Tag Archives: Europa

Cosmos 5: Blues for a Red Planet

by Shane L. Larson

More than any other world in the solar system, Mars has captured the imagination of the human race (except maybe for Pluto, but it’s not a planet, right?). Mars has dominated our imaginings of other worlds for more than a century, beginning with H.G. Wells’ masterpiece of invasion, The War of the Worlds.  Since The War of the Worlds was first written, many other tales of adventure, danger and horror have been penned or filmed concerning Mars — Kim Stanley Robinson’s epic Mars Trilogy, the classic 1964 film Robinson Crusoe on Mars, Elton John’s sonorous musings that Mars is no place to raise a family in “Rocketman,” and many many more.

Mars in fiction. (L) The frontpage of the first edition of The War of the Worlds. (C) The poster for Robinson Cruse on Mars. (R) The three volumes of Kim Stanley Robinson's Mars Trilogy.

Mars in fiction. (L) The frontpage of the first edition of The War of the Worlds. (C) The poster for Robinson Crusoe on Mars. (R) The three volumes of Kim Stanley Robinson’s Mars Trilogy.

Ray Bradbury [Wikimedia Commons.]

Ray Bradbury [Wikimedia Commons.]

I was first exposed to Mars in elementary school, through the reading of Ray Bradbury’s The Martian Chronicles, followed closely by viewing the 1979 screen adaptation of those Chronicles starring Rock Hudson. Bradbury’s Mars was a distant frontier, populated by indigenies resisting the influx of pioneers from Earth. Those pioneers were attempting to create a human civilization on Mars, ignorant of the fading race of natives who lived on the red sands before them. Having grown up in the American West, descended from a long line of ranchers who had homesteaded on the front range in Colorado, it was a familiar tale to me cast on a fantastical tapestry of rocket ships and alien landscapes. Bradbury’s tales of Mars are stories humans have always told about the frontier — tales of discovery, of finding out who we are by looking through the lens of our interaction with (and ignorance of) other lifeforms we have discovered.  In this case, the other lifeforms are the Martians.

The word “Martians” has come to mean more than just beings of Mars; the name has become synonymous with any alien species, vaguely if not outright humanoid.  Tales of Martians are often an allegorical mirror of the best ideals and worst fears we have about our own species.  Sometimes Martians are wise and benevolent; some, like the ghosts in The Martian Chronicles are noble and introspective in the face of extinction. Sometimes Martians are implacable and malevolent conquerers bent on owning the Earth, like the invaders in The War of the Worlds.

It was only natural that Mars become a focal point for our musings about other intelligent species.  Since the invention of the telescope, Mars has sung a siren song to the human race. It is the only planet whose surface can be seen through a telescope, giving us tantalizing glimpses of icy polar caps, vast dark plains that change with the Martian seasons, and long sinuous markings that look for all the world like river channels. It is easy to tempt our imaginations with the idea that Mars could be much like the Earth.

Mars, as seen by the Hubble Space Telescope. (L) The Tharsis Bulge, showing the large shield volcanoes of Mars, and the Valles Marineris in the lower right. (R) The large, dark plain of Syrtis Major, as well as polar ice caps and fleeting clouds. [Images by NASA]

Mars, as seen by the Hubble Space Telescope. (L) The Tharsis Bulge, showing the large shield volcanoes of Mars, and the Valles Marineris in the lower right. (R) The large, dark plain of Syrtis Major, as well as polar ice caps and fleeting clouds. [Images by NASA]

By the 1970s we discovered that Mars was indeed much like the Earth — volcanoes and canyons, ice caps and river valleys. Our landers sent pictures of rocky red deserts, studded with boulders and rolling landscapes that terminate at the foot of mountains on the distant horizon.  But Mars is simultaneously unlike its neighbor, the Earth. The volcanoes are the largest known in the solar system; the largest canyon is a rift valley that is large enough to stretch from New York to Los Angeles; craters stud the surface, worn by the ages but not completely disappeared; and there is not an open body of water to be found anywhere on the planet.  Perhaps most importantly, we have failed to find any sign of life anywhere on the planet.  Unlike our home the Earth, Mars may very well be a dead world, if indeed it was ever alive at all.

