Explore the vast range of titles available.

Needle in a haystack: tracking down the fragments of asteroid 2008 TC 3 On 6 October 2008, a small Earth-bound asteroid designated 2008 TC 3 was discovered by the Catalina Sky Survey. Some 19 hours — and many astronomical observations — later it entered the atmosphere and disintegrated at 37 km altitude. No macroscopic fragments were expected to have survived but a dedicated search along the approach trajectory in a desert in northern Sudan has recovered 47 meteorites, fragments of a single body named Almahata Sitta, with a total mass of 3.95 kg. The asteroid and meteorite reflectance spectra identify the asteroid as surface matter from a class 'F' asteroid, material so fragile that it was not previously represented in meteorite collections. To have recovered meteorites from a known class of asteroids is a coup on a par with a successful spacecraft sample-return mission — without the rocket science. On 6 October 2008, a small asteroid designated 2008 TC3 hit the Earth in northern Sudan. Jenniskens et al . searched along the approach trajectory and luckily found 47 bits of a meteorite named Almahata Sitta. Analysis reveals it to be a porous achondrite and a polymict ureilite, and so the asteroid was F-class (dark carbon-rich anomalous ureilites). 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 , 2 , 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 TC 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.

Asteroids two-by-two The increased interest in the observation of main-belt asteroids in recent years has led to the identification of tens of asteroid pairs, which follow near-identical orbits around the Sun even though they are not physically bound together. Rotational fission of larger bodies has been hypothesized as a mechanism for their formation, an idea that gains support with some new observations. Theory predicts that the mass ratios of two asteroids in a pair will be than about 0.2 and that as the mass ratio approaches this upper limit, the spin period of the larger body is extended. Accordingly, photometric observations of 35 asteroid pairs reveal none with mass ratios greater than 0.2, and as mass ratios approach 0.2, primary periods grow longer. This suggests that asteroid pairs form by rotational fusion of a parent asteroid into a short-lived proto-binary system. Rotational fission may explain the formation of pairs of asteroids that have similar heliocentric orbits but are not bound together. These authors report photometric observations of a sample of asteroid pairs revealing that the primaries of pairs with mass ratios much less than 0.2 rotate rapidly, near their critical fission frequency. In agreement with crucial predictions, they do not find asteroid pairs with mass ratios larger than 0.2, and as the mass ratio approaches 0.2 the primary period grows long. Pairs of asteroids sharing similar heliocentric orbits, but not bound together, were found recently 1 , 2 , 3 . Backward integrations of their orbits indicated that they separated gently with low relative velocities, but did not provide additional insight into their formation mechanism. A previously hypothesized rotational fission process 4 may explain their formation—critical predictions are that the mass ratios are less than about 0.2 and, as the mass ratio approaches this upper limit, the spin period of the larger body becomes long. Here we report photometric observations of a sample of asteroid pairs, revealing that the primaries of pairs with mass ratios much less than 0.2 rotate rapidly, near their critical fission frequency. As the mass ratio approaches 0.2, the primary period grows long. This occurs as the total energy of the system approaches zero, requiring the asteroid pair to extract an increasing fraction of energy from the primary's spin in order to escape. We do not find asteroid pairs with mass ratios larger than 0.2. Rotationally fissioned systems beyond this limit have insufficient energy to disrupt. We conclude that asteroid pairs are formed by the rotational fission of a parent asteroid into a proto-binary system, which subsequently disrupts under its own internal system dynamics soon after formation.

On 26 September 2022, NASA’s Double Asteroid Redirection Test (DART) mission successfully impacted Dimorphos, the natural satellite of the binary near-Earth asteroid (65803) Didymos. Numerical simulations of the impact provide a means to find the surface material properties and structures of the target that are consistent with the observed momentum deflection efficiency, ejecta cone geometry and ejected mass. Our simulation that best matches the observations indicates that Dimorphos is weak, with a cohesive strength of less than a few pascals, like asteroids (162173) Ryugu and (101955) Bennu. We find that the bulk density of Dimorphos ρ B is lower than ~2,400 kg m − 3 and that it has a low volume fraction of boulders (≲40 vol%) on the surface and in the shallow subsurface, which are consistent with data measured by the DART experiment. These findings suggest that Dimorphos is a rubble pile that might have formed through rotational mass shedding and reaccumulation from Didymos. Our simulations indicate that the DART impact caused global deformation and resurfacing of Dimorphos. ESA’s upcoming Hera mission may find a reshaped asteroid rather than a well-defined crater. Numerical simulations of the DART impact on asteroid Didymos’s moon Dimorphos highlight its rubble-pile nature with a low bulk density and boulder volume fraction. These results indicate that Dimorphos formed from reaccumulated material shed from Didymos via rotation or impact.

Dynamical simulations of the coupled rotational and orbital dynamics of binary near-Earth asteroid 66391 (1999 KW4) suggest that it is excited as a result of perturbations from the Sun during perihelion passages. Excitation of the mutual orbit will stimulate complex fluctuations in the orbit and rotation of both components, inducing the attitude of the smaller component to have large variation within some orbits and to hardly vary within others. The primary's proximity to its rotational stability limit suggests an origin from spin-up and disruption of a loosely bound precursor within the past million years.

