A Majestic End for a Faithful Friend

by Shane L. Larson

We live in an age where digital technology can make anything seem real. Movies have become immersive experiences where any landscape, real or imagined is possible. Physics defying stunts are rendered on screens as tall as buildings and with sound louder than thunder. Creatures long extinct or completely imagined spring to life, and actors long since passed from the world magically return to the screen, appearing as they did in their youth. Anything seems possible, and the boundaries of reality are blurred, to say the least.

Anything can be given realism with modern technology, whether they be long dead creatures, imagined aircraft, or an architectural plan for a new building. [all images from Wikimedia Commons]

We are so used to this, that when confronted by real pictures of the real world, we often forget what we are looking at. Fantastic and awe-inspiring pictures slip past us and don’t always capture our attention. Photographers capture massive migrations of animals across the land and sea, forlorn sights of abandoned corners of our cities, and the vibrant colors of rainbows and autumn leaves. When we see those pictures, at just the right moment, we experience a visceral moment of joy and set our phone screens and computer desktops to the image, to remind us of that moment of wonder. But more often than not, we don’t remember that real pictures of the real world can evoke emotional responses in us. Some small part of our brain remembers, of course, else we wouldn’t takes selfies in front of restaurants where we enjoy fantastic dinners, or pictures of sunsets against the skyline of our backyards.

On many days, as the woes of the world sidle past me on my computer screen, I am reminded of something that I became aware of in my youth: the true masters of real pictures of the real world are the folks at NASA. They have long been part of the storytelling narrative, reminding us that we are part of a far larger Universe, showing us that with concerted effort and imagination and perseverance, we can overcome tremendous obstacles, solve incredibly difficult problems, and discover that the world around us is filled with unimagined and awe-inspiring grandeur. The Cosmos is alive and breathing around you, reminding you that you are part of something greater that the usual bibble-babble washing out of your device screen.

NASA’s digital artists are masters of putting us at the center of the action, even if it is impossibly far away. L to R: Curiosity skycraning onto Mars; Juno arriving at Jupiter; Cassini arriving at Saturn. [Images by NASA]

In the last few years, our friends at NASA have upped their game. Not only have they regaled us with real pictures of the real world, but they’ve picked up the story-telling torch, and as masterfully as any filmmaker in the world catapulted us into the drama of exploring the Cosmos. You may remember this when they told us about the Seven Minutes of Terror as we lowered the Curiosity rover onto Mars using a robotic, rocket-powered skycrane. Last year, they told us the tale of returning to the unknown regions around Jupiter with a hearty spacecraft called Juno, diving into the radiation belts where anything could happen. But recently, they turned their attention to a far-away world called Saturn, and a steadfast spacecraft we sent there called Cassini….

Saturn has been known to humans since antiquity, one of the bright moving lights in the sky known as the planētes asteres, the “wandering stars.” Like the other naked eye planets, Saturn moved slowly among the stars, tracing out a path along the band of constellations known as the Zodiac, cementing itself in the folklore and mythology of sky-gazers who watched it closely. In the 17th century, the era of Saturnian exploration began when the first telescopes were pointed skyward. The first fuzzy, warbling views of the world showed it was not like the stars at all. Telescopes improved rapidly, as did the views they showed of this far away planet, until at last we discovered the truth — Saturn was magnificently bejeweled by a brilliant, encircling ring. Since that time, Saturn has reigned supreme among all the planets for the awe it evokes at its splendor and beauty. More than any other planet, it looks like it is supposed to look. Today, millions of telescopes around the world are set-up in backyards and on sidewalks on clear nights, giving ordinary people like me and you views of one of the Cosmos’ great spectacles — you can have your own Saturn Moment.

View of Saturn you will have through a modern backyard telescope, taken with an iPhone [Image courtesy of Andrew Symes]

Like most things in space, Saturn is unfathomably far away. At a distance of 1.3 billion kilometers from Earth, it would take you about 1400 years to drive to Saturn’s orbit in your car, or about 150 years to fly there at the speed of a passenger jet. We are, by and large, restricted to staring at it from afar, gleaning what we can from the meager light gathered in our telescopes. The arrival of the Space Age put a new possibility on the table: travelling across the void. Suddenly, we had the chance to see Saturn up close.

While there are effervescent dreams to send humans, Saturn is still too distant to imagine easily crossing the void ourselves, so our attention has been focused on sending quasi-intelligent emissaries in our stead: robotic explorers whose sole purpose is to gather as much information and take as many pictures as possible, and transmit all of that information back to Earth.

