Re: Chelyabinsk Meteorite

grantcblair May 24, 2013

I believe the short answer to why nobody saw it coming is that it was tiny (too small) and came pretty much out of the direction of the sun. Even if it hadn't come out of the direction of the sun, it was too small to detect anyway until it was VERY close.

Something like find_orb needs multiple observation points along an orbit to be able to determine the orbital elements and be able to generate an ephemeris. If it's not observed in space, you don't have any reference points. Once you're in the very close vicinity of a planet, perturbations by that planet can make the original orbit extremely difficult to determine.


Grant


--- In find_orb@yahoogroups.com, "Glen Deen" <glen.deen@...> wrote:
>
> Is this topic appropriate for this group? Maybe so if you read my last
> paragraph.
>
> An Australian friend of mine asked me:
>
> "I was amazed that there was no heads-up on the
> meteorite that struck in Russia recently.
> Is NORAD not able to track these?"
>
> I found these articles using Google. My friend could have found them too.
> http://ogleearth.com/2013/02/reconstructing-the-chelyabinsk-meteors-path-wit
> h-google-earth-youtube-and-high-school-math/
> http://www.technologyreview.com/view/511691/astronomers-calculate-orbit-of-c
> helyabinsk-meteorite/
> And this paper.
> http://arxiv.org/abs/1302.5377
>
> 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?
>
> How did this meteorite sneak up on us without having been observed while
> inbound?
>
> With a direct orbit, I think it should have been observable after sunset
> while
> it was inbound. Has anybody calculated its proper motion relative to its
> radiant
> position in the sky? Was it too small for the motion to be noticed?
>
> Would I be wasting my time if I used Find_Orb to study this question? I
> would
> attempt to compute the proper motion of this body as a function of time over
>
> many days while it was inbound to start with. Then I would use Guide to plot
>
> the incoming radiant in the field of stars to see if there is any bright
> star nearby
> that would hide this object in its glare. If so, that might be considered
> to be an
> observation over several days at the same position. Then I might look at how
>
> sensitive the displacement from that radiant was to variations in each of
> the
> heliocentric orbital elements. Does any of that sound feasible to you?
>
> -Glen
>