[meteorite-list] Son of Rosetta?

[lebofsky at lpl.arizona.edu]

Rob:

I may try to contact the people who observed it and see what they think.
This thing is smaller than Rosetta by a bunch (9 meters if 10% albedo).

Larry

On Fri, November 16, 2007 1:06 am, Rob Matson wrote:
> Hi Larry and List,
>
>
> Just when the "asteroid" Rosetta case of mistaken identity was finally
> starting to settle down, things took a turn for the bizarre earlier today.
> Another object has been discovered on a very similar trajectory
> trailing Rosetta (see Minor Planet Electronic Circular MPEC 2007-V119 for
> object 2007 VF189). Link: http://cfa-www.harvard.edu/mpec/K07/K07VB9.html
>
>
> It was picked up November 12th at Mt. Lemmon. Compare the orbital
> elements of it with those of Rosetta when it was mistakenly reported as
> minor planet 2007 VN84 (designation now retired):
>
> 2007 VF189                                              Earth MOID =
> 0.0014
> AU
> Epoch 2007 Oct. 27.0 TT = JDT 2454400.5                 MPC
> M 302.93114              (2000.0)            P               Q
> n   0.75186100     Peri.   84.69614     -0.72209792     -0.68599714 a
> 1.1977817      Node    51.95276     +0.58124996     -0.67166613
> e   0.3857965      Incl.    6.51444     +0.37513076     -0.27977230 P
> 1.31           H   28.3           G   0.15           U   6
>
>
> Orbital elements:
> Rosetta                                                 Earth MOID =
> 0.0001
> AU
> Epoch 2007 Oct. 27.0 TT = JDT 2454400.5                 MPC
> M 302.66563              (2000.0)            P               Q
> n   0.76181070     Peri.   79.69236     -0.65353221     -0.75645089 a
> 1.1873297      Node    51.14851     +0.68070296     -0.60243373
> e   0.3412776      Incl.    1.91562     +0.33096698     -0.25466771 P
> 1.29           H   26.3           G   0.15           U   9
>
>
> The main difference between these two is ~4.6 degrees in orbital
> inclination.  Nevertheless, the coincidence was a bit of an eye-opener when
> the MPEC was issued this morning:  two objects that passed inside the
> Moon's orbit on similar trajectories in the space of a few hours!
>
>
> One possibility that was initially considered was that the trailing
> object could be the Ariane 5 upper stage that deployed Rosetta in March
> 2004.  But the chances of this are extremely remote, given
> that Rosetta had undergone two gravity assist fly-bys (one of earth, one of
> Mars) ~prior~ to the most recent earth flyby this past Tuesday.
>
>
> In order for the object to be associated with Rosetta, it would have
> to have been shed more recently -- certainly after the first earth flyby in
> 2005, and probably after the Mars gravity assist earlier
> this year.  And yet, if it had, the inclinations would match better.
>
> So, crazy as it sounds, the second object appears to be just a
> "rock" ... or maybe it's a probe launched by the curious inhabitants
> of 67P/Churyumov-Gerasimenko... ;-)  --Rob
>
> -----Original Message-----
> From: meteorite-list-bounces at meteoritecentral.com
> [mailto:meteorite-list-bounces at meteoritecentral.com]On Behalf Of
> lebofsky at lpl.arizona.edu Sent: Tuesday, November 13, 2007 7:39 AM
> To: Sterling K. Webb
> Cc: lebofsky at comcast.net; Meteorite List; mexicodoug at aol.com
> Subject: Re: [meteorite-list] Rosetta gravity assist flyby
>
>
>
> Hi Sterling, et al.:
>
>
> The "asteroid" (Rosetta) was discovered near midnight on November 7 and
> was confirmed the next night at 2 other sites.
>
> I did a calculation of size vs magnitude for the "asteroid" at discovery.
>
>
> Its H magnitude (how bright it would be at 1 astronomical unit, 1 AU,
> from the Earth) was 26.3. That would make it 23 meters in diameter with a
> 10%
> reflectivity (gray). The darkest asteroids reflect 5% of the light the hits
> them which would give a diameter of about 30 to 35 meters.
>
> At the time of discovery, it was 0.04 AU from the Earth (about 6,000,000
> km) was magnitude 19.7 (about 1,000,000 times fainter than the faintest
> stars one can see with the naked eye) and was moving at a little less
> than 2 arc-minutes a day (mostly north to south).
>
>
> The diameter of the Moon is 30 arc-minutes (1/2 degree) for comparison.
> It
> turns out that the main belt asteroid Ceres was in the same area of the sky
> and was moving about 1/2 as fast north to south, but 15 times faster west
> to east at this time. Why the difference? Ceres is moving in its orbit
> around the Sun while Rosetta was aiming right at the Earth (nearly so), so
> even though is was much closer to Earth, it was going almost directly
> toward us! (if an object is getting brighter but with no apparent motion,
> duck!)
>
> The whole idea behind discovering Earth-approaching asteroids is to find
> them not when they come by the first time (not much you can do about them)
>  but to get an "early warning" for when it might be coming by the next
> time, as in the case of Apophis. For comparison, I think that Apophis was
>  moving at several degrees a day at the time of discovery. At that point
> you have a chance to do something about it (beyond just running for
> cover).
>
> So, to answer Sterling's question, VN84 was not discovered because of its
>  fast motion OR brightness, but more for how slow it was moving west to
> east relative to its north-south motion! I will try to track this down.
>
> Larry
>
>