Enceladus is one of the most promising candidates to find life elsewhere in the Solar System. The Saturnian satellite is an icy moon with water-rich plumes being ejected from its south polar region, an indication of a potential subsurface ocean of liquid water.
These plumes have been studied in detail by NASA's Cassini spacecraft, but in the latest run of observations, astronomers spotted something that didn’t fit predictions. The plumes are made by smaller jets, which appear to get stronger when the moon is farther away from Saturn. The probe detected one particular jet that was emitting four times more water than expected.
The observations were possible thanks to the light from the star Epsilon Orionis, the middle star in Orion’s belt, passing through Enceladus. On March 11, the moon’s plume and the star were aligned with the Cassini spacecraft, and the probe was able to use its Ultraviolet Imaging Spectrometer (UVIS) to snap some pictures.
Cassini had previously observed three times as much icy dust being ejected from the moon around the furthest point from Saturn, but until now scientists had not been able to see if the water vapor increased as well, as water makes up for 90 percent of the material in the plume.
Surprisingly they discovered that the plumes, which extend out to 500 kilometers (310 miles) from the surface, only had a 20 percent increase in the total amount of gas. Something must be propelling the icy dust outwards, so the team looked at the small jets that are closer to the surface. One jet, in particular, was seen to provide 8 percent of the plumes' water content, instead of the usual 2 percent.
"We had thought the amount of water vapor in the overall plume, across the whole south polar area, was being strongly affected by tidal forces from Saturn," said Larry Esposito, UVIS team leader, in a statement. "Instead, we find that the small-scale jets are what's changing."
While the new observations took an unexpected turn, the data collected will give physicists a better understanding on how Saturn heats up the interior of Enceladus.
"Since we can only see what's going on above the surface, at the end of the day, it's up to the modelers to take this data and figure out what's going on underground," added Candy Hansen, who led the planning of the observation.
Understanding the processes within Enceladus will give us better constraints on the potential subsurface ocean, and even what the chances are of life forming on this curious moon.