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TOPIC: Asteroids
Blobrana


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University of Arizona Scientists Find Asteroids Are Missing, and Possibly Why
The patterns of missing asteroids are like the footprints of wandering giant planets preserved in the asteroid belt.
University of Arizona scientists have uncovered a curious case of missing asteroids.
The main asteroid belt is a zone containing millions of rocky objects between the orbits of Mars and Jupiter. The scientists find that there ought to be more asteroids there than researchers observe. The missing asteroids may be evidence of an event that took place about 4 billion years ago, when the solar system's giant planets migrated to their present locations.
UA planetary sciences graduate student David A. Minton and UA planetary sciences professor Renu Malhotra say missing asteroids is an important piece of evidence to support an idea that the early solar system underwent a violent episode of giant planet migration that might possibly be responsible for a heavy asteroidal bombardment of the inner planets.

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Blobrana


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If you ever go hiking on an asteroid, you'll want to pack one of Robert Gaskell's maps.
Gaskell, a senior scientist at the Planetary Science Institute, is to our solar system's frontier what Lewis and Clark were to the American West - the guy producing the most accurate and detailed maps available.
His maps of the asteroid Itokawa are "... the highest resolution description of an asteroid," according to his NASA Exceptional Achievement medal. It's good to better than 40 cm, a lot better than you could do with your GPS.

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Blobrana


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Title: The shape distribution of asteroid families: Evidence for evolution driven by small impacts
Authors: Gyula M. Szabóa, László L. Kiss

A statistical analysis of brightness variability of asteroids reveals how their shapes evolve from elongated to rough spheroidal forms, presumably driven by impact-related phenomena. Based on the Sloan Digital Sky Survey Moving Object Catalogue, we determined the shape distribution of 11,735 asteroids, with special emphasis on eight prominent asteroid families. In young families, asteroids have a wide range of shape elongations, implying fragmentation–formation. In older families we see an increasing number of rough spheroids, in agreement with the predictions of an impact-driven evolution. Old families also contain a group of moderately elongated members, which we suggest correspond to higher-density, more impact-resistant cores of former fragmented asteroids that have undergone slow shape erosion. A few percent of asteroids have very elongated shapes, and can either be young fragments or tidally reshaped bodies. Our results confirm that the majority of asteroids are gravitationally bound “rubble piles.”

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Blobrana


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The asteroids that pepper our solar system come in all shapes, sizes and ages. What causes such a variety among space rocks has been something of a mystery, until now.
Researchers have been using a vast database to study a staggering 11,735 asteroids. They have discovered that asteroids change shape over time, and they think they know the reason why.
Gyula Szabó from the University of Szeged is the lead author of the study, which was published in the July edition of Icarus.

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Blobrana


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Asteroids, meaning star-alike in Greek, are rocky, metallic, celestial bodies in the solar system without atmospheres orbiting the sun. Since they are relatively small to be acknowledged as planets, they are termed minor planets as preferred by the International Astronomical Union (IAU). Although asteroids are hurtling towards the earth and beyond the trail of the ringed-planet Saturn, myriads of asteroids congregate in vast, weirdly doughnut-shaped rings located between Mars and Jupiter. They bump into each other and are continually breaking up into exiguous lumps.

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Blobrana


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Undergraduate astronomy students at the University of Washington combing through images from a specialised telescope have discovered more than 1,300 asteroids that had never before been observed. That is about one out of every 250 known objects in the solar system.
The five students set out in 2005 to find exploding stars outside our solar system but their efforts were quickly sidetracked.

"We started searching for supernovae using data from the second phase of the Sloan Digital Sky Survey and all these asteroids were in the way" - Andrew Becker, a UW research assistant professor in astronomy.