Our robotic emissaries, Pioneer 11 (left) and Voyagers 1 and 2 (right). These are the only spacecraft to have ever visited the gas giant worlds of the Solar System. [Images by NASA]

In the 60 years since the start of the Space Age, only 4 spacecraft have ever visited Saturn. The first was a resolute robotic explorer called Pioneer 11.  In 1979, it flew by Saturn skimming through just 20,000 kilometers above the cloud tops, returning the first up close pictures of Saturn, but only a few. It was followed by Voyager 1 in 1980, and Voyager 2 in 1981. The Voyagers returned wide planetary views of Saturn that became iconic to an entire generation of humans, and showed us an ensemble of moons that are each unique and tantalizing, demanding their own careful program of exploration. All of these missions flew past Saturn, returning quick passing views before sailing onward. Today, Pioneer 11 and Voyagers 1 and 2 are on an unknown voyage, destined to drift in the great cosmic dark between the stars for a billion years.

Closeup views of Saturn by Pioneer (left) and Voyager (right). Their time with Saturn was short because they were doing flybys (try taking a picture of your friend on the sidewalk as you drive by at 50 miles per hour…). [Images by NASA]

The most recent of the quartet of august explorers is a two tonne spacecraft called Cassini. It spent seven years crossing the void to Saturn, and has spent the last 13 years circling Saturn, probing the ringworld and its remarkable moons. Twenty years ago, it was cocooned up inside its rocket, and hurled into space. No human has seen it since.

This image is one of the last pictures taken of Cassini in 1997, before launch; the whole spacecraft, together with a few of the people who gave it life. Not soon after, the rocket fairing was lowered into place and closed, cocooning Cassini inside. That was the last any human ever saw of it. [Image by NASA]

For more than a decade, we have been treated to remarkable images, ranging from the strange divided faces of Iaepetus, to the mangled surface of small, tumbling Hyperion. We saw stunning views of the blue-white ice of Enceladus, and ephemeral views of Saturn and its rings, backlit by the distant Sun.

The images returned by Cassini have been stunning, and are far too numerous to do justice to here. A few favorites include: Hyperiod (top left), Enceladus (top center), Iapetus (top right), and Saturn backlit by the Sun (lower). [Images by NASA]

But never among these has there been an image of Cassini itself. Unlike its siblings, the Mars rovers, Cassini cannot take a selfie. But our artists have continued to insert Cassini into imagined views of the Saturnian system, seen as if we were sailing along side it, snapping pictures for the family photo album. Cassini cruising over Titan; Cassini plummeting through the ice plumes of Enceladus; Cassini looking back toward a distant blue star that is Earth.

Artist imaginings of Cassini during its decades long exploration of Saturn. [Images by NASA]

Now, after a two decade journey, we are nearing the end. Cassini’s tasks are nearly over. Unlike Pioneer 11 and Voyager 1 and 2, Cassini is bound to Saturn forever; it will not embark on a lonely voyage to the stars, and in fact, it can’t: there simply isn’t enough fuel in its rockets. Instead, the humans who lovingly crafted it and meticulously planned its journey have planned a magnificent send-off. We call it The Grand Finale. The end of the journey is stunning, worthy of an adventurer as bold and brave as Cassini. But we won’t be able to see it, so once again we turn to our artists to illuminate the images in our minds eye.

Some images from Cassini’s Grand Finale. (L) Saturn’s polar regions, up close as Cassini loops over the top of the planet for another ring pass. (C) One of the highest resolution images of the rings ever taken. (R) The small moon Daphnis, carving out a corridor in the rings. [Images by NASA’s Cassini Imaging Team]

In a series of slowly descending orbits, Cassini will voyage closer to Saturn than any spacecraft before. Looping high over the planet, it will plunge down through the rings for the first time, then loop back around and do it again. Over and over again, it will pass through the rings and skim the top of Saturn’s atmosphere. In all, the Grand Finale consists of just more than 22 orbits. On each orbit it dutifully records what it finds, and relays that information back to us here on Earth. Already we have received stupendous views of the rings, of the cloudtops from closer than we’ve ever seen, and the nearby moons framed by a sky simultaneously more majestic and more alien than any we could imagine in a Hollywood studio.

But at the very end, when there is no where else to go, Cassini will finally succumb to the inexorable gravitational pull of Saturn, and be drawn down into the atmosphere. Travelling more than 75,000 miles per hour, it will burn up in a colossal fireball. One of a thousand meteors that might hit Saturn on any day, but this one from a nearby world. We won’t see Cassini. As it falls, it will be linked to Earth only by the tenuous thread of its radio link, faithfully relaying the last of its observations as it sinks forever into the ocean of Saturn’s atmosphere.  At some point, we don’t know when, Cassini will be gone. With no one to see it, Cassini will disintegrate into nothing. Out of our sight, the last of our dreams and aspirations for Cassini will come to an ultimate end.

