Thursday 6 March 2014

The breakup of Main Belt object P/2013 R3 (Catalina-Pan STARRS)

Main Belt object P/2013 R3 (Catalina-Pan STARRS) was discovered on 15 September 2013, by both the University of Arizona's Catalina Sky Survey in the Catalina Mountains north of Tucson, and the Pan-STARRS telescope at the University of Hawaii's Institute for Astronomy. It is located in the Main Asteroid Belt, with an orbit that takes it from 2.20 AU from the Sun (i.e. 2.20 times the average distance between the Earth and the Sun) to 3.86 AU from the Sun, and which is tilted to slightly less than 1 degree from the plain of the Solar System. At the time of its discovery it had a dust envelope resembling that of a comet, and was therefore classified as a Main Belt Comet (a comet that orbits in the Main Asteroid Belt, and which produced a small tail at the closest point in its orbit to the Sun), rather than an asteroid.
In a paper published on the online arXiv database at Cornell University Library on 5 March 2013, a team of scientists led by  David Jewitt of the Department of Earth and Space Sciences and Department of Physics and Astronomy at the University of California Los Angeles describe a series of follow up observations made by the Keck 10 m Telescope in Hawaii, which revealed that P/2013 R3 had recently broken up, and was in the process of dispersing as a number of smaller objects.
The asteroid is thought to have broken up into at least 10 smaller objects, none larger than 10 m in diameter, between February and September 2013. The resultant debris cloud had expanded to cover a volume with a cross sectional diameter of between 21 and 29 km, at the time of observation. Around 800 000 tonnes of dust was released during this volume, spectographic analysis of which suggested that the parent body was a chondrite stony asteroid rather than a comet; no traces of comet-type outgassing was discovered.
Objects in space have previously been observed to break up for a variety of reasons; they can be torn apart by a close encounter with a larger object such as a planet or the Sun, directly smashed in a collision with another object, be torn apart by the pressure of internal gasses sublimating (turning directly from solids to gasses) as they warm, or be torn apart by rotational stresses.
P/2-13 R3 does not have an orbit which takes it close to any body large enough to produce a tidal force which could have caused its breakup, so this can be ruled out as the source of its disruption. Similarly its breakup appears to have been gradual, over a period of several months, which would appear to rule out a collision with another object, since such an event would be expected to produce a single sudden breakup. It does appear to have contained some water ice, but this is unlikely to have produced enough pressure to disrupt the parent body by sublimating at these distances from the Sun; such an effect could be produced by the sublimation of more volatile compounds, such as carbon monoxide, at this distance, but there is no evidence for such compounds having been present. For these reasons Jewitt et al. conclude that the breakup of P/2013 R3 was caused by rotational stresses, leading to a profound structural failure in the parent body.

Four epochs of R3 imaging from 2013 shown as raw images (left column) and spatially altered to suppress diffuse coma (right column). October 01 data are from Keck, all the rest from HST. Each panel has North to the top, East to the left and has dimensions 14" X12". The projected anti-solar direction is shown by a yellow arrow marked "-S". Projected negative velocity vector is indicated by a green arrow marked "-V". Jewitt et al (2014).

Follow Sciency Thoughts on Facebook.