The extreme Centaur 2013 AZ60

Kiss, Cs. and Horner, J. and Pál, A. and Szakáts, R. and Vilenius, E. and Müller, Th. G. and Acosta-Pulido, J. and Licandro, J. and Sárneczky, K. and Szabó, Gy. and Duffard, R. and Thirouin, A. (2014) The extreme Centaur 2013 AZ60. In: Asteroids, Comets, Meteors 2014, June 30 - July 4, 2014, Helsinki.

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Abstract

2013 AZ60 is an extreme Centaur moving on a highly eccentric orbit of e = 0.9922, with a semi-major axis of 1021.09 au, and a perihelion distance of 7.91 au. 2013 AZ60 was observed with the PACS camera of the Herschel Space Observatory, and we were able to derive an effective size of D=66.5±3.7 km and a geometric albedo of pV = 0.026 ± 0.003. Photometric measurements revealed a low-amplitude light curve (0.045±0.007 mag in the r’ band) with a likely full period of P = 9.39 h. A dynamical analysis shows that the orbit of 2013AZ 60 is highly unstable, with a 50% probability the target will be ejected from the Solar System within ~700 kyr. This high level of instability indicates that 2013 AZ60 may just have recently been captured to its current orbit. Investigating the total time the target could have spent at small heliocentric distances (< 100 au), it seems to be likely that this has only been at most 100 to 1000 years and it has a low probability that the target could reach Earth-crossing orbits (i.e., < 1 au). As the likely origin of this target is the Oort Cloud, these together suggests a relatively unaltered, pristine surface, in contradiction with the very low albedo (2.6%) derived from the thermal infrared measurements. The low albedo and red colours rather indicates an ”extinct cometary” surface

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