Book
Princeton University Press
IN THE late 1970s, two different voyages of discovery transformed our ideas about alien life. In 1977, hydrothermal vents were found, belching out “smoke” in the Galapagos rift at the bottom of the Pacific Ocean. The smoke was actually a superheated fluid rich in hydrogen, methane, hydrogen sulphide and minerals essential to life.
The chimneys were host to never-before-seen creatures, thriving in a place we had previously thought was completely and utterly lifeless. Two years later, in 1979, NASA’s Voyager spacecraft flew past Jupiter and gathered the first evidence that some of the gas giant’s moons contained oceans.
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Kevin Hand is a child of that historical collision between ocean and interplanetary discovery. While his adventures exploring hydrothermal vents provide him with a cracking opening chapter to his new book, Alien Oceans, he is better known for his later work, being NASA’s deputy chief scientist for solar system exploration, where he has spearheaded an effort to land a spacecraft on Jupiter’s moon Europa.
Life on the underside of the ice on Europa, says Hand, “could be like an inverted version of life we see lining the cracks of a sidewalk”.
Wresting secrets from Europa’s hidden ocean will be a frustrating business. You can’t peer through the surface to the sea floor. You will have to get up close with a robotic submersible. Then you will have to contend with the fact that no electronic mode of navigation or communication will be able to interact with the outside world through the ice, so the submersible will need to be fully autonomous, coming to the surface periodically to report back what it finds.
But Hand’s more immediate problem is logistical. Nothing is likely to land on Europa before 2040 because NASA’s subcontractors can’t find a large enough skilled workforce to complete their existing projects.
While he waits, Hand can only analyse what information is available, plan future missions as best he can and speculate about what we might one day find in the outer reaches of our solar system – a zone we expected little from, but that turns out to contain the best real estate for life.
We know that physics and chemistry will work the same way, however far we venture. What we don’t know is whether biology does the same. “It is the phenomenon that defines us,” Hand writes, “and yet we do not know whether it is a universal phenomenon.”
Surprisingly many places in our solar system turn out to be capable of supporting “our kind of life”: carbon-based life organised around RNA or DNA. But whether we ultimately find life in those places is quite another question. After all, a world that is habitable could have the conditions needed to support life, but not necessarily those needed for life to get going in the first place – or it may have just not happened yet.
“Any life discovered in Titan’s liquid methane lakes would have a very different biochemistry from ours”
More generally, is “our kind of life” the only kind of life there is, or might there be others?
Saturn’s moon Titan has a water-ice surface carved and shaped by falling and flowing liquid methane. Beneath that icy shell, there probably resides a deep ocean of liquid water, which could host life as we know it. But any life discovered in the liquid methane lakes on Titan’s surface would have a biochemistry completely different from ours.
We used to think that life could only exist in a “Goldilocks zone” dictated by distance from the sun. Too close, and life would fry; too far, and it would freeze. Hand leads the reader through today’s more complex picture, where liquid water is surprisingly common but other limiting factors pertain.
For example, a lack of rocky mantle, or a seabed pressure so high that the water there turns to unfamiliar forms of heavy ice, could leave an ocean without the minerals necessary for life. Or if a moon has too circular an orbit, it won’t provide tidal heating sufficient to keep water on its surface in a liquid state.
In a book that is likely to prove one of the year’s most enthralling first-person accounts of a life in science, Hand maps the likely limits on life and liveability. Equally, he is out to excite us with the possibilities. Imagine vast carbonate chimneys, kilometres high, rising above Enceladus’s sea floor like geological skyscrapers! Imagine geothermally active rogue planets transporting fish, squid and octopuses from star to star! “Perhaps one is even on its way toward us now,” says Hand.
