* Astronomy

Blobrana · L

RE: Asteroids

Blobrana · L

Un article publié dans l'Astronomical Journal, dont deux chercheurs de l'Observatoire de la Côte d'Azur sont co-auteurs du groupe de Planétologie/Gaïa du laboratoire Cassiopée à Nice présente de nouvelles analyses d'observation d'astéroïdes par le télescope spatial Spitzer (NASA). Ces analyses révèlent que les astéroïdes dont la trajectoire passe à proximité de la Terre, appelés NEA (selon l'appellation anglaise Near-Earth Asteroid), constituent une population riche en composition. Comme un cake contenant toute sorte d'ingrédients allant du chocolat aux fruit secs, ces astéroïdes nous arrivent avec des couleurs et compositions assorties. Certains sont très sombres, d'autres sont très claires. Les observations Spitzer de 100 NEAs démontrent que leur diversité est bien plus grande qu'on le pensait auparavant et fournissent un échantillon d'objet plus vaste qui contient certainement quelques bons candidats pour les projets de missions spatiales de visite d'un Near Earth Object.
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College of Staten Island astronomer puts planetoids up for sale

A College of Staten Island professor is putting the naming rights for two minor planets he discovered up for sale.
The 69-year-old astronomer -- who is entitled to name the planetoids since he found them -- is willing to let others put their permanent mark on the Milky Way.
But it comes with a price.
Irving Robbins was given credit by the International Astronomical Union, the worlds governing body in astronomy, for research leading to the discovery of 2009 VH24 and 2009 XNO7.
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Asteroid Ice May Be 'Living Fossil' With Clues to Oceans' Origins

The first-ever discovery of ice and organic molecules on an asteroid may hold clues to the origins of Earths oceans and life 4 billion years ago.
University of Central Florida researchers detected a thin layer of water ice and organic molecules on the surface of 24 Themis, the largest in a family of asteroids orbiting between Mars and Jupiter.
Their unexpected findings will be published Thursday, April 29 in Nature, which will feature two complementary articles by the UCF-led team and by another team of planetary scientists.
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Small asteroids 'just lumps of gravel'

The galaxy is littered with small, fast-spinning asteroids that are little more than piles of gravel held together by weak physical forces, say researchers.
The study, led by US asteroid scientist Professor Daniel Scheeres from the University of Colorado, Boulder, has been submitted to the journal Icarus.
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Title: Scaling forces to asteroid surfaces: The role of cohesion
Authors: D.J. Scheeres, C.M. Hartzell, P. Sanchez, M. Swift

The scaling of physical forces to the extremely low ambient gravitational acceleration regimes found on the surfaces of small asteroids is performed. Resulting from this, it is found that van der Waals cohesive forces between regolith grains on asteroid surfaces should be a dominant force and compete with particle weights and be greater, in general, than electrostatic and solar radiation pressure forces. Based on this scaling, we interpret previous experiments performed on cohesive powders in the terrestrial environment as being relevant for the understanding of processes on asteroid surfaces. The implications of these terrestrial experiments for interpreting observations of asteroid surfaces and macro-porosity are considered, and yield interpretations that differ from previously assumed processes for these environments. Based on this understanding, we propose a new model for the end state of small, rapidly rotating asteroids which allows them to be comprised of relatively fine regolith grains held together by van der Waals cohesive forces.

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Were Asteroids Born Big?
In most models, it's a three-step process: (1) dust settles into a flattened disk and collects into countless planetesimals a mile or so (1 to 10 km) across; (2) the planetesimals collide and form Moon- to Mars-size planetary embryos; and (3) the embryos smash into one another until basically all that remains are a handful of rocky inner planets and a second handful of rocky "super-Earth" cores that eventually become the giant outer planets. In other words, the solar system's building blocks grew smoothly and systematically from small bodies to large ones.
But recent studies have punched huge holes in this traditional thinking.

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Title: Contamination of the asteroid belt by primordial trans-Neptunian objects
Authors: Harold F. Levison, William F. Bottke, Matthieu Gounelle, Alessandro Morbidelli, David Nesvorný & Kleomenis Tsiganis

The main asteroid belt, which inhabits a relatively narrow annulus approx 2.1-3.3 au from the Sun, contains a surprising diversity of objects ranging from primitive icerock mixtures to igneous rocks. The standard model used to explain this assumes that most asteroids formed in situ from a primordial disk that experienced radical chemical changes within this zone. Here we show that the violent dynamical evolution of the giant-planet orbits required by the so-called Nice model leads to the insertion of primitive trans-Neptunian objects into the outer belt. This result implies that the observed diversity of the asteroid belt is not a direct reflection of the intrinsic compositional variation of the proto-planetary disk. The dark captured bodies, composed of organic-rich materials, would have been more susceptible to collisional evolution than typical main-belt asteroids. Their weak nature makes them a prodigious source of micrometeorites - sufficient to explain why most are primitive in composition and are isotopically different from most macroscopic meteorites

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La plupart des corps primitifs peuplant la ceinture d'astéroïdes, entre Jupiter et Mars, seraient en fait des comètes. Cette découverte, réalisée par une équipe internationale composée de chercheurs du Laboratoire de minéralogie et cosmochimie du Muséum (LMCM) et de l'Observatoire de la Côte d'Azur, bouleverse la vision du système solaire. Les résultats paraissent dans la revue Nature du 16 juillet 2009.

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Asteroid belt's icy fringe explained
A reshuffle of the planets in the early Solar System may explain how ancient ice balls ended up in the asteroid belt.
This new hypothesis, based on a popular theory of Solar System formation known as the 'Nice model', upends a previously held view that the asteroid belt is the remnant of a protoplanetary disc that surrounded the Sun early in its evolution.

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