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Posted by: john_s Dec 11 2010, 11:11 PM

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

Posted by: nprev Dec 11 2010, 11:15 PM

Wow, breaking news! Do you have a link, John?

Posted by: john_s Dec 11 2010, 11:40 PM

No link so far- this was just an e-mail I received, which didn't have much more information. There was a picture, but I'd want to get Steve's permission before posting it here.

John

Posted by: nprev Dec 11 2010, 11:42 PM

Understood.

This sounds extremely interesting. Are the Hubble people getting tired of urgent retargeting requests for sudden Solar System events yet?

Posted by: Hungry4info Dec 11 2010, 11:51 PM

Wow. Will be watching this topic closely.

Posted by: tasp Dec 11 2010, 11:58 PM

Amazing!

If confirmed, it would be an interesting exercise for the UMSF Computational Division to analyze all the other cataloged asteroids' orbital elements and see if any have had a recent close (ahem, really close) approach to 596 Scheila.

Regarding Hubble, it is easier to check out 596 Scheila than to look at all the other asteroids to make sure they are all still present and accounted for.

Posted by: nprev Dec 12 2010, 12:14 AM

If this was in fact an impact I rather doubt that the object was large enough to have been previously detected, though.

Relative velocity is probably a much bigger factor here than the impactor's mass or volume; look at what Deep Impact did to Temple 1!

Posted by: tasp Dec 12 2010, 12:24 AM

Yeah, figured I had better put a smiley on my post.

This is really exiting news though. Nice Christmas present for those of us interested in such things.

I see 596 Sheila might have produced a visible occulatation back in 2005 for our friends in Australia and New Zealand. Wonder if we have any data on satellites?

Posted by: Explorer1 Dec 12 2010, 01:54 AM

Hubble watched something like this once before (three times to be exact):

http://hubblesite.org/newscenter/archive/releases/2010/34

Of course, this time one of the participants has been seen before, I'm sure they'll take a peek.

Posted by: Gsnorgathon Dec 12 2010, 06:54 AM

http://remanzacco.blogspot.com/2010/12/comet-like-appearance-of-596-scheila.html have posted an image on their blog. Very cool!

Posted by: ZLD Dec 12 2010, 07:07 AM

Awesome. It'll be interesting to see this unfold. Heres a quick cleanup (really rough).

Posted by: nprev Dec 12 2010, 07:20 AM

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 http://aartscope.blogspot.com/2010/12/whats-up-with-scheila-596.html 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.

Posted by: Rob Pinnegar Dec 13 2010, 04:33 PM

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?

Posted by: NGC3314 Dec 13 2010, 05:12 PM

Here's a recent image, from the 1m SARA remote telescope on Kitt Peak. Start at 0939 UT on Dec 13, 10m exposure with V filter by student Erin Darnell and me. The apparent motion was slow enough that we could use a guide star to track at sidereal rate (the telescope often doesn't track open-loop that well for such times). It looks much as if there are two distinct plumes, unless the 3D geometry is pretty twisted.

Posted by: algorimancer Dec 14 2010, 01:46 PM

I was thinking that it looked a lot like the simulations I've seen of a grazing impact --- the bulk of the debris goes off in the direction of the impact, a smaller portion goes the opposite. Expect a ring and grooves, perhaps

Posted by: Paolo Mar 29 2011, 07:41 AM

I didn't have the time to read it yet, but I noticed this on arXiv today: http://arxiv.org/abs/1103.5456

Posted by: stevesliva Mar 29 2011, 11:14 PM

kablam!

Posted by: ElkGroveDan Mar 30 2011, 12:08 AM

Asteroid 596 Scheila was named for the Queen by an Australian who was heard to say, "She's a good Scheila Bruce, and not at all stuck up."

Posted by: Astro0 Mar 30 2011, 05:11 AM

Dan, please leave the room and when we think you have thought long enough about what you have done and understand why it was wrong, we will let you come back inside

Posted by: eoincampbell Mar 30 2011, 05:52 AM

A few outbursts though...