Panoramas from the surface of Mars, shot by our rovers.  From top to bottom: (1) Ares Vallis from Mars Pathfinder. (2) Lookout Panorama from Spirit, looking up the slope of Husband Hill. (3) Everest Panorama from Spirit, from the summit of Husband Hill, looking out over Gusev Crater. (4) Opportunity's view of Endurance Crater.

Panoramas from the surface of Mars, shot by our rovers. From top to bottom: (1) Ares Vallis from Mars Pathfinder. (2) Lookout Panorama from Spirit, looking up the slope of Husband Hill. (3) Everest Panorama from Spirit, from the summit of Husband Hill, looking out over Gusev Crater. (4) Opportunity’s view of Endurance Crater.

Thus, I was electrified on a summer’s day in 1996 when a stunning announcement was made. Tiny, mineralized structures had been found using high resolution images of a Martian meteorite known as ALH84001 (name decode, from right to left: 001 = first meteorite found, 84 = in 1984, ALH = in the Allan Hills region of Antarctica).  The structures looked very much like microbes one might encounter on Earth, leading to the very real possibility that the mineralized structures may be fossilized infusoria from the planet Mars.

(L) ALH84001 is a chunk of Mars that drifted through space and landed in Antarctica, where it was discovered in 1984. (R) Micrograph images of structures found in ALH84001, highly suggestive shapes like bacteria.

(L) ALH84001 is a chunk of Mars that drifted through space and landed in Antarctica, where it was discovered in 1984. (R) Micrograph images of structures found in ALH84001, highly suggestive shapes like bacteria.

Like all monumental discoveries in science, the announcement generated tremendous debate. The evidence is not completely unambiguous, and there is still much skepticism about what ALH84001 is telling us.  But it opened up the very real possibility that microbial life could have arisen on Mars, suddenly forcing all of our idle speculations and daydreams about Martians into a definite shape and form.  The human brain is fickle, particularly with regard to the kinds of daydreams it finds compelling — a Universe where all the life in the Cosmos consists of Earthlings and a few microbes on Mars just isn’t that exciting!  Microbes, shmicrobes! So it comes as no surprise to me that I have noticed a subtle uptick in the number of adventure stories told not about Mars, but about other worlds in the solar system: Europa near Jupiter, or Saturn’s enigmatic moons, cloud-swathed Titan and cryovolcanic Enceladus.

New worlds where we might search for life.  Left to right, (L) Jupiter's moon Europa, (C) Saturn's moon Titan, and (R) Saturn's moon Enceladus.

New worlds where we might search for life. Left to right, (L) Jupiter’s moon Europa, (C) Saturn’s moon Titan, and (R) Saturn’s moon Enceladus.

Why is that?  Why are we, at least sub-conciously, singing blues for the Red Planet? I suspect it is because we have landed on Mars and mapped the planet in exquisite detail from orbit.  Mars is by no means a fully explored world; we have roved only over 49 km of  Mars, but the planet has a total surface area roughly equal to the land area of Earth.  There is no way our 4 little rovers (Sojourner, Spirit, Opportunity, and Curiosity), and a handful of landers have seen every nook and cranny of the vast Martian frontier.

Our robotic explorers on Mars: (L) Sojourner micro-rover, (C) Mars Exploration Rovers, Spirit and Opportunity are identical, (R) Curiosity.

Our robotic explorers on Mars: (L) Sojourner micro-rover, (C) Mars Exploration Rovers, Spirit and Opportunity are identical, (R) Curiosity.

Never-the-less, we have yet to see indications of any large lifeforms.  Our cameras have sent back no pictures of Martian tapirs, no pictures of many-legged thoats, no pictures of giant sandworms. The net result: we have given up on the idea of there being substantial lifeforms. We’ve seen enough to convince ourselves that if there is life on Mars, it will be microbial.

Don’t get me wrong — without a doubt, the discovery of a single Martian micro-organism will transform biology forever, but it is not what we’re really looking for! Microbes are not what we long to discover — we long to find companions in the Cosmos. The discovery of a single large organism, whether it is the Martian equivalent of a squirrel, or stag beetle, or snail, would tremendously boost our hopes of one day finding life we can communicate with. 

A Europa cryobot submarine mission concept from NASA.

A Europa cryobot submarine mission concept from NASA.

