Herschel observations of the debris cloud of C/2010 X1 (Elenin)
Abstract
We report Herschel observations of defunct Comet C/2010 X1 (Elenin), aimed at detecting its infrared ghost: the debris cloud and any remaining inert cometessimals that may have been released in the break-up of the nucleus, taking advantage of the comet’s very close pass to Earth in mid-October 2011. These observations would have allowed us to detect both individual surviving fragments of the nucleus of »100m diameter and the expanding dust cloud, being particularly sensitive to coarse dust and boulders in the millimetre to metre size range. No discrete bodies were detected by Herschel to this limiting size, although there is a possible, very low signal-to-noise, detection of the debris cloud.Although most comets exhibit a (relatively) predictable behaviour, a minority of objects deviate considerably from the norm, either by showing sudden outbursts in brightness or, more rarely, by fading unexpectedly. The archetypal event in this latter category was the intensely observed sudden disruption of Comet C/1999 S4 (LINEAR) in July 2000 as it passed perihelion: it was found to have disintegrated into a cloud of cometessimals plus an expanding dust cloud, which faded rapidly, becoming undetectable within 20 days of disruption. Observations of Comet C/2010 X1 (Elenin) in August 2011 showed a similar pattern of evolution of coma morphology into an expanding, amorphous cloud of rapidly decreasing surface brightness (Mattiazzo & McNaught, 2011, CBET 2801) shortly before perihelion passage. However, the comet’s difficult viewing geometry at the time of disruption made it impossible to study the event using high-resolution imaging techniques and, in particular, to measure the ratio of dust to cometessimals which gives information on the internal structure of the nucleus before disruption. Our observations allow us to put a strong upper limit on the maximum size of the building blocks of the nucleus and to contrast this with the predictions of the rubble pile model (Weissman, P.R.: 1986, Nature, 320, 242; Samarasintha, N.H.: 2001, Icarus, 154, 540), while at the same time measuring directly the amount of coarse dust released on disruption.
- Publication:
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IAU General Assembly
- Pub Date:
- August 2015
- Bibcode:
- 2015IAUGA..2258330K