Although life can not be confirmed, the clues from Enceladus all indicate the conditions for life exist on the oceans of Enceladus, the sixth-largest moon of Saturn.
With all of this optimism, the fact remains that NASA has not discovered any evidence of living organisms living on Enceladus.
The study authors suggested that the hydrogen found in the plume comes from hydrothermal processing of rock, similar to systems on Earth when water reacts with rocks containing reduced iron-bearing minerals producing molecular hydrogen. The findings on Jupiter's moon Europa were discovered by the Hubble telescope, NASA said at a news conference in Washington.
The data was collected by the Cassini spacecraft that has been orbiting Saturn since 2004.
"We now know that Enceladus has nearly all of the ingredients that you would need to support life as we know it on Earth", she said at a NASA news conference. "Chemical disequilibrium that is known to support microbial life in Earth's deep oceans is also available to support life in the Enceladus ocean".
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NASA stresses the findings, that were announced in the journal Science, do not mean that there is life on either moon, but that there may be favourable conditions to harbour life.
The plumes are 98 percent water, scientists said, with traces of molecules including ammonia, carbon dioxide and methane. "It remains for a future mission to detect life at Enceladus". Cassini has found almost all of the ingredients for life on Enceladus: liquid water, a source of energy and the chemical elements - carbon, hydrogen, nitrogen, oxygen, phosphorous and sulfur - that we know contributed to the formation of life on Earth. After that, they would need to find signs of life by entering the water plumes coming out of the surface and looking for different acids and isotopes that could present signs of life, even if that is a minuscule change.
Beneath the ice surface of the Enceladus, there is a deep ocean, whose water Cassini has now sampled. Such emissions are seen as a key factor that likely spurred the development of life on Earth, because the gas combines with the carbon dioxide in water to provide metabolic energy. The Hubble Space Telescope has observed what looks to be plumes, or long clouds, coming from Europa.
"This is the closest we have come, so far, to identifying a place with some of the ingredients needed for a habitable environment", said Thomas Zurbuchen, associate administrator of NASA's Mission Directorate, in a statement. We know Europa and the moons around Jupiter existed 4 billion years ago so that is a lot more time for life to have emerged and start taking advantage of these energy sources.
"If there are plumes on Europa, as we now strongly suspect, with the Europa Clipper we will be ready for them", said Jim Green, Director of Planetary Science, at NASA Headquarters.