- ID:
- ivo://CDS.VizieR/J/A+A/638/L15
- Title:
- (16) Psyche. VLT/SPHERE images and shape models
- Short Name:
- J/A+A/638/L15
- Date:
- 23 Mar 2022
- Publisher:
- CDS
- Description:
- 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.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/546/A86
- Title:
- R absolute magnitudes of Kuiper Belt objects
- Short Name:
- J/A+A/546/A86
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- 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.
- ID:
- ivo://CDS.VizieR/J/AJ/157/186
- Title:
- r'-band photometry of comet 96P/Machholz 1
- Short Name:
- J/AJ/157/186
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We observed comet 96P/Machholz 1 on a total of nine nights before and after perihelion during its 2017/2018 apparition. Both its unusually small perihelion distance and the observed fragmentation during multiple apparitions make 96P an object of great interest. Our observations show no evidence of a detectable dust coma, implying that we are observing a bare nucleus at distances ranging from 2.3 to 3.8 au. Based on this assumption, we calculated its color and found average values of g'-r'=0.50+/-0.04, r'-i'=0.17+/-0.03, and i'-z'=0.06+/-0.04. These are notably more blue than those of the nuclei of other Jupiter-family and long-period comets. Furthermore, assuming a bare nucleus, we found an equivalent nuclear radius of 3.4+/-0.2 km with an axial ratio of at least 1.6+/-0.1. The lightcurve clearly displays one large peak, one broad flat peak, and two distinct troughs, with a clear asymmetry that suggests that the shape of the nucleus deviates from that of a simple triaxial ellipsoid. This asymmetry in the lightcurve allowed us to constrain the nuclear rotation period to 4.10+/-0.03 hr and 4.096+/-0.002 hr before and after perihelion, respectively. Within the uncertainties, 96P's rotation period does not appear to have changed throughout the apparition, and we conclude a maximum possible change in rotation period of 130 s. The observed properties were compared to those of comet 322P and interstellar object 1I/'Oumuamua in an attempt to study the effects of close perihelion passages on cometary surfaces and their internal structure and the potential interstellar origin of 96P.
- ID:
- ivo://CDS.VizieR/J/A+A/615/A93
- Title:
- Reconstructed decadal sunspot numbers
- Short Name:
- J/A+A/615/A93
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The solar activity in the past millennia can only be reconstructed from cosmogenic radionuclide proxy records in terrestrial archives. However, because of the diversity of the proxy archives, it is difficult to build a homogeneous reconstruction. All previous studies were based on individual, sometimes statistically averaged, proxy datasets. Here we aim to provide a new consistent multiproxy reconstruction of the solar activity over the last 9000 years, using all available long-span datasets of ^10^Be and ^14^C in terrestrial archives. A new method, based on a Bayesian approach, was applied for the first time to solar activity reconstruction. A Monte Carlo search (using the x2 statistic) for the most probable value of the modulation potential was performed to match data from different datasets for a given time. This provides a straightforward estimate of the related uncertainties. We used six ^10^Be series of different lengths (from 500-10000 years) from Greenland and Antarctica, and the global ^14^C production series. The 10Be series were resampled to match wiggles related to the grand minima in the ^14^C reference dataset. The stability of the long data series was tested. Results. The Greenland Ice-core Project (GRIP) and the Antarctic EDML (EPICA Dronning Maud Land) ^10^Be series diverge from each other during the second half of the Holocene, while the ^14^C series lies in between them. A likely reason for the discrepancy is the insufficiently precise beryllium transport and deposition model for Greenland, which leads to an undercorrection of the GRIP series for the geomagnetic shielding effect. A slow 6-7-millennia variability with lows at ca. 5500 BC and 1500 AD in the longterm evolution of solar activity is found. Two components of solar activity can be statistically distinguished: the main component, corresponding to the 'normal' moderate level, and a component corresponding to grand minima. A possible existence of a component representing grand maxima is indicated, but it cannot be separated from the main component in a statistically significant manner. A new consistent reconstruction of solar activity over the last nine millennia is presented with the most probable values of decadal sunspot numbers and their realistic uncertainties. Independent components of solar activity corresponding to the main moderate activity and the grand-minimum state are identified; they may be related to different operation modes of the dynamo.
- ID:
- ivo://CDS.VizieR/J/A+A/568/L7
- Title:
- Reflectance spectra of 12 Trojans and Hildas
- Short Name:
- J/A+A/568/L7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- 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.
