In September, Cassini will end a 13-year mission exploring Saturn and its entourage of 62 known moons.
The primary ingredients required to sustain life include liquid water; a source of energy for metabolism; and the right chemical ingredients, primarily carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur. The spacecraft, orbiting Saturn for more than a decade, went through a spouting plume of water shot out of the moon's surface, which revealed evidence of hydrogen gas. The remaining ingredients are also believed to exist there. Hydrogen is an excellent source of chemical energy that supports life near deep sea hydrothermal vents on Earth.
The Cassini spacecraft perceived the presence of hydrogen in the gas plumes and other materials, which were emanating from Enceladus.
Enceladus, a frozen moon nearly 10 times as far from the sun as Earth, at 900 million miles, was one of the least likely candidates. 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.
The thermal similarities between the two moons will need to be investigated further - especially with more observations of Europa, said William Sparks of the Space Telescope Science institute in Baltimore, who led the Hubble work.
Like Enceladus, Jupiter's moon Europa also has ocean plumes erupting.
A discovery of molecular hydrogen was made in October 2015 - but has only now come to light - when NASA's Cassini spacecraft took samples as it passed 30 miles (49 km) above the moon's southern pole.
Meanwhile, Dr. David Clements, astrophysicist at Imperial College London, said: 'This discovery does not mean that life exists on Enceladus, but it is a step on the way to that result'. "It would be like a candy store for microbes", said Hunter Waite, lead author of the study appearing today in the journal Science.
If the plumes and the warm spot are linked, it could be indicative of water being vented from beneath the moon's icy crust and warming the surrounding surface.
Zurbuchen added that the missions were getting humans closer to understanding whether they were "indeed alone or not". Hydrogen molecules in geysers on the moon are a possible sign of life.
To be clear, scientists haven't discovered evidence of organisms on Enceladus, but they encouraged by the processes producing chemical energy, which could feed life.
NASA's Planetary Science Division Director, James Green, said: "We're pushing the frontiers".
The Europa Clipper is set to launch in the 2020s and will make close flybys to Europa to study the oceans there to determine whether or not the same thing is happening there as on Enceladus, and importantly whether or not the moon could possibly support life.