7/26: Jupiter's moon Io
 

http://cellar.org/pictures/jupitermoonio.jpg

Oh cmon, do my work for me and tell me why this picture of Jupiter's moon Io is interesting. I forget. Could it be that this shot was taken by the craft Cassini, on its way past Jupiter this past Spring?

All I know is that Io is about the same size as Earth's own moon, and that it's the most volcanic item in the solar system, which is weird considering that it's in the middle of nowhere. Shouldn't it have cooled down by now?

is it me or does this shot make Io look like a moldy orange? :p

Re: 7/26: Jupiter's moon Io
 

It's not in the middle of nowhere, it's near Jupiter, the second most happening place in the system (next to the Sun). IIRC, tidal forces from Jupiter's gravity are supposed to drive Io's vulcanism.

Russotto is right on about the tidal forces driving the vulcanism. It's like when you take a tennis ball and squeeze it, then release, then squeeze, then release and the ball heats up. That's EXACTLY what Jupiter does to Io. Voyager spotted something like 7 erupting volcanoes on its first pass of the moon.

Another amazing thing about Io is that it's slowly sending all its matter back to Jupiter with all these eruptions. You can actually SEE material erupt that never comes back down again.

There is evidence that the other moons of Jupiter have suffered the same as Io. Europa has strange patterns all along its surface that look like cracking and refreezing. Neat stuff :)

Sidenote
 

I believe it was Europa that everyone expects to actually have life on it. It's all ice on top, and all fire below, so in the middle of these two zones is a temperate, aqueous region that could very well have alive things in it. Personally, I'm waiting for somebody to bring something back in a jar (I work with computers, I've seen way too many things fail in an environment where they can't possibly fail). But still, the concept of life, maybe even intelligent life, on another planet within our solar system is too damn cool to pass up.

picture of Europa
 

[IMG]C:/personal/Europa.jpg[/IMG]

The straight lines going every direction are cracks in the ice covering Europa that refrozen. These scars are probably a result of the same tidal forces that cause Io's vulcanism.

I think the theories of what's actually under the icy surface of Europa vary. Because it's so cold, liquid H20 seemed unlikely, but an ocean of hydrocarbons was a very plausible answer. I guess the current theory is water again. An entire OCEAN of hydrocarbons, exxon would pee their pants. I love this stuff.

check this out:

http://antwrp.gsfc.nasa.gov/apod/ap010715.html

Damn good catch kz! I do get a lot of images from the Astronomy Pic of the Day but had missed that one somehow.

One thing I still don't understand. That writeup says the heat of Io is due to the tidal gravity stretching it. I can see how it would stretch it, but wouldn't the stretching just get to some point and then stop?

Is Io different from the Moon in that it doesn't always face one side towards the planet?

No, it's tidally locked. But there's the three other Galilean moons which produce perturbations which affect Io's orbit (and therefore its tides) and prevent a static tidal bulge like that of the moon.