Paso de los Toros, Uruguay
Paso de los Toros, Uruguay

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Roland S.,Observatorio Astronomico Los Molinos | Bruzzone S.,University of Western Ontario
Icarus | Year: 2015

The small asteroid Itokawa was visited in 2005 by the Japanese spacecraft Hayabusa. The images of the surface showed a scenario different to previously visited asteroids. Itokawa has a small number of large craters and many large boulders randomly distributed on most of the surface.We analyse images taken at different surface resolution and configurations corresponding to several regions on the asteroid's surface. By overlapping visual images and maps of the total potential and surface gravity, we observe a correlation between the distribution of boulders and these parameters. The boulders on the surface were identified by visual inspection of several images. After fitting ellipses to every boulder, we computed their size and the size distribution from decimeters to several meters at different locations in the surface. We found that the size distribution is correlated with the total potential and the surface gravity. A steeper size distribution shifted towards the small objects is observed in the low negative total potential (high surface gravity), which corresponds to the Muses-C region. Meanwhile, in the "head" and "bottom" regions of high potential (low surface gravity), we obtain a shallower size distribution, shifted towards the large boulders.We confirm there is a size segregation that is correlated with the gravity field which can be explained under the action of the Brazil nut effect. There is a global relocation of boulders, with large ones going into the high potential regions and small ones into the low potential ones. A shape segregation is also observed on the location of the boulders: more rounded ones are found in the regions of high potential, while more elongated ones are frequent in regions of low potential. © 2014 Elsevier Inc.

Cikota S.,University of Split | Ortiz J.L.,Institute Astrofisica Of Andalucia | Cikota A.,University of Innsbruck | Morales N.,Institute Astrofisica Of Andalucia | Tancredi G.,Observatorio Astronomico Los Molinos
Astronomy and Astrophysics | Year: 2014

It is well known that some Main Belt asteroids show comet-like features. A representative example is the first known Main Belt comet 133P/(7968) Elst-Pizarro. If the mechanisms causing this activity are too weak to develop visually evident comae or tails, the objects stay unnoticed. We are presenting a novel way to search for active asteroids, based on looking for objects with deviations from their expected brightnesses in a database. Just by using the MPCAT-OBS Observation Archive we have found five new candidate objects that possibly show a type of comet-like activity, and the already known Main Belt comet 133P/(7968) Elst-Pizarro. Four of the new candidates, (315) Constantia, (1026) Ingrid, (3646) Aduatiques, and (24 684) 1990 EU4, show brightness deviations independent of the object's heliocentric distance, while (35 101) 1991 PL16 shows deviations dependent on its heliocentric distance, which could be an indication of a thermal triggered mechanism. The method could be implemented in future sky survey programmes to detect outbursts on Main Belt objects almost simultaneously with their occurrence. © ESO, 2014.

Braga-Ribas F.,Observatorio Nacional | Sicardy B.,Observatoire de Paris | Sicardy B.,University Pierre and Marie Curie | Ortiz J.L.,Institute Astrofisica Of Andalucia Csic | And 52 more authors.
Astrophysical Journal | Year: 2013

We present results derived from the first multi-chord stellar occultations by the transneptunian object (50000) Quaoar, observed on 2011 May 4 and 2012 February 17, and from a single-chord occultation observed on 2012 October 15. If the timing of the five chords obtained in 2011 were correct, then Quaoar would possess topographic features (crater or mountain) that would be too large for a body of this mass. An alternative model consists in applying time shifts to some chords to account for possible timing errors. Satisfactory elliptical fits to the chords are then possible, yielding an equivalent radius Requiv = 555 ± 2.5 km and geometric visual albedo pV = 0.109 ± 0.007. Assuming that Quaoar is a Maclaurin spheroid with an indeterminate polar aspect angle, we derive a true oblateness of , an equatorial radius of km, and a density of 1.99 ± 0.46 g cm-3. The orientation of our preferred solution in the plane of the sky implies that Quaoar's satellite Weywot cannot have an equatorial orbit. Finally, we detect no global atmosphere around Quaoar, considering a pressure upper limit of about 20 nbar for a pure methane atmosphere. © 2013. The American Astronomical Society. All rights reserved.

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