Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Phil Crane on 09/03/2010 13:30:02

Title: Why don't terrestrial planets have rings like Saturn?
Post by: Phil Crane on 09/03/2010 13:30:02

Phil Crane  asked the Naked Scientists:
   
Hi,

All of the gas giants have a ring system but none of the terrestrial planets do.

Is this just a coincidence, or is there a reason for it? Would it be expected that other solar systems would be the same?

thanks,

Phil,
Sacramento, California


What do you think?

Title: Why don't terrestrial planets have rings like Saturn?
Post by: notme on 24/02/2011 13:14:49

Okay, planets have rings because stuff held together by gravity can't exist where the rings are due to the strong tidal force near the planet. Anything like moons will be ripped apart as their surfaces rise and fall with the tides. 

The minimum distance from the planet center that you can still have a nice round moon is called the "Roche Limit".  For huge planets, it exists far away from the planet, so stuff in a close orbit will be torn apart (though actually, the stuff is prevented from condensing into a single object). 

However small planets like Earth have so little mass that their Roche limit is actually beneath the planets' surface.  That means that nothing in any orbit will be torn apart by tides.

-faye kane

Title: Why don't terrestrial planets have rings like Saturn?
Post by: Pikaia on 24/02/2011 16:37:57

If Earth had rings: