CAPE CANAVERAL, FLORIDA ¨C Scientists using the Hubble Space Telescope have confirmed that the Jupiter-orbiting moon Ganymede has an ocean beneath its icy surface, raising the prospects for life, NASA said on Thursday.

The finding resolves a mystery about the largest moon in the solar system after NASA¡¯s now-defunct Galileo spacecraft provided hints that Ganymede has a subsurface ocean during exploration of Jupiter and its moons from 1995 to 2003.

Scientists told reporters on a conference call that it took some detective work to confirm the discovery.

Like Earth, Ganymede has a liquid iron core that generates a magnetic field, though Ganymede¡¯s field is embedded within Jupiter¡¯s magnetic field. That sets up an interesting dynamic with telltale visuals ¡ª twin bands of glowing aurora around Ganymede¡¯s northern and southern polar regions.

As Jupiter rotates, its magnetic field shifts, causing Ganymede¡¯s aurora to rock. Scientists measured the motion and found it fell short. Using computer models, they realized that a salty, electrically conductive ocean beneath the moon¡¯s surface was counteracting Jupiter¡¯s magnetic pull.

¡°Jupiter is like a lighthouse whose magnetic field changes with the rotation of the lighthouse. It influences the aurora,¡± said geophysicist Joachim Saur, with the University of Cologne in Germany. ¡°With the ocean, the rocking is significantly reduced.¡±

Scientists ran more than 100 computer models to see if anything else could be having an impact on Ganymede¡¯s aurora. They also repeated the seven-hour, ultraviolet Hubble observations and analyzed data for both belts of aurora.

¡°This gives us confidence in the measurement,¡± Saur said.

NASA Associate Administrator Jim Green called the finding ¡°an astounding demonstration.¡±

¡°They developed new approach to look inside a planetary body with a telescope,¡± Green said.

Ganymede joins a growing list of moons in the outer solar system with subsurface water. On Wednesday, scientists reported that Saturn¡¯s moon Enceladus has hot springs beneath its icy crust. Other water-rich worlds include Jupiter moons Europa and Callisto.

Scientists estimate the ocean is 60 miles (100 km) thick, 10 times deeper than Earth¡¯s oceans, and is buried under a 95-mile (150-km) crust of mostly ice.

¡°It is one step further toward finding that habitable, water-rich environment in our solar system,¡± said astronomer Heidi Hammel with the Washington-based Association of Universities for Research in Astronomy.