Asteroid (16) Psyche is the target of the NASA Psyche mission. It is considered one of the few main-belt bodies that could be an exposed proto-planetary metallic core and that would thus be related to iron meteorites. Such an association is however challenged by both its near- and mid-infrared spectral properties and the reported estimates of its density. Here, we aim to refine the density of (16) Psyche to set further constraints on its bulk composition and determine its potential meteoritic analog. We observed (16) Psyche with ESO VLT/SPHERE/ZIMPOL as part of our large program (ID 199.C-0074). We used the high angular resolution of these observations to refine Psyche's three-dimensional (3D) shape model and subsequently its density when combined with the most recent mass estimates. In addition, we searched for potential companions around the asteroid. We derived a bulk density of 3.99+/-0.26g/cm^3^ for Psyche. While such density is incompatible at the 3-sigma level with any iron meteorites (~7.8g/cm^3^), it appears fully consistent with that of stony-iron meteorites such as mesosiderites (density ~4.25g/cm^3^). In addition, we found no satellite in our images and set an upper limit on the diameter of any non-detected satellite of 1460+/-200m at 150km from Psyche (0.2%xR_Hill_, the Hill radius) and 800+/-200m at 2000km (3%xRHill). Considering that the visible and near-infrared spectral properties of mesosiderites are similar to those of Psyche, there is merit to a long-published initial hypothesis that Psyche could be a plausible candidate parent body for mesosiderites.
Asteroid (16) Psyche is the largest M-type asteroid in the main belt and the target of the NASA Psyche mission. It is also the only asteroid of this size (D>200km) known to be metal rich. Although various hypotheses have been proposed to explain the rather unique physical properties of this asteroid, a perfect understanding of its formation and bulk composition is still missing. We aim to refine the shape and bulk density of (16) Psyche and to perform a thorough analysis of its shape to better constrain possible formation scenarios and the structure of its interior. We obtained disk-resolved VLT/SPHERE/ZIMPOL images acquired within our ESO large program (ID 199.C-0074), which complement similar data obtained in 2018. Both data sets offer a complete coverage of Psyche's surface. These images were used to reconstruct the three-dimensional (3D) shape of Psyche with two independent shape modeling algorithms (MPCD and ADAM). A shape analysis was subsequently performed, including a comparison with equilibrium figures and the identification of mass deficit regions. Our 3D shape along with existing mass estimates imply a density of 4.20+/-0.60g/cm^3, which is so far the highest for a solar system object following the four telluric planets. Furthermore, the shape of Psyche presents small deviations from an ellipsoid, that is, prominently three large depressions along its equator. The flatness and density of Psyche are compatible with a formation at hydrostatic equilibrium as a Jacobi ellipsoid with a shorter rotation period of ~3h. Later impacts may have slowed down Psyche's rotation, which is currently ~4.2h, while also creating the imaged depressions. Our results open the possibility that Psyche acquired its primordial shape either after a giant impact while its interior was already frozen or while its interior was still molten owing to the decay of the short-lived radionuclide ^26^Al.
The results of new reduction of 1545 photographic observations of 14 selected asteroids' obtained with Normal Astrograph of Pulkovo observatory from 1948 to 1990 years presented. Photographic plates, stored in observatory's archive, was digitized using consumer flatbed scanner with special designed technique. The accuracy of measured photoplates was performed. The UCAC3 was used as reference catalog. The analysis of instrumental systematic effects, revealing in common distortion and magnitude equation, was performed and taken into account. The equatorial coordinates of 1378 single observations of selected asteroids was obtained and was made their comparison with results of reduction of this material obtained earlier. 1475 positions of stars with large proper motions from LSPM catalog was measured among background objects.
We present the results of the observations of the Uranian satellites made with the 26-inch refractor at the Pulkovo Observatory in 2007-2016. During this time we got 17 normal positions of Ariel, 43 normal positions of Umbriel, 112 normal positions of Titania and 122 normal positions of Oberon. The observations were performed every year from the end of august to the beginning of January. Our results show a good quality of contemporary theories of Uranian satellites' and planets' motion. Published positions of the Uranian satellites can be useful for construction of future theories. Almost 7000 CCD frames were analyzed and reduced using the UCAC4 catalog. Observation processing and coordinate measurement were performed with the IZMCCD software package (izmccd.puldb.ru). Special approach was used to eliminate a scattered halo caused by the bright planet.
Ever since the very first photometric studies of Centaurs and Kuiper belt objects (KBOs) their visible color distribution has been controversial. This controversy has triggered a prolific debate on the origin of the surface colors of these distant icy objects of the solar system. Two scenarios have been proposed to interpret and explain the large variability of colors, hence surface composition. Are the colors mainly primordial and directly related to the formation region, or are they the result of surface evolution processes? To date, no mechanism has been found that successfully explains why Centaurs, which are escapees from the Kuiper belt, exhibit two distinct color groups, whereas KBOs do not. We re-address this issue using a carefully compiled set of B-R colors and H_R{alpha}_ magnitudes (as proxy for size) for 253 objects, including data for 10 new small objects. We find that the bimodal color distribution of Centaurs is a size-related phenomenon, common to both Centaurs and small KBOs, i.e. independent of dynamical classification. Furthermore, we find that large KBOs also have a bimodal distribution of surface colors, albeit distinct from the small objects and strongly dependent on the `Haumea collisional family' objects. When plotted in B-R, H_R{alpha}_ space, the colors of Centaurs and KBOs display a peculiar N shape.
