The Atacama Cosmology Telescope: A Search for Planet 9

We use Atacama Cosmology Telescope (ACT) observations at 98 GHz (2015–2019), 150 GHz (2013–2019), and 229 GHz (2017–2019) to perform a blind shift-and-stack search for Planet 9. The search explores distances from 300 au to 2000 au and velocities up to 6.′3 per year, depending on the distance (r). For a 5 Earth-mass Planet 9 the detection limit varies from 325 au to 625 au, depending on the sky location. For a 10 Earth-mass planet the corresponding range is 425 au to 775 au. The predicted aphelion and most likely location of the planet corresponds to the shallower end of these ranges. The search covers the whole 18,000 square degrees of the ACT survey. No significant detections are found, which is used to place limits on the millimeter-wave flux density of Planet 9 over much of its orbit. Overall we eliminate roughly 17% and 9% of the parameter space for a 5 and 10 Earth-mass Planet 9, respectively. These bounds approach those of a recent INPOP19a ephemeris-based analysis, but do not exceed it. We also provide a list of the 10 strongest candidates from the search for possible follow-up. More generally, we exclude (at 95% confidence) the presence of an unknown solar system object within our survey area brighter than 4–12 mJy (depending on position) at 150 GHz with current distance 300 au < r < 600 au and heliocentric angular velocity 1 .′ 5 yr − 1 < v · 500 au r < 2 .″ 3 yr − 1 , corresponding to low-to-moderate eccentricities. These limits worsen gradually beyond 600 au, reaching 5–15 mJy by 1500 au.

Gaia spectroscopic view of the asteroid main belt and beyond

&lt;div class=&quot;&quot;&gt;Asteroids reflectance spectra in the visible light will be one of the novel products of the Gaia Data Release 3 (DR3). These spectra are produced from Gaia observations obtained by means of the blue and red photometers &amp;#8212; the so-called BP and RP, respectively. We will review the strategy adopted to produce asteroid reflectance spectra from BP-RP data, focusing on the choice of spectro-photometric calibrations computed taking into account solar system object astrometry and suitable lists of solar-analog stars.&lt;/div&gt; &lt;div class=&quot;&quot;&gt;&amp;#160;&lt;/div&gt; &lt;div class=&quot;&quot;&gt;Our preliminary investigation shows that we will be able to obtain reflectance spectra for asteroids as small as some km in the main belt, by exploiting the fact that each object has been observed multiple times by Gaia. We will show the capability of Gaia to probe the detailed compositional gradient of the main belt down to small sizes and to study correlations between spectral classes and other asteroid physical parameters, such as albedo and size.&lt;/div&gt; &lt;div class=&quot;&quot;&gt;&amp;#160;&lt;/div&gt; &lt;div class=&quot;&quot;&gt;Concerning the brightest asteroids, we expect to have substantial signal at wavelengths shorter than 450 nm, allowing Gaia to examine this region of the spectrum that has been poorly investigated by ground-based asteroid spectroscopic surveys. This region is characterised by the presence of a reflectance downturn that is diagnostic for the composition of classes of primitive asteroids, for instance those including the parent bodies of carbonaceous chondrites. These asteroids may have played an important role for the delivery of prebiotic compounds to Earth during the early phases of solar system' s history and, as such, are at the center of attention of the planetary science community.&amp;#160;&lt;/div&gt;

The physical and dynamical characteristics of the asteroid 4940 Polenov

The asteroid (1986 QY4) 4940 Polenov is the first Solar system object whose 3D shape is determined using the observations from the newly built Astronomical Station Vidojevica (ASV). Here we present the results of photometric observations for Polenov, gathered from the ASV, and from the Bulgarian National Astronomical Observatory (BNAO) Rozhen, during 2014, 2019 and 2020 apparitions. Polenov is a 17.8km object located in the outer part of the main belt and belongs to the asteroid family Themis. We have determined the lightcurves, the synodic period of 4.161?0.001 h, as well as the solution for the shape and spin axis. Using the lightcurve inversion method, the combination of our lightcurves and the sparse data from ATLAS{HKO and ATLAS-MLO, we also found the sidereal period, indicating a retrograde rotation of the asteroid, with two possible mirrored pole solutions. The ratio of the largest to smallest reecting surface is about 1.4. In addition, we studied the dynamical properties of the asteroid and obtained a long stability time that exceeds 0.4 Gyrs.

Asteroid (16) Psyche’s primordial shape: A possible Jacobi ellipsoid

Context. 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 > 200 km) 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. Aims. 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. Methods. 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. Results. Our 3D shape along with existing mass estimates imply a density of 4.20 ± 0.60 g 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 ∼4.2 h, while also creating the imaged depressions. Conclusions. 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 26Al.

Solar System Object Image Search: A precovery search engine

While regular astronomical image archive searches can find images at a fixed location, they cannot find images of moving targets such as asteroids or comets. The Solar System Object Image Search (SSOIS) at the Canadian Astronomy Data Centre allows users to search for images of moving objects, allowing precoveries. SSOIS accepts as input either an object designation, a list of observations, a set of orbital elements, or a user-generated ephemeris for an object. It then searches for observations of that object over a range of dates. The user is then presented with a list of images containing that object from a variety of archives. Initially created to search the CFHT MegaCam archive, SSOIS has been extended to other telescopes including Gemini, Subaru/SuprimeCam, WISE, HST, the SDSS, AAT, the ING telescopes, the ESO telescopes, and the NOAO telescopes (KPNO/CTIO/WIYN), for a total of 24.5 million images. As the Pan-STARRS and Hyper Suprime-Cam archives become available, they will be incorporated as well. The SSOIS tool is located on the web at http://www.cadc-ccda.hia-iha.nrc-cnrc.gc.ca/en/ssois/.