Title: A short-duration event as the cause of dust ejection from Main-Belt Comet P/2012 F5 (Gibbs) Authors: Fernando Moreno, Javier Licandro, Antonio Cabrera-Lavers
We present observations and an interpretative model of the dust environment of Main-Belt Comet P/2010 F5 (Gibbs). The narrow dust trails observed can be interpreted unequivocally as an impulsive event that took place around 2011 July 1st with an uncertainty of ±10 days, and a duration of less than a day, possibly of the order of a few hours. The best Monte Carlo dust model fits to the observed trail brightness imply ejection velocities in the range 8-10 cm s^{-1} for particle sizes between 30 cm and 130 µm. This weak dependence of velocity on size contrasts with that expected from ice sublimation, and agrees with that found recently for (596) Scheila, a likely impacted asteroid. The particles seen in the trail are found to follow a power-law size distribution of index ~-3.7. Assuming that the slowest particles were ejected at the escape velocity of the nucleus, its size is constrained to about 200-300 m in diameter. The total ejected dust mass is \gtrsim 5 x 10^8 kg, with represents approximately 4 to 20% of the nucleus mass.
Los asteroides, a diferencia de los cometas, no se caracterizan por exhibir una cola, pero existen una decena de excepciones. Investigadores españoles han observado a uno de estos raros asteroides desde el Gran Telescopio Canarias y han descubierto que algo le pasó sobre el 1 de julio de 2011 para que le apareciera su 'apéndice'. Quizá una ruptura interna o la colisión con otro asteroide. Read more
Title: Characterisation of Active Main Belt Object P/2012 F5 (Gibbs): A Possible Impacted Asteroid Authors: R. Stevenson, E. A. Kramer, J. M. Bauer, J. R. Masiero, A. K. Mainzer
In this work we characterise the recently discovered active main belt object P/2012 F5 (Gibbs), which was discovered with a dust trail > 7' in length in the outer main belt, 7 months prior to aphelion. We use optical imaging obtained on UT 2012 March 27 to analyse the central condensation and the long trail. We find nuclear B-band and R-band apparent magnitudes of 20.96 and 19.93 mag, respectively, which give an upper limit on the radius of the nucleus of 2.1 km. The geometric cross-section of material in the trail was ~ 4 x 10^8 m^2, corresponding to a dust mass of ~ 5 x 10^7 kg. Analysis of infrared images taken by the Wide-Field Infrared Survey Explorer in September 2010 reveals that the object was below the detection limit, suggesting that it was less active than it was during 2012, or possibly inactive, just 6 months after it passed through perihelion. We set a 1-sigma upper limit on its radius during this time of 2.9 km. P/2012 F5 (Gibbs) is dynamically stable in the outer main belt on timescales of ~ 1 Gyr, pointing towards an asteroidal origin. We find that the morphology of the ejected dust is consistent with it being produced by a single event that occurred on UT 2011 July 7 ± 20 days, possibly as the result of a collision with a small impactor.