View Full Version : How deep can a “rubble pile” planetary surface be?

Jean Tate
2018-Nov-03, 05:56 AM
As in small asteroids rubble pile. So the depth of sand dunes, or pulverized rock (due to planet quakes, slides, meteor impacts).

Or, how deep do you have to go before all is solid rock, no cracks etc (but tiny pores OK)?

Doesn’t make sense for gas planets, or moons like Europa with subsurface oceans.

2018-Nov-03, 06:18 AM
Depends on the size of the body.

A small asteroid has precious little gravity, so the rubble layer will be much deeper than a moon- or planet- sized body, and may even go all the way to the centre.

Roger E. Moore
2018-Nov-03, 11:13 AM
For a true rubble-pile asteroid (not planet), you can go down only 5 km by definition before reaching the center of the largest possible one. See paper below. Bigger than that, the core becomes solid through, I assume, gravitational pressure and compression.


Rubble Pile Asteroids

Kevin J. Walsh (Submitted on 3 Oct 2018)

The moniker rubble pile is typically applied to all solar system bodies with Diameter between 200m and 10km - where in this size range there is an abundance of evidence that nearly every object is bound primarily by self-gravity with significant void space or bulk porosity between irregularly shaped constituent particles. The understanding of this population is derived from wide-ranging population studies of derived shape and spin, decades of observational studies in numerous wavelengths, evidence left behind from impacts on planets and moons and the in situ study of a few objects via spacecraft flyby or rendezvous. The internal structure, however, which is responsible for the name rubble pile, is never directly observed, but belies a violent history. Many or most of the asteroids on near-Earth orbits, and the ones most accessible for rendezvous and in situ study, are likely byproducts of the continued collisional evolution of the Main Asteroid Belt.

Jean Tate
2018-Nov-03, 12:51 PM

5 km seems quite small; I’d’ve thought a mid-sized crater could create rubble at least that deep, especially on a smaller world. Time for me to check Ries, for example.

Also, I didn’t mean to imply only rocks; we know at least some comets have a lot of void space, and that the surface of Titan is sorta “rocky” in the multiple ice boulders way.