Artist impression of water vapour erupting from Europa (Nasa ESA, and M. Kornmesser)

The Hubble Telescope has discovered water vapour erupting from the surface of Europa, one of Jupiter's sixth closest moon.

Nasa experts say the discovery reinforces Europa as the most likely candidate for hosting extraterrestrial life.

The water vapour plumes were identified near the moon' south pole and are the first observational evidence of water vapour being ejected from its surface.

Europa is already believed to have a liquid ocean beneath its icy crust, making it one of the key targets in the search for habitable planets.

Lorenz Roth, from the Southwest Research Institute in San Antonio, Texas, said: "The discovery that water vapour is ejected near the south pole strengthens Europa's position as the top candidate for potential habitability. However, we do not know yet if these plumes are connected to subsurface liquid water or not."

Europa's water vapour plumes were first discovered in December last year, when the Space Telescope Imaging Spectrograph saw a faint ultraviolet light coming from an aurora at the South Pole.

Hubble telescope
Hubble spotted the water vapour at the moon's South Pole (Nasa)

The aurora, driven by Jupiter's magnetic field, causes particles to reach extremely high speeds that can split water molecules, resulting in hydrogen and oxygen ions.

Joachim Saur, study co-author principal investigator of the Hubble observing campaign, said: "We pushed Hubble to its limits to see this very faint emission. Only after a particular camera on the Hubble Space Telescope had been repaired on the last servicing mission by the Space Shuttle did we gain the sensitivity to really search for these plumes."

This is only the second time water vapour has been discovered on a moon in the solar system. It was first seen by Nasa being spewed from the surface of Saturn's moon Enceladus.

Researchers also note that the plumes on Enceladus also contained ice and dust particles unlike Europa, which only had water vapour.

Astronomers will now look to find the exact locations and sizes of the vents to find out where the water comes from.

Roth said: "Do the vents extend down to a subsurface ocean or are the ejecta simply from warmed ice caused by friction stresses near the surface?"