beaches and deserts are, and how deep the shifting sands run, and figure out how many handfuls of sand would cover them all. Multiplying my the number of grains in my hand, you would find there are some 10 billion billion (1019) grains of sand on the planet Earth.  That’s a BIG number; a number that is beyond ordinary human understanding, beyond our everyday experience.

The night sky over the Pando Forest in central Utah. Pando is an 80,000 year old aspen grove -- it has seen almost 30 million nights like this one, but very little has changed. The constellations change over thousands of years, but the sky is still full of stars, and the Milky Way still arches over the sky, giving the impression that the Universe is unchanging. [Image: Shane L. Larson]

The night sky over the Pando Forest in central Utah. Pando is an 80,000 year old aspen grove — it has seen almost 30 million nights like this one, a sky full of stars [Image: Shane L. Larson]

But imagine for a moment comparing it to the total number of stars in all the Cosmos. The Hubble Deep Fields have convinced us there must be something like 100 billion galaxies in the Cosmos. A galaxy like the Milky Way has more than 100 billion stars in it, so multiplying those two numbers together, there are some 10,000 billion billion (1022) stars in all the Cosmos, more than all the grains of sand on Earth. An even bigger number, well beyond our everyday experience.

When there is so much we don’t understand here on our own small planet, it is easy to be overwhelmed by the immense size, the immense possibilities of what we don’t understand in a Universe far larger than our brains can easily imagine. We could very easily crawl into our shells, hide from the immensity, and turn our vision inward, with nary another glance outward into the deep vastness that doesn’t even notice we are here.

But we don’t do that. We have, for countless generations, stared into the immensity in an ongoing  (and surprisingly successful) camapign to understand and explain all we can about the Universe. But when everything is so impossibly far away, when the Cosmos is full of so many different and unknown things, how is it that we can know anything?  The answer to that question is that we ask questions.

questionMarkConsider a popular game that most of us have played since we were kids (I have a 9 year old — I get to play this A LOT).  Here is a box (with a question mark on it). You want to figure out what is under this box by asking 20 “Yes-No” questions. Go!

  • Is it alive? No.
  • Is it something made by humans? Yes.
  • Is it small enough to hold in my hand? Yes.
  • Is it edible? No.
  • Does it have batteries? No.

So there we have asked just 5 questions. The answers are nothing more than a simple yes or no. But the tremendous power of asking questions is clear. Despite the vastness of the Cosmos, despite its immense size and the mind-boggling large number of things it contains, you have eliminated almost ALL of it from consideration with only 5 simple questions. You know it is not something huge (galaxy, star, planet, white dwarf, asteroid, comet, …). You know it is not alive, so every organism on Earth — plant, animal, bacteria, fungus, protozoan — is eliminated.  Your attention is now focused on only things that humans make, and only those things that aren’t powered by batteries.

me_ndgt_legoAnd you have 15 questions left! With 20 carefully constructed questions, you will be able to figure out almost anything I wanted to hide under that question mark, with a high degree of success! If we went on and I let you ask the rest of your 15 questions, I am confident you would eventually arrive at the fact that hiding in my question mark box is a little Lego version of me and Neil deGrasse Tyson.

We could have done this with anything in the Cosmos. I could have had anything under that box — an elephant, a quasar, a piece of Pluto, the left foreleg of a carpenter ant, a circle of paper from a hole punch, a cough drop wrapper, an oyster shell, that little plastic do-hickey that holds your gas cap on your car, a Calving & Hobbes sketch, a molybdenum atom, Marie Curie’s lab notebook, a lost pawn from a Sorry game, and so on. ANYTHING!

But you can figure out what it is with only a few questions so reliably we’ve made it into a game children can play and enjoy! It’s usually called “20 questions,” but it also goes by the name science. Except when we play science, we don’t limit ourselves to just 20 questions — we ask as many as we want! You can learn a LOT with carefully constructed questions. And we have learned a lot. We have collected and gathered and recorded our knowledge of the Cosmos so effectively that much of it has passed into the communal memory of our species, integrating itself into the fabric of who and what we are so effectively that we often don’t give it a second thought. We’ve forgotten how hard it was to earn that knowledge, the struggle our forbears went through to wrest some secrets from Nature and then understand what they meant.

A 1/2 globe of the Moon, roughly 5 feet in diameter, made before spacecraft had ever flown to the far side. You can see this in the Rainbow Lobby of the Adler Planetarium in Chicago.

A 1/2 globe of the Moon, roughly 5 feet in diameter, made before spacecraft had ever flown to the far side. You can see this in the Rainbow Lobby of the Adler Planetarium in Chicago.

To understand this, consider the Moon. What do you know about the Moon? It orbits around the Earth. It is spherical, and is illuminated by the Sun. The near side always faces the Earth. It is covered with lowlands (called maria, lunar “seas”), highlands (called terrae, the brighter areas), mountains, craters, and canyons. All of this is common knowledge, which if you didn’t know it you could have found out using the electronic web that girdles our world. I’m pretty sure almost everyone reading this has not been to the Moon. In all the history of our species, only 24 humans have ever crossed the gulf between the Earth and the Moon; only 12 humans have ever walked on the Moon and seen what we know with their own eyes. The pictures of the Moon, taken by the Apollo astronauts and robotic emissaries have virtually erased from our memory what it was like to not know what the Moon was like.

