Exploring Alien Oceans

Extraterrestrial seas may be the next frontier for planetary science.

Underneath the cracked ice of Jupiter's moon Europa, there is likely a global ocean. Bluish ice in this Galileo spacecraft image is more pure water ice, while the reddish areas are ice mixed with other substances.

In his book Alien Oceans: The Search for Life in the Depths of Space, Kevin Peter Hand takes what scientists have discovered about Earth’s oceans to imagine what kind of life might lurk in the vast oceans that lie beneath the icy crusts of the moons of Jupiter and Saturn. Hand, a planetary scientist at NASA’s Jet Propulsion Laboratory, spoke with Air & Space senior associate editor Diane Tedeschi in July.

Air & Space: Why did you decide to write this book?

Hand: Little has been written in the popular-science literature about the science of Europa, Enceladus, Titan, and the many other ocean worlds of the outer solar system. I wanted to communicate the beautiful physics, chemistry, geology, and biology of these worlds in a way that was accessible to non-scientists and that would inspire excitement about the exploration of Earth’s ocean and these distant oceans.

What do Earth’s oceans tell us about the oceans on the moons of Saturn and Jupiter?

The deepest regions of Earth’s ocean are cut off from sunlight, and that’s also true of the ice-covered oceans of the outer solar system. Within Earth’s ocean we find incredible organisms—large and small—thriving around chemically-rich hydrothermal vents in the darkest depths of the ocean. The base of the food chain of the ecosystems around hydrothermal vents is driven by chemosynthesis instead of photosynthesis (which of course powers the food chain on the sunlit surface of the Earth). The microbes around hydrothermal vents use the chemistry of the vents to power their growth, metabolisms, and reproduction. We think that this process of chemosynthesis around vents on a rocky seafloor could also be happening in the depths of these distant alien oceans beyond Earth. In other words, the physical, chemical, and geologic conditions within Earth’s ocean can help guide us in assessing whether or not some of these alien oceans might be habitable—or even inhabited.

How much do we know about the oceans of Europa?

We know that Europa’s ocean is salty, similar to our own ocean. We can see salts on the surface, using spectroscopy, and we can also detect the electromagnetic signature of Europa’s salty ocean. Much of this data comes from the Galileo spacecraft, which flew by Europa in the late 1990s and early 2000s. Some of it also comes from the Hubble Space Telescope and telescopes here on the ground. We also know that Europa’s ocean can’t be that cold—it’s close to the freezing temperature of water, but it’s not actually frozen. The water temperature in much of the ocean may be around 0 to -10 Celsius—or 32 to 14 degrees Fahrenheit—and the variation may be related to the saltiness of the ocean. That’s obviously cold to us, but it’s not that cold to many organisms on Earth. In other words, based on what we know about Europa’s ocean so far, it appears that life as we know it could potentially survive [there].

Many of the photos depicting the moons of Jupiter and Saturn make them look sterile. Do you think these moons could be beautiful in the way that Earth and Mars are beautiful?

Earth and Mars both have atmospheres, and part of the beauty that we experience when we look at these worlds comes from the sun shining through these atmospheres, scattering light in many different ways. Europa and Enceladus do not have atmospheres—their icy surfaces are directly exposed to the cold black of space. Sunlit regions are bright, and the shadowed regions are nearly pitch black. That is part of why the surfaces might look sterile. But with this comes a different kind of beauty. These worlds are covered in ice, and the ice is fractured, shifted, and overturned as they orbit Jupiter and Saturn respectively. Jets of ocean water erupt from the icy fractures of Enceladus, and may also emanate from Europa’s ice. Standing on the surface of these worlds you would be surrounded by shimmering ice, snow from nearby plumes might settle down onto your spacesuit, and off on the horizon Jupiter or Saturn would loom large and bright. Europa and Enceladus are worlds much different from our own, but with that comes a different kind of beauty.

When will our knowledge about the moons of Saturn and Jupiter become more concrete?

It all depends on how fast we can get to the launch pad. I like to say that there are no magic wands needed to explore these worlds—there is no crazy technology that needs to be invented. The most critical ingredient is persistent, visionary leadership that can carry us through to the launchpad and beyond. If we have that in place, then we could be landing [robotically] on the surfaces of these worlds within 20 years.

What is the most memorable place you have visited for your work as a scientist?

That’s a tough question, as different places can be very memorable for so many different reasons. I guess I would point toward an experience from just a few years ago that serves as a nice contrast to being in a submersible at the bottom of the ocean. In 2016 I was part of a team exploring the Arctic ocean, not far from the North Pole—we were at 87 degrees North. We were searching for hydrothermal vents and studying the sea ice floating on the ocean above. I have very fond memories of standing on the sea ice, far from the safety of the ship, gazing out at the crystalline landscape of ice. Though it was cold and harsh, I knew that just below me—beneath the five or so feet of ice that was holding me up—lay a vast liquid-water ocean a couple miles in depth. Within that ice-covered ocean swam all sorts of beautiful creatures that I could not see, nor could they know that I was standing precariously on the ice above.

What is your opinion of the art of Chesley Bonestell?

Bonestell’s art is nothing short of visionary. His paintings are to solar system exploration what Ansel Adams’ photographs are to environmentalism. I think that if Bonestell were alive today, he would be in awe of the exploration and discoveries we’ve made, but he would also be surprised that we haven’t done more.

What is the best thing about being a planetary scientist?

Well, there are a lot of different things for which I’m grateful, but I guess one of my favorite things is that whenever we look at, and study, these worlds far out in the solar system, we always learn something new about our home planet. Earth is a very complex planet and while we are doing a lot of great research on, and about, planet Earth, it can be very helpful to examine the physics, chemistry, geology, and possibly even biology of these other worlds to better understand how our planet works. For example, back when he was writing the book Gaia, James Lovelock was at the Jet Propulsion Laboratory studying the different atmospheres of Earth, Venus, and Mars. The runaway greenhouse effect on Venus has helped inform our understanding of the greenhouse effect and climate change here on Earth. I hope that our exploration of distant alien oceans beyond Earth will also help catalyze new discoveries and insights about how our own ocean works and what makes it such an incredible abode for life on Earth.

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Alien Oceans: The Search for Life in the Depths of Space

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