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.
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.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.
Science 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.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. 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. 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? 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.
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 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.
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