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TOPIC: Main Belt Comets

Blobrana

L

Posts: 131433

Date: Aug 27 05:45 2014

RE: Main Belt Comets	Permalink

Title: Main-belt comets as tracers of ice in the inner Solar system Author: Henry H. Hsieh As a recently recognised class of objects exhibiting apparently cometary (sublimation-driven) activity yet orbiting completely within the main asteroid belt, main-belt comets (MBCs) have revealed the existence of present-day ice in small bodies in the inner solar system and offer an opportunity to better understand the thermal and compositional history of our solar system, and by extension, those of other planetary systems as well. Achieving these overall goals, however, will require meeting various intermediate research objectives, including discovering many more MBCs than the currently known seven objects in order to ascertain the population's true abundance and distribution, confirming that water ice sublimation is in fact the driver of activity in these objects, and improving our understanding of the physical, dynamical, and thermal evolutionary processes that have acted on this population over the age of the solar system. Read more (1486kb, PDF) __________________

Blobrana

L

Posts: 131433

Date: Dec 23 02:34 2011

Active Asteroids	Permalink

Title: The Active Asteroids Authors: Dave Jewitt Some asteroids eject dust, unexpectedly producing transient, comet-like comae and tails. First ascribed to the sublimation of near-surface water ice, mass losing asteroids (also called "main-belt comets") can in fact be driven by a surprising diversity of mechanisms. In this paper, we consider eleven dynamical asteroids losing mass, in nine of which the ejected material is spatially resolved. We address mechanisms for producing mass loss including rotational instability, impact ejection, electrostatic repulsion, radiation pressure sweeping, dehydration stresses and thermal fracture, in addition to the sublimation of ice. In two objects (133P and 238P) the repetitive nature of the observed activity leaves ice sublimation as the only reasonable explanation while, in a third ((596) Scheila), a recent impact is the cause. Another impact may account for activity in P/2010 A2 but this tiny object can also be explained as having shed mass after reaching rotational instability. Mass loss from (3200) Phaethon is probably due to cracking or dehydration at extreme (~1000 K) perihelion temperatures, perhaps aided by radiation pressure sweeping. For the other bodies, the mass loss mechanisms remain unidentified, pending the acquisition of more and better data. While the active asteroid sample size remains small, the evidence for an astonishing diversity of mass loss processes in these bodies is clear. Read more (2780kb, PDF) __________________

Blobrana

L

Posts: 131433

Date: Aug 17 01:17 2011

Main Belt Comets	Permalink

Title: Limits on the Size and Orbit Distribution of Main Belt Comets Authors: S. Sonnett, J. Kleyna, R. Jedicke, J. Masiero The seven known main belt comets (MBCs) have orbital characteristics of main belt asteroids yet exhibit dust ejection like comets. In order to constrain their physical and orbital properties we searched the Thousand Asteroid Light Curve Survey (TALCS; Masiero et al. 2009) for additional candidates using two diagnostics: tail and coma detection. This was the most sensitive MBC survey effort to date, extending the search from MBCs with H~18 (D~1 km) to H~21 (D~150 m). We fit each of the 924 TALCS objects to a PSF model incorporating both a coma and nuclear component to measure the fractional contribution of the coma to the total surface brightness. We determined the significance of the coma detection using the same algorithm on a sample of comparable null detections. We did not identify any MBC candidates with this technique to a sensitivity limit on the order of cometary mass loss rate of about 0.1 kg/s. Our tail detection algorithm identified statistically significant flux in a segmented annulus around the candidate object. We show that the technique can detect tail activity throughout the asteroid belt to the level of the currently known MBCs. Although we did not identify any MBC candidates with this technique, we find a statistically significant detection of faint activity in the entire ensemble of TALCS asteroids. This suggests that many main belt asteroids are active at very low levels. We set 90% upper confidence limits on the number distribution of MBCs as a function of absolute magnitude, semimajor axis, eccentricity, and inclination. There are <~ 400000 MBCs in the main belt brighter than H_V=21 (~150 m) and the MBC:MBA ratio is <~ 1:400. We further comment on the ability of observations to meaningfully constrain the snow line's location. Under some reasonable and simple assumptions we claim 85% confidence that the contemporary snow line lies beyond 2.5 AU. Read more (6958kb, PDF) __________________

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