When NASA’s Cassini spacecraft swooped past Saturn‘s moon Enceladus last year, it got a close-up view of the water vapor and ice plumes that stream away from the small moon. After analyzing the data, researchers say the evidence suggests that the material in the plumes originates as liquid water trapped beneath the moon’s icy surface, which increases the possibility that microbial, extraterrestrial life could exist in the lakes. “We think liquid water is necessary for life and there is more evidence that there is liquid water there,” said lead researcher Candice Hansen…. Scientists are aware of only three places where liquid water exists near the surface of a planet or other body – Earth, Jupiter’s moon Europa and now Enceladus [Telegraph].
Researchers identified four distinct jets within the plume where the water vapor appears to be traveling faster than 1,300 miles per hour. Such high speeds imply that the jets are fed by pressurised water vapour that shoots through narrow openings – which act like rocket nozzles – in the moon’s icy surface. The simplest way to generate such pressures is by evaporating a reservoir of liquid water that lies close to the moon’s surface [New Scientist], researchers say.
For the study, published in Nature [subscription required], the Cassini spacecraft observed the way the plume dimmed starlight shining from behind as the probe zipped past Enceladus in 2005 and 2007. The data allowed scientists to determine the vapor jets’ speed and density as low as 9 miles … above the surface [National Geographic News]. But some researchers disagree with Hansen’s conclusion that the jets’ high speeds were created by pressurized water, and argue that her model doesn’t account for all the energy needed to create the plumes.
In another Cassini flyby in March 2008, NASA scientists steered the spacecraft through the plume and detected not only water vapor but also methane, carbon dioxide, and other organic molecules. If the presence of liquid water is confirmed by further studies, the combination of factors will get ET hunters very excited. “This is more evidence that there is liquid water there. You also need energy, you need nutrients, you need organics [for microbial life to evolve]. It looks like the pieces are there. Whether or not there’s actually life, of course, we can’t say,” Hansen said [Reuters].
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Image: Karl Kofoed