Hi Alessandro,

> Do you see any chance that asteroids 1991 VG and 2013 GH66 are
> also examples of lunar ejecta ?

For the former, I'm virtually certain of it. 1991 VG was tracked
over nearly half a year; its area/mass ratio comes out as
(-1.7 +/- 1.3) x 10^-4 m^2/kg, with H=28.4 (should be about
four meters across). So it's too heavy to be space junk.

For the latter... I dunno. For it, AMR=(14.2 +/- 20) x 10^-4 m^2/kg.
It's not constrained well enough to tell us one way or the other.
There are also no radar data for this object.

I was thinking about all this after looking at Alan Harris' presentation :

http://targetneo.jhuapl.edu/pdfs/2013_Presentations/session2/Session2_Harris_Presentation.ppt

Near the end, he mentions 2010 KQ = RK252A5, an object that was clearly
artificial (determined both by its spectrum, and because its area/mass
ratio was (97.9 +/ 0.3) x 10^-4 m^2/kg). Similarly, J002E3 turned out
to be a leftover booster from Apollo 12, and the Rosetta spacecraft got
MPECed before we figured out it wasn't really a rock. Fortunately, we
got a solid ID for both objects relatively quickly: J002E3 had the
spectrum of white titanium paint, and Rosetta was being actively
tracked.

On the flip side, 2009 BD has AMR = (2.1 +/- 0.3) m^2/kg; it's a rock.
2006 RH120 is a rock both by AMR and radar data. I looked at a few others
that I recalled or scrounged from e-mails (2010 UE51, 2000 SG344, 2010 VQ98,
2011 MD), but they had high enough uncertainties that you couldn't tell
what they were from AMR.

I found quite a few presentations of interest along with Alan's at

http://targetneo.jhuapl.edu/sessions.php

One is a presentation by Paul Chodas in which he lists (slide 10)
fourteen of these "low energy" objects. He also states (slide 18) that
"...natural objects outnumber artificial objects by 1 or 2 orders of
magnitude."

-- Bill