And so, our imaginations have moved on to new unexplored worlds that could still hide the greatest discovery we have ever imagined.  Foremost among these, is Jupiter’s icy moon Europa.  Europa is sheeted in ice, a solid blanket covering a sub-surface ocean.  What lies beneath the ice?  With so much water, could it perhaps harbor life? There must be heat sources to keep the sub-surface ocean liquid. Perhaps the constant squeezing by Jupiter’s gravity has produced volcanic thermal vents that provide the heat to keep the ocean liquid. On Earth, deep ocean thermal vents were discovered by  explorers in 1977 aboard the Alvin manned submersible. Much to everyone’s surprise, the area around the vent was thriving with life, despite the intense heat and high acidity of the water.

Examples of extremophile life. (L) The Sully Vent in the Pacific; extremophile bacteria glean energy from the extreme heat and acidic water [NOAA image]. (R) The Grand Prismatic Spring in Yellowstone; different colored algae are tolerant of different water temperatures, giving the spring its banded appearance [National Park Service image].

Examples of extremophile life. (L) The Sully Vent in the Pacific; extremophile bacteria glean energy from the extreme heat and acidic water [NOAA image]. (R) The Grand Prismatic Spring in Yellowstone; different colored algae are tolerant of different water temperatures, giving the spring its banded appearance [National Park Service image].

The discovery of life around the hydrothermal vents startled us, but scientists soon realized they were seeing an example of extremophiles — lifeforms that have evolved to uniquely survive in an environment that would normally be too extreme for fragile beings such as us to survive in.  This epiphany opened our eyes, and we see extremophiles everywhere on Earth. A famous and prominent example are the microbial algae mats around the thermal features in Yellowstone National Park — the colored bands surrounding a feature like the Grand Prismatic Spring are simply different species of algae, each tolerant of different water temperatures. In most extreme environments, the extremophiles are microbes, so even a planet like Mars could harbor life, despite the cold, despite the aridness, and despite the ultraviolet radiation.

Tubeworms around a hydrothermal vent survive because the bacteria break down the acids, providing a way for the worms to chemically synthesize energy [NOAA image].

Tubeworms around a hydrothermal vent survive because the bacteria break down the acids, providing a way for the worms to chemically synthesize energy [NOAA image].

The discovery of microbial extremophiles has amplified our confidence in the odds that there is life elsewhere in the Cosmos, but it has done little to dampen our enthusiasm for large lifeforms.  In reality, microbial extremophiles should boost our chances of finding more complex organisms, if the conditions are right.  The deep ocean thermal vents are particularly interesting examples when considering life on Europa, not just because there may be similar vents heating the Europan oceans, but because of the ecosystems we see growing around the vents on Earth.  The microbes that thrive in the immediate vicinity of the vents themselves are the base for a very localized ecosystem and food chain. Other, larger, more complex organisms, such as giant tubeworms, also glom onto the thermal vent, feeding farther down the food chain from the microbes who have learned to exploit the extreme environment.  If we could sink a cryogenic robot beneath the Europan ice, maybe we could find a similar, complex ecosystem.

We have yet to explore beneath the ice of Europa. But in the minds eye of our fiction writers the adventure is on, and already we are by-passing microbes in favor of speculation about there being big Europans, complex lifeforms against which we can compare ourselves.  I was first exposed to adventures on Europa by Arthur C. Clarke’s novel, 2010 (and the associated 1984 film starring Roy Scheider), where the Monolith (already a  manifestation of an alien intelligence beyond our own) fosters the growth of big lifeforms on Europa after collapsing Jupiter into a small star.  More recently, we have all been charmed by “Europa Report” which follows an expedition to Europa to discover not only microbial life, but something more.

The depiction of the unambiguous discovery of microbial life is very tell-tale of our desperate desire to not be alone in the Cosmos.  The first discovery of life beyond the Earth will be a monumental event, but the depiction of discovering extraterrestrial microbes in the movies is similar in excitement to the construction of a new frozen yogurt shop down the street.  Discovering alien life should be an Earth shattering event for our culture: we will know for the first time that we are not alone in the Cosmos!  But perhaps our fictional heroes, like us, have become immune to wonder at the discovery of microbes.  They want to discover something more, something bigger.  Microbes, shmicrobes.  Why is Europa a destination in stories now?  Because Mars, at best, will be the home of microbes, so we are searching for new arenas upon which to cast our dreams, fears, and hopes.

I dream of camping on Mars, whether there be Martians or not.

