Science & Technology

Earth Is the Driest World with an Ocean in the Solar System

Earth is one in a million — actually, make that one in billions of billions. We're just the right distance from our sun, we've got some nice, firm ground to walk on, and of course, there's all this beautiful water. That makes us special, right? Well, comparatively, we don't have that much water at all. Of all the celestial bodies with oceans in the solar system, ours is the driest.

Triton, one of Neptune's moons

Water You Talking About?

Here's something you might not have known: Earth isn't the only body in the solar system with an ocean — it's just one of nine. To be clear, we're not talking about just any world with water. It's got to be liquid, and it's got to cover a pretty substantial portion of the terrain. And in terms of volume, Earth's water content is dead last by a longshot. Our wet-looking world is only 0.12 percent water and 99.88 percent everything else (that "70 percent water, 30 percent land" figure you've heard is about surface area, not volume). The next driest is Triton, a moon of Neptune, which weighs in at 0.3 percent water. And Jupiter's Callisto, the next driest after that, comes in with a full 9 percent. On the high end of the spectrum is another one of Jupiter's moons, Ganymede, which has the most compared to its size (46 percent) and the most by total volume (27 times more than Earth's oceans).

Speaking of volume, even Earth's relatively tiny oceans are large enough to be measured not in gallons, not in liters, but in zettaliters. A zettaliter is equal to one billion cubic kilometers (621,371,192 cubic miles) of water. Our planet's oceans add up to about 1.3 zettaliters while Europa, the next celestial body in line, has about twice that. We're right down the middle in terms of water volume, with four other bodies ranking lower than us and four ranking higher. You know, for all the hullaballoo over our tiny blue dot, you would think that our water would set us apart more.

Surf and Turf

It's almost enough to make you feel like our planet isn't so special after all. But don't fret — the Earth is still an outlier in all the right ways. Even on the round-up of the wettest worlds, it sets itself apart as the largest body on the list, and the only planet. There's also the question of the state of the water on its surface. Sure, Ganymede has a whole lot more liquid water than we do, but all of that water is trapped beneath a thick crust of ice. And on Titan, you'll have to get through surface oceans of smelly methane before you get to the subterranean water and ammonia oceans. We're not going to be investing in a timeshare there anytime soon. We like our oceans just fine, thank you.

Wherever else water can be found, it's undeniable that its shaped all of our lives here on Earth. In environmental engineer Alice Outwater's "Water: A Natural History," readers follow the flow back from modern plumbing to the early days of living on and around water. We handpick reading recommendations we think you may like. If you choose to make a purchase through that link, Curiosity will get a share of the sale.

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Written by Reuben Westmaas June 5, 2018

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