Confirmed: Jupiter's moon Ganymede has a salt water ocean

Ganymede

Excerpt from latimes.com


Astronomers have found the most conclusive evidence yet that a large

watery ocean lies beneath the surface of Jupiter’s moon Ganymede.

Scientists have

suspected for decades that a subterranean ocean might slosh between the

rocky mantle and icy crust of the largest moon in our solar system, but

they had not been able to prove it definitively until now.

Using

the Hubble Telescope, a team of researchers has detected slight

fluctuations in two bands of glowing aurorae in Ganymede’s atmosphere

that they say could occur only if the moon contained a salty body of

water.

“The solar system is now looking like a pretty soggy

place,” said Jim Green, director of planetary science at NASA. “The more

we look at individual moons, the more we see that water is really in

enormous abundance.”

Ganymede is the only moon in the solar system

that has its own magnetic field. However, it is also affected by the

magnetic field of Jupiter – the giant planet next door.

The

effect of Jupiter’s magnetic field on Ganymede changes every 10 hours,

which is the length of time it takes the planet to make a full rotation

on its axis. For five hours its magnetic field points toward Ganymede,

then for another five hours it points away.
“It’s like a lighthouse,” said Joachim Saur of the University of Cologne in Germany, who led the research.

Saur

figured that these regular shifts in Jupiter’s magnetic field would

affect the position of the aurorae in Ganymede’s atmosphere differently

depending on whether or not the moon has a subsurface ocean.

Computer

models show that if Ganymede did not have a subsurface ocean, the

changes in Jupiter’s magnetic field should cause the bands of hot,

electrically charged gas to rock six degrees over a 10-hour period.

However, if the moon contained a salty ocean, it would reduce the

rocking of the auroras to just two degrees.

The reason for the

difference is that a saltwater ocean is electrically conductive and

creates a secondary magnetic field that would suppress the effects of

Jupiter’s magnetic field.

Saur

looked at measurements taken by the Hubble Telescope in 2010 and 2011

of auroras over both the north and south poles of Ganymede and saw that

the auroras only moved two degrees over a seven-hour period.

“We

ran more than 100 models on supercomputers with different parameters,

but every time we got the same result – with no ocean present the

aurorae rock by six degrees, if you add an ocean it reduces the rock to

two degrees,” Saur said at a news conference Thursday announcing the

findings.

The new technique of looking to aurorae for signs of a

liquid ocean could lead to discoveries of water on bodies far beyond our

solar system, researchers say.

“Imagine

a magnetically active star with a planet close by,” said Heidi Hammel,

executive vice president of Assn. of Universities for Research in

Astronomy. “By monitoring the auroral activity on that exoplanet we can

infer the presence of water.”

A telescope larger than Hubble may

be required to observe distant aurorae, but “now we have a tool that we

didn’t have before,” she said.

Source Article from http://feedproxy.google.com/~r/AscensionEarth2012/~3/joTubkbi47E/confirmed-jupiters-moon-ganymede-has.html

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Confirmed: Jupiter's moon Ganymede has a salt water ocean