Monday, September 26, 2016

Could Europa be Spewing Signs of Life?

In an eagerly anticipated announcement, NASA just revealed new evidence that plumes of water are intermittently expelled from the surface of Europa, one of Jupiter’s moons.
It’s not quite as exciting as finding little green men skating across Europa’s ice-covered surface, but it could be a step in that direction. If alien life exists in our solar system, we’ll probably find it on Europa. Miles beneath its icy surface there is a liquid, saltwater ocean that could harbor life. If that’s the case, and if water sometimes spews out through the ice, that means we can study the water and look for signs of life without drilling through an unknown number of miles of ice to reach the ocean.

The puzzling, fascinating surface of Jupiter's icy moon Europa, made
from images taken by NASA's Galileo spacecraft in the late 1990s.
Image Credit: NASA/JPL-Caltech/SETI Institute.
The evidence comes from a set of 2014 images taken in ultraviolet light by the Hubble Space Telescope. Each image was taken as Europa passed directly in front of Jupiter. Water and ice absorb ultraviolet light, so in these images Jupiter appears bright and Europa dark. If the moon did expel plumes of water, as some researchers suspected, an ultraviolet image would show this as a dark silhouette in front of Jupiter that is not explained by the surface of Europa. The study consisted of ten images, and three of them showed evidence of plumes. The results are being published this week in The Astrophysical Journal.

The researchers say this work adds to the evidence in support of plumes, but caution that these ultraviolet images push the limits of what Hubble can do at that wavelength. They haven’t found anything else that could explain their results, but are eager for confirmation of their findings from more images or other techniques.

The first and, so far, only other evidence for water plumes also came from the Hubble. Spectroscopic data taken in 2012 indicated higher than expected amounts of hydrogen and oxygen above Europa’s surface, likely the result of water molecules from a plume and breaking up in the atmosphere. Both this and the new result suggest that the activity is primarily located around its south pole.
Europa’s surprisingly smooth surface was first revealed by NASA’s Voyager II space probe in 1978. The lack of craters and mountains suggested a deep ocean hidden beneath ice. If an object crashes into the Earth, we get a crater. If it crashes into Europa, it leaves behind a hole in the ice that refreezes. In addition, the pattern of cracks and streaks running across Europa’s surface is reminiscent of the icy surface of Antarctica where glaciers break apart, drift, and refreeze.

Scientists think that heat produced by tidal forces keeps the ocean from freezing solid. Volcanoes on the ocean floor could play a role as well. Although Europa has a thin atmosphere and Jupiter sends a lot of harmful radiation its way, life developing in the ocean would be protected by the icy cover.
A couple of years ago, scientists discovered what seems to be a huge saltwater lake just under Europa’s surface. This lake could act as a path along which energy and nutrients travel between the ice and the liquid ocean, creating an environment more conducive to life. Exactly how water might reach and break through the thick layer of ice covering the moon, even if it’s coming from the lake, is uncertain. Scientists have proposed models that show it is possible, but we really need more information to figure out what is happening.
An artist's conception of one possible scenario for getting
water to Europa's surface. Jupiter looms off to the right.
Image Credit: NASA/JPL-Caltech.
Last year NASA announced plans for a mission to Europa during which a spacecraft will conduct several close flybys of the moon. The goal is to see whether the conditions are right for life and look for signs of it. With a planned launch in the 2020s, scientists are working on instruments to explore the composition, temperature, and thickness of the ice and search for lakes below the surface. The mission would also look for water in the atmosphere and measure the strength of Europa’s magnetic field, which would provide information on the depth and salt concentration of the ocean. Check out the short video Alien Ocean: NASA’s Mission to Europa for a great overview of the project.

It’s tough to imagine life as we know it on an ice-covered planet, but where there is water on Earth, there is life. And if history is any indication, Europa likes making waves. Discovered in 1610 by Galileo Galilei, and independently by Simon Marius, Europa and the other three “Galilean moons” upset the accepted order of things at that time. Their trek through the sky clearly shows that not all celestial objects revolve around the Earth, an assertion that played a role in Galileo’s trial for heresy and house arrest. Of course, its ultimate acceptance was a huge leap forward for science and society. Will this new result bring us closer to another major turning point?

Kendra Redmond

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