Io is an interesting little place. Not the kind of place I’d like to go on holiday, mind you.
10 years ago, New Horizons caught a gravitational slingshot from Jupiter to send it on its way to Pluto. As it did, it caught a fantastic view of Io. Io is, quite simply, the most volcanically active place in the entire Solar System. As a result of Jupiter’s immense gravity continually stretching and squeezing Io with titanic tidal forces, Io’s constantly seething with hot sulfrous magma.
Over 400 volcanoes are expected to dot the surface of Io. While this is a lot fewer than the roughly 1500 potentially active volcanoes on Earth, Io is a lot smaller. It’s barely larger than our moon, resulting in a surface pockmarked by a dense collection of volcanic craters and lava formations. It’s also quite a mountainous little place, with many mountains reaching over 6 km. The tallest, Boösaule Montes stands up to 18.2 km tall – well over twice as tall as Everest and only 3.7 km shorter than Olympus Mons.
With a combination of explosive volcanism and low gravity, Io is quite a dramatic little world, with volcanoes able to propel gas and pyroclastic material up to 500 km from the little moon’s surface. These result in umbrella-like fountains like the one in the image above.
Those volcanoes are actually responsible for Io’s atmosphere – a tenuous whisper of sulfur dioxide blanketing the moon. In fact, it’s possible for some of the sulfur from Io to actually reach escape velocity. A fair amount of it ends up in orbit around Jupiter. Ionised by sunlight and charged particles, it forms a thin ring around Jupiter called the Io Plasma Torus★. Some people think this may even be where the sulfur seen on Europa’s surface originally came from – though it’s difficult to be certain without much closer inspection.
It would be very interesting to send a few robots to look at Io in closer detail, especially given how rapidly its surface changes from all that volcanism. Sending people, however, may not be such a good idea. With a surface blasted by Jupiter’s radiation belts, covered in corrosive and toxic chemicals, this is a giant leap that humankind may need to wait awhile before attempting.
★ Yes that would make a good name for a band, but I have my suspicions that someone somewhere has already thought of that.