March 27 – Water, Water Everywhere

Today’s factismal: The Earth has less water than Europa, Pluto, or Titan (to name just three planets).

Water is a wonderful thing. You can swim in it, you can drink it, and you can watch as it makes plate tectonics work. But there is surprisingly little of it on Earth; just1,386,000,000 gigatonnes or about 0.05% of the total mass of the planet is water. If you were to squeeze all of the water from the oceans and lakes and atmosphere and rocks, you’d end up with a sphere about 860 miles across. To scientists perhaps the most important thing about water is that it helps to make life (as we know it) possible. Water is a universal solvent, which allows it to mediate in chemical reactions which makes it darn near indispensable for living things (on Earth, anyways). And that’s why folks who study how life arose and what life might look like on other planets are always excited when we find a source of water somewhere other than Earth.

The two sides of Europa, one of Jupiter's ice-covered moons (Image courtesy NASA)

The two sides of Europa, one of Jupiter’s ice-covered moons
(Image courtesy NASA)

For example, consider Europa. This tiny moon of Jupiter is just one quarter the diameter of Earth but has twice as much water as we do! The water forms the thick, icy crust on Europa’s outside and may also create a salty ocean just underneath the icy crust. What excites many astrobiologists about Europa is that the ice isn’t all one color; instead, it has bright white parts (which we expected) and deep red parts (which we didn’t {that’s why we go places like this: to be surprised and learn new things}). Though there haven’t been any in-depth analyses of the red parts, mainly because Europa has never been visited by an orbiter, many scientists think that it could be indicative of organic material which is how scientists say “there’s life in them thar hills!”. And Europa is hardly alone.

Ceres rotates under DAWN's watchful gaze (Image courtesy NASA)

Ceres rotates under DAWN’s watchful gaze
(Image courtesy NASA)

Right now, NASA’s DAWN probe is circling Ceres, the largest asteroid and one of the smallest planets in the Solar System. This tiny little rock is just 590 miles across but may contain nearly 30% water by weight. That means that it could have a water layer up to 60 miles thick near the surface. Those bright spots we see? They may be where other asteroids crashed into Ceres and exposed fresh water ice. And while the water on Ceres is probably solid right now, it wasn’t always that way. Back when Ceres first formed, it could have had liquid water which means that it may also have hosted life. But wait – it gets better!

Titan with the moon Enceladus peeking out from behind. (Wait. That's no moon!) (Image courtesy NASA)

Titan with the moon Enceladus peeking out from behind.
(Image courtesy NASA)

Titan is the second largest moon in the Solar System. Even more amazing, it has an atmosphere of methane and a surface covered with sticky hydrocarbons. (Think of it as the largest oil spill in the galaxy.) And underneath that, it has a layer of water that may be 250 miles thick. For comparison, the deepest part of Earth’s oceans is Challenger Deep which is a mere seven miles deep; all told, Titan has nearly fifty times as much water as Earth. As with Europa, there is abundant heat from Titan’s interior. Unlike Europa, we know that Titan has lots of organic material (those hydrocarbons) that may serve as the basis for a food chain. And then there is Pluto.

The best view we've got of Pluto right now (Image courtesy NASA)

The best view we’ve got of Pluto right now
(Image courtesy NASA)

Good old Pluto is one of the small planets that hide out near the Kuiper belt. This region is what astronomers like to think of as the beginning of the end of the Solar System. It begins about 30 times the distance from the Earth to the Sun (an astronomical unit or AU) and extends out to 50 AU. (The actual end of the Solar System is nearly 100,000 AU out, at the edge of the Oort cloud.) Based on our studies thus far, there may be as many as 200 planets out there, all roughly the size of Pluto and with about the same composition: rock and ice. Lots of ice. how much ice? Enough that Pluto, which is just 20% as wide as Earth, has three times as much water as our big blue marble holds. And, like the other planets we’ve discussed, some of that water may be liquid. That’s right; there is a small possibility that there may be life in Pluto!

And that is why the New Horizons probe is so cool (so to speak). Though it won’t be able to detect life inside the planet, it may be able to see evidence on the outside, just as Voyager 2 did at Europa. And that’s where the citizen science starts! Because the data will be coming in hot and heavy during the few days when the probe is close enough to get a good view of the planet and its moons, the scientists are lining up the names for those things now – and they want your help! They have set up a web form for us to vote on various names for Pluto’s features and to propose names of our own. Of course, even if a name is popular, that’s no guarantee that it will be used; the IAU (the folks who don’t know what a planet is) overruled the name picked by the discoverer of Pluto’s fifth Moon (Vulcan) for one of their own (Kerberos). But it will still be fun to name the features and learn more about this amazing planet as New Horizons swings by the planet. For more information, zoom on over to:
http://www.ourpluto.org/vote

2 thoughts on “March 27 – Water, Water Everywhere

  1. Pingback: July 10 – In Hot Water | Little facts about science

  2. Pingback: July 14 – Calling All Planets | Little facts about science

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