Dynamical resonances in the asteroid belt are the gateway for the production of near-Earth asteroids 1 (NEAs). To generate the observed number of NEAs, however, requires the injection of many asteroids into those resonant regions. Collisional processes have long been claimed as a possible source 1 , 2 , 3 , but difficulties with that idea have led to the suggestion that orbital drift arising from the Yarkovsky effect 4 , 5 , 6 , 7 dominates the injection process 8 , 9 , 10 . (The Yarkovsky effect is a force arising from differential heating—the ‘afternoon’ side of an asteroid is warmer than the ‘morning’ side.) The two models predict different rotational properties of NEAs: the usual collisional theories 2 are consistent with a nearly isotropic distribution of rotation vectors, whereas the ‘Yarkovsky model’ predicts an excess of retrograde rotations. Here we report that the spin vectors of NEAs show a strong and statistically significant excess of retrograde rotations, quantitatively consistent with the theoretical expectations of the Yarkovsky model.

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 effort in photometry of near-Earth asteroids (NEAs) at Modra Observatory has been enhanced following a recent collaboration with Ondřejov Observatory. We present a part of our collaborative work on measuring rotation lightcurve data for 10 NEAs. We derived following synodic periods P and amplitudes of their composite lightcurves: (3553), 3.1944 h, 0.08 mag; (22753), 10.24 h, 0.11 mag; (31669), 5.807 h, 0.07–0.27 mag; (40267), 4.9568 h, 1.01–1.11 mag; (66146), 2.3774 h, 0.12–0.15 mag; (88188), 2.6906 h, 0.06 mag; (103067), 9.489 h, 0.49 mag; 2001 CB21, 3.302 h, 0.19 mag; 2004 LJ1, 2.7247 h, 0.17–0.59 mag; 2004 XO14, 8.417 h, 0.19–0.25 mag. While the derived periods are unique (the reliability code U=3) for most of the objects, those of (3553), (22753) and 2001 CB21 are somewhat less reliable (U=2). We checked all the U=3 data for deviations from strict periodicity, but found no significant attenuation that would indicate the presence of a satellite. Absolute magnitudes in Cousins R band (HR) were derived for (3553), 16.05; (40267), 15.59; (88188), 16.04; 2004 XO14, 15.84; errors of the first three HR estimates are 0.20 mag, but that of 2004 XO14 is <0.10 mag.

We have used the ESO Very Large Telescope (VLT) to perform as trometric observations of Near Earth Asteroids (NEAs) having remote collision possibilities with the Earth. The observations were made for those objects which became too faint to be observed elsewhere. Using the 4 hours allocated in the semester April–September 2003, 5 faint NEAs were observed. As a result, no NEA that could impact the Earth was lost.

Asteroids are frequently colliding with small projectiles. Although each individual small collision is not very important, their cumulative effect can substantially change topography and also the overall shape of an asteroid. We run simulations of random collisions onto a single target asteroid represented by triaxial ellipsoid. We investigated asteroids of several hundred meters to about 18 km in diameter for which we assumed all material excavated by the collision to escape the asteroid. The cumulative effect of these collisions is an increasing elongation of the asteroid figure. However, the estimated timescale of this process is much longer than the collisional lifetime of asteroids. Therefore, we conclude that small collisions are probably not responsible for the overall shape of small asteroids.

The rotational properties of asteroids provide critical information about not only their internal structure but also their collisional and thermal histories. Previous work has revealed a bimodal distribution of asteroid spin rates, dividing populations into fast and slow rotators, but to date this separation remains poorly understood (e.g. its dependency on composition). We investigate whether the valley separating fast and slow rotators in rotational period-diameter space depends on the composition of the asteroid, approximated by asteroids' spectral class. First, we extended the Minor Planet Physical Properties Catalogue (MP3C) to include the available spectral classes of asteroids. Then, for each asteroid we selected the best diameter, rotational period, and spectral class. Building upon a semi-supervised machine-learning method, we quantify the valley between fast and slow rotators for S- and C-complex asteroids, which are linked to ordinary and carbonaceous chondrites respectively. The method iteratively fits a linear boundary between the two populations in rotational period-diameter space to maximise their separation. We find a clear compositional dependence of the valley: for C-complex asteroids the transition occurs at longer periods than for S-complex, with P* = 14.4 D_km^0.739 (C-complex) and P* = 11.6 D_km^0.718 (S-complex), where period and diameter are given in hours and kilometres respectively. This corresponds to mu Q approximately 2 and 13 GPa, respectively, where mu is the rigidity and Q the quality factor. The dependence of the valley on spectral classes likely reflects compositional and structural differences: C-complex asteroids, being more porous and weaker, dissipate angular momentum more efficiently than stronger, more coherent S-complex asteroids. This represents quantitative evidence of class-dependent rotational valleys within asteroid populations.