It suggests that the gas is being produced in a series of complex chemical reactions happening in hydrothermal vents on the bottom of the moon's ocean.
In deep thermal vents beneath the oceans here on Earth known as "white smokers", hydrogen gas is formed through interactions between the heated water and surrounding rock. But, according to NASA, beneath that inhospitable crust there could actually be life thriving in the moon's far warmer underground seas.
Periodically, waters will erupt through Enceladus' crust thanks to this added hydrogen.
Silica nanoparticles were also detected, indicating a hot rocky interior reacting chemically with alkaline water.
It is the closest the missions have come to identifying a place with the ingredients needed for a habitable environment, where there could be alien life.
"The new finding is hydrogen coming from the plume of Enceladus, and it could contain microbes from the sea floor of Enceladus", announced Linda Spilker, Cassini project scientist at NASA's Jet Propulsion Laboratory, at a press conference on Thursday. The craft also collected samples during an earlier flyby.
The measurement was made using Cassini's Ion and Neutral Mass Spectrometer (INMS) instrument, which sniffs gases to determine their composition. Because so much hydrogen is making its way into space, it could be a sign that there's very little life (if any) there. We're not assuming. Well, kinda...
NASA officials said Cassini detected the hydrogen during one of its final dives through a plume of material spraying from Enceladus in October 2015. These microbes would use the hydrogen to obtain energy by combining the hydrogen with carbon dioxide in the water. So they figure if methanogenesis helped Earth's humans develop, why can't it help Enceladus' aliens? This would be critical for possible life on Enceladus as the moon is too far from the Sun for it to rely on sunlight for energy.
NASA scientists today revealed the discovery of molecular hydrogen on the moon, suggesting there could be life thriving under its icy shell.More news: Pirates scratch OF Polanco vs Cubs because of groin injury
"Although we can't detect life, we've found that there's a food source there for it".
Lead scientist Dr Hunter Waite said the result showed the moon's environment would be "like a candy store for microbes" with a constant and plentiful food source. Researchers are still trying to confirm the presence of phosphorus and sulfur on Enceladus, but they are confident it exists. Geological turmoil caused by the effect of Saturn's gravity on the moon's core is believed to produce enough heat to keep the ocean warm and to send geyser-like plumes of water spewing out into space. The plume's reach was apparently 62 miles (100 kilometers) above Europa's surface.
A photograph of Enceladus taken by Cassini in November 2016.
The discovery allows NASA to include instruments on the Europa Clipper, another JPL mission scheduled to launch to Jupiter in the 2020s, that could more fully investigate that moon's habitability. It's also likely this event is taking place in one, consistent spot.
This is now the third detection of plumes near the southern polar region of Europa.
Because that region of the solar system traps atomic particles from the sun, the radiation of the area around Jupiter is unsafe to spacecraft. The map is based on observations by the Galileo spacecraft. The Hubble Space Telescope has observed what looks to be plumes emanating from Europa.
"We still have a long way to go in our understanding", said Seewald, who was not involved in the study.
The observations were made past year at the same location that the Hubble telescope saw evidence of a plume in 2014. The fact that Hubble has seen them twice has led NASA to believe that they might be part of a regular lunar feature and quite possibly be evidence of water vapor eruptions.