A large fast-rotating asteroid

02 February 2018

A few weeks ago the Pan-STARRS survey discovered a new NEO, temporarily identified as P10G8tt and then formally designated 2018 AM12. Follow-up observations over the next few days allowed the determination of its distance, and consequently its absolute magnitude, which turned out to be roughly 21.4. This brightness should correspond to a diameter between about 150 m and 300 m, depending on the unknown albedo of the object's surface.


A few days later one of our collaborators, Erwin Schwab, was using the 0.8-metre Schmidt telescope in Calar Alto, Spain, to collect observations of the asteroid, while he noticed that the object was an extremely fast rotator, with a rotation period of roughly 12.5 minutes. He collected data over about two hours, which resulted in the lightcurve shown in the figure below.

This fast period is unusual for an object of this size, since it is known that almost all objects larger than ~200 m tend to have periods longer than 2 hours (the so-called spin barrier).

The object is now approximately of magnitude 20, but it is getting fainter quite fast. Obtaining a taxonomical classification of it, or any other proxy for its albedo, would allow us to determine its actual size more accurately. If the object turns out to be larger than the spin barrier, it would be interesting to investigate its physical properties in greater detail.

The results of these observation have been submitted for publication to the Minor Planet Bulletin.






Lightcurve of 2018 AM12 obtained on 2018 January 16 with the Calar Alto Schmidt telescope, phased with the detected rotational period of 12.64 minutes. Credit: E. Schwab