Will will mourn. But always we will return to the vast photo album we have assembled over its 20 year life. Like a long time friend departing for the other side of the veil of death, we can’t help but be simultaneously overwhelmed by sadness together with admiration for everything that this little robot has accomplished, against all odds. Cassini has forever transformed our understanding of Saturn. Saturn is a real place, as much a part of the story of our solar system and our home as anything we have ever seen.

Once again our artists capture what we cannot see, rendered in NASA’s End of Mission video, using the tools of entertainment to tell us the story of our long departed emissary in it last moments over Saturn. More than any other art or video I’ve seen, they’ve succeeded in evoking how truly huge and majestic Saturn is, and how tiny Cassini is by comparison. All that we know, all that we’ve discovered, we owe to a tiny robot immeasurably dwarfed by the planet it has so faithfully explored.

You owe it to yourself to go watch this video; reflect on all that Cassini is and was, and know that we are capable of doing tremendous things.

Ad astra per aspera. Fare thee well, Cassini.

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.

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.

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.

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.

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.

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

(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

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.

Cosmos 6: Travellers’ Tales

by Shane L. Larson

Sitting at the gate at Chicago’s O’Hare International Airport, staring at the thousands of other people around me, I am struck by how remarkably connected the modern world is.  I’m not thinking about smartphones and instant personal communication; rather I’m staring out the window at a Boeing 777 and thinking that I can go travelling virtually anywhere on the Earth, in just a day or so, by walking down the jetway.  And we all do it in a blink of an eye.  Sometimes we go for work, to exotic places like Dallas or Albuquerque.  Sometimes we go to visit family, like grandma in Mobile, or Aunt Becky and Uncle Bob in Bemidji.  But sometimes, we jet off across the world, just to go exploring.  We go to see the grand Buddha of Leshan, or the primeval rain forests of the Amazon, or the volcanoes near Reykjavik, or Gaudi’s Sagrada Familia in Barcelona.

(L) The Grand Buddha of Leshan. (R) Sagrada Familia. [Photos by S. Larson]

While on our adventure, we take selfies, we send text messages that say “Guess where I am?”, and we wonder at the marvels of the world. When we return home, we may bring a few trinkets — a silk shirt, a wall hanging, a journal embossed with foreign words and images.  But the things we return to time and again, years after our voyage, either in idle strolls down memory lane or to show family and friends, are our pictures.  Pictures are the single most common and important thing brought back from adventure voyages, as they alone have the magic to transport us  back to those far away lands, with our friends alongside us.

Text messages and selfies, some of the most common travellers’ tales of the modern age.

There was a time when our world was not so easily accessible, when the far corners of the Earth had not yet been discovered, and adventurers didn’t know what they would find on a long voyage of discovery. In the 1700’s, Captain James Cook made three epic voyages around the world, aboard ships whose names have become synonymous with exploration and discovery: HMS Endeavour (a name latter passed onto a United States space shuttle orbiter), and HMS Resolution. Cook’s papers and journals of those voyages were collected and studied for many years after his death, but one of the greatest treasures returned from the voyages were images of far away lands. In those days of exploration, every ship was crewed not just by sailors, but by professionals.  Some were scientists tasked with observing and recording discoveries along the voyage, and others were artists tasked with capturing images of the voyage to record and relay the adventure to those left behind. Without those artists eyes, we would never know what Cook saw on those first, epic voyages.

Images by artist William Hodges, who accompanied James Cook on his second voyage. (L) The HMS Resolution near Antarctica, and (R) HMS Resolution in Matavai Bay, Tahiti.

Today, the world is completely mapped, cultures (for the most part) have been found and documented, and there are precious few places humans have not yet tread.  Voyages of new discovery come more rarely, and people like you and me have adventures that begin with airplane rides and are documented through the lenses of smartphones.  While you and I have set our sights on worldly adventures like visiting Mammoth Cave in Kentucky, or picnicking in the shadow of Moai on Easter Island, our species’ thirst for adventure has grown beyond the Earth.  We have embarked on a new adventure to seek out new horizons and unknown landscapes far out into the Cosmos. The primary commodity of these new adventures are pictures — thousands and thousands of stunning pictures of cosmic vistas that move our spirits in ways we could have never imagined.