I dream of camping on Mars, whether there be Martians or not. [Illustration by S. Larson]

But despite our civilization’s fleeting wonder about life on Mars, I still often dream about adventures on the Red Planet and what might be found there.  It is still a world full of mysteries, and as worthy of exploration as any corner of the Earth, or any other world in the solar system. What a grand adventure it would be to go hiking across Mars with my daughter, camping near the now dead Spirit rover, to toss rocks over the edge of the Valles Marineris,  and take iPhone panoramas of the vast rocky deserts of the Red Planet.  I would love to spend an afternoon chipping open rocks on the shoulders of the Tharsis volcanoes, looking for some sign of ancient microbial life as we watch dust devils spin lazily on the plains below.

martian-chroniclesIt may yet be true that Mars harbors no indigenous life, but we’ll never know until we ourselves go, and turn over every rock we can find. It will be the work of a lifetime, indeed of uncountable lifetimes if the exploration of the Earth is any kind of indicator.  In the end, there will be Martians, but as Carl Sagan so aptly noted (and Rock Hudson discovered at the end of The Martian Chronicles), the Martians will be us.

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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

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Cosmos 4: Heaven and Hell

by Shane L. Larson

I am writing this on the 45th anniversary of one of the most iconic photographs of the Space Age. As Bill Anders, Frank Borman and Jim Lovell rounded the far side of the Moon, after traveling farther than any humans in history, they beheld a sight that had never been seen before — the distant blue sphere of the Earth rising over the horizon of the Moon. This single image captured an idea which up to that time was a mere abstraction — that the Earth is a single world, without borders and boundaries, interconnected and bound together in ways that are simultaneously obvious and subtle.

(L) The original Earthrise image, shot by Bill Anders on Apollo 8's 4th lunar orbit in 1968. (R) Recreated Earthrise image by NASA's Lunar Reconnaissance Orbiter.

(L) The original Earthrise image, shot by Bill Anders on Apollo 8’s 4th lunar orbit in 1968. (R) Recreated Earthrise image by NASA’s Lunar Reconnaissance Orbiter.

This is the nature of great voyages of exploration and discovery — finding the unexpected, and realizing it was the most important thing that happened. The Earthrise image, like image of Buzz Aldrin’s bootprint on the Moon, or the Genesis rock found by Apollo 15 Commander Dave Scott on the delta of Hadley Rille — those are transformative moments from the Age of Space Exploration that changed how we think about who we are. 

(L) The Apollo 15 Genesis Rock, in situ as found on the Moon at Hadley Rille, and in the Lunar Sample Laboratory at Johnson Space Center. (R) Aldrin's bootprint experiment on the surface of the Moon [Apollo image AS11_40_5880], and the iconic image that symbolizes humanity's first voyage beyond the Earth [Apollo image AS11_40_5878].

(L) The Apollo 15 Genesis Rock, in situ as found on the Moon at Hadley Rille, and in the Lunar Sample Laboratory at Johnson Space Center. (R) Aldrin’s bootprint experiment on the surface of the Moon [Apollo image AS11_40_5880], and the iconic image that symbolizes humanity’s first voyage beyond the Earth [Apollo image AS11_40_5878].

To be connected to the Cosmos, to know why we are here and understand the part we play in the design of the grand machine of Nature — these are the deepest passions of the human psyche, passions that fuel art, exploration, and science, endeavours one and all whose sole purpose is to figure out what it all means.

Human beings are good at figuring things out. Sometimes we do it for recreation — we play tangrams, we play matchstick riddles, we solve Soduku puzzles.  Sometimes we do it because we have to, because our very survival depends on it — we figure how to shore up the banks of a river before it floods a town, we figure how to rescue a family who’s car has skidded off an icy road into a ravine, or we figure how to increase grain yields to feed a million starving people.  Sometimes we do it to improve our lives — we know how to make the human body invincible against the polio virus, we know how to forecast the arrival of a hurricane along our seaboards, and we know how to make the sum total of all the knowledge of the human race available to anyone on a device that fits in your pocket.

waveRockHydenScience is a way of thinking about the world specifically geared toward figuring out how things are related. That everything on Earth is deeply interconnected is one of the great realizations of the last two hundred years. Consider the Wave Rock in the Hyden Wildlife Park of Western Australia: 14 meters high, and 110 meters long, Wave Rock has the shape of an enormous cresting wave on the ocean, but the nearest seashore is 300 km away. That Wave Rock is a natural formation is clear. But how did it get there? How did it form?  This formation is an example of weathering and erosion.  Constant and continued exposure to weather, wind and rain have eroded the rockface away, leaving the flared shape of a cresting wave.  It happened slowly, over millions of years, far too slowly for humans to observe, but we figured it out.

