Io Creates Lightning on Jupiter

Jupiter’s moon Io is one exciting place. Beyond the volcanoes and the lava lakes and the spewing of sulfur dust into space, it actually shoots bolts of electricity at Jupiter!

If you could stand at the cloud tops of Jupiter – difficult because you’d be standing on a gigantic cloud of hydrogen gas – and looked up at Io, you’d see a moon that would appear to be about the same size in the sky as our own. Although Io’s a little bigger than our moon, it’s also just a little farther away, making it about the same size. But everything else would be different.

You’d see an orange-yellow moon with dark splotches on it. If you got out your trusty binoculars and looked at her horizon you’d see plumes of matter pouring into space. You might even be able to detect the glow of lava pouring out of the ground.

Io is one of three sister moons – her siblings are Europa and Ganymede. Her big sisters are cruel to her, however, and constantly torture the smaller moon.

If it weren’t for Europa and Ganymede, Io’s orbit would be nearly circular. When the other two moons are on the other side of Jupiter, Io tries to return to that orbit, being pulled in slightly by Jupiter’s immense gravity.

But when one or both of the other moons appears over the planet’s limb their gravitational fields are so strong that they try to pull little Io out towards them. Ganymede pulls Io in one direction while Europa pulls it in another. Under all these gravitational pulls, Io’s orbit slips into a wacky ellipse.

Just as the moon pulls our ocean towards it Jupiter pulls on Io’s surface. On Earth the moon pulls our oceans up as much as 60 feet. On Io the surface raises as much as 330 feet. But it’s not water: the moon’s crust rises and falls. All these gravitational and tidal forces heat up Io’s interior, making her the most volcanic body in the solar system. Her volcanoes shoot lava 150 miles into the sky.

Io’s orbit take iher in and out of Jupiter’s magnetosphere. As a result, Io’s tortured surface is turned into a electrical dynamo – generating a charge of 400 thousand volts at 3 million amperes. This enormous electrical charge zaps off of Io when she next encounters the magnetosphere and sizzles across the lines of the electromagnetic field back to Jupiter’s surface, where it crackles through the Jovian atmosphere as lightning.

Plumes of molten material are ejected from the little moon by her never-ending volcanism. The clouds of sulfur fall inward toward Jupiter and completely coat the tiny moon Amalthea, making it the reddest object in the solar system.

But Jupiter’s magnetosphere also pulls physical material right off of the moon’s surface as it passes – as much as a ton per second of Io’s surface is torn away as the lines of magnetic force pass over it. This matter is ionized as it is ripped away and falls in towards Jupiter, creating an aurora at the gas giant’s poles.

One would assume that Io’s days are numbered at that rate of material loss. Indeed they are, although you would number the time remaining not in days but in millions of years, and you’d have to plan her being around for hundreds more of those.

You can learn more about fascinating, terrifying little Io at NASA’s Planets site or at Nine Planets.

Although it’s actually larger than the Earth’s moon, Io is a victim of a gravitational tug of war between these two moons and Jupiter itself. 

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