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Blobrana


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Searching for the Grandest Asteroid Tour
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 Asteroids are Earth's closest celestial neighbours, sometimes passing closer to Earth than even the Moon. And yet, to date, only two spacecraft have ever remained in proximity to one of these bodies. Last month, orbit mechanics experts from around the world met to discuss methods for finding the best possible spacecraft trajectory, or flight path, for visiting a sequence of asteroids. The gathering was part of the second Global Trajectory Optimisation Competition, organised by JPL.
The idea of an asteroid grand tour is a celestial analogue to the Grand Tour embarked upon by Renaissance travellers seeking to further their cultural knowledge of Europe. Just as the traveller had to judge carefully which cities to visit based on his or her available resources, so must designers of a spacecraft flight path contend with limited resources and constraints. Such restrictions include the rocket's ability to launch the spacecraft into space, the strength of the spacecraft's thruster, orbital positions of the various asteroids over time, and the spacecraft's longevity.

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Blobrana


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Title: Developing space weathering on the asteroid 25143 Itokawa
Authors: Takahiro Hiroi, Masanao Abe, Kohei Kitazato, Shinsuke Abe, Beth E. Clark, Sho Sasaki, Masateru Ishiguro and Olivier S. Barnouin-Jha

Puzzlingly, the parent bodies of ordinary chondrites (the most abundant type of meteorites) do not seem to be abundant among asteroids. One possible explanation is that surfaces of the parent bodies become optically altered, to become the S-type asteroids which are abundant in the main asteroid belt. The process is called 'space weathering'—it makes the visible and near-infrared reflectance spectrum of a body darker and redder. A recent survey of small, near-Earth asteroids suggests that the surfaces of small S asteroids may have developing stages of space weathering. Here we report that a dark region on a small (550-metre) asteroid—25143 Itokawa—is significantly more space-weathered than a nearby bright region. Spectra of both regions are consistent with those of LL5-6 chondrites after continuum removal. A simple calculation suggests that the dark area has a shorter mean optical path length and about 0.04 per cent by volume more nanophase metallic iron particles than the bright area. This clearly shows that space-weathered materials accumulate on small asteroids, which are likely to be the parent bodies of LL chondrites. We conclude that, because LL meteorites are the least abundant of ordinary (H, L, and LL) chondrites, there must be many asteroids with ordinary-chondrite compositions in near-Earth orbits.

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Blobrana


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Asteroids gradually become coated with iron dust in space, becoming darker and redder with time, close-up observations of the asteroid Itokawa suggest. This confirms long-held suspicions about why asteroids look different than the space rocks that land on Earth as meteorites.

Chunks of asteroids that were broken off during collisions are thought to make up the most common kind of meteorite found on Earth – called ordinary chondrites. But strangely, the light spectra of these meteorites look different from the spectra of the most common type of asteroid, called S-type asteroids.
Some scientists have suggested that this is because the S-type asteroids have been "weathered" in space. In this process, fast-moving dust grains or energetic particles from the Sun could vaporise chunks of iron in the asteroid. The resulting cloud of iron particles would then rain back down on the space rock, leaving a reddish coating on its surface. Over time, the surface would become darker and redder.

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Blobrana


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Asteroid Spectroscopy
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Title: Asteroids as radial velocity and resolving power standards for medium and high resolution spectroscopy
Authors: Tomaz Zwitter (1), Francois Mignard (2), Francoise Crifo (3) ((1) University of Ljubljana, Department of Physics, Ljubljana, Slovenia, (2) Observatoire de la Cote d'Azur, Nice, France, (3) Observatoire de Paris, GEPI, Meudon, France)

Echelle spectra of 10 bright asteroids are presented and compared against an observed twilight spectrum and a computed Solar spectrum. Spectra covering a 2130 A spectral range centred on 5785 A are of high resolving power and high signal to noise ratio. So we focus on a comparison of detailed properties of spectral lines and not on albedo variations. It is shown that the normalised Solar and asteroid spectra are identical except for radial velocity (RV) shifts which can be predicted at the accuracy level of 1 m/s. So asteroids are proposed as new and extremely accurate radial velocity standards. Predicted and measured RVs of observed asteroids indeed match within limits of accuracy of the instrument. There are numerous absorption lines in the reflected Solar spectrum. This allows a direct mapping of the resolving power of a spectrograph between and along echelle spectral orders. So asteroid spectra can be used to test wavelength calibration and resolving power of spectrographs on the ground as well as in space, including the Gaia mission of ESA. All spectra are also given in an electronic form.

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