Saturn's moon Enceladus and Jupiter's moon Europa have been deemed the places most likely to host life outside of Earth, according to NASA scientists.
On Thursday NASA announced that two missions have captured new observations of active ocean worlds right here in our solar system. The findings were presented in papers published by researchers with NASA’s Cassini mission to Saturn and work on the Hubble Space Telescope.
Cassini scientists detected hydrogen molecules — which could potentially provide a chemical energy source for life — in water pouring into the subsurface ocean of Enceladus from hydrothermal activity on the seafloor.
The Cassini spacecraft found hydrogen in the plume of gas and icy material spraying from Enceladus during its last, and deepest, dive through the plume on October 28, 2015. Cassini also sampled the plume's composition during flybys earlier in the mission. From these observations scientists have determined that nearly 98 percent of the gas in the plume is water, about 1 percent is hydrogen and the rest is a mixture of other molecules, including carbon dioxide, methane and ammonia. It is believed the hydrogen came from a hydrothermal reaction between the moon's ocean and its rocky core.
The presence of ample hydrogen in the moon's ocean means that microbes – if any exist there – could use it to obtain energy by combining the hydrogen with carbon dioxide dissolved in the water, according to the NASA release. This chemical reaction, known as "methanogenesis" because it produces methane as a byproduct, is key to forming life. (It could even have been critical to the origin of life on our planet.)
"Now, Enceladus is high on the list in the solar system for showing habitable conditions," said Hunter Waite, leader of the Cassini Ion and Neutral Mass Spectrometer team at the Southwest Research Institute in San Antonio and lead author of the Enceladus paper, according to the release.
Meanwhile, scientists using the Hubble Space Telescope observed a warm jet of water shooting out of the warmest part of Europa, one of Saturn's moons that is composed of an icy layer over a salty liquid ocean of water. A plume of water had already been observed in the same spot, which is how scientists knew to be watching for it.
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The newly imaged plume rises about 62 miles above Europa’s surface, while the one observed in 2014 was estimated to be about 30 miles high. Both correspond to the location of an unusually warm region that contains features that appear to be cracks in the moon’s icy crust, seen in the late 1990s by NASA's Galileo spacecraft. Researchers speculate that, as with Enceladus, this could be evidence of water erupting from the moon’s interior.
“This is the closest we've come, so far, to identifying a place with some of the ingredients needed for a habitable environment,” Thomas Zurbuchen, associate administrator for NASA's Science Mission Directorate at Headquarters in Washington, stated. ”These results demonstrate the interconnected nature of NASA's science missions that are getting us closer to answering whether we are indeed alone or not.”