Re: [find_orb] Chelyabinsk Meteorite

Alan W Harris May 24, 2013

Actually, following 2008 TC3, I did an estimation of how often one might
expect to see something on the way in. The short answer is that impacts
the size of TC3 (few meter diameter object) occur about annually. On
studying the arrival details of TC3 and similar objects, I estimated that
current surveys, like G96, could spot it about one day out (as they did),
and they cover the area of the sky away from the sunward direction a couple
times a month, or about once a week for a given patch of sky. So they have
roughly a 10% chance of seeing one on the way in, or one would expect to
catch one about once a decade -- again, just about what they did with the
surveys having operated about a decade at this level.

Future surveys will do better, so we can expect such things more often than
once a decade, but even so, the majority will arrive undetected in advance,
simply because about half of them come from the direction of the sun.

Alan



At 02:20 PM 5/24/2013, Bill Gray wrote:
>
>
>Hi Glen,
>
> > As I understand it, the authors of that paper used NOVAS to calculate
> > the orbit. Couldn't they just as well have used Find_Orb?
>
>Yes. Very shortly after the impact, I got an inquiry about this
>from someone hoping the object might be found on recent survey images.
>That resulted in my posting this pseudo-MPEC, with a (G96)-centric
>ephemeris to see if any of the southwestern US folks might have
>gotten the object on the way in :
>
>http://www.projectpluto.com/temp/chelyab.htm
>
>You'll notice that this was computed on the day of the impact, and
>was intended just to get a rough idea (enough to say, "Sorry, no,
>there aren't going to be any precovery images.") I'm sure Esko
>Lyytinen and/or Rob Matson and/or somebody else got more and better
>data after that. But even the very approximate data were enough to
>make it clear: this object came from too low an elongation to be
>spotted on its way in.
>
>I will not be surprised if it's a long time before another case
>occurs of an impactor observed before impact. It _has_ happened
>once (2008 TC3), and I keep an eye on NEOCP for objects that might
>do this. (The key sign is that the ephemerides show virtually no
>motion, then suddenly show _lots_ of motion. That was what clued
>me in for 2008 TC3.) But I'm not really optimistic.
>
>-- Bill

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