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Asteroid 596 Scheila "Outburst"
john_s
post Dec 11 2010, 11:11 PM
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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
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nprev
post Dec 11 2010, 11:15 PM
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Wow, breaking news! Do you have a link, John?


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john_s
post Dec 11 2010, 11:40 PM
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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
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nprev
post Dec 11 2010, 11:42 PM
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Understood.

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


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Hungry4info
post Dec 11 2010, 11:51 PM
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Wow. Will be watching this topic closely.


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tasp
post Dec 11 2010, 11:58 PM
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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.

smile.gif
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nprev
post Dec 12 2010, 12:14 AM
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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!


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tasp
post Dec 12 2010, 12:24 AM
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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?

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Explorer1
post Dec 12 2010, 01:54 AM
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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.
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Gsnorgathon
post Dec 12 2010, 06:54 AM
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Ernesto Guido & Giovanni Sostero have posted an image on their blog. Very cool!
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ZLD
post Dec 12 2010, 07:07 AM
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Awesome. It'll be interesting to see this unfold. Heres a quick cleanup (really rough).
Attached Image
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nprev
post Dec 12 2010, 07:20 AM
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My, my, my. smile.gif 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.


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Rob Pinnegar
post Dec 13 2010, 04:33 PM
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QUOTE (nprev @ Dec 12 2010, 12:20 AM) *
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?
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NGC3314
post Dec 13 2010, 05:12 PM
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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.

Attached Image
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algorimancer
post Dec 14 2010, 01:46 PM
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QUOTE (NGC3314 @ Dec 13 2010, 11:12 AM) *
... looks much as if there are two distinct plumes, unless the 3D geometry is pretty twisted.

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 smile.gif
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