Dwarf planet Ceres (empty set similar to 940 km) is the largest object in the main asteroid belt. Investigations suggest that Ceres is a thermally evolved, volatile-rich body with potential geological activity, a body that was never completely molten, but one that possibly partially differentiated into a rocky core and an ice-rich mantle, and may contain remnant internal liquid water. Thermal alteration and the infall of exogenic material contribute to producing a (dark) carbonaceous chondritic-like surface containing ammoniated phyllosilicates. Here we report imaging and spectroscopic analyses of data on the bright Oxo crater derived from the Framing Camera and the Visible and Infrared Spectrometer on board the Dawn spacecraft. We confirm that the transitional complex crater Oxo (empty set similar to 9 km) exhibits exposed surface water-ice. We show that this water-ice-rich material is associated exclusively with two lobate deposits at pole-facing scarps, deposits that also contain carbonates and admixed phyllosilicates. Due to Oxo's location at -4802 m below the cerean reference ellipsoid and its very young age of only 190 ka (1 sigma: +100 ka, -70 ka), Oxo is predestined for ongoing water-ice sublimation.

We analyzed data from the first year of a survey for Near-Earth Objects (NEOs) that we are carrying out with the Dark Energy Camera (DECam) on the 4 m Blanco telescope at the Cerro Tololo Inter-American Observatory. We implanted synthetic NEOs into the data stream to derive our nightly detection efficiency as a function of magnitude and rate of motion. Using these measured efficiencies and the solar system absolute magnitudes derived by the Minor Planet Center for the 1377. measurements of 235. unique NEOs detected, we directly derive, for the first time from a single observational data set, the NEO size distribution from 1. km down to 10 m. We find that there are 106.6 NEOs larger than 10 m. This result implies a factor of 10 fewer small NEOs than some previous results, though our derived size distribution is in good agreement with several other estimates.

Small near-Earth asteroids (NEAs) (< 20 m) are interesting, because they are progenitors for meteorites in our terrestrial collection. The physical characteristics of these small NEAs are crucial to our understanding of the effectiveness of our atmosphere in filtering low-strength impactors. In the past, the characterization of small NEAs has been a challenge, because of the difficulty in detecting them prior to close Earth flyby. In this study, we physically characterized the 2 m diameter NEA 2015 TC25 using ground-based optical, near-infrared and radar assets during a close flyby of the Earth (distance 128,000 km) in 2015 October 12. Our observations suggest that its surface composition is similar to aubrites, a rare class of high-albedo differentiated meteorites. Aubrites make up only 0.14% of all known meteorites in our terrestrial meteorite collection. 2015 TC25 is also a very fast rotator with a period of 133 +/- 6 s. We combined the spectral and dynamical properties of 2015 TC25 and found the best candidate source body in the inner main belt to be the 70 km diameter E-type asteroid (44) Nysa. We attribute the difference in spectral slope between the two objects to the lack of regolith on the surface of 2015 TC25. Using the albedo of E-type asteroids (50%-60%) we refine the diameter of 2015 TC25 to 2 m, making it one of the smallest NEAs ever to be characterized.

We present an analysis of new and published data on P/2013 R3, the first asteroid detected while disintegrating. Thirteen discrete components are measured in the interval between UT 2013 October 01 and 2014 February 13. We determine a mean, pair-wise velocity dispersion among these components of Delta nu = 0.33. +/- 0.03 ms(-1) and find that their separation times are staggered over an interval of similar to 5 months. Dust enveloping the system has, in the first observations, a cross-section of. similar to 30 km(2) but fades monotonically at a rate consistent with the action of radiation pressure sweeping. The individual components exhibit comet-like morphologies and also fade except where secondary fragmentation is accompanied by the release of additional dust. We find only upper limits to the radii of any embedded solid nuclei, typically similar to 100-200 m (geometric albedo 0.05 assumed). Combined, the components of P/2013 R3 would form a single spherical body with a. radius of less than or similar to 400 m, which is our best estimate of the size of the precursor object. The observations are consistent with rotational disruption of a weak (cohesive strength of similar to 50 to 100 N m(-2)) parent body, similar to 400 m in radius. Estimated radiation (YORP) spin-up times of this parent are. less than or similar to 1 Myr, shorter than the collisional lifetime. If present, water ice sublimating at as little as 10-3 kg s(-1) could generate a torque on the parent body rivaling the YORP torque. Under conservative assumptions about the frequency of similar disruptions, the inferred asteroid debris production rate is greater than or similar to 10(3) kg s-1, which is at least 4% of the rate needed to maintain the Zodiacal Cloud.

This overview paper describes the legacy prospect and discovery potential of the Dark Energy Survey (DES) beyond cosmological studies, illustrating it with examples from the DES early data. DES is using a wide-field camera (DECam) on the 4 m Blanco Telescope in Chile to image 5000 sq deg of the sky in five filters (grizY). By its completion, the survey is expected to have generated a catalogue of 300 million galaxies with photometric redshifts and 100 million stars. In addition, a time-domain survey search over 27 sq deg is expected to yield a sample of thousands of Type Ia supernovae and other transients. The main goals of DES are to characterize dark energy and dark matter, and to test alternative models of gravity; these goals will be pursued by studying large-scale structure, cluster counts, weak gravitational lensing and Type Ia supernovae. However, DES also provides a rich data set which allows us to study many other aspects of astrophysics. In this paper, we focus on additional science with DES, emphasizing areas where the survey makes a difference with respect to other current surveys. The paper illustrates, using early data (from 'Science Verification', and from the first, second and third seasons of observations), what DES can tell us about the Solar system, the Milky Way, galaxy evolution, quasars and other topics. In addition, we show that if the cosmological model is assumed to be I >+cold dark matter, then important astrophysics can be deduced from the primary DES probes. Highlights from DES early data include the discovery of 34 trans-Neptunian objects, 17 dwarf satellites of the Milky Way, one published z > 6 quasar (and more confirmed) and two published superluminous supernovae (and more confirmed).

Hubble Space Telescope observations of active asteroid 324P/La Sagra near perihelion show continued mass loss consistent with the sublimation of near-surface ice. Isophotes of the coma measured from a vantage point below the orbital plane are best matched by steady emission of particles having a nominal size. of. a similar to 100 mu m. The inferred rate of mass loss, dM(d)/dt similar to 0.2 kg s(-1), can be supplied by sublimation of water ice in thermal equilibrium with sunlight from an area as small as 930 m(2), corresponding to about 0.2% of the nucleus surface. Observations taken from a vantage point only 0.degrees 6. from the orbital plane of 324P set a limit to the velocity of ejection of dust in the direction perpendicular to the plane, V-perpendicular to < 1 m s(-1). Short-term photometric variations of the near-nucleus region, if related to rotation of the underlying nucleus, rule-out periods <= 3.8 hr and suggest that rotation probably does not play a central role in driving the observed mass loss. We estimate that, in the previous orbit, 324P lost about 4 x 10(7) kg in dust particles, corresponding to 6 x 10(-5) of the mass of a 550 m spherical nucleus of assumed density rho = 1000 kg m(-3). If continued, mass loss at this rate would limit the lifetime of 324P to similar to 1.6 x 10(4) orbits (about 10(5) years). To survive for the 100-400 Myr timescales corresponding to dynamical and collisional stability requires a duty cycle of 2 x 10(-4) <= f(d) <= 8 x 10(-4). Unless its time in orbit is overestimated by many orders of magnitude, 324P is revealed as a briefly active member of a vast population of otherwise dormant ice-containing asteroids.

Many topics in planetary studies demand an estimate of the collision probability of two objects moving on nearly Keplerian orbits. In the classic works of Opik and Wetherill, the collision probability was derived by linearizing the motion near the collision points, and there is now a vast amount of literature using their method. We present here a simpler and more physically motivated derivation for non-tangential collisions in Keplerian orbits, as well as for tangential collisions that were not previously considered. Our formulas have the added advantage of being manifestly symmetric in the parameters of the two colliding bodies. In common with the Opik-Wetherill treatments, we linearize the motion of the bodies in the vicinity of the point of orbit intersection (or near the points of minimum distance between the two orbits) and assume a uniform distribution of impact parameter within the collision radius. We point out that the linear approximation leads to singular results for the case of tangential encounters. We regularize this singularity by use of a parabolic approximation of the motion in the vicinity of a tangential encounter.

The first transiting planetesimal orbiting a white dwarf was recently detected in K2 data of WD 1145+017 and has been followed up intensively. The multiple, long and variable transits suggest the transiting objects are dust clouds, probably produced by a disintegrating asteroid. In addition, the system contains circumstellar gas, evident by broad absorption lines, mostly in the u' band, and a dust disc, indicated by an infrared excess. Here we present the first detection of a change in colour of WD 1145+017 during transits, using simultaneous multiband fast-photometry ULTRACAM measurements over the u'g'r'i' bands. The observations reveal what appears to be 'bluing' during transits; transits are deeper in the redder bands, with a u' - r' colour difference of up to similar to-0.05 mag. We explore various possible explanations for the bluing, including limb darkening or peculiar dust properties. 'Spectral' photometry obtained by integrating over bandpasses in the spectroscopic data in and out of transit, compared to the photometric data, shows that the observed colour difference is most likely the result of reduced circumstellar absorption in the spectrum during transits. This indicates that the transiting objects and the gas share the same line of sight and that the gas covers the white dwarf only partially, as would be expected if the gas, the transiting debris and the dust emitting the infrared excess are part of the same general disc structure (although possibly at different radii). In addition, we present the results of a week-long monitoring campaign of the system using a global network of telescopes.