Icy Moons

The sky is teeming with life. There are an estimated nine billion earth-like planets orbiting sun-like stars in the Milky Way alone. Include the earth-like planets of red dwarfs, and the number gets even larger. Earth-like planets are where something we'd recognize as life might arise, so those are where we focus our search for extraterrestrial life. That's chauvinistic.

Life is more robust than we give it credit for, and probably more varied than we understand. Where there is liquid, a life form could develop. Liquid water supports life. Life may also have evolved in Titan's liquefied natural gas lakes. We don't understand life well enough to recognize it if we found it there, but that doesn't mean it isn't alive.

Extraterrestrial life may be a lot closer than the planets of a nearby star. There's liquid water beyond the Goldilocks zone. There's plenty of liquid water on the icy moons of gas giant planets. Voyager first noted cryovolcanos spewing molten ice from Enceladus. Since that discovery, Cassini measurements have added details about those moons.

Jupiter's ice moon Europa is a prime candidate for life. Cassini data indicate that Europa has a large ocean buried under ten miles of ice. It is estimated to have more salt water than earth does.

Saturn's ice moon Enceladus is also a leading candidate. It has a fresh-water Great Lake buried thirty miles deep under its south pole.

These moons and a few others have abundant liquid water. What's it like under all that ice? It's dark. No sunlight can penetrate all that ice. It's cold-colder than freezing water here on earth. Water expands when it freezes. It has to push against miles of ice to turn solid. Dissolved materials depress the freezing point even more. Their nearby giant host planets create ferocious tides that churn the water and keep it from freezing.

How could life exist in such a harsh environment? Low temperature and high pressure both increase its solubility of oxygen. There should be plenty of it, but what about food? It's dark: photosynthesis is out. Geological energy sources are possible-just as they do in Earth's deep ocean volcano vents.

There is ice-locked water closer than Jupiter and Saturn. The lakes of Antarctica resemble those of Europa and Enceladus. They are cold and dark under miles of ice. They have been cut off from sunlight and air for half a million years or longer. They have long been assumed sterile.

The Antarctic lakes are a lot easier to get to, but their exploration is only beginning. Two lakes have been probed. Three thousand five hundred unique species have been identified in the first water and sediment samples. The presence or absence of more complex species is unsettled at this time.

If life can flourish under the Antarctic ice cap, why not under Europa's or Enceladus'?

The sky is filled with billions of Goldelocks planets capable of hosting life. They're just right for liquid water. Life is out there. It's just too far to reach it.
Alien life may be closer than the nearest star. There's liquid water under miles of ice on some of the moons of Saturn and Jupiter. They're a lot like the lakes under the Antarctic ice. They harbor extremophile life. Why not the waters of those moons?

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