Examples of weathering processes on Earth. (L) The Grand Canyon of the Yellowstone. (C) Rub' al Khali, the "Empty Quarter" on the Arabian Penninsula. (R) The Elephant's Foot Glacier, in Greenland.  [Images from Wikimedia Commons.]

Examples of weathering processes on Earth. (L) The Grand Canyon of the Yellowstone. (C) Rub’ al Khali, the “Empty Quarter” on the Arabian Penninsula. (R) The Elephant’s Foot Glacier, in Greenland. [Images from Wikimedia Commons.]

The idea that the weather and climate of the Earth are responsible for some of its physical features is not at all immediately obvious, but part of figuring things out about the Cosmos is connecting the dots.  Rivers run in channels, clearly carved into the skin of the Earth. Wind moves vast dunes of sand as it blasts across the empty quarters of the Earth’s deserts.  Ice, in the areas where it persists, also shapes and molds the land in stunning and pictueresque ways.  At the heart of all of this, is water. The most common substance we encounter everyday, our planet is a veritable water paradise.  We encounter it all of its forms, and all are spectacular eye candy — ice, liquid, and vapor. When we see the Earth from the near reaches of outer space, seen as the Apollo astronauts saw Earth from the Moon, what is immediately noticeable is the water — the blue oceans, the white clouds. Water is the stuff of life, the single most important substance that, to our biology, makes the Earth a paradise without peer.

Water in all three forms found on Earth: liquid, ice, and vapor (clouds). [Image from Wikimedia Commons.]

Water in all three forms found on Earth: liquid, ice, and vapor (clouds). [Image from Wikimedia Commons.]

A hot Jupiter near its parent star. [Image from NASA.]

A hot Jupiter near its parent star. [Image from NASA.]

It is not surprising then that, as we begin to search the Cosmos for other worlds and planets, our prejudice is always skewed toward worlds that remind us of home, worlds that harbor water in some shape or form.  In the last two decades, we have tallied up an impressive catalogue of planets, 1056 as of the time of this writing.  But this number is only the smallest fraction of all the worlds that must exist; these are only those that we have found so far. In their number, we have yet to find any that have the biological friendliness of Earth.  There are many which can only be described as hellish.  Consider the “Hot Jupiters,”  which are sometimes called “roasters.”  These planets orbit closer to their star than any planet we have ever seen. The first hot Jupiter discovered was the first planet found beyond our solar system, called 51 Pegasi b (sometimes known as Bellerophon).  This planet orbits its parent star once every 4.2 days!  By contrast, Mercury, the closest planet to the Sun, orbits once every 88 days!  51 Pegasi is located 50 lightyears from Earth, so we may never know what it is like on that far away world, but we can be quite certain it is nothing like the Earth; I’m willing to bet it is not a water paradise.

(L) Saturn's moon Titan, seen up close by the Cassini spacecraft in ultraviolet light. (R) Titan's liquid hydrocarbon lakes, displayed in false color (colored by computer). [Images from Wikimedia Commons.]

(L) Saturn’s moon Titan, seen up close by the Cassini spacecraft in ultraviolet light. (R) Titan’s liquid hydrocarbon lakes, displayed in false color (colored by computer). [Images from Wikimedia Commons.]

Closer to home, we have discovered many worlds that may harbor some water in some form, but none have exactly the perfect balance of energy, water, and air to produce the veritable garden that is the hallmark of Earth.  The only other world in the solar system known to have liquid of any sort on its surface is Saturn’s moon, Titan.  We have sent our spacecraft to reconnoiter Titan, and have even landed on its surface. Our maps are colored in a way that is pleasing to the eye, seductive in its suggestions of land and sea.  But the seas of Titan are unlike any that humans have sailed. They are not water at all; they are liquid methane, roiling under the “oppressive heat” of the distant Sun at Titan’s surface temperature of -180 ºC.  Closer, but still beyond easy reach, is Jupiter’s icy moon Europa. Only slightly smaller than Earth’s Moon, Europa is covered in a thick layer of water ice, laced with vast  enigmatic colored striations known as linae (scientists believe these are fractures where Europa’s icy crust has broken and shifted back and forth). Europa is too far from the Sun for enough radiant energy to keep water liquid on the surface, though there is strong evidence that below the ice may lie a sub-surface ocean.  What might we find, if we could dive below the ice shield, and skim the seas of another world?

