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Register a new userThe Discovery of Cometary Activity in Near-Earth Asteroid (3552) Don Quixote
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The near-Earth object (NEO) population, which mainly consists of fragments from collisions between asteroids in the main asteroid belt, is thought to include contributions from short-period comets as well. One of the most promising NEO candidates for a cometary origin is near-Earth asteroid (3552) Don Quixote, which has never been reported to show activity. Here we present the discovery of cometary activity in Don Quixote based on thermal-infrared observations made with the Spitzer Space Telescope in its 3.6 and 4.5 {mu}m bands. Our observations clearly show the presence of a coma and a tail in the 4.5 {mu}m but not in the 3.6 {mu}m band, which is consistent with molecular band emission from CO2. Thermal modeling of the combined photometric data on Don Quixote reveals a diameter of 18.4 (-0.4/+0.3) km and an albedo of 0.03 (-0.01/+0.02), which confirms Don Quixote to be the third-largest known NEO. We derive an upper limit on the dust production rate of 1.9 kg s^-1 and derive a CO2 gas production rate of (1.1+-0.1)10^26 molecules s^-1. Spitzer IRS spectroscopic observations indicate the presence of fine-grained silicates, perhaps pyroxene rich, on the surface of Don Quixote. Our discovery suggests that CO2 can be present in near-Earth space over a long time. The presence of CO2 might also explain that Don Quixotes cometary nature remained hidden for nearly three decades.
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We report on observations of near-Earth asteroid 2011 MD with the Spitzer Space Telescope. We have spent 19.9 h of observing time with channel 2 (4.5 {mu}m) of the Infrared Array Camera and detected the target within the 2{sigma} positional uncertainty ellipse. Using an asteroid thermophysical model and a model of nongravitational forces acting upon the object we constrain the physical properties of 2011 MD, based on the measured flux density and available astrometry data. We estimate 2011 MD to be 6 (+4/-2) m in diameter with a geometric albedo of 0.3 (+0.4/-0.2) (uncertainties are 1{sigma}). We find the asteroids most probable bulk density to be 1.1 (+0.7/-0.5) g cm^{-3}, which implies a total mass of (50-350) t and a macroporosity of >=65%, assuming a material bulk density typical of non-primitive meteorite materials. A high degree of macroporosity suggests 2011 MD to be a rubble-pile asteroid, the rotation of which is more likely to be retrograde than prograde.
We conducted a polarimetric observation of the fast-rotating near-Earth asteroid (1566) Icarus at large phase (Sun-asteroid-observers) angles $alpha$= 57 deg--141deg around the 2015 summer solstice. We found that the maximum values of the linear polarization degree are $P_mathrm{max}$=7.32$pm$0.25 % at phase angles of $alpha_mathrm{max}$=124$pm$8 deg in the $V$-band and $P_mathrm{max}$=7.04$pm$0.21 % at $alpha_mathrm{max}$=124$pm$6 deg in the $R_mathrm{C}$-band. Applying the polarimetric slope-albedo empirical law, we derived a geometric albedo of $p_mathrm{V}$=0.25$pm$0.02, which is in agreement with that of Q-type taxonomic asteroids. $alpha_mathrm{max}$ is unambiguously larger than that of Mercury, the Moon, and another near-Earth S-type asteroid (4179) Toutatis but consistent with laboratory samples with hundreds of microns in size. The combination of the maximum polarization degree and the geometric albedo is in accordance with terrestrial rocks with a diameter of several hundreds of micrometers. The photometric function indicates a large macroscopic roughness. We hypothesize that the unique environment (i.e., the small perihelion distance $q$=0.187 au and a short rotational period of $T_mathrm{rot}$=2.27 hours) may be attributed to the paucity of small grains on the surface, as indicated on (3200) Phaethon.
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We have carried out simulations to predict the performance of a new space-based telescopic survey operating at thermal infrared wavelengths that seeks to discover and characterize a large fraction of the potentially hazardous near-Earth asteroid (NEA) population. Two potential architectures for the survey were considered: one located at the Earth-Sun L1 Lagrange point, and one in a Venus-trailing orbit. A sample cadence was formulated and tested, allowing for the self-follow-up necessary for objects discovered in the daytime sky on Earth. Synthetic populations of NEAs with sizes >=140 m in effective spherical diameter were simulated using recent determinations of their physical and orbital properties. Estimates of the instrumental sensitivity, integration times, and slew speeds were included for both architectures assuming the properties of new large-format 10 um detector arrays capable of operating at ~35 K. Our simulation included the creation of a preliminary version of a moving object processing pipeline suitable for operating on the trial cadence. We tested this pipeline on a simulated sky populated with astrophysical sources such as stars and galaxies extrapolated from Spitzer and WISE data, the catalog of known minor planets (including Main Belt asteroids, comets, Jovian Trojans, etc.), and the synthetic NEA model. Trial orbits were computed for simulated position-time pairs extracted from the synthetic surveys to verify that the tested cadence would result in orbits suitable for recovering objects at a later time. Our results indicate that the Earth-Sun L1 and Venus-trailing surveys achieve similar levels of integral completeness for potentially hazardous asteroids larger than 140 m; placing the telescope in an interior orbit does not yield an improvement in discovery rates. This work serves as a necessary first step for the detailed planning of a next-generation NEA survey.
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