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Asteroid Belt
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A new astronomy theory says the solar system's main asteroid belt is littered with icy invaders from far away.
The so-called invaders are asteroids that seem more like primitive frozen comets than the baked rocks that make up the overwhelming majority of asteroids between Mars and Jupiter.

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RE: Asteroids
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On January 1, 1801, the first day of the 19th century, astronomer-monk Giuseppe Piazzi discovered a new world between the orbits of Mars and Jupiter. The object, which he named Ceres, was hailed as a new planet - the first discovered since William Herschel found Uranus in 1781. The following year, Heinrich Olbers discovered Pallas in the same region. Olbers told Herschel that he believed Ceres and Pallas to be fragments of a destroyed planet. Herschel suggested that they and any other bodies found between Mars and Jupiter should be considered members of a new category of Solar System bodies, not planets. He suggested that they be called asteroids.
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Asteroid Colour
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The surfaces of asteroids take on a reddish colour within just a million years of forming, a new study finds. The results could complicate efforts to find a convenient way to date rocky bodies based on their colour.
Asteroids are thought to change colour with time, because their surfaces appear redder and darker than the interiors of meteorites found on Earth.


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RE: Asteroids
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Title: Formation of sharp edges and planar areas of asteroids by polyhedral abrasion
Authors: G. Domokos, A. Á. Sipos, Gy. M. Szabó, P. L. Várkonyi

While the number of asteroids with known shapes has drastically increased over the past few years, little is known on the time-evolution of shapes and the underlying physical processes. Here we propose an averaged abrasion model based on micro-collisions, accounting for asteroids not necessarily evolving toward regular spheroids, rather (depending on the fall-back rate of ejecta) following an alternative path, thus confirming photometry-derived features, e.g. existence of large, relatively flat areas separated by edges. We show that our model is realistic, since the bulk of the collisions falls into this category.

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Asteroid Colour
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Asteroids become redder the longer they stay out in the sun, a finding that could help determine our planetary origins, say US and European researchers.
The research, which appears in the latest edition of Nature led by, found that the fresh surface of asteroid fragments redden in less than a million years, much faster than previously thought.


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Offenbar ist die Weltraumverwitterung von Asteroidenoberflächen sehr viel schneller und durchgreifender als bislang angenommen. Eine Untersuchung einer internationalen Forschergruppe um Pierre Vernazza bei der Europäischen Weltraumagentur ESA konnte nun bestätigen, dass der Sonnenwind die wahrscheinlichste Ursache für die Oberflächenveränderungen von Asteroiden ist.

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RE: Asteroids
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A European Space Agency-led team of astronomers has determined the rapid space weathering seen on asteroid surfaces is most likely caused by the solar wind.
The study led by ESA scientist Pierre Vernazza reveals that solar wind ages and reddens asteroid surfaces much more quickly than previously thought -- in less than a million years. The scientists said their finding will help astronomers relate the appearance of an asteroid to its actual history and identify any after effects of a catastrophic impact with another asteroid.


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Asteroid colour
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Une équipe internationale comprenant des chercheurs appartenant à deux laboratoires associés à l'INSU-CNRS et à l'Observatoire de Paris viennent de mettre en évidence l'influence du vent solaire sur les jeunes surfaces des astéroïdes. Le vent solaire en moins d'un million d'années vieillit leur surface leur donnant une apparence très âgée. Ils ont également montré que l'observation d'astéroïdes géocroiseurs ayant une surface jeune peut s'expliquer par un renouvellement des matériaux de surface dû aux forces de marée gravitationnelle lors de leur passage près de la Terre, compensant ainsi l'effet vieillissant du vent solaire. Ces résultats seront publiés dans la revue Nature le 23 avril 2009.

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RE: Asteroids
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Title: Solar wind as the origin of rapid reddening of asteroid surfaces
Authors: P. Vernazza, R. P. Binzel, A. Rossi, M. Fulchignoni & M. Birlan

A comparison of the laboratory reflectance spectra of meteorites with observations of asteroids revealed that the latter are much 'redder', with the spectral difference explained by 'space weathering', though the actual processes and timescales involved have remained controversial. A recent study of young asteroid families concluded that they suffered only minimal space weathering. Here we report additional observations of those families, revealing that space weathering must be a very rapid process - the final colour of a silicate-rich asteroid is acquired shortly after its 'birth' (within 10^6 years of undergoing a catastrophic collision). This rapid timescale favours solar wind implantation as the main mechanism of space weathering, as laboratory experiments have shown that it is the most rapid of several competing processes. We further demonstrate the necessity to take account of composition when evaluating weathering effectiveness, as both laboratory and asteroid data show an apparent dependence of weathering on olivine abundance. The rapid colour change that we find implies that colour trends seen among asteroids are most probably due to compositional or surface-particle-size properties, rather than to different relative ages. Apparently fresh surfaces most frequently seen among small near-Earth asteroids may be the result of tidal shaking that rejuvenates their surfaces during planetary encounters.

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Solar wind tans young asteroids
A new study published in Nature this week reveals that asteroid surfaces age and redden much faster than previously thought - in less than a million years, the blink of an eye for an asteroid. This study has finally confirmed that the solar wind is the most likely cause of very rapid space weathering in asteroids. This fundamental result will help astronomers relate the appearance of an asteroid to its actual history and identify any after effects of a catastrophic impact with another asteroid.

"Asteroids seem to get a 'sun tan' very quickly. But not, as for people, from an overdose of the Sun's ultraviolet radiation, but from the effects of its powerful wind" - lead author Pierre Vernazza.

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