Earth has a lot of water; it covers roughly 75% of the planet’s surface, and it gets pretty deep - not quite 7 miles deep at one point. And for a long time, it seemed maybe Earth was the only planet in this solar system that had water.
If we sent people to explore or colonize any of the other planets, we would have to send water with them. The more people we sent, the more water they would need. Did Earth have enough? Would we completely drain the oceans?
Thankfully, we’ve learned better than that by now, since we are - tentatively - thinking about how best to colonize other planets. A brief recap:
1989 - Voyager studied Neptune’s magnetic field, leading to the conclusion that it has a subsurface ocean of water that is 4000°F (Hot!) and is under tremendous pressure.
1998 - Recent discoveries convince scientists that Callisto (a moon of Jupiter) might have a subsurface ocean.
2006 - Neptune has a large amount of water mixed in with its hydrogen/helium atmosphere. This is true also for Uranus, and since its density is only slightly higher than water, there is speculation that most of Uranus is water, in all its forms, with only a tiny rocky core.
2009 - Traces of water were found on the moon, then a ‘significant’ amount of water. Plans are being made for mining it, should we ever decide to colonize or set up a station there.
2010 - Water ice was found on two asteroids. Some surmised that there might be lots of water ice in the asteroid belt.
2011 - It was concluded that dark streaks on Martian slopes were made as salty water (ice) melts and slides down the slope. Water ice is also trapped in Mars’ polar caps, which can reach halfway to its equator during the winter. And a huge slab of underground water ice has been found in its northern hemisphere.
2014 - Ceres, the dwarf planet in the asteroid belt, was found to be spewing water vapor into space. It was speculated that Ceres might have more water than Earth does.
2014 - Gravity measurements suggest that a huge ocean sloshes around under the icy surface of Saturn’s moon Enceladus, which also spews water vapor from vents in its south pole. Titan, another Saturn moon, has an under-crust ocean saltier than Earth’s Dead Sea.
2014 - Scientists re-examined data from 1989, and now wonder if there is a subsurface ocean on Triton, Neptune’s largest moon - even if it does have the coldest surface in the solar system.
2015 - Using the Hubble Space Telescope, scientists found that Jupiter’s moon Ganymede has a huge salty ocean buried under a thick crust of ice. Laboratory experiments lead to the conclusion that there’s a subsurface salty ocean on Europa, another of Jupiter’s moons.
2015 - Water ice sheets were discovered on Pluto.
You get the idea - there’s plenty of water out there. It’s so fascinating a subject because life AS WE KNOW IT needs water. So when we find water - especially liquid water - in places you would think would be too cold, the next question is, Is there life there?
Let’s go find out.