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Space Exploration

All the Heavens Are Rejoicing

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“Sing me a new song; all the world is transfigured; all the Heavens are rejoicing.”
Friedrich Nietzsche, Letter to Peter Gast, 4th of January 1889

On the 15th of September at 0455 local time, NASA scientists and engineers at the Jet Propulsion Laboratory in California received their last signal from the Cassini probe. This fiery plunge was a fitting end to a 20-year mission: even in its final seconds it was transmitting sample data on the composition of Saturn’s atmosphere back to Earth. During its two decade visit to the “King of the Titans”, Cassini studied the giant planet’s magnetosphere, the structure of the famous rings, successfully landed the Huygens probe on the surface of the moon Titan, analyzed the structure of the ice moon Enceladus, and meanwhile redefined almost everything we thought we knew about Saturn.

Of all the exciting discoveries, the two that stand out are the possibilities of non-terrestrial life on two of Saturn’s moons: Titan and Enceladus. Both satellites show such promise that researchers are already planning return missions focused on finding those elusive signs of life. But excitement must be tempered by patience: the outbound trip alone takes seven years and any definitive proof of life would almost certainly require another seven year return trip for scientists to confirm the existence of alien biota on Saturn’s moons. But the possibility of answering one of mankind’s oldest questions within our lifetimes cannot help but fire the imagination.

At first glance, Titan seems to be the better bet for harboring life. It is the second largest satellite in our solar system, only slightly smaller than the planet Mercury and half again as large as Luna. It is also the only moon with a dense atmosphere. The Huygens lander has confirmed that it has a rocky and geologically active surface with few craters, as well as standing bodies of liquid hydrocarbons: a primordial atmosphere and seas of methane. Titan remains much drier than the Earth, with most of the methane lakes concentrated in the polar regions, but the presence of liquid, of energy and of a potential food source make Titan an exciting candidate for the presence of anaerobic microorganisms – just like the extremophile archaea on Earth that cluster in deep-water volcanic vents and that thrive without oxygen.

Enceladus, in contrast, was long dismissed as too small and too cold to be a good candidate for life, a rock in space with a solid layer of ice all the way to the moon’s icy surface. At 310 miles in diameter, it is only 1/10th the size of her massive sister moon Titan. But Cassini’s first flyby in 2005 revealed something extraordinary: Enceladus had a thin atmosphere of hydrogen and water vapor where none should exist. Hydrogen is the most common element in the universe and the lightest as well; this means that it is the first to escape from any small body with a weak gravity. 99.9% of the hydrogen in our Solar System is concentrated in the Sun and most of the rest in the four outer gas giants[1]. The Earth has quantities of hydrogen, but it is mostly locked up with other atoms to form heavier elements, like the ubiquitous and essential H2O. What gaseous hydrogen (H2) the Earth does produce through chemical reactions is quickly lost to space: our gravity is just too weak to hold it.

Enceladus, with its much weaker gravity, should have no atmosphere at all, much less one that shows clear traces of light gases. Yet that is what Cassini found and confirmed on a second flyby. To the shocked and delighted scientists back in Pasadena, the answer was clear: something on Enceladus was producing continuously producing hydrogen. Of course, they did not immediately declare that this “something” was biological; there are a number of purely inorganic explanations. The southern polar surface of Enceladus is relatively smooth and shows far fewer craters than other areas of the moon; Cassini also confirmed the presence of a large subsurface ocean in the south and active geysers that sprayed water vapor columns several miles high into the atmosphere, thickening it and then falling back as snow to help smooth surface irregularities over time. These are all features of a geologically active body, possibly through tidal forces similar to what power the violent volcanism of little Io in the Jovian system.

During the second close flyby in 2008, Cassini flew close enough to the surface of Enceladus to actually pass through and analyze those geyser plumes. Its mass spectrometer detected water vapor, carbon dioxide and hydrocarbons, as well as temperature peaks from the plumes’ origins. These reading are similar to those of the deep-water hydrothermal vents on Earth which are home to a variety of unicellular and multicellular life forms that are specially adapted for such environments. Heat, liquid and nutrients: the essential preconditions for life. The other is time: if Enceladus has been tidally active for geologically long periods of time, the probability of some kind of life forming in the nutrient rich “soup” of her southern oceans increases. But there is also the possibility that all of Saturn’s inner moons are of relatively recent origin: perhaps as recently as 100 million years[2].

Finding out if life has developed on Enceladus or Titan, or Europa[3], will not be easy. There are daunting challenges: even sending a robotic probe to the outer reaches of the Solar System is no guarantee that they will arrive or work as designed. Even if they do arrive, they must be prepared to face incredibly hostile and challenging conditions: to travel through the near absolute zero and vacuum of space and then plunge into some kind of atmosphere, land, possibly drill through ice, enter a liquid medium and then navigate to and approach a strong heat source. A probe that gets this far will then still need to identify what might be an alien lifeform and take sterile samples that will need to be preserved for later analysis back on Earth. And it will need to do all of this autonomously, since a radio signal from Saturn to Earth is a round trip of almost 3 hours.

We must embrace these challenges. We must overcome them. Understanding the origins of life in the universe is within our grasp and it would fundamentally change humanity’s conception of itself. Overthrowing our nonsensically homocentric conceit will be as beneficial to our civilization as the overthrown of the Ptolemaic system by Copernicus in 1543. Achieving this no longer depends upon little green men suddenly showing up on Earth; it does not depend on some impossibly lucky radio signal from the remotest reaches of space. It does not even depend on the accurate interpretation of tea leaves or ancient manuscripts in dead languages. It depends only on our ingenuity and our will: two resources which humanity has in abundance. We have only to reach out and grasp this opportunity.

God knows we need it. Our attention is increasingly drawn by the sordid violence and squalor which seems to dominate the news, barbarities increase and new technologies threaten us with a dire future – yet humanity is on the verge of a new age. We are preparing to emerge from a long, dark night into a new dawn. Within our lifetimes, we could and should have established a permanent colony on Mars and revisited the outer planets in a systematic search for life. I believe we shall find it; I believe that the Maker of Life revels in its abundance and that we will find it to be ubiquitous in the universe[4]. As we take the first cautious steps on our infinite journey to the stars, we will ensure the continuation of our species; we will gain a greater and more humble understanding of our place in the cosmos; and it is hoped that we may revitalize the tired old Earth before it is too late.

Sources and Notes

[1] Jupiter, Saturn, Uranus and Neptune.

[2] Still a very significant length of time in evolutionary terms, but since we don’t know how long it took life to first form on Earth, the relatively rapid pace of evolution after that fact is not indicative of the time needed for it to have developed on other planets.

[3] The third prime candidate for extraterrestrial life in our Solar System is the sixth moon of Jupiter.

[4] Though not necessarily intelligent life. Our own experience up until now rather strongly suggests that intelligent life is a self-destructive proposition.

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