The paper from researchers with the Cassini mission was published Thursday in the journal Science.

And on Jupiter's moon Europa, that Hubble Space Telescope has spotted an huge plume above its icy crust.

Cassini's discovery led to it being re-tasked to fly through Enceladus's plumes. Cassini project scientist Linda Spilker added that the confirmation - that the chemical energy for life exists within Enceladus' ocean - is an important milestone in mankind's search for habitable worlds beyond Earth. With the findings announced today, Enceladus is known to have all of those except phosphorus and sulfur. No phosphorus or sulfur has been found on Enceladus, but scientists suspect their presence.

Enceladus is a small (502km in diameter) moon with an icy surface, a rocky interior and an ocean of liquid water sandwiched between the two.

The findings on Saturn's moon Enceladus are more solid, scientifically speaking.

The finding indicates that if microbes are on Enceladus, they can thrive in the environment.

"It would be like a candy store for microbes". "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".

This graphic illustrates how Cassini scientists think water interacts with rock at the bottom of the ocean of Saturn's icy moon Enceladus, producing hydrogen gas.

An ocean world locked under ice is now showing signs it could support life. Comparing it with thermal map that NASA's Galileo mission gathered in the 1990s, Hubble scientists discovered that the location corresponds to a thermal anomaly on Europa, a warm region on the otherwise frozen moon. It was only three years later that Cassini spotted evidence of plumes erupting from the Enceladus' south polar terrain, sending vapor and solid particles hundreds of miles into space.

The plumes on Europa are an attractive site for future robotic explorations of the subsurface ocean.

Alien life was once only thought possible on habitable planets within the "Goldilocks zone" - far away enough from our sun not to be a fireball, but not so far as to be freezing.

Europa is about the same size as Earth's moon, but holds more water than Earth, Sparks said.

"We're pushing the frontiers", says Dr. Jim Green, a NASA planetary scientist.

Autonomous drones being tested in the oceans of the Earth. "The water reacts with the rock and you can get molecular hydrogen, depending upon what minerals are present", said Jonathan I. Lunine, the David C. Duncan Professor in the Physical Sciences.

On Earth, methane-making bugs flourish in the vicinity of hydrothermal vents, fissures in the ocean floor that gush water heated by volcanic activity. Could life exist out there, in our solar system?

As for Jupiter's moon Europa, the observation is less definitive and more remote, coming from the Hubble Space Telescope.

Scientists at the Goddard Space Center compared ultraviolet photos the Hubble space telescope took of Europa in 2014, when it first saw the gaseous spray emanating from the moon, and found it again in a 2016 picture.