Tag Archives: Galileo

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.

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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:  http://wp.me/p19G0g-xB

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).

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Gravity 2: The Road to General Relativity

by Shane L. Larson

Science is, to some extent, a skill set that can be learned. Like playing piano or solving Rubik’s cubes or cooking Belgian cuisine. Using scientific thinking and applying it to the world is in large part a matter of practice and relentless dedication to getting better. But like all artforms, there is a small element of je ne sais quoi to it as well — a hidden reservoir of intuition and stupendous insight that is unleashed only sometimes.

einsteinAppleApple once had an ad campaign built around the mantra, “Think Different” (grammarians, hold your tongues, and your “ly”s and follow the mantra!). There were images of famous thinkers through the ages who approached the world differently than the rest of us. One of those was Albert Einstein.

Among a community of bright and creative people, it gives me pause to consider those people that we all think of as being remarkable. Albert Einstein is arguably the most famous scientist in history of the world, commanding the respect not just of the general populous, who have grown up immersed in his legend, but also the respect of the scientific community. Why is that? My colleague Rai Weiss, now an emeritus professor at MIT, recently noted that it wasn’t just that Einstein was smart, it was that he exhibited tremendous intuition. His great ability was to look at the same world the rest of us look at every day, and think different.

When Einstein began his quest to refine our understanding of gravity, he knew he was going to have to “think different” — this was, after all, what had led to special relativity in the first place! One of the earliest musings on the road to general relativity was a simple question: how do you know if gravity is pulling on you?

Everything I need to start developing some new ideas about gravity!

Everything I need to start developing some new ideas about gravity!

It’s a seemingly simple question, but it led to an interesting thought experiment. Imagine you and I are each in a small, windowless room with nothing but an apple and our smartphones (so we can text each other the results of the experiment I am about to describe).

Each of us drops our apple, and we see that it accelerates downward — it falls!  The apple starts from rest (at our hands) and speeds up as it falls toward the floor of our small room.  We excitedly text the result to each other and tweet pictures of apples on floors. Should we conclude from these experiments that we are both conducting experiments under the influence of a gravitational field?

[Top] You and I conduct identical experiments (dropping apples) in enclosed spaces and get identical results. [BOTTOM] The reality of what is outside our little rooms may be completely different! A falling apple is equally well explained by the gravity of a planet, or by an accelerating rocket!

[Top] You and I conduct identical experiments (dropping apples) in enclosed spaces and get identical results. [BOTTOM] The reality of what is outside our little rooms may be completely different! A falling apple is equally well explained by the gravity of a planet, or by an accelerating rocket!

Einstein realized the answer to that question should be “No!” There are multiple ways to explain what we saw.  One way is to assume our little rooms are sitting on the surface of planet Earth, where the planet’s gravity pulled the apple down. But another, equally valid way to explain this experiment is to assume the little rooms are really the space capsules of rocket ships, accelerating through empty space (the apple is pressed down to the floor — “falls” — the same way you are pressed back in your seat when a jetliner takes off).  What Einstein realized is that there is no way, based on our experimental results, to tell the difference between these two cases. As far as experiment is concerned, there is no fundamental difference — that is to say, no observational difference — between them. Einstein knew that the laws of physics had to capture this somehow.

[TOP] You and I both find ourselves weightless, floating without feeling forces acting on us. [BOTTOM] The reality external to our rooms could be that we are floating in space, or that we are in a freely falling elevator plummeting to our doom.

[TOP] You and I both find ourselves weightless, floating without feeling forces acting on us. [BOTTOM] The reality external to our rooms could be that we are floating in space, or that we are in a freely falling elevator plummeting to our doom.

What if we consider a slightly different case? Imagine you and I both suddenly found ourselves and our apples drifting weightlessly in the middle of our small rooms. We excitedly text each other that we finally made it to space and tweet messages that we are officially astronauts. Should we conclude that we are both deep in interplanetary space, far from the gravitational influence of a planet? Once again, Einstein realized the answer to that question should be “No!” There is no way to know if we are drifting inside a space capsule in deep space, or if we are merely inhabiting an elevator whose cable has snapped and we are plummeting downward toward our doom!

tweetEquivalence_smallIt is this freefall experiment that really illustrates how we have to learn to “think different” when expanding our understanding of Nature. In Newtonian gravity, we always look at problems with an exterior, omniscient eye toward the problem. A Newtonian approach to the free fall problem says “Of course you are falling under the influence of gravity! I can see the Earth pulling you down from the top of the skyscraper toward your doom at the bottom of the elevator shaft!” But Einstein asked a different question: What does the person in the elevator know? What experiments can they do to detect they are in a gravitational field? The answer is “none.”  There is no observational difference between these two situations, and the laws of physics should capture that.

