Satellite Formation with Gaseous Planets

[sheeny (Al)]

This is from Nature Contents this morning.

Al.

A common mass scaling for satellite systems of gaseous planets

Robin M. Canup1 and William R. Ward1
Top of page Abstract

The Solar System's outer planets that contain hydrogen gas all host systems of multiple moons, which notably each contain a similar fraction of their respective planet's mass (10-4). This mass fraction is two to three orders of magnitude smaller than that of the largest satellites of the solid planets (such as the Earth's Moon), and its common value for gas planets has been puzzling. Here we model satellite growth and loss as a forming giant planet accumulates gas and rock-ice solids from solar orbit. We find that the mass fraction of its satellite system is regulated to 10-4 by a balance of two competing processes: the supply of inflowing material to the satellites, and satellite loss through orbital decay driven by the gas. We show that the overall properties of the satellite systems of Jupiter, Saturn and Uranus arise naturally, and suggest that similar processes could limit the largest moons of extrasolar Jupiter-mass planets to Moon-to-Mars size.

Editor's Summary

15 June 2006
How massive the moon

The outer giant planets in the Solar System each have a following of multiple moons, and each set of moons contains a similar fraction of their respective planet's mass — the planets are about 100,000 times greater in mass than all their moons combined. A possible explanation for this convergence has now been found. In a numerical model of a growing giant planet accumulating hydrogen gas and rock-ice solids, the mass fraction of its satellite system is regulated to one-to-100,000 by a balance between two processes: inflow of new material to the satellites and the loss of material via gas-induced orbital decay. This has implications for extrasolar planets: the idea that Earth-sized moons around Jupiter-sized planets might be habitable needs to tempered by the news that only Mars- to Moon-sized satellites are likely to develop there.

[[1ponders] (Paul)]

I can't seem to find the link now Al but what you have posted complements something I read a few weeks ago. By rights the inner planets would not form moons by the accretion theory. Due to the heating up of the Solar nebula lighter elements are forced to the outer parts of the solar system and the remaining rocky debris should all form single planets without moons eventually. And this is what would have happened if earth had not been hit by a very large planetesimal early on and budded off the moon. As for Mars Phobos and Deimos are captured asteroids ejected from the Asteroid belt by Jupiter.

I'll have a dig and see if I can find the link again. It was a very interesting read.

[sheeny (Al)]

Yeah, Paul I have a vague recollection of seeing something similar.

Probably on one of my Nature or Physics emails... or could've been in a nature or Naked Scientist podcast... hmmm not sure where.

Al.