View from Io
Published on Feb 11, 2007 at 10:02 pm.
3 Comments.
Filed under extraterrestrial moons.
Io is a Moon of Jupiter. It is the closest of the four big Galilean moons, though four other of Jupiter’s 63 known moons are closer to the planet. Io orbits Jupiter in just about 1.77 days. Being close to the planet, each orbit carries Io behind Jupiter. If you were on Io, you’d see a total eclipse of the Sun, as shown in the simulated view above. It would be quite a view! Jupiter is the largest planet in the Solar System, and Io oribts only about 350,000 kilometers above its surface. Jupiter subtends an angle of about 11.5° as seen from Io. That’s about 23 times larger than our Moon appears in our sky. That makes for one major eclipse! A solar eclipse on Io can last over 3.5 hours. During that time, the Sun would not be shining on Io. You’d think that would mean that Io would cool off, but it really doesn’t cool very much.
Io is an interesting world. I say world because it is so big that no one would even question calling it a planet were it to orbit the Sun instead of Jupiter. When the Voyager spacecraft flew past Io in 1979, no craters were seen. That was an odd finding. Then, Linda Morabito was observing images of Io some time later when she saw a strange feature on the limb of the moon (the “limb” is the edge of the moon). What she saw turned out to be a volcanic plume. Carefully observing other Voyager images showed nine active volcanos. That is phenominally active! Imagine taking a few random photos of Earth. We know that Earth is volcanically active, but would you expect to see nine eruptions at once? The Galileo later imaged over 100 active volcanoes, and it is thought that that may have been only 1/3 of the ones there! Io is, by far, the most
volcanically active body in the Solar System. In fact, it is so volcanically active that enough material is ejected by these volcanoes to completely cover the surface of the Moon to a depth of nearly an inch every year. And those volanic plumes, such as seen here and above, are big, rising 300 to 400 kilometers above Io’s surface!
So, what makes this moon so vollanically active? The answer lies in Jupiter and the other moons. Jupiter’s four largest moons are all planet sized. They orbit fairly close to one another, and so they are caught in a tidal tug of war between one another and Jupiter. The closer moons of Io and Europa get the most tugging. In fact, the surface of Io can rise and fall by 100 meters in all of this. This continual flexing heats the moon. In fact, it is enough to melt the interior of Io. This molten rock spews out onto the surface, and erupts in geysers of molten material, creating the plumes. Nearly 100,000 tons of material per second is spewed out this way. The colors on Io are those that you expect from heated sulfur, and early speculation was that the lava flows were molten sulfur. Howerver, the Galileo space probe showed that the temperatures of several pools of molten material was far too high to be sulfur (it would vaporize at those temperatures), and was more typical of molten silicate rocks. This is a moon of fire and brimstone fitting of Dante’s Inferno.
Europa, the next of the big moons out is also heated, but not nearly to such an extreme. Nevertheless, it is believed that said heating could produce volcanic activity that would keep an ocean of salt water liquid below Europa’s icy surface.
You can look at Jupiter, and if you watch for a while when Io is near the limb of Jupiter, you can actually see it move. I have also watched Io pass behind, or emerge from behind Jupiter, and I’ve even seen it pass in front of Jupiter, with its shadow following along behind it. These events actually happen rather frequently, and such publications as Sky and Telescope will give a list of times when they occur. So, you can go out and watch them, too, once Jupiter is in a more convenient position in the sky to observe.
-Astroprof
(Io images courtesy of NASA, JPL; View from Io created using Starry Night Pro software)
Mark Smith (Astro Mark) on February 12, 2007 at 7:15 am: 1
Great post Jupiter and its four largest moons is my favourite planet to observe. Just seeing the movement of the moons from day to day is amazing. Keep up the good work
mark_smith
A Ler…-- Rastos de Luz on February 12, 2007 at 3:36 pm: 2
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Darnell Clayton on February 12, 2007 at 7:41 pm: 3
Jupiter’s moons never cease to fascinate me!
What is really cool about them is that each are unique and distinct from each other, truly making this planetary system one of the most fascinating ones in our solar system IMHO (after Earth, that is).
Great post!