Expert: Jayendra Upadhye - 4/15/2005

Question
Io is very volcanically active as it is torn between the gravitational fields of Jupiter and the sun. It radiates heat energy as part of this process. If you consider the system to involve only these 3 bodies and heat energy is being lost from this system then it stands to reason, I think, that potential energy is being converted to heat energy- Where does this energy come from ? is this changing Io's orbit. I greatly look forward to your thoughts

Answer
Hi Damien,
No! If that were so, poor io is so small, that in a couple of million years it would have lost all its potential energy and spiralled into the core of jupiter!

It is the Tidal interaction of jupiter that continuously distorts the face of io that is facing jupe.
Rather like the moon does (and the sun) on the earth.

Indeed major earthquakes have been known to be triggered at early dawn by the "approaching" distortion of the bulge in the earth's crust at dawn!

These tidal forces make the bulge in the satellite's crust travel along its periphery (unless the satellite has got "phase locked" and keeps one face permanently towards its parent, as in case of our moon), and dissipate a lot of energy in the process.

This happens at the expense of the total angular momentum of the system.
And you know, jupe is truly massive! This tidal lock (slippery) actually speeds up the satellite in its orbit and slows down the parent planet in its spin about its axis.

Our moon recedes away from us in this process at 4 cm a year!

I dont know about the recession rate of io, but that is something you could find out on the web.

Here is a nice link to show you how tidal forces govern the lives of satellites in any system.

you might view as pdf document too:
http://64.233.183.104/search?q=cache:0SlRrAwq_FQJ:groups.colgate.edu/cjs/student...

here is another beautiful site for you:
http://www.es.ucl.ac.uk/research/planetaryweb/undergraduate/grindrod/io/io.htm

here is one regarding our own lunar recession rate:
http://www.nwcreation.net/wiki/index.php?title=CE110

hope that sets you thinking along a different direction (hopefully the right one!) :)
regards..
jayen