New images from the Hubble Space Telescope show jets of water vapor shooting up from Europa, an ice-covered moon of Jupiter long thought to have an underground ocean.

Researchers used the giant orbiting telescope late last year to observe 125-mile-high plumes rising from Europa's south polar region.

The vapor jets were not detected during Hubble's observations in the same region in October 1999, or even November 2012. Nor did recordings from the since-ended Galileo probe, which flew by Europa nine times in the late 1990s, show any plumes.

Scientists suspect the water vapor may be escaping from cracks in Europa's southern polar ice that open when the moon is its farthest from Jupiter.

"When Europa is close to Jupiter, it gets stressed and the poles get squished and the cracks close up. Then, as it moves further away from Jupiter, it becomes un-squished, the pole moves outward and that's when the cracks open," planetary scientist Francis Nimmo of the University of California in Santa Cruz told Reuters.

Research team leader Lorenz Roth, a planetary scientist at the Southwest Research Institute in San Antonio, Texas, explained the newly-detected spouts are many times the height of potential Europa plumes calculated by some theorists --- meaning they reach higher than the volcanic eruptions on Jupiter's moon Io, but not as high as the towering spouts on neighboring moon Enceladus, which has 12 times less gravity than Europa and can therefore shoot its vaor plumes a lot farther into space.

Europa and Enceladus, the latter of which is currently being studied by the Saturn-orbiting Cassini spacecraft, are each extracting about seven tons of water vapor per second.

"Now that we know where (the plumes) are, that narrows the window that we have in comparison to the passes that we've made," said NASA's planetary sciences chief, Jim Green. "I think we'll have some other great results, or another controversy."

Some scientists have suggested life may exist in Europa's ocean, living on minerals. A separate study based on data compiled by the Galileo mission revealed clay-like minerals on the surface of Europa that could have come from collisions with asteroids or comets.

Organic materials are important building blocks for life and are often found in comets and asteroids. Finding the rocky impact residues could trigger a new round of research into the possibility of life on Europa, said a NASA spokesman.

Europa is believed by many in the scientific community to be the best place in the solar system to find existing life.