Consider the globe of the Moon shown here. It is about 5 feet in diameter, and lives up to our expectations of a rugged, desolate landscape covered in mountains and craters. How far away from this globe would I have to stand, for it to look roughly the same as the Moon in the sky?  About 140 feet. The full moon in the sky, is about the size of a US dime, held at arm’s length.

When you see the Moon in the sky, it is quite small, roughly the size of a dime held at arm's length. The detail your eye can see is minimal -- mostly just dark and light shading, with no topography! [Image: Shane L. Larson]

When you see the Moon in the sky, it is quite small, roughly the size of a dime held at arm’s length. The detail your eye can see is minimal — mostly just dark and light shading, with no topography! [Image: Shane L. Larson]

When the Moon is that small, you can’t tell it has any topography at all. It is clearly shaded in some irregular pattern (which allows you to make the famous Moon shadows), but there are no craters or mountains to be seen. Go out and look, but don’t look with your brain plugged in to what you know; just look at what you can see. This is how the Moon has always look to the naked eye; it wasn’t until the  application of the telescope to astronomy that we knew anything different.

Galileo's early views of the Moon through his telescope revealed previously unknown topography.

Galileo’s early views of the Moon through his telescope revealed previously unknown topography.

In 1609, Galileo Galilei was the first person to plumb the depths of the sky with a telescope, and what he saw shook the foundations of what we thought we knew about the Cosmos. In 1610, he published one of the seminal works in astronomy: Sidereus Nuncius, “The Starry Messenger,” wherein he described all that he had seen during his first excursions in 1609.  He wrote of the Moon

“... the Moon certainly does not possess a smooth and
polished surface, but one rough and uneven, and, just
like the face of the Earth itself, is everywhere full
of vast protuberances, deep chasms, and sinuosities.”

Two things stand out to me about this passage. The first is how he initially describes the Moon: a smooth and polished surface. This is how people thought of the Moon — it is, in a very real sense, what the Moon looks like, and what you would think if you had never been taught that there were craters and mountains on its surface. The second is when he describes what he saw on the Moon: just like the face of the Earth itself. The telescope allowed us to see that the Moon had features and topography that were at once recognizable and intimately familiar, appearing just like the topography we see here on Earth. In a singular moment of discovery, the telescope deprovincialized our view of the Earth. The Moon is, in a very real sense, the first world other than the Earth that we ever discovered, and this is how it happened.

Galileo's planet sketches, while not showing the detail of his lunar observations, were no less revolutionary.

Galileo’s planet sketches, while not showing the detail of his lunar observations, were no less revolutionary.

There were many other startling revelations Galileo had looking through the telescope. In addition, he was the first person to look at the planets through a telescope. And what he found was that the planets were not stars at all, but also were other worlds. Every planet showed size, and round shape. The planet Saturn had odd protrusions; Galileo wrote “Saturn has ears.”  Turning his telescope to Venus, Galileo found that it went through phases, just like the Moon, a fact that was easily explained by the still new Copernican idea that the Sun was at the center of the solar system.  But Jupiter revealed one of the greatest secrets of all — it held in its grasp its own entourage of moons, that orbited the great world much as our own Moon orbits the Earth. Today, they are known as Io, Europa, Ganymede, and Callisto — the Galilean moons.

When I think about these momentous discoveries, my mind always wanders to the following, often overlooked fact: even though Copernicus’ De revolutionibus orbium coelestium had been published more than 60 years before Galileo’s observations, and placed the Earth in orbit around the Sun, Galileo’s observations were the first to reveal the planets were indeed other worlds. To put an even finer point on it, Galileo’s observations were the first to definitively show that the Earth was a planet, possibly not unlike the other planets that orbit the Sun. Galileo’s telescope allowed us to discover the planet Earth.

Galileo's telescopic observations of the Pleiades revealed stars that could not be seen with the naked eye. There was an unseen -- an unknown -- part of the Cosmos to discover.

Galileo’s observations of the Pleiades revealed stars that could not be seen with the naked eye. There was an unseen — an unknown — part of the Cosmos to discover.

Galileo also peered at stars. He found that when he looked at the Pleiades, the Seven Sisters, the telescope revealed stars that could not be seen with the unaided eye. When he peered at the diaphanous glow of the Milky Way, arching horizon to horizon in the dark skies of 17th Century Italy, he found it was comprised of uncountable numbers of individual stars, so far away and so dim that without the telescope their combined light looked no more than an evanescent fog in the dark.  The scale of the Universe was suddenly much larger. The structure of the Universe was suddenly more complex. Larger and more complex than humans had ever imagined. The revelation of the Cosmos had begun.


This post is the second in a series of three that capture the discussion in a talk I had the great pleasure of giving for Illinois Humanities as part of their Elective Studies series, a program that seeks to mix artists with people far outside their normal community, to stimulate discussion and new ideas for everyone.  The first post can be found here:

The idea of describing science in the context of 20 Questions is one I was introduced to at a very young age, by Carl Sagan in “Cosmos: A Personal Voyage” (in Episode 11: Persistence of Memory).