Earlier today, NASA made an announcement after several days of anticipation: Astronomers have seen what they believe are water vapor plumes erupting from the surface of Europa, one of Jupiter's largest moons, using the Hubble Space telescope.
Europa is one of the solar system's most studied and speculated upon moons. One reason for this is the moon's huge global ocean that contains twice as much water as the Earth's ocean. This ocean, however, is covered with a thick layer of ice. We have no idea how thick the shell of ice covering Europa is, but it does pose a problem to astronomers: We can't see below it.
Why should we care so much about a moon covered with water? Well, think about the Earth. How much life is contained within our oceans' waters? It's speculated there is more far life, both number of species and members of those species, in our ocean than on land. Astronomers and planetary scientists consider Europa one of the most promising places in our solar system for life to exist.
So what's so exciting about these water plumes? Well, as I said, there is a layer of extremely cold and thick ice that separates us from whatever is below in the depths of Europa's ocean. If we wanted to study what's under there, we'd have to drill through the ice to collect a sample of the material beneath. There are a lot of unknowns there, and astronomers (and investors!) don't like unknowns, especially where expensive missions are involved--and there is no such thing as a cheap space mission. But if water vapor is indeed erupting from Europa, it is perceivable that a space craft in low orbit around Europa could collect this material relatively easily. We wouldn't have to develop drills and other equipment to collect samples. We wouldn't have to land and take off from Europa's surface. This is extremely exciting because this simplifies a Europa mission a great deal.
How likely is it that astronomers actually did see water vapor vapor? The terminology they are using over at NASA seems to be very cautious. But that's because they are scientists. They don't want to make a statement of absolutes. Only Sith deal in absolutes. But there is a lot of supporting evidence for these plumes. The team who made these observations, led by William Sparks of the Space Telescope Science Institute in Baltimore, MD, watched Europa pass in front of Jupiter through the Hubble Space Telescope ten times. On three of these occasions, they observed what they thought could be plumes of water vapor. In 2012, another team of scientists led by Lorenz Roth of Southwest Research Institute in San Antonio, TX, observed evidence of a vapor plume near Europa's southern polar region. Each of these teams used different methods to arrive at their conclusions of water vapor plumes, though both used Hubble's Imagine Spectrograph instrument to make their observations. I imagine that next on the agenda is for two different teams to observe the same plume at the same time using independent methods. That would increase the likelihood that what we are seeing are indeed water vapor plumes. Another possibility to get a better idea of what's going on on Europa is to observe it with the infrared equipment on the James Webb Space Telescope, which is set to launch in 2018. NASA is also preparing an actual mission to Europa, which would certainly help confirm the existence of the plumes.
Europa wouldn't be the first moon in the solar system to spew water vapor. In 2005, the Cassini orbiter detected water vapor and dust shooting from Enceladus, one of Saturn's moons.
We truly live in exciting times, where we can observe things and learn things about our solar system we never have been able to before. Now, the question is...what DOES exist below Europa's thick shell of ice? Any guesses?
Melanie R. Meadors is an author and editor of science fiction and fantasy, blogger at The Once and Future Podcast, and a professional author publicist. She studied physics and astronomy at Northern Arizona University, where no day was complete without a heated debate over relativity versus quantum mechanics. You can find her at her website, melaniermeadors.com, on Facebook, and Twitter, @melaniermeadors.