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In the absence of a firm link between individual meteorites and their asteroidal parent bodies, asteroids are typically characterized only by their light reflection properties, and grouped accordingly into classes (1-3). On 6 October 2008, a small asteroid was discovered with a flat reflectance spectrum in the 554-995 nm wavelength range, and designated 2008 T[C.sub.3] (refs 4-6). It subsequently hit the Earth. Because it exploded at 37 km altitude, no macroscopic fragments were expected to survive. Here we report that a dedicated search along the approach trajectory recovered 47 meteorites, fragments of a single body named Almahata Sitta, with a total mass of 3.95 kg. Analysis of one of these meteorites shows it to be an achondrite, a polymict ureilite, anomalous in its class: ultra-fine-grained and porous, with large carbonaceous grains. The combined asteroid and meteorite reflectance spectra identify the asteroid as F class (3), now firmly linked to dark carbon-rich anomalous ureilites, a material so fragile it was not previously represented in meteorite collections., The asteroid was discovered by the automated Catalina Sky Survey telescope at Mount Lemmon, Arizona on October 6 06:39 uTc (ref. 4). Early orbital solutions showed an impact 19 h [...]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2005.06.003 Byline: D. VokrouhlickA1/2 (a), D. Aapek (a), S.R. Chesley (b), S.J. Ostro (b) Keywords: Asteroids; Yarkovsky effect; Orbit determination Abstract: We consider the possibility of detecting the Yarkovsky orbital perturbation acting on binary systems among the near-Earth asteroids. This task is significantly more difficult than for solitary asteroids because the Yarkovsky force affects both the heliocentric orbit of the system's center of mass and the relative orbit of the two components. Nevertheless, we argue these are sufficiently well decoupled so that the major Yarkovsky perturbation is in the simpler heliocentric motion and is observable with the current means of radar astrometry. Over the long term, the Yarkovsky perturbation in the relative motion of the two components is also detectable for the best observed systems. However, here we consider a simplified version of the problem by ignoring mutual non-spherical gravitational perturbations between the two asteroids. With the orbital plane constant in space and the components' rotation poles fixed (and assumed perpendicular to the orbital plane), we do not examine the coupling between Yarkovsky and gravitational effects. While radar observations remain an essential element of Yarkovsky detections, lightcurve observations, with their ability to track occultation and eclipse phenomena, are also very important in the case of binaries. The nearest possible future detection of the Yarkovsky effect for a binary system occurs for (66063) 1998 RO.sub.1 in September 2006. Farther out, even more statistically significant detections are possible for several other systems including 2000 DP.sub.107, (66391) 1999 KW.sub.4 and 1996 FG.sub.3. Author Affiliation: (a) Institute of Astronomy, Charles University, V HoleA oviAkach 2, CZ-18000 Prague 8, Czech Republic (b) Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109-8099, USA Article History: Received 14 December 2004; Revised 7 June 2005

We consider the possibility of detecting the Yarkovsky orbital perturbation acting on binary systems among the near-Earth asteroids. This task is significantly more difficult than for solitary asteroids because the Yarkovsky force affects both the heliocentric orbit of the system's center of mass and the relative orbit of the two components. Nevertheless, we argue these are sufficiently well decoupled so that the major Yarkovsky perturbation is in the simpler heliocentric motion and is observable with the current means of radar astrometry. Over the long term, the Yarkovsky perturbation in the relative motion of the two components is also detectable for the best observed systems. However, here we consider a simplified version of the problem by ignoring mutual non-spherical gravitational perturbations between the two asteroids. With the orbital plane constant in space and the components' rotation poles fixed (and assumed perpendicular to the orbital plane), we do not examine the coupling between Yarkovsky and gravitational effects. While radar observations remain an essential element of Yarkovsky detections, lightcurve observations, with their ability to track occultation and eclipse phenomena, are also very important in the case of binaries. The nearest possible future detection of the Yarkovsky effect for a binary system occurs for (66063) 1998 R[O.sub.1] in September 2006. Farther out, even more statistically significant detections are possible for several other systems including 2000 DP107, (66391) 1999 K[W.sub.4] and 1996 F[G.sub.3]. Keywords: Asteroids; Yarkovsky effect: Orbit determination

We show that, over the next two decades, the current radar and optical astrometric technology is adequate to allow detection of the Yarkovsky effect acting on at least two dozen NEAs from a variety of orbital regimes and with effective diameters ranging from about ten meters up to several kilometers. The Yarkovsky effect will likely be detected for objects of rarer spectral types X, C, and E, as well as the more common S and Q. The next predicted detection of the Yarkovsky effect is for 4179 Toutatis in October 2004, which would be also the first multi-kilometer case. The Asteroid 25143 Itokawa, with a likely detection at the end of 2005, could offer an important test due to the independent 'ground-truth' measurements of the asteroid mass and surface thermal inertia expected from the Hayabusa spacecraft. Earth co-orbital asteroids (e.g., 2000 PH5 or 2003 YN107) are the best placed for rapid determination of the Yarkovsky effect, and the timespan between discovery of the object and detection of the Yarkovsky effect may be as short as 3 years. By 2012, the motion of potential Earth impactor (29075) 1950 DA will likely reveal the magnitude of the Yarkovsky effect, which in turn will identify which of two possible pole orientations is correct. Vis-a-vis the 2880 impact, this new information will allow a substantial improvement in the quality of long term predictions. Keywords: Asteroids; Yarkovsky effect; Orbit determination

Integration of the orbit of asteroid (29075) 1950 DA, which is based on radar and optical measurements spanning 51 years, reveals a 20-minute interval in March 2880 when there could be a nonnegligible probability of the 1-kilometer object colliding with Earth. Trajectory knowledge remains accurate until then because of extensive astrometric data, an inclined orbit geometry that reduces in-plane perturbations, and an orbit uncertainty space modulated by gravitational resonance. The approach distance uncertainty in 2880 is determined primarily by uncertainty in the accelerations arising from thermal re-radiation of solar energy absorbed by the asteroid. Those accelerations depend on the spin axis, composition, and surface properties of the asteroid, so that refining the collision probability may require direct inspection by a spacecraft., Useful predictions of asteroid encounters with planets, in which the statistical uncertainty in the time of closest approach is ± 10 days or less, are generally limited to an interval [...]

Reports on the landing of the NEAR-Shoemaker spacecraft on asteroid 433 Eros. Controlled descent of the spacecraft to provide high resolution images; Properties and distribution of ejecta blocks; Transition from the blocky surface to a smooth area.