Physical properties of the extreme centaur and super-comet candidate 2013 AZ60

TL;DR

This study characterizes the physical and dynamical properties of the extreme Centaur 2013 AZ60, revealing its dark surface, rapid rotation, and unstable orbit, suggesting a pristine cometary nature despite lacking activity.

Contribution

It provides the first detailed physical and dynamical analysis of 2013 AZ60, combining optical, thermal, and simulation data to infer its composition, surface properties, and orbital stability.

Findings

Diameter of 62.3 km with low albedo of 2.9%

High thermal inertia of >50 Jm^{-2}K^{-1}s^{-1/2}

Unstable orbit with 50% ejection probability within 700,000 years

Abstract

We present estimates of the basic physical properties -- including size and albedo -- of the extreme Centaur 2013 AZ60. These properties have been derived from optical and thermal infrared measurements. Our optical measurements revealed a likely full period of ~9.4 h with a shallow amplitude of 4.5%. By combining optical brightness information and thermal emission data, we are able to derive a diameter of 62.3 +/- 5.3 km and a geometric albedo of 2.9% -- corresponding to an extremely dark surface. Additionally, our finding of ~> 50 Jm^{-2}K^{-1}s^{-1/2} for the thermal inertia is also noticeably for objects in such a distance. The results of dynamical simulations yield an unstable orbit, with a 50% probability that the target will be ejected from the Solar System within 700,000 years. The current orbit of this object as well as its instability could imply a pristine cometary surface. This possibility is in agreement with the observed low geometric albedo and red photometric colour indices for the object, which are a good match for the surface of a dormant comet -- as would be expected for a long-period cometary body approaching perihelion. Despite the fact it was approaching ever closer to the Sun, however, the object exhibited star-like profiles in each of our observations, lacking any sign of cometary activity. By the albedo, 2013 AZ60 is a candidate for the darkest body among the known TNOs.