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How A Soggy Solar System Can Spark A New Human Future

A falling drop of water.

Let's begin with your great-great-great-etc.-grandparents. I'm talking eight or nine of those "greats," meaning your ancestors living around the first decades of the 1800s.

Here is what I want you to consider: Those guys never raced across the sky, 5 miles above the planet, at 400 miles an hour, in a chair, in a pressurized tube. They didn't carry around little boxes in their pockets that gave them instant access to every corner of the planet, as well as to the entire storehouse of human information. They didn't live in cities fully illuminated at all hours of the night. They never saw pictures of the insides of their bodies, or inside their brains, when they went to a doctor (if they ever went to a doctor). But you do this all the time. Routinely. So, I want you to keep those great-great-great-etc.-grandparents in mind for what's coming next.

We have just discovered that the solar system is all wet.

Well, maybe not "just discovered," but it's a recognition that has been building steam (no pun intended) for 10 years or so. Last week, we got back-to-back scientific papers building an even deeper case for slushy space. First we learned that Ganymede, a moon of Jupiter, has a deep subsurface liquid ocean with more water than Earth. Then, we learned that Enceladus, a moon orbiting Saturn, harbors not just a subsurface ocean, but one that is actually balmy enough to allow complex chemistry.

We astronomers have long suspected that Europa, another moon of Jupiter, hosts a deep ocean under its constantly shifting ice surface. But based on what has happened in the past few years, it seems like we need to acknowledge that many of the large moons circling our sun's giant planets are awash in water.

Now, if you're interested in the evolution of life outside of the solar system, all these wet moons are really good news. Once you consider that a subsurface ocean on a moon may be warmed from below by geothermal energy (which is the Enceladus story) the possibilities for life get really interesting. More importantly, they take us in entirely new directions from just hoping we can find a little moisture on Mars. As the eminent astrobiologist Chris McKay put it in an interview with The New York Times: "After spending so many years going after Mars, which is so dry and so bereft of organics and so just plain dead, it's wonderful to go to the outer solar system and find water, water everywhere."

So, yes, there could be life in them thar oceans. That would be super cool. But what does any of this have to do with your great-great-great-etc.-grandma?

Well, there's another kind of life we need to pay attention to in all this wet solar system news: ours. That's because, in the long run, these discoveries might just prove to be critical for the future of the human species.

Remember, for a moment, the world your ancestors inhabited 200 years ago. Now, ask yourself this — what kind of world might your great-great-great-etc.-grandkids inhabit 200 years from now?

I've argued elsewhere that — unless a miracle occurs — we won't be traveling back and forth to the stars anytime soon. The distances are just too large. But what we might do, if we can hold it together as a civilization, is colonize the solar system. We might put "tents" across hundred-mile-wide craters and then pressurize them and build cities on their plains. We might bore out mountain-sized asteroids and spin them up so we can live on the inner surfaces of their hollow insides. There is a lot we could do — and the point is that there are a lot of places out there in the solar system to do things on. Using our ever-expanding technologies, we might find ways to make a lot of these places habitable and that, very well, might be the best and brightest shape for our future.

But you can't do any of that without water.

This is not simply an issue of having stuff to drink. As astronomer Philip Metzger describes, water is vital in so many ways. It can be broken down to make rocket fuel. It can be used to create electric fuel cells. Water can be split apart to get the oxygen needed for breathing. And, of course, water will be necessary to grow the food any large human presence anywhere is going to require.

But, of course, we aren't going to spread across the solar system in large numbers unless we can build economies out there. Space-water is essential in this domain, too. Any kind of large-scale industry activity in space (including on other worlds such as the moons of the giant planets) is going to require a lot of water. It's also going to need other kinds of things called volatiles — stuff like methane and ammonia and CO2 — all of which are also proving easier to find than we might have thought decades ago.

Now, you could discount everything I'm telling you as science-fiction whimsy. But that might have been what your great-great-great-etc.-grandpa might have said, if you tried to describe a major airport, a modern chemical engineering plant or Hong Kong at night. Humanity faces a whole lot of challenges, but we also have a whole lot of opportunities. The discovery of all this water across the solar system has just made those long-term possibilities a whole lot more possible.

Adam Frank is a co-founder of the 13.7 blog, an astrophysics professor at the University of Rochester, a book author and a self-described "evangelist of science." You can keep up with more of what Adam is thinking on Facebook and Twitter: @adamfrank4.

Copyright 2021 NPR. To see more, visit https://www.npr.org.

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