In its final swoop close to the surface of Enceladus, NASA’s Cassini spacecraft has delivered a stunning cliffhanger by detecting the most remarkable hints yet that there may be life on Saturn’s sixth-largest moon.
That swoop took place in October 2015, but research published this month in Science reveals that the spacecraft – which is due to end its 22-year mission by plunging into the planet’s surface in a few months – detected hydrogen gas in a plume of material erupting from the moon’s surface.
Analysing the data, a team of scientists from the South West Research Institute (SWRI) in Texas, USA, suggests that the gas might indicate the presence of hydrothermal vents deep in Enceladus’s subsurface ocean.
If so, the vents might be analogous to those found deep underwater on Earth, which are home to bacterial species dubbed “extremophiles”. These species do not rely on light, but instead live by using the chemical energy derived from the minerals and chemical compounds spewing from the vents to convert carbon dioxide into sugar – a process known as chemosynthesis.
None of the data relayed by Cassini conclusively identifies chemosynthetic life on Enceladus, but neither does it rule it out – and this alone is enough to excite the researchers at SWRI.
“The discovery of hydrogen gas and the evidence for ongoing hydrothermal activity offer a tantalising suggestion that habitable conditions could exist beneath the moon’s icy crust,” says principal investigator Hunter Waite.
To make its measurements, Cassini was programmed to fly very close to the moon, and straight through a plume of gas and ice grains erupting from cracks on the surface.
Once the data was received, Waite’s team subjected it to many months of detailed analysis and simulation. In particular, the scientists were intent on determining whether the hydrogen detected could have come from other sources on or near Enceladus.
“Everything indicates that the hydrogen originates in the moon’s rocky core,” Waite says.