Alien Oceans: The Search for Life in the Depths of Space
By Kevin Peter Hand
Princeton University Press, 2020

Life on Earth originated in the ocean, and since life on Earth is still the only life we know about anywhere, it’s natural for humans to assume that oceans are essential prerequisites for the appearance of life. This rules out most of the inner planets of Earth’s solar system; Mercury is just a barren rock, and although Venus and Mars very likely had oceans in the distant past, they’re both more or less completely water-free right now. So enthusiasts for the idea of extraterrestrial life have begun to look farther out from the sun.

This is where Alien Oceans, the new book by NASA Jet Propulsion Laboratory scientist Kevin Peter Hand, turns a big part of its attention: to the big moons of the middle solar system. Some of those moons, like Titan, Callisto, Ganymede, Triton, Europa, and Enceladus, are likely home to very large oceans trapped under thick layers of crust or ice that protect those waters from the deadly winds of solar radiation that lash their surface. If those subterranean oceans have had even the smallest seeding of microorganisms in the past few million years - and particularly if those oceans are warmed from within by some kind of geothermal forces. It’s not the easiest set of conditions for life to develop, but it’s well within a new conception of the “goldilocks zone”: water, at least some source of nutrients, and protection from hard radiation.

“These ice-covered oceans have no beaches or sandy shores, but they are potentially wonderful, and plentiful, places to call home,” Hand writes. “The dark depths of those distant oceans may look similar to the deepest regions of our own ocean.” And in order to draw the fullest picture of that possible parallel, and also because Hand is omnivorously curious and a born teacher, the book spends a good deal of time describing the ways of life in Earth’s oceans, particularly in the darkest, most inhospitable depths of Earth’s oceans, where weird creatures live and mate and evolve under pressures that can crush steel. 

The more of this describing Hand does, the more the possibilities seem to multiply, and that’s a thrilling reading experience in its own right. The farthest places of Earth’s oceans are revealed as deeply, deeply alien places, and by sympathetic obverse, the oceans of Enceladus or Titan (or even poor persecuted Pluto, a speck at the edge of the solar system whose Sputnik Planitia may even so roof a sloshing black ocean of heated water) come to seem less alien, less impossible as possible homes for some kind of microbial muck - or whatever fantastic things alien microbial muck might become over millions of years. 

One curiously encouraging sub-theme running through Alien Oceans is precisely this affirmation of life’s sheer dogged tenacity. This is bolstered by the fact that Hand himself is obviously a true believer. “From an ancient ocean on Venus to a bizarre chemical blend of liquids within Pluto,” he writes, “if the chemistry of life’s origins is common, then life itself may also be common.” Science fiction fans will appreciate how science fact continues rather easily to keep pace with their wildest imaginings.

—Steve Donoghue is a founding editor of Open Letters Monthly. His book criticism has appeared in The Boston Globe, The Wall Street Journal, The Washington Post, and The American Conservative. He writes regularly for The National, The Vineyard Gazette, and The Christian Science Monitor. His website is http://www.stevedonoghue.com.