Asteroid 596 Scheila "Outburst" Options

[john_s]

I just saw a report that Steve Larson of the University of Arizona observed a "comet" last night (Saturday morning, December 11th UT), which turned out to be asteroid 596 Scheila. The asteroid, which is quite big (about 113 km in diameter) is surrounded by a vaguely spiral-shaped dust cloud. A recent impact, maybe? If so, it would be the first recorded impact on a large asteroid.

Interesting!
John

[nprev]

My, my, my. That looks like a considerable amount of material; let's see how long it keeps coming out.

I wonder if right now we're looking nearly straight down 596 Schelia's rotation axis.

EDIT: Just found this blog by an observer in New Mexico, who has an image less than 2 hrs. old posted as I write this; he's trying for some color images later today.

[Rob Pinnegar]

I wonder if right now we're looking nearly straight down 596 Schelia's rotation axis.

That image does make it appear that way, but I think it's probably got more to do with the geometry of the collision as viewed from Earth.

I don't have Schelia's rotation period handy, but let's assume it's 24 hours for simplicity. If Schelia is a 113-km sphere (a bad assumption, but no worse than the first one) that gives an equatorial rotation speed of about 4 *metres* per second. So, even if the rotation period is significantly less than 24 hours, the relative velocity of the collision (probably on the order of kilometres per second) is going to overwhelm any rotational effects.

Actually... if that plume is really orbiting around Schelia (or at least being affected by its gravity), which its shape does suggest, then by observing it over the course of a few days we ought to be able to get (1) a decent value for Schelia's mass, and (2) given that, perhaps even an estimate of the impact geometry and relative velocity -- and maybe (3) a rough idea of the mass of the impactor?