There’s a lot of totally understandable excitement in the scientific community around exploring the Jovian moon Europa. With NASA planning to launch two multi-billion dollar missions to Europa, some scientists are pointing out that a much more tempting target is getting short shrift. Saturn’s moon Enceladus has many of the same properties as Europa, and our greater knowledge of this moon could make it easier to detect life.
Europa entered the public consciousness thanks to the revelation that it most likely has a subsurface liquid ocean under the ice sheet. Tidal forces from Jupiter’s massive gravity keep the planet’s interior warm enough for the sea to remain in this state, but we don’t know much more. We can safely say that Europa has a thick icy shell, but no one knows for certain how thick. Neither of the upcoming Europa missions are likely to deliver breakthroughs in the search for extraterrestrial life.
Enceladus, meanwhile, has been studied up close for more than a decade. NASA’s Cassini spacecraft discovered cryovolcanic geysers of water on the surface of Enceladus way back in 2005. The spacecraft even flew through these geysers on several occasions. These vents most likely provide a way into the planet’s subsurface ocean, and Cassini has managed to analyze the chemical makeup of that water. Enceladus has complex organic molecules that are necessary for the development of life, and there’s molecular hydrogen to serve as an energy source. We have some evidence of similar water plumes on Europa, but that’s far from certain.
Saturn is farther away than Jupiter, but it’s much easier to study. Jupiter has intense radiation fields that can fry the electronics in spacecraft. That’s why the Juno orbiter is on an elongated path around Jupiter — it’s minimizing the amount of time it spends in the thick of the radiation. Cassini orbited Saturn happily for 13 years, retiring only when it ran low on fuel. The upcoming Europa Clipper mission will just conduct a series of flybys of Europa. A mission to Enceladus could remain in orbit for a long time gathering information.
There’s still a great deal we don’t know about moons in the outer solar system, and that includes Enceladus. We’re still years away from peeking inside the oceans of these worlds to look for life, but Enceladus does look like a more rewarding target in the short term. NASA has limited resources, so spreading mission funding around is probably smart.
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