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Register a new userA collision in 2009 as the origin of the debris trail of asteroid P/2010 A2
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The peculiar object P/2010 A2 was discovered by the LINEAR near-Earth asteroid survey in January 2010 and given a cometary designation due to the presence of a trail of material, although there was no central condensation or coma. The appearance of this object, in an asteroidal orbit (small eccentricity and inclination) in the inner main asteroid belt attracted attention as a potential new member of the recently recognized class of Main Belt Comets (MBCs). If confirmed, this new object would greatly expand the range in heliocentric distance over which MBCs are found. Here we present observations taken from the unique viewing geometry provided by ESAs Rosetta spacecraft, far from the Earth, that demonstrate that the trail is due to a single event rather than a period of cometary activity, in agreement with independent results from the Hubble Space Telescope (HST). The trail is made up of relatively large particles of millimetre to centimetre size that remain close to the parent asteroid. The shape of the trail can be explained by an initial impact ejecting large clumps of debris that disintegrated and dispersed almost immediately. We determine that this was an asteroid collision that occurred around February 10, 2009.
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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$pm$0.046 at the $R_c$-band (650 nm) and 1.131$pm$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.
Quasi-Hilda asteroid P/2010 H2 (Vales) underwent a spectacular photometric outburst by 7.5 magnitudes (factor of 1000) in 2010. Here, we present our optical observations of this event in the four month period from April 20 to August 10. The outburst, starting UT 2010 April 15.76, released dust particles of total cross-section 17,600 sq km (albedo 0.1 assumed) and mass 1.2e9 kg, this being about 1e-4 of the mass of the nucleus, taken as a sphere of radius 1.5 km and density 500 kg/m3. While the rising phase of the outburst was very steep (brightness doubling time of hours), subsequent fading occurred slowly (fading timescales increasing from weeks to months), as large, low velocity particles drifted away from the nucleus. A simple model of the fading lightcurve indicates that the ejected particles occupied a broad range of sizes, from microns to centimeters, and followed a differential power-law distribution with index 3.6+/-0.1 (similar to that in other comets). The fastest particles had speeds 210 m/s, indicating gas-drag acceleration of small grains well-coupled to the flow. Low energy processes known to drive mass loss in active asteroids, including rotational disruption, thermal and desiccation stress cracking, and electrostatic repulsion, cannot generate the high particles speeds measured in P/Vales, and are discounted. Impact origin is unlikely given the short dynamical lifetimes of the quasi-Hildas and the low collision probabilities of these objects. The specific energy of the ejecta is estimated at 220 J/kg. The outburst follows a series of encounters with Jupiter in the previous century, consistent with the delayed activation of buried supervolatiles (and/or the crystallization of sub-surface amorphous ice) by conducted heat following an inward displacement of the perihelion. A potential origin in the debris cloud produced by avalanche is also considered.
Asteroid 2009 FD could impact Earth between 2185 and 2196. The long term propagation to the possible impacts and the intervening planetary encounters make 2009 FD one of the most challenging asteroids in terms of hazard assessment. To compute accurate impact probabilities we model the Yarkovsky effect by using the available physical characterization of 2009 FD and general properties of the Near Earth Asteroid population. We perform the hazard assessment with two independent methods: the first method is a generalization of the standard impact monitoring algorithms in use by NEODyS and Sentry, while the second one is based on a Monte Carlo approach. Both methods generate orbital samples in a 7 dimensional space that includes orbital elements and the parameter characterizing the Yarkovsky effect. The highest impact probability is $2.7 times 10^{-3}$ for an impact during the 2185 Earth encounter. Impacts after 2185 corresponding to resonant returns are possible, the most relevant being in 2190 with a probability of $3 times 10^{-4}$. Both numerical methods can be used in the future to handle similar cases. The structure of resonant returns and the list of the possible keyholes on the Target Plane of the scattering encounter in 2185 can be predicted by an analytic theory.
The asteroid belt was dynamically shaped during and after planet formation. Despite representing a broad ring of stable orbits, the belt contains less than one one-thousandth of an Earth mass. The asteroid orbits are dynamically excited with a wide range in eccentricity and inclination and their compositions are diverse, with a general trend toward dry objects in the inner belt and more water-rich objects in the outer belt. Here we review models of the asteroid belts origins and dynamical history. The classical view is that the belt was born with several Earth masses in planetesimals, then strongly depleted. However, it is possible that very few planetesimals ever formed in the asteroid region and that the belts story is one of implantation rather than depletion. A number of processes may have implanted asteroids from different regions of the Solar System, dynamically removed them, and excited their orbits. During the gaseous disk phase these include the effects of giant planet growth and migration and sweeping secular resonances. After the gaseous disk phase these include scattering from resident planetary embryos, chaos in the giant planets orbits, the giant planet instability, and long-term dynamical evolution. Different global models for Solar System formation imply contrasting dynamical histories of the asteroid belt. Vesta and Ceres may have been implanted from opposite regions of the Solar System -- Ceres from the Jupiter-Saturn region and Vesta from the terrestrial planet region -- and could therefore represent very different formation conditions.
Photometric observations of asteroid (596) Scheila were obtained during and after its 2010 outburst. The estimated radius of the body (spherical approximation of the asteroidal body) was 51.2 km and 50.67 km for different methods. The ejected dust mass from the asteroid ranged from 2.5*10e7 to 3.4*10^7 kg for different methods. An impact mechanism for triggering Scheilas activity is discussed. A few days before the impact, Scheila passed through the corridors of two potential cometary streams.
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