* Astronomy

Title: Multiband Optical Observation of P/2010 A2 Dust Tail
Authors: Junhan Kim, Masateru Ishiguro, Hidekazu Hanayama, Sunao Hasegawa, Fumihiko Usui, Kenshi Yanagisawa, Yuki Sarugaku, Jun-ichi Watanabe, Michitoshi Yoshida

An inner main-belt asteroid, P/2010 A2, was discovered on January 6th, 2010. Based on its orbital elements, it is considered that the asteroid belongs to the Flora collisional family, where S-type asteroids are common, whilst showing a comet-like dust tail. Although analysis of images taken by the Hubble Space Telescope and Rosetta spacecraft suggested that the dust tail resulted from a recent head-on collision between asteroids (Jewitt et al. 2010; Snodgrass et al. 2010), an alternative idea of ice sublimation was suggested based on the morphological fitting of ground-based images (Moreno et al. 2010). Here, we report a multiband observation of P/2010 A2 made on January 2010 with a 105 cm telescope at the Ishigakijima Astronomical Observatory. Three broadband filters, g', R_c, and I_c, were employed for the observation. The unique multiband data reveals that the reflectance spectrum of the P/2010 A2 dust tail resembles that of an Sq-type asteroid or that of ordinary chondrites rather than that of an S-type asteroid. Due to the large error of the measurement, the reflectance spectrum also resembles the spectra of C-type asteroids, even though C-type asteroids are uncommon in the Flora family. The reflectances relative to the g'-band (470 nm) are 1.096±0.046 at the R_c-band (650 nm) and 1.131±0.061 at the I_c-band (800 nm). We hypothesize that the parent body of P/2010 A2 was originally S-type but was then shattered upon collision into scaterring fresh chondritic particles from the interior, thus forming the dust tail.

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Title: Pre-Discovery Observations of Disrupting Asteroid P/2010 A2
Authors: David Jewitt, Joseph S. Stuart, Jing Li

Solar system object P/2010 A2 is the first-noticed example of the aftermath of a recently disrupted asteroid, probably resulting from a collision. Nearly a year elapsed between its inferred initiation in early 2009 and its eventual detection in early 2010. Here, we use new observations to assess the factors underlying the visibility, especially to understand the delayed discovery. We present prediscovery observations from the LINEAR telescope and set limits to the early-time brightness from SOHO and STEREO satellite coronagraphic images. Consideration of the circumstances of discovery of P/2010 A2 suggests that similar objects must be common, and that future all-sky surveys will reveal them in large numbers.

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The mystery object was discovered on January 6, 2010, by the Lincoln Near-Earth Asteroid Research (LINEAR) sky survey. The object appears so unusual in ground-based telescopic images that discretionary time on NASA's Hubble Space Telescope was used to take a close-up look. The observations show a bizarre X-pattern of filamentary structures near the point-like nucleus of the object and trailing streamers of dust. This complex structure suggests the object is not a comet but instead the product of a head-on collision between two asteroids travelling five times faster than a rifle bullet. Astronomers have long thought that the asteroid belt is being ground down through collisions, but such a smashup has never before been seen.

The dusty wreckage thrown out in the explosive collision of two asteroids has been pictured by spacecraft.
The debris stretches for hundreds of thousands of kilometres.
US and European scientists tell the journal Nature that a remnant rock about 120m in size sits at the head of this shattered stream of material.
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