The critical point here is that if you are in free fall, you feel no force! Einstein’s great insight was that the central difficulty with gravitational theory up to that point was that it was anchored in thinking about forces. This thought experiment convinced him that the right thing to think about was not force, but the motion of things.

This thought experiment came to Einstein in 1907 on a languid afternoon in the Bern patent office. Later in his life, Einstein would recall that moment and this idea with great fondness, referring to it as the happiest thought of his life.  This experiment is known as the “universality of free fall,” which physicists like to give the moniker “the Equivalence Principle.”

This is how I often imagine Einstein’s life during the years he worked in the Bern patent office! [From "The Far Side" by Gary Larson]

This is how I often imagine Einstein’s life during the years he worked in the Bern patent office! [From “The Far Side” by Gary Larson]

I have a very strong memory of my father first telling me about the universality of free-fall in about fifth or sixth grade. When you’re not used to it, the notion that falling in an elevator is the same as floating in outer space engenders a spontaneous and vehement response: “That can’t be true!” We had many long debates about this (it was following hot on the heels of my meltdown over the existence of negative numbers — maybe my dad was trying to forestall another meltdown…), and I don’t think it ever quite sank in. I, of course, feigned understanding and dutifully repeated the tale of the falling elevator to my classmates, reveling in their confusion and indignant denial of the logic of it.  I was a tween — what did you expect?

The "Leaning Tower of Niles," a half-scale replica of the tower in PIsa. Located in Niles, IL (a suburb of Chicago).

The “Leaning Tower of Niles,” a half-scale replica of the tower in PIsa. Located in Niles, IL (a suburb of Chicago).

But now, many years later and with a LOT of physics under my belt, I know that that the outcome of these thought experiments derive from a very old result that we are all familiar with — that all objects fall identically, irrespective of their mass. Galileo taught that, at least in folklore, by dropping various masses off of the Leaning Tower of Pisa. The obvious question to ask is “how is Galileo’s experiment connected to Einstein’s thought experiments?”

For the moment, imagine the various parts of your body as having different masses.  Your head masses about 5 kg (a little bit more than the 8 pounds you learned from watching Jerry Maguire), where as a good pair of running shoes may mass about 1.5 kg.  If you are standing happily in the elevator when the cable snaps, the traditional explanation is that everything begins to fall.

If objects of different mass fell at different rates, then your head would be pulled down faster than your shoes — you would feel a force between your head and your shoes. That force could be used to deduce the existence of a pulling force.  But Galileo taught us that is not the way gravity works — your head and your shoes will get pulled down at strictly the same rate in a uniform gravitational field. Every little piece of you, from your head to your toes, your kneecaps to your freckles, falls at the same rate — there are no different forces between the different parts of your body and so you feel (you observe) yourself to be weightless. This is sometimes called the Galilean Principle of Equivalence, or the Weak Equivalence Principle.

Okay — so what? Apples and freefall, elevators and rockets. What does any of this have to do with developing a deeper understanding of gravity?

What this thought experiment reveals, what the Equivalence Principle tells us, is that thinking about forces is not the best way to think about the world because we can’t always be sure of what is going on! Instead, we should think about what we can observe — how particles move — and ways to describe that. That simple intuitive leap would, in the end, change the face of gravity. Particles move through space and time, which had brilliantly been unified by Einstein’s teacher and colleague, Hermann Minkowski, into a single unified medium called “spacetime.”

What is spacetime? It is the fabric of the Cosmos —  it can be stretched and deformed. The fundamental idea of general relativity is that gravity can be described not by a force, but by the curvature of spacetime, the medium on which particles move.  That will be the subject of our next little chat.

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This post is part of an ongoing series written for the General Relativity Centennial, celebrating 100 years of gravity (1915-2015).  You can find the first post in the series, with links to the successive posts in this series here: http://wp.me/p19G0g-ru

A Pale Blue Glow

by Shane L. Larson

One of the great things about being a scientist is I’m exposed to amazing and awesome things. Every. Single. Day. Sometimes I am astonished by Nature itself, and other days I am amazed by our ingenuity and abilities as we come of age in the Cosmos. Today was one of those days.

The first picture of the Moon and Earth together in space, taken by Voyager 1.

The first picture of the Moon and Earth together in space, taken by Voyager 1.

