WASHINGTON — NASA has new evidence that the most likely places to find life beyond Earth are Jupiter’s moon Europa or Saturn’s moon Enceladus. In terms of potential habitability, Enceladus particularly has almost all of the key ingredients for life as we know it, researchers said.
New observations of these active ocean worlds in the solar system have been captured by two NASA missions and were presented in two separate studies in an announcement at NASA headquarters in Washington on Thursday.
Using a mass spectrometer, the Cassini spacecraft detected an abundance of hydrogen molecules in water plumes rising from the “tiger stripe” fractures in Enceladus’ icy surface.
Saturn’s sixth-largest moon is an ice-encased world with an ocean beneath. The researchers believe the hydrogen originated from a hydrothermal reaction between the moon’s ocean and its rocky core.
If that is the case, the crucial chemical methane could be forming in the ocean as well.
“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 study.
“The presence of hydrogen established another reference point saying there is hydrothermal activity inside this body, and that’s interesting because we know in our own oceans, those are very important places that are teeming with life, and they are probably one of the earliest places where life happened on Earth.”
Additionally, the Hubble Space Telescope showed a water plume erupting on the warmest part of the surface of Europa, one of Jupiter’s moons with an icy crust over a salty liquid water ocean containing twice as much water as Earth’s seas.
This is the second time a plume has been observed in this exact spot, which has researchers excited that it could prove to be a feature on the surface.
“This is significant, because the rest of the planet isn’t easy to predict or understand, and it’s happening for the second time in the warmest spot,” said Britney Schmidt, second author on the Europa study.
The necessary ingredients for life as we know it include liquid water, energy sources, and chemicals such as carbon, hydrogen, oxygen, nitrogen, sulfur and phosphorus.
But life finds a way in the harshest of Earth’s environments, like vents in the deepest parts of the ocean floor. There, microbes don’t receive energy from sunlight, but use methanogenesis, a process that reduces carbon dioxide with hydrogen, to form methane.
Europa and Enceladus are showcasing some of these key ingredients for life in their oceans, which is why researchers believe they are the best chance for finding life beyond Earth in our own solar system.
Previous results from the Cassini mission’s flybys of Enceladus already had researchers intrigued.
First, they could see plume material linked to interior water. They determined that the moon had a global ocean, and then a cosmic dust analyzer revealed silicon dioxide grains, indicating warm hydrothermal activity.
“This (molecular hydrogen) is just like the icing on the cake,” Waite said. “Now, you see the chemical energy source that microbes could use. The only thing we haven’t seen is phosphorus and sulfur, and that’s probably because they were in small enough quantities that we didn’t see them. We have to go back and look and search for signs of life as well.”
Earth is considered an ocean world because those bodies of water cover the majority of the planet’s surface.
Other ocean worlds in the solar system, besides Europa and Enceladus, potentially include Jupiter’s moons Ganymede and Callisto; Saturn’s moons Mimas and Titan; Neptune’s moon Triton; and the dwarf planet Pluto.
It is believed Venus and Mars were once ocean worlds, but the greenhouse gas effect and a vulnerable atmosphere, respectively, caused those planets to lose their oceans.