Jupiter's moon Europa is covered in a thick layer of ice, but it has a turbulent ocean that lies beneath. Today astronomers announced that new observations show this water is erupting in massive plumes like water volcanoes. It's a discovery that could have serious implications for Europa's potential to harbor life.
Astronomers have never before seen any geological activity on the surface of Europa. They'd speculated that it had an active subsurface ocean (which was confirmed independently by magnetometer measurements) and they knew its scarred, icy surface known as chaos terrains was the result of turbulent waters near the lower latitudes. Still, the moon's active ocean was known only by inference. Nor had they observed any kind of noteworthy weather; the moon has an incredibly thin atmosphere comprised of trace amounts of oxygen.
Water in the Ultraviolet
But after scanning the moon with the Hubble Space Telescope back in November and December of last year, astronomer Lorenz Roth and colleagues identified what may be transient plumes of water vapor erupting from beneath the surface. Ultraviolet imaging revealed statistically significant amounts of hydrogen and oxygen emanating from two distinct regions near the moon's southern hemisphere.
And we're not talking little geysers. These plumes are huge, with water being sprayed upwards at a height of 125 miles (200 km). These surpluses of hydrogen and oxygen were persistently found in the same area over a period of about seven hours.
But when looking at older data from 1999, the astronomers could not detect the plumes — a possible indication that these eruptions, like Old Faithful in Yosemite park, may be periodic.
Apocenter
And indeed, this is precisely the case. As Europa orbits around Jupiter, and as it reaches its apocenter point (the furthest distance from Jupiter), the southern polar regions erupt. When Europa is at its pericenter (the closest distance from Jupiter), all is quiet.
According to the astronomers, tidal acceleration is creating a tremendous amount of pressure — enough to force the water through surface cracks. Models affirmed these suspicions.
"The plume variability, if real, verifies a key prediction of tidal-flexing models based on the existence of a subsurface ocean," write the authors in the study.
Interestingly, these plumes may be similar to those of Saturn's moon, Enceladus, with high-pressure vapor emissions escaping from very narrow cracks.
The Search for Life
If these plumes are confirmed as consisting of water, it shows that the moon's subsurface ocean has relatively easy access to the surface, at least at certain periods and in specific geographical regions.
Europa, with its warm liquid water, turbulent subsurface ocean currents, and active tectonics, is an interesting candidate for extraterrestrial life. Astrobiologists speculate about the potential for Europa to spawn extremophiles — microbial life capable of surviving the harshest of conditions.
The discovery that this water can reach the surface could have implications for future explorations of this Jovian moon. So, in addition to combing the chaos terrains, we should focus on the southern polar regions as well.
Read the entire study at Science: "Transient Water Vapor at Europa's South Pole".
Images: K. Retherford, Southwest Research Institute, Lorenz Roth, Southwest Research Institute / USGS.
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