I often dream of being able to visit the Moai of Easter Island. [Illustration by S. Larson]

The sky has always compelled us to look up.  Even were we not fascinated with the strange and unearthly things we have found in the sky, the sky presents events that compel us to look up.  Consider the case of eclipses.  The Sun is the most brilliant source of light in the solar system, and every object it shines on casts a shadow, including the Earth. The Moon, on its rounds about the Earth, sometimes fleets through the shadow of the Earth.  As it passes into the shadow, it begins to disappear, an ever growing curve of shadow slowly eating the bright disk of the Moon. When it reaches the center of the shadow, the Moon takes on a deep reddish hue, cast in scarlet tones by the sunlight streaming around the Earth and through its atmosphere — an Earth sunset on our closest neighbor in the Cosmos.  This event is called a lunar eclipse.

(L) The geometry of a lunar eclipse. (R) iPhone image of the total lunar eclipse on 10 Dec 2011. [images by S. Larson]

The Moon also casts a shadow, and sometimes that shadow falls on the surface of the Earth, casting a fleeting moment of darkness wherever it falls.  Seen from the Earth, the Moon creeps across the Sun, an ever growing curve as the Moon blocks the brilliant solar disk.  At the center of the eclipse, the Moon covers the Sun and those standing in the center of the shadow are treated to a rare sight — the blazing corona of the Sun.  This event is called a solar eclipse.  Eclipses in our ancient past were unexpected and likely inspired fear and superstition.  Today, we can predict when they occur and where to stand to see them. People from all over the world step onto airplanes, and fly to stand in the shadow of the Moon.  They take their cameras with them, and capture images of the event to share with friends and family when they return from their travels.

(L) The geometry of a solar eclipse. (C) Image of total solar eclipse taken by Arthur Eddington in 1919. (R) Hydrogen alpha image of the annular solar eclipse on 20 May 2012 in Cedar City, Utah. [by S. Larson]

Another, rare kind of eclipse is called a Transit of Venus, when Venus passes between us and the Sun, appearing as a small black dot traversing the solar disk. Beautiful and inspiring to see, observing a transit of Venus was one of the first ways that people figured out to measure the distance from the Earth to the Sun. Transits can be seen in pairs roughly every 121 or 105 years (a 243 year pattern), when the orbits of Earth and Venus are aligned just right. The most recent pair of transits was in 2004 and 2012. Two scientists, Charles Green and Daniel Solander, accompanied James Cook on his first voyage, tasked with observing a transit of Venus, which they did from Tahiti on 3 June 1769.

Transit of Venus seen from Wasilla, Alaska on 5 June 2012 [iPhone photo, through a solar telescope, by S. Larson]

While one could spend a lifetime standing on the surface of the Earth looking up into the Cosmos, some part of us knows that we could learn so much more if we just go up there.  And so we have.  For the most part, our emissaries beyond the Earth have been robots — machines of human design, supremely instrumented and exquisitely engineered to make interplanetary voyages that we cannot. Our robots have sailed the interplanetary sea and visited every major world in the solar system, providing tantalizing and brief glimpses of alien shores through pictures radioed back to their creators on faint radio links.  Travellers’ tales, recorded through the electronic eyes of semi-intelligent robots, are the principal commodity of the age of space exploration. Tales that paint a tapestry of wonders brilliant and evocative, tempting us with the promise of what we might discover if we were to dig deeper, push farther, and continue the exploration.

Of all the many worlds in the solar system of which we are aware, there are only five on which we have landed and returned images from the surface: the Moon, Venus, Mars, Saturn’s moon Titan, and the asteroid Eros. These are the only worlds beyond the Earth whose surfaces we have tread upon, and only on the Moon and Mars have we ventured away from the landing site (using rovers). At all of the sites, we have tantalizing pictures of alien shores that sing a siren song of adventure when we look out across them. 

(A) Surface of Eros by NEAR-Shoemaker. (B) Surface of Titan by Huygens. (C) Surface of Venus by Venera 14. (D) Apollo 15, station 9 on Hadley Rille. (E) Surface of Mars, near Bonneville Crater by the Spirit Rover.

But most of our probes are not landers — they are semi-intelligent cans of electronics, wires, metal and composites that we have hucked out into the Cosmic sea, leaving them destined to drift forever in the sky.  Most of the images they return are all taken from orbit or on a one chance “flyby.”  The stories they tell are a bit like describing a state by looking out the window of a plane as it passes overhead, but the tales are riveting mysteries of the past, present and future of the worlds in our solar system. 

