A little over a month ago, NASA announced the discovery of seven Earth-like worlds a distant 39 light-years away, but we may get confirmation of alien life much closer to home.
In a live news conference Thursday, officials announced that two moons in our solar system, Saturn's Enceladus and Jupiter's Europa, may harbor conditions conducive to supporting life. Both moons contain massive oceans underneath a thick surface layer of ice, with Europa alone estimated to contain two to three times more water in volume than Earth.
On Enceladus, the Cassini spacecraft detected molecular hydrogen within plumes of water vapor venting into space from cracks in the moon's icy surface. On Europa, the Hubble Space Telescope observed similar plumes emanating from the location of an unusually warm region. (Less is known about Europa currently because it has mostly been studied via telescope, either from Earth or from space, but the findings emphasize the need for more exploration.)
"This is the closest we've come, so far, to identifying a place with some of the ingredients needed for a habitable environment," said Thomas Zurbuchen, associate administrator for NASA's Science Mission Directorate at Headquarters in Washington. "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."
The case for Enceladus
The presence of hydrogen on Enceladus confirms nearly all of the conditions necessary for life to form. According to NASA, life as we know it requires liquid water, a source of energy for metabolism, and chemical ingredients carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur. The only missing pieces that have yet to be verified are phosphorus and sulfur. Because Enceladus' core is thought to be chemically similar to meteorites, which are rich in both elements, it likely has the necessary ingredients to support life.
In findings published in the journal Science, the researchers say the only plausible explanation for the presence of hydrogen on Enceladus was hydrothermal reactions of rock on the ocean floor containing minerals and organic materials. This in turn can lead to the production of methane, which alone can support vast underwater colonies of bacteria on Earth even in the absence of light.
"This free energy is really a game-changer for Enceladus," researcher Hunter Waite, lead author of a paper detailing the hydrogen discovery, told Scientific American. "The presence of molecular hydrogen shows there is the chemical potential there to support metabolic systems like methanogenic microbes. This suggests we’ve found a potential food source that would support the habitability of Enceladus’s interior ocean."
Heightened interest in Europa Clipper mission
Both discoveries are bolstering the excitement around NASA's Europa Clipper mission, planned for launch sometime in the 2020s. The spacecraft will specifically target Europa, conducting 40 to 45 flybys at close range to determine whether its ocean has the necessary ingredients for supporting life. The discovery of potential plumes from its surface provides yet another fantastic opportunity to sample its chemical makeup.
“If there are plumes on Europa, as we now strongly suspect, with the Europa Clipper we will be ready for them,” Jim Green, director of Planetary Science at NASA Headquarters, said in a statement.
You can learn more about NASA's announcement on our solar system's "water worlds" below.