- ID:
- ivo://CDS.VizieR/J/AJ/160/238
- Title:
- Reflectivity of 4 Gallilean satellites with ISS
- Short Name:
- J/AJ/160/238
- Date:
- 10 Dec 2021
- Publisher:
- CDS
- Description:
- For terrestrial exoplanets with thin or no atmospheres, the surface contributes light to the reflected light signal of the planet. Measurement of the variety of disk-integrated brightnesses of bodies in the solar system and the variation with illumination and wavelength is essential for both planning imaging observations of directly imaged exoplanets and interpreting the eventual data sets. Here we measure the change in brightness of the Galilean satellites as a function of planetocentric longitude, illumination phase angle, and wavelength. The data span a range of wavelengths from 400 to 950nm and predominantly phase angles from 0{deg} to 25{deg}, with some constraining observations near 60{deg}-140{deg}. Despite the similarity in size and density between the moons, surface inhomogeneities result in significant changes in the disk-integrated reflectivity with planetocentric longitude and phase angle. We find that these changes are sufficient to determine the rotational periods of the moon. We also find that at low phase angles, the surface can produce reflectivity variations of 8%-36%, and the limited high phase angle observations suggest variations will have proportionally larger amplitudes at higher phase angles. Additionally, all of the Galilean satellites are darker than predicted by an idealized Lambertian model at the phases most likely to be observed by direct imaging missions. If Earth-sized exoplanets have surfaces similar to that of the Galilean moons, we find that future direct imaging missions will need to achieve precisions of less than 0.1ppb. Should the necessary precision be achieved, future exoplanet observations could exploit similar observation schemes to deduce surface variations, determine rotation periods, and potentially infer surface composition.
- ID:
- ivo://CDS.VizieR/J/AJ/156/33
- Title:
- 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.
- ID:
- ivo://CDS.VizieR/J/AJ/127/3023
- Title:
- R magnitudes of Kuiper Belt object 2001QG298
- Short Name:
- J/AJ/127/3023
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- 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.
- ID:
- ivo://CDS.VizieR/J/A+A/569/A3
- Title:
- Rotational properties of TNOs
- Short Name:
- J/A+A/569/A3
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results for the short-term variability of Binary Trans-Neptunian Objects (BTNOs). We performed CCD photometric observations using the 3.58m Telescopio Nazionale Galileo (TNG), the 1.5m Sierra Nevada Observatory (OSN) telescope, and the 1.23m Centro Astronomico Hispano Aleman (CAHA) telescope at Calar Alto Observatory. We present results based on five years of observations and report the short-term variability of six BTNOs. Our sample contains three classical objects: (174567) 2003 MW_12_, or Varda, (120347) 2004 SB_60_, or Salacia, and 2002 VT_130_; one detached disk object: (229762) 2007 UK_126_; and two resonant objects: (341520) 2007 TY_430_ and (38628) 2000 EB_173_, or Huya. For each target, possible rotational periods and/or photometric amplitudes are reported. We also derived some physical properties from their lightcurves, such as density, primary and secondary sizes, and albedo. We compiled and analyzed a vast lightcurve database for Trans-Neptunian Objects (TNOs) including centaurs to determine the lightcurve amplitude and spin frequency distributions for the binary and non-binary populations. The mean rotational periods, from the Maxwellian fits to the frequency distributions, are 8.63+/-0.52h for the entire sample, 8.37+/-0.58h for the sample without the binary population, and 10.11+/-1.19h for the binary population alone. Because the centaurs are collisionally more evolved, their rotational periods might not be so primordial. We computed a mean rotational period, from the Maxwellian fit, of 8.86+/-0.58h for the sample without the centaur population, and of 8.64+/-0.67h considering a sample without the binary and the centaur populations. According to this analysis, regular TNOs spin faster than binaries, which is compatible with the tidal interaction of the binaries. Finally, we examined possible formation models for several systems studied in this work and by our team in previous papers.
- ID:
- ivo://CDS.VizieR/J/A+A/407/1139
- Title:
- RVB photometry of Kuiper-Belt object 1999 TD10
- Short Name:
- J/A+A/407/1139
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present photometric observations of the Kuiper-Belt object 1999 TD_10_ at different phase angles and for three different broad band filters (B, V and R). This object was observed with the Danish 1.54-m telescope of ESO in Chile during six different observing nights corresponding to a phase angle of 0.30, 0.37, 0.92, 3.43, 3.48 and 3.66{deg}. Extra observations were obtained in September 2002 with the VLT UT1/FORS1 combination to confirm that 1999 TD_10_ does not exhibit any cometary activity, and in October 2001 with the Sierra Nevada Observatory 1.50-m telescope in order to add relative magnitudes to improve the determination of the rotation period.
