There could be life in one of the oceans in our Solar System, according to Nasa.
Take a trip on Cassini as it dives through Saturn's rings in this Nasa video
Molecular hydrogen, one of the essential parts of life on Earth, has been found on Saturn's moon Enceladus.
While no evidence for life has been found, the discovery means the moon can potentially support living organisms.
Enceladus has a global subsurface saltwater ocean, which was discovered by Cassini in 2008. Now, hydrogen - which could provide the energy for life - has been found in the plumes of liquid shooting out of the moon's surface.
“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 presence of hydrogen in the moon's ocean means microbes could use it to obtain energy by combining the hydrogen with carbon dioxide dissolved in the water.
This chemical reaction, known as "methanogenesis," because it produces methane as a byproduct, is at the root of the tree of life on Earth, and could even have been critical to the origin of life on our planet.
"Although we can't detect life, we've found that there's a food source there for it. It would be like a candy store for microbes," said Hunter Waite, lead author of the Cassini study.
The new discovery comes from the Cassini spacecraft, which flew through a huge plume of water being shot out of the surface of Enceladus.
"Confirmation that the chemical energy for life exists within the ocean of a small moon of Saturn is an important milestone in our search for habitable worlds beyond Earth," said Linda Spilker, Cassini project scientist at Nasa’s Jet Propulsion Laboratory (JPL) in Pasadena, California.
Cassini has been orbiting Saturn since 2004. Its mission to discover more about Enceladus began in 2005. Cassini’s cameras obtained the first-ever detailed images of the south polar region of Enceladus, showing huge plumes of water.
During a close flyby in 2008, Cassini's instruments sampled the plume directly and detected a surprising mix of volatile gases, water vapour, carbon dioxide and carbon monoxide, as well as organic materials.
The density of organic materials was about 20 times denser than expected.
Next month, Cassini will start a five-month descent into the atmosphere of Saturn, where it will eventually burn up in the planet’s atmosphere.
On April 26, Cassini will begin its first in a series of dives through the 1,500-mile-wide (2,400km) gap between Saturn and its rings, which will eventually see it destroyed by the planet's atmosphere.
Last week, ahead of Cassini’s suicide mission, WIRED asked two Cassini scientists what they considered was Cassini’s most exciting discovery so far. “Definitely Enceladus and its ocean,” Curt Niebur, Cassini’s programme manager at Nasa told WIRED, before the new announcement was made.
Dr Nicolas Altobelli, project scientist for Cassini at the European Space Agency, also said the ocean on Enceladus was his favourite Cassini discovery. “This is a tantalising prospect for astrobiology and clearly demonstrates the need to explore further the icy moons around gas giants,” Altobelli told WIRED.
Cassini’s data has also been used in the past to study the moon Titan, along with Saturn’s icy rings, its magnetosphere and its atmosphere. It is likely to be an emotional day in September, when Cassini finally dives into Saturn. “I think everyone’s emotions will run the full spectrum,” Niebur told WIRED.
“It’s impossible to not feel sad when moving on from something that has played such a huge part of your life, but that is overshadowed by the joy of having been part of it.”