Editing 2002 AA29 (section)

=== Brightness and size ===
Relatively little is known about {{mp|2002 AA|29}} itself. With a size of about {{convert|20|-|100|m|ft|sigfig=1}} it is very small, on account of which it is seen from the Earth as a small point even with large [[telescope]]s, and can only be observed using highly sensitive [[Charge-coupled device|CCD]] cameras. At the time of its closest approach in January 2003 it had an [[apparent magnitude]] of about 20.4.<ref name="MPEC2003-A17"/>

So far nothing concrete is known about the composition of {{mp|2002 AA|29}}. Because of its nearness to the Sun, it cannot however consist of [[Volatile (astrogeology)|volatile substances]] such as [[ice|water ice]], since these would [[evaporation|evaporate]] or [[Sublimation (chemistry)|sublime]]; one can clearly observe this happening to a [[comet]] as this forms the visible tail. Presumably it will have a dark, [[carbon]]-bearing or somewhat lighter [[silicate minerals|silicate]]-rich surface; in the former case the [[albedo]] would be around 0.05, in the latter somewhat higher at 0.15 to 0.25. It is due to this uncertainty that the figures for its diameter cover such a wide range.

A further uncertainty arises from [[radar astronomy|radar]] echo measurements at the [[Arecibo Observatory|Arecibo]] [[Radio Telescope]], which could only pick up an unexpectedly weak radar echo, implying that {{mp|2002 AA|29}} is either smaller than estimated or reflects radio waves only weakly. In the former case it would have to have an unusually high albedo.<ref name="Icarus2">Steven J. Ostro, Jon D. Giorgini, Lance A. M. Benner, Alice A. Hine, Michael C. Nolan, Jean-Luc Margot, Paul W. Chodas, Christian Veillet: [http://echo.jpl.nasa.gov/asteroids/ostro+2003_aa29_icarus.pdf ''Radar detection of Asteroid 2002 AA29''] in: ''[[Icarus (journal)|Icarus]].'' Elsevier, San Diego 166.2003, 12, p271–275. {{ISSN|0019-1035}} (online on the Icarus Server: {{doi|10.1016/j.icarus.2003.09.001}})</ref> This would be evidence in support of the speculation that it, or at least the material of which it is composed, is different from most other asteroids so far discovered on near-Earth orbits, or represents a fragment thrown off by the collision of a medium-sized asteroid with the Earth or the Moon.<ref name="lpsc2004" />