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Jupiter's Largest Moon Could be Hiding a Secret Ocean 10 Times Deeper Than Earth's

Mar 13, 2015 01:04 AM EDT
(Photo : NASA/ESA)

Believe it or not, astronomers are abuzz about another sea that may be a home for life, and it's not on Saturn's Titan or Enceladus, or Jupiter's icy satellite Europa. New observations have found that Europa's neighbor, Ganymede, which happens to be the largest moon in our solar system, may play host to a massive habitable ocean - one hiding just beneath its rugged surface.

Ganymede is more than 3,270 miles (~5,200 km) in diameter and the only known moon in our solar system to have its own magnetosphere. It's also the third of the massive Galilean moons that orbit Jupiter - each of which would be classified as its own terrestrial planet or protoplanet (like Pluto and Ceres) if it were orbiting the Sun rather than it's host gas giant. It has been estimated that Ganymede is also eight percent larger than Mercury, but only has about 45 percent of the sweltering planet's mass.

Still, with all these impressive characteristics, it's a wonder why experts have not previously considered it as habitable. After all, Europa has long been suspected to have a thick and chilly ocean (perhaps too cold for life) beneath its frozen surface. Why would Ganymede be no different?

But it's important to note that on face value, this massive moon is nothing but an ice and rock wasteland. It actually took a great deal of brainstorming and ingenuity, as well as the Hubble Space Telescope, to find out if there was actually anything hiding beneath Ganymede's droll exterior.

"I was always brainstorming how we could use a telescope in other ways," Joachim Saur, of the University of Cologne in Germany, explained 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."

What Saur is going on about is what makes Ganymede unique as a moon despite its boring terrain. Because the natural satellite has its own magnetic field, it also has its own stunning auroras. Charged particles from the Sun are trapped and excited by the magnetosphere until the point that they can even be seen with the naked eye. (Scroll to read on...)

(Photo : NASA/ESA) NASA Hubble Space Telescope images of Ganymede's auroral belts (colored blue in this illustration) are overlaid on a Galileo orbiter image of the moon.

Of course, the moon is also affected by its host planet, Jupiter, with its powerful magnetic field also having an effect on the moon's dancing lights. This interplay between two magnetic fields would cause the aurorae to rock, but careful observations by Saur and his team using the Hubble Space Telescope have revealed that this rocking is a lot more subtle than it should be.

So what's going on? The most likely explanation, according to the researchers, is that there is a stunningly large saltwater ocean just beneath the moon's surface that can counter the effects of Jupiter's field.

Saur explained in a NASA release that the sea's own "magnetic friction" could suppress Jupiter's field so strongly that it reduces the rocking of aurorae to 2 degrees, instead of the normal 6 degrees if the ocean was not present.

But this would also mean that the ocean would have to be an average of 60 miles deep - that's 10 times deeper than Earth's expansive oceans. And what's more, this ocean would have to be beneath an estimated 95 miles of ice and stone. That may mean humanity will be a long way away from checking out this subterranean ocean world for ourselves, even if plans to investigate the oceans of Europa and Enceladus with unmanned landers see fulfillment within the next few generations.

It should also be noted that this isn't the first time that experts have suggested that the massive moon plays host to an ocean, but it is the first time where strong evidence is presented in favor of the theory. Before that, astronomers simply held a suspicion, comparing the moon to other icy worlds.

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