Jupiter's largest moon has an ocean, say scientists

A salty ocean is lurking beneath the surface of Jupiter's largest moon, Ganymede, scientists using the Hubble Space Telescope have found.

The ocean onGanymede which is buried under a thick crust of ice could actually harbor more water than all of Earth's surface water combined, according to NASA officials. Scientists think the ocean is about 60 miles (100 kilometers) thick, 10 times the depth of Earth's oceans, NASA added. The new Hubble Space Telescope finding could also help scientists learn more about the plethora of potentially watery worlds that exist in the solar system and beyond.

"The solar system is now looking like a pretty soggy place," Jim Green, NASA's director of planetary science, said during a news teleconference today (March 12). Scientists are particularly interested in learning more about watery worlds because life as we know it depends on water to thrive. [See amazing photos of Ganymede]

Scientists have also found that Ganymede's surface shows signs of flooding. Youngparts of Ganymede seen in a videomap may have been formed by water bubbling up from the interior of the moon through faults or cryo-volcanos at some point in the moon's history, Green said.

Scientists have long suspected that there was anocean of liquid water on Ganymede the largest moon in the solar system, at about 3,273 miles (5,268 kilometers) across has an ocean of liquid water beneath its surface. The Galileo probe measured Ganymede's magnetic field in 2002, providing some data supporting the theory that the moon has an ocean. The newly announced evidence from the Hubble telescope is the most convincing data supporting the subsurface ocean theory yet, according to NASA.

Scientists used Hubble to monitor Ganymede's auroras, ribbons of light at the poles created by the moon's magnetic field. The moon'saurorasare also affected by Jupiter's magnetic field because of the moon's proximity to the huge planet.

When Jupiter's magnetic field changes, so does Ganymede's. Researchers were able to watch the two auroras "rock" back and forth with Hubble. Ganymede's aurora didn't rock as much as expected, so by monitoring that motion, the researchers concluded that a subsurface ocean was likely responsible for dampening the change in Ganymede's aurora created by Jupiter.

"I was always brainstorming how we could use a telescope in other ways," Joachim Saur, geophysicist and team leader of the new finding, said in a statement. "Is there a way you could use a telescope to look inside a planetary body? Then I thought, the aurorae! Because aurorae are controlled by the magnetic field, if you observe the aurorae in an appropriate way, you learn something about the magnetic field. If you know the magnetic field, then you know something about the moon's interior."

Hunting for auroras on other worlds could potentially help identify water-rich alien planets in the future, Heidi Hammel, executive vice president of the Association of Universities for Research in Astronomy, said during the teleconference. Scientists might be able to search for rocking auroras on exoplanets that could potentially harbor water using the lessons learned from the Hubble observations of Ganymede.

Astronomers might be able to detect oceans on planets near magnetically active stars using similar methods to those used by Saur and his research team, Hammel added.

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Jupiter's largest moon has an ocean, say scientists