What might lie beneath the icy surface of Europa? Future missions may tell us. [Illustration by S. Larson

What might lie beneath the icy surface of Europa? Future missions may tell us. [Illustration by S. Larson]

Venus, as seen by Mariner 10 in February 1974.

Venus, as seen by Mariner 10 in February 1974. [Image by NASA.]

Perhaps the most interesting nearby world is Venus. Nearly the twin of Earth in terms of size and gravity, Venus lies slightly closer to the Sun, on the edge of what astronomers call the “habitable zone” — the distance from a star where the laws of physics make the existence of liquid water “easy.”  Like the Earth, Venus lies just far enough from the Sun that water could remain liquid and not freeze. But unlike the Earth, the atmosphere of Venus is dominated by carbon dioxide, a gas that traps energy on the surface of the planet.  As a result, the temperature has sky-rocketed to 462ºC (863º F) — hot enough to melt lead. Like an oven, the blanket of heat fills every far flung corner of the planet — there are no tropical, temperate or polar zones on Venus. The entire planet is consumed by the pressing heat; the planet is a hellish world without peer.

The knowledge that Venus is a hothouse without equal has passed into the collective knowledge of our civilization, a bit of information that most people know and can use to win a Saturday night game of Trivial Pursuit.  But we have not always known this fact; it was something we figured out.  That Venus was shrouded in an apparently eternal cloud layer was a fact known since the invention of the telescope. Having little experience with clouds other than those on Earth, it was oft assumed that the clouds were water-based, and that Venus was a watery, swampy morass — perhaps not a heavenly paradise, but certainly no less-liveable than the jungles of the Congo or the back-bayous of southern North America.

Approximately true color image from the surface of Venus, taken by the Soviet Venera 14 lander in 1981.

Approximately true color image from the surface of Venus, taken by the Soviet Venera 14 lander in 1981.

But science is a self-correcting process. When new information is discovered, we revisit old thoughts, old models, old assumptions and view them anew, asking ourselves “how have we fooled ourselves this time?”  We generate new ideas that explain all of the old information and the new information together.  Such is the case with Venus. In the 1950’s, the advent of electronic technology allowed us, for the first time, to detect microwaves being emitted from our nearby sister world.  This was a startling revelation — how could it be that a planet was emitting copious amounts of microwaves?  The puzzle was resolved by a young Carl Sagan in 1960, who in his Ph.D. thesis demonstrated the basic runaway-greenhouse effect model that successfully explains the character of Venus.  The clue to the existence of the greenhouse effect was the microwaves — hot gasses produce copious amounts of microwaves. This was confirmed directly by the Soviet Venera 9 spacecraft, which soft-landed on Venus on 20 October 1975. It was the first human spacecraft to return pictures from the surface of another planet; it survived for 53 minutes.  Today, Venera 9 is slowly eroding away under the oppressive heat, pressure, and acidic rain, a decaying testament to the human penchant for figuring things out.

The Venera landers lived very short lives on the hellish landscape of Venus. Long ago fallen silent, they are now slowly eroding away. [Illustration by S. Larson]

The Venera landers lived very short lives on the hellish landscape of Venus. Long ago fallen silent, they are now slowly eroding away. [Illustration by S. Larson]

The desire to find a world like Earth is a reflection of our understanding of how fragile and, so far as we know, unique the Earth is. The paucity of Earth-like worlds might be reason for discouragement, but we are still figuring out how to find other planets, and we aren’t giving up yet. But one thing is true — there are no worlds like Earth anywhere close to us; there are no places we can go and exist as easily as we do in the garden of Earth.  The idea that we as a civilization can and are changing our planet in dramatic (and possibly irreversible) ways is something we are just figuring out. The existence of worlds like Venus should serve as gigantic flashing billboards to our civilization screaming “Do not Enter! Wrong way!”  Part of exploration is discovering not just who we are, but what the future may hold.

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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