This story has its origins long ago. On 5 September 1977 we hucked a 722 kg spacecraft into the sky, named Voyager 1. That was the last time any of us ever saw Voyager 1 with our own eyes. But Voyager has been on a 37-year journey to act as our eyes in the Solar System. On 18 September 1977, barely 13 days after launch, when it was 7.25 million miles from Earth, Voyager sent home the first picture ever of the Earth and Moon together in space. It went on to Jupiter, where it took pictures of clouds and storms that look for all the world like the finest paintings on Earth, and discovered the first active volcanoes beyond the Earth on the enigmatic moon Io. At Saturn, it returned the first high-resolution images of an exquisite ring system, and showed us a shattered Death Star like Moon known as Mimas, dominated by an enormous crater named Herschel. But for all the wondrous pictures, we never saw Voyager. Like your Mom taking pictures of your childhood, we have never once seen the photographer chronicling our growth.

Just a sample of the kinds of discoveries made by Voyager 1. (TopL) Exquisite cloud structure on Jupiter. (TopR) Active volcanism on Jupiter's moon, Io. (BottomL) Tremendous structure in Saturn's rings. (BottomR) Saturn's moon, Mimas.

Just a sample of the kinds of discoveries made by Voyager 1. (TopL) Exquisite cloud structure on Jupiter. (TopR) Active volcanism on Jupiter’s moon, Io. (BottomL) Tremendous structure in Saturn’s rings. (BottomR) Saturn’s moon, Mimas.

But today, I saw something that made me smile. Since it began its long outbound journey, we’ve been talking with Voyager 1 on a radio. In all, it only transmits about 20 watts of power, something typical of a larger compact-fluorescent-lightbulb. The total power received on Earth from Voyager is about a ten-billionth of a millionth of a watt. In one second, we receive less than a trillionth the energy a single snowflake delivers to your shoulder as you’re walking to work.

VLBI image of Voyager 1, diligently beaming its signal back to Earth.

VLBI image of Voyager 1, diligently beaming its signal back to Earth.

But take a look at the picture above, released by NASA last fall. See that pale blue dot right there? That is Voyager 1, seen through the eyes of the Very Long Baseline Interferometer, an array of linked radio telescopes that stretches from one side of the Earth to the other. It sees the sky in radio light. Normally it looks at quasars and distant nebulae, but this image is of Voyager 1, shining its radio back at Earth. This is the first radio signal of human origin ever to be received from outside the solar system. It is also the first picture of Voyager 1 taken since its launch. It’s a bit like seeing your friend in the dark, waving their cellphone at you from a distant mountaintop.  But it’s there, and we can see it — the pale radio beacon of Voyager 1, drifting alone in the immense dark between the stars.

Long after it runs out of power, Voyager 1 will continue to drift alone through the galaxy.

Long after it runs out of power, Voyager 1 will continue to drift alone through the galaxy.

What will happen to Voyager 1? It will continue to talk to us for a little while longer. It is powered by a small nuclear power plant, gleaning energy from the decay of plutonium. But that energy supply is dwindling, and sometime around the mid 2020’s, just more than a decade from now, Voyager 1 will fall silent. The pale blue glow will disappear forever; there will be no more pictures of our loyal emissary. Voyager 1 will continue onward however, bound for the depths of the galaxy, a dead hulk built by a race of curious lifeforms that call themselves “humans.”

But now this has me thinking. All of our knowledge of the outer solar system has been gleaned with telescopes, and with robotic emissaries.  None of the sights you have seen in pictures has ever been witnessed directly by human eyes. Not the dual-tone colors of Saturn’s enigmatic moon Iapetus; not the spider-web of canyons in Mercury’s Caloris Basin; not the misty depths of the Valles Marineris on Mars. Instead, Casinni has been twirling through the Saturn system for almost a decade, and has returned the highest resolution images of Iapetus we’ve ever seen.  Mercury MESSENGER, only the second spacecraft ever to visit Mercury, finally arrived in 2011 and sent high resolution images of the Spider Crater back to Earth. And Mars? Well, Mars has its own fleet of orbiting satellites and ranging rovers to investigate its mysteries.

(L) Saturn's moon Iapetus has a light and a dark side. (C) The Spider Crater on the floor of Mercury's Caloris Basin. (R) Fog in the Valles Marineris on Mars.

(L) Saturn’s moon Iapetus has a light and a dark side. (C) The Spider Crater on the floor of Mercury’s Caloris Basin. (R) Fog in the Valles Marineris on Mars.

What happens to all our tiny robots, sent out into the Cosmos all on their own? We’ve been tossing them into space almost non-stop since the start of the Space Age — what happens to all of them?