R- and I-band photometry of 506 asteroids with CNEOST
Short Name:
J/AJ/160/73
Date:
09 Mar 2022
Publisher:
CDS
Description:
We initiated the bilateral collaboration between the Lulin Observatory and the Purple Mountain Observatory to collect asteroid lightcurves using the Chinese Near-Earth Object Survey Telescope at the Xuyi Observation Station. The primary goal of this collaboration was to discover super-fast rotators (SFRs) and study their physical properties. Two campaigns have been conducted: (a) a survey of ~45{deg}^2^ using 8minute cadence during 2017 February 26-March 2, and (b) a survey of ~60{deg}^2^ using 10minute cadence during 2018 March 9-12. Our samples are mainly main-belt asteroids and some Hildas and Jupiter Trojans. Out of 4522 collected lightcurves, 506 reliable rotation periods were obtained. Among the reliable rotation periods, we found 16 candidates with a possible rotation period of <2.2hr, in which (134291) 2006 DZ6 shows a very convincing folded lightcurve and the other 15 candidates only have a likely trend. Further confirmation is needed for the rotation periods of these SFR candidates. In addition, (2280) Kunikov seems to have an eclipsing feature on its lightcurve with a relatively long rotation period suggesting that it is likely a fully synchronized binary asteroid. When the preliminary spin-rate distributions were carried out for asteroids using different sizes, no obvious difference was found.
We present the K2 light curves of a large sample of untargeted main-belt asteroids (MBAs) detected with the Kepler Space Telescope. The asteroids were observed within the Uranus superstamp, a relatively large, continuous field with a low stellar background designed to cover the planet Uranus and its moons during Campaign 8 of the K2 mission. The superstamp offered the possibility of obtaining precise, uninterrupted light curves of a large number of MBAs and thus determining unambiguous rotation rates for them. We obtained photometry for 608 MBAs, and were able to determine or estimate rotation rates for 90 targets, of which 86 had no known values before. In an additional 16 targets we detected incomplete cycles and/or eclipse-like events. We found the median rotation rate to be significantly longer than that of the ground-based observations, indicating that the latter are biased toward shorter rotation rates. Our study highlights the need and benefits of further continuous photometry of asteroids.
Hilda asteroids and Jupiter Trojans are two low-albedo (p_v_~0.07) populations for which the Nice model predicts an origin in the primordial Kuiper Belt region. However, recent surveys by WISE and the Spitzer Space Telescope (SST) have revealed that ~2% of these objects possess high albedos (p_v_>=0.15), which might indicate interlopers --that is, objects not formed in the Kuiper Belt-- among these two populations. Here, we report spectroscopic observations in the visible and/or near-infrared spectral ranges of twelve high-albedo (p_v_>0.15) Hilda asteroids and Jupiter Trojans. These twelve objects have spectral properties similar to those of the low-albedo population, which suggests a similar composition and hence a similar origin for low- and high-albedo Hilda asteroids and Jupiter Trojans. We therefore propose that most high albedos probably result from statistical bias or uncertainties that affect the WISE and SST measurements. However, some of the high albedos may be true and the outcome of some collision-induced resurfacing by a brighter material that could include water ice. Future work should attempt to investigate the nature of this supposedly bright material. The lack of interlopers in our sample allows us to set an upper limit of 0.4% at a confidence level of 99.7% on the abundance of interlopers with unexpected taxonomic classes (e.g., A-, S-, V-type asteroids) among these two populations.
Resonance sticking in the population of scattering TNOs
Short Name:
J/AJ/156/33
Date:
21 Oct 2021
Publisher:
CDS
Description:
A substantial fraction of our solar system's trans-Neptunian objects (TNOs) are in mean-motion resonance with Neptune. Many of these objects were likely caught into resonances by planetary migration-either smooth or stochastic- approximately 4 Gyr ago. Some, however, gravitationally scattered off of Neptune and became transiently stuck in more recent events. Here we use numerical simulations to predict the number of transiently stuck objects, captured from the current actively scattering population, that occupy 111 resonances at semimajor axes a=30-100 au. Our source population is an observationally constrained model of the currently scattering TNOs. We predict that, integrated across all resonances at these distances, the current transient-sticking population comprises 40% of the total transiently stuck+scattering TNOs, suggesting that these objects should be treated as a single population. We compute the relative distribution of transiently stuck objects across all p:q resonances with 1/6=<q/p=<1, p<40, and q<20, providing predictions for the population of transient objects with H_r_<8.66 in each resonance. We find that the relative populations are approximately proportional to each resonance's libration period and confirm that the importance of transient sticking increases with semimajor axis in the studied range. We calculate the expected distribution of libration amplitudes for stuck objects and demonstrate that observational constraints indicate that both the total number and the amplitude distribution of 5:2 resonant TNOs are inconsistent with a population dominated by transient sticking from the current scattering disk. The 5:2 resonance hence poses a challenge for leading theories of Kuiper Belt sculpting.
Extensive time-resolved observations of Kuiper belt object 2001 QG298 show a light curve with a peak-to-peak variation of 1.14+/-0.04mag and single-peaked period of 6.8872+/-0.0002hr. The mean absolute magnitude is 6.85mag, which corresponds to a mean effective radius of 122(77)km if an albedo of 0.04(0.10) is assumed. This is the first known Kuiper belt object and only the third minor planet with a radius greater than 25km to display a light curve with a range in excess of 1mag. We find the colors to be typical for a Kuiper belt object (B-V=1.00+/-0.04, V-R=0.60+/-0.02), with no variation in color between minimum and maximum light.
