MIAMI • More evidence of possible water plumes erupting from the surface of Jupiter's icy moon Europa has been spotted using Nasa's Hubble Space Telescope, the US space agency has said.

Europa, one of more than 50 moons circling the gas giant, is considered by Nasa as a "top candidate" for life elsewhere in the Solar System because it is believed to possess a massive, salty, sub-surface ocean that is twice the size of Earth's.

The latest finding has given scientists fresh hope that a robotic spacecraft could one day fly past these potential plumes and learn about their contents without having to drill deep into the moon's icy shell.

"Today, we are presenting new Hubble evidence for water vapour plumes being expelled from the icy surface of Europa," Dr William Sparks, an astronomer with the Space Telescope Science Institute in Baltimore, told reporters on Monday during a conference call.

Using ultraviolet images taken by Hubble, a space telescope that was launched in 1990, the potential plumes are seen around the southern edge of Europa and appear as "dark fingers or pat- ches of possible absorption", Dr Sparks said.

They were spotted on three separate occasions over the course of 15 months in 2014 when scientists observed Europa passing in front of Jupiter.

The potential plumes were observed only three out of 10 times when Europa passed by Jupiter, suggesting that the eruptions are intermittent, he said. They also appeared to emerge near the same places, mostly along Europa's southern edge, where a previous team of scientists in 2012 - using a different instrument aboard Hubble - detected evidence of water vapour reaching more than 160km into space.

But Dr Sparks cautioned that more evidence is needed for scientists to be sure, whether by more Hubble observations or by some independent observing technique.

Nasa last year announced that it intends to send a robotic spacecraft, equipped with a suite of scientific instruments, to circle Europa in the 2020s.

AGENCE FRANCE-PRESSE