On Mercury, we’ve found a vast impact basin, just discovered in 2008 by the MESSENGER spacecraft. The basin is more than 700 kilometers across; if it were on Earth it would stretch from San Francisco to Seattle.  A vast circular hollow excavated in the early days of the solar system, the central plains are a vast expanse of ancient lavas criss-crossed with ridges and troughs that have been frozen into the landscape since their formation — there is no weather on Mercury to weather and fade the scars of ancient geologic trauma.  We’ve named it Rembrandt after the famous Dutch painter — a fitting name for such a picturesque place.

(L) Rembrandt, on Mercury. (R) Saturn by Cassini.

At Saturn, Cassini has radioed back exquisite images of the subtle tawny clouds of Saturn, always framed by the brilliant arc of the great rings.  But on its way to Saturn, Cassini did a little sight-seeing, and as it sailed past Jupiter toward Saturn, recorded a mesmerizing movie of that planet’s banded clouds. The clouds swirl and rotate as they are pressed before winds blowing as fast as 500 kilometers per hour, nearly twice as fast as the strongest winds ever seen on Earth.  

Jupiter’s cloud bands, as seen by Cassini (click to animate).

Among all the space probes we have set adrift, five hold a special place of honor.  They are Pioneer 10, Pioneer 11, Voyager 1, Voyager 2, and New Horizons.  These are the only probes we’ve built that are destined for interstellar space after their reconnaissance of the solar system.  Thousands of years from now, their creators long forgotten and returned to dust, these spacecraft will sail on into the interstellar void of the galaxy.

Now fallen silent, their energy reserves exhausted, the Pioneers no longer send tales home to Earth. But each carries a story with it, in the form of a small plaque telling the tale of the probes’ origins, should any intelligent being find it in the distant future.  A bottle cast into the Cosmic Ocean, I often wonder about those who might one day stumble on Pioneer 10 and 11.  Will they be alien intelligences?  Or perhaps will they be some impossibly distant descendant of humans, stumbling on a forgotten remnant of their past? Will they understand the message, and understand what Pioneer was doing in a long forgotten epoch of time?

(L) The Pioneer plaque, amidships on Pioneer 10. (R) The two sides of the Voyager record. You can explore the Voyager record online (at the JPL Voyager site, or at a complete online archive), or in the (now out of print) book Murmurs of Earth.

Both Voyager spacecraft also carry a message in the form of a Golden Record. The record contains instructions for use, a map pointing back toward Voyager’s origin, and its own set of travellers’ tales: a set of 55 greetings in different languages of Earth, 116 images of life on Earth, and 90 minutes of music from around the world ranging from masterpieces by Mozart, to Chuck Berry’s Johnny B. Goode, to a traditional Peruvian wedding song.  The record bears one final message, inscribed on its inner edge, a handwritten message: “To the makers of music — all worlds, all times” (etched by Timothy Ferris, the producer, when the record was completed).

The ADS All Sky Survey, a rotatable interactive map showing where we’ve taken pictures of the sky.

The principal commodity of science, and astronomy in particular, is knowledge. The tangible evidence of that knowledge is pictures.  Images capture both scientific knowledge and cultural aesthetic; they can be appreciated by everyone for the wonder they evoke and the questions they provoke.  At a recent gathering of the American Astronomical Society, some of my colleagues showed a new kind of astronomical map.  It is a map of the entire sky, but instead of showing us the secrets veiled away in the deep Cosmos, the map shows us how often we have looked at or studied — taken a picture of — a particular place in the sky. To the trained eye, you can see the Andromeda Galaxy, the Large and Small Magellanic Clouds, the plane of the Milky Way, the plane of the Solar System, and the area covered by the Sloan Digital Sky Survey.  But what amazes me most about this picture is how LITTLE of the sky we have seen — most of the map is  black, meaning no picture has been taken there.  That is a staggering shame, since as the Hubble Deep Field as shown (and its successors, the Ultra Deep Field, and the Extreme Deep Field), even the most remote, dark and (we thought) empty places in the sky are filled with uncountable mysteries.  The sky is a BIG place, and we are far from having seen it all.

And so we continue to stare, we continue to take pictures, and we continue to spin travellers’ tales about what we’ve seen, what we know, and what we still would like to discover.

The Hubble Ultra Deep Field (UDF), showing what is unseen but can be found if you stare at an empty part of the sky for long enough.

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This post is part of an ongoing series, celebrating the forthcoming science series, Cosmos: A Spacetime Odyssey by revisiting the themes of Carl Sagan’s classic series, Cosmos: A Personal Voyage.  The introductory post of the series, with links to all other posts may be found here:  http://wp.me/p19G0g-dE