Only 5 will ever travel beyond the solar system. Pioneers 10 and 11 are both bound for interstellar space, now quiet and dead after their power supplies failed in 2003 and 1995. Voyager 1 and 2, having completed their Grand Tour of the outer solar system, are also outbound; we expect to lose contact with them within the next 10 to 20 years. And lastly, there is New Horizons, bound for Pluto and the Kuiper Belt beyond. It is by far the youngest of this august group of explorers. It was designed to have power for 20-25 years, but it has already spent the last eight-and-a-half years just getting to Pluto — it should last another 15 years or so.

Spacecraft that are going to escape from the solar system. (L) Pioneer (C) Voyager (R) New Horizons

Spacecraft that are going to escape from the solar system. (L) Pioneer (C) Voyager (R) New Horizons

(T) When Spirit got stuck on Mars, NASA engineers recreated the situation on Earth, trying to figure out how to free the rover. (C) Artist's imaging of what Galileo looked like as it burned up in the Jovian atmosphere. (B) The LCROSS mission before impact.

(T) When Spirit got stuck on Mars, NASA engineers recreated the situation on Earth, trying to figure out how to free the rover. (C) Artist’s imaging of what Galileo looked like as it burned up in the Jovian atmosphere. (B) The LCROSS mission before impact.

Many of our robots, like the Voyagers and Pioneers, will just die. This famously happened to the Spirit rover on Mars. It trundled around the Martian surface for 2269 days (perhaps, some say, trying to earn a trip back home) before we lost contact with it. Spirit had become stuck in a Martian sand dune and was unable to free itself. Stuck on flat ground, unable to tilt itself toward the Sun to keep warm in the cold Martian winter, we last spoke with Spirit on 22 March 2010.

The Galileo mission, which spent more than seven-and-a-half years exploring the Jovian system, was crashed into Jupiter, to prevent it from tumbling out of control when its power failed, possibly contaminating a moon like Europa, where we can imagine extraterrestrial life may exist. On 21 September 2003, it was plowed into Jupiter. We couldn’t see it take the final plunge, but we listened to it faithfully radioing us everything it could for the last few hours before its end.

Sometimes, we crash our spacecraft on purpose, for science! One of the most spectacular examples of the was LCROSS, the Lunar Crater Observation and Sensing Satellite. The goal of this mission was to look for water ice in the perpetually shadowed craters on the surface of the Moon; water on the Moon would have important implications for the sustainability of lunar colonies. LCROSS had two pieces — it’s Centaur rocket stage, and the Shepherding Spacecraft that carried the science instruments. On 9 Oct 2009, the Centaur rocket impacted the Moon at a speed of about 9000 kilometers per hour; the Shepherding Spacecraft flew through the cloud of debris and radioed the composition back to Earth. This exquisitely timed dance was a planned suicidal flight for the Shepherding Spacecraft; its unavoidable fate was to impact on the Moon about 6 minutes after the Centaur stage. The result? There is water, frozen in the lunar soil.

But the saddest fate to me, is that of Mercury MESSENGER. MESSENGER was the first spacecraft to visit Mercury since Mariner 10 flew by three times in 1974. Despite three passes, Mariner 10 only mapped out about 45% of the surface; until MESSENGER’s arrival in 2011, we had no idea what more than half of Mercury looked like.  It took MESSENGER 7 years to get to Mercury. It has been there for about three-and-a-half years at this point, and we are looking ahead to the end. Over time, the closest point of MESSENGER’s orbit has been getting lower and lower, affording us the opportunity to understand Mercury’s gravitational field and to map and  probe the surface of Mercury with exquisite resolution. But lowering the orbit, to get a closer view of the planet, is a one way ticket, eventually leading to MESSENGER’s impact on the surface of Mercury.

Mercury MESSENGER

Mercury MESSENGER

The end will come sometime after March of 2015, on the far side of Mercury from our view.  MESSENGER will die alone, cut-off from us by distance and astronomical happenstance. In the words of MESSENGER PI, Sean Solomon, “This will happen in darkness, out of view of the Earth. A lonely spacecraft will meet its fate.”

This emotional attachment and personification of machines seems disingenuine to some people; spacecraft aren’t people, they are collections of wires and circuits and nuts and bolts — they don’t have souls to become attached to.  I dunno. I think they do have souls. They are the embodiment of every one who ever imagined them, worked on them, or stared at the data and pictures they returned. These little robots, in a way, are us. They are our dreams. Dreams of adventure, of knowledge, of a better tomorrow, of understanding who and what we are in a Cosmos that is vast and daunting.

And so today I smiled at the pale blue picture of our long departed friend, Voyager 1. And on the day it falls silent, I’ll shed a tear and drink a drink to its remarkable voyage, a voyage it made for you and me.