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Which leads us, circuitously, to news this week from the not-so-balmy beaches of Saturn’s largest moon, Titan, where a dearth of hydrocarbons rather than an excess as in the Gulf has spurred world headlines. First, the facts: The Cassini spacecraft currently orbiting Saturn recently detected lower-than-predicted levels of acetylene and ethane, two simple hydrocarbons, on Titan’s surface. Additionally, new results from a numerical simulation based on Cassini data hint that something on or immediately below Titan’s surface is sucking large amounts of hydrogen out of Titan’s atmosphere.
These arcane details of planetary chemistry have sparked such interest chiefly because they might be faint signatures of extraterrestrial life. In many ways, Titan is Earth’s mirror image, except frozen, chilled to nearly -200°C by its remoteness from the warming Sun. Like our own planet, Titan has a dense atmosphere chiefly of nitrogen, and a surface rich with complex organic molecules. Methane raindrops fall from hydrocarbon clouds in seasonal patterns, forming rivers that flow and pool into shallow seas ringed by icy shorelines.
These similarities have led astrobiologists to speculate that microbial life could exist on Titan that is based on liquid methane, rather than liquid water. If so, life on Titan might obtain energy from things like hydrogen, ethane, and acetylene similar to how we on Earth get energy from substances like oxygen, carbon dioxide, and sugar. Thus, an interrelated and dynamic depletion of hydrogen, ethane, and acetylene just might be evidence for methane-based life on Titan.
There are competing explanations. The computer model used to predict the anomalous hydrogen flux could be flawed. An unknown mineral at Titan’s surface could be somehow catalyzing the conversion of hydrogen and ethane into methane, or ill-defined interactions between Titan’s upper and lower atmospheric layers could transport hydrogen downward. But if these scenarios are ruled out, abundant microbial life on Titan may be the most plausible explanation left.
Finding life on Titan would be world-changing, but for reasons perhaps not immediately obvious. Statistically speaking, the discovery of a separate and biochemically distinct origin of life within our own solar system would strongly suggest that life is not only exceedingly common in the universe, but also not necessarily limited to those few environments where liquid water can persist. Life could then conceivably be lurking unrecognized almost everywhere we have ever looked. Which could suggest in turn a set of reasons why we’ve yet to be indisputably visited or contacted by any other cosmic cultures: Somewhere on the developmental pathway from life’s multitudinous origins to the emergence of an intelligent, technological, galaxy-faring civilization, there must be roadblocks, one or more filters beyond which few if any forms of life progress.
These filters could be astrophysical, geological, biological, technological, or sociological in nature. Finding evidence of present or past life somewhere like Mars or Titan, the key question would change from “Are we alone,” to “Is a roadblock behind or ahead of us?” If behind, humanity could rest assured that it stood a good chance of enduring long into the future. If ahead, then our era might already be drawing to a close.
Of course, to definitively settle any of this, we quite possibly would have to send human explorers all the way to Titan—and even further afield. And there’s the rub—or perhaps a cosmic roadblock, if you will, though it’s a limitation imposed more by choice than by the laws of physics. Last week saw the successful maiden voyage of the Falcon 9, a relatively inexpensive, privately developed rocket that NASA officials hope could decrease the high cost of access to orbit and aid the commercialization of outer space. But consider this: Also last week, researchers from the Applied Physics Laboratory at Johns Hopkins University released a design study estimating the minimum costs and technological requirements for human exploration of the outer solar system by 2100. Among their conclusions was a rough calculation that such a program would conservatively require at least 10 percent of current global GDP, or about one-and-a-half times the total US expenditure on World War II.
In other words, to get people to Titan, something like the Falcon 9 simply won’t cut it, nor would something like the entire Apollo program that placed men on the Moon. As impressive as this past and present space exploration may seem to us now, Nature will probably not be so easily fooled, here or elsewhere in the cosmos. And so, in light of current events, where the most powerful nations and corporations on Earth can’t plug a hole in the ground, repair oil-poisoned ecosystems, balance budgets, or cooperate to constrain carbon-dioxide emissions, a world possessing the unity, power, money, and will to achieve grander things beyond hand-to-mouth survival is one that seems more alien from our own with every passing day. May it not always be so.
Lee Billings is a staff editor for Seed. He likes space.
Originally published June 11, 2010
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