Spectral evolution of dark asteroid surfaces induced by space weathering over a decade

The surface of airless bodies like asteroids in the Solar System are known to be affected by space weathering. Experiments simulating space weathering are essential for studying the effects of this process on meteorite samples, but the problem is that the time spent to reproduce space weathering in these experiments is billions of times shorter than the actual phenomenon. In December 2010, the T-type asteroid 596 Scheila underwent a collision with a few-tens-of-meters impactor. A decade later, there is an opportunity to study how the surface layer of this asteroid is being altered by space weathering after the impact. To do so, we performed visible spectrophotometric and near-infrared spectroscopic observations of 596 Scheila. The acquired spectrum is consistent with those observed shortly after the 2010 impact event within the observational uncertainty range. This indicates that the surface color of dark asteroids is not noticeably changed by space weathering over a 10-year period. This study is the first to investigate color changes due to space weathering on an actual asteroid surface in the Solar System. Considering that fresh layers are regularly created on asteroid surfaces by collisions, we suggest a genetic link between D/T-type and dark (low albedo) X-complex asteroids and very red objects such as 269 Justitia, 732 Tjilaki (and 203 Pompeja). New observations show that 203 Pompeja has a X-type-like surface, with some local surface areas exhibiting a very red spectrum.Comment: 16 pages, 9 figures, 2 tables, Accepted for publication in ApJ Letter

Spectral Type and Geometric Albedo of (98943) 2001 CC21, the Hayabusa2# Mission Target

We conducted optical polarimetry and near-infrared spectroscopy of JAXA's Hayabusa2# mission target, (98943) 2001 CC21, in early 2023. Our new observations indicated that this asteroid has a polarimetric inversion angle of ~21 deg, absorption bands around 0.9 and 1.9 um, and a geometric albedo of 0.285 +- 0.083. All these features are consistent with those of S-type but inconsistent with L-type. Based on this evidence, we conclude that JAXA's Hayabusa2# spacecraft will explore an S-type asteroid with albedo and size (0.42-0.56 km when we assume the absolute magnitude of 18.6) similar to (25143) Itokawa.Comment: 5 pages, 3 figures, Submitted to MNRAS Letter on 2023 April

Thermal radiation pressure as a possible mechanism for losing small particles on asteroids

Context. Recent observations of dust ejections from active asteroids, including (3200) Phaethon, have drawn considerable interest from planetary astronomers studying the generation and removal of small dust particles on asteroids. Aims. In this work, we aim to investigate the importance of thermal radiation pressure from asteroid regolith (AR) acting on small dust particles over the surface of the AR. In particular, we aim to understand the role of thermal radiation in the near-Sun environment. Methods. We describe the acceleration of particles over the AR within the radiation fields (direct solar, reflected (scattered) solar, and thermal radiation) in addition to the asteroid’s rotation and gravitational field. Mie theory is used because the particles of interest have sizes comparable to thermal wavelengths (~1–100 μm), and thus the geometric approximation is not applicable. A new set of formalisms is developed for the purpose. Results. We find that the acceleration of particles with spherical radius ≲1 μm to ~10 μm is dominated by the thermal radiation from the AR when the asteroid is in the near-Sun environment (heliocentric distance rh ≲ 0.8 au). Under thermal radiation dominance, the net acceleration is towards space, that is, outwards from the AR. This outward acceleration is the strongest for particles of ~1 μm in radius, regardless of other parameters. A preliminary trajectory integration using the Phaethon-like model shows that such particles escape from the gravitational field within about 10 min. Our results are consistent with the previous observational studies on Phaethon in that the ejected dust particles have a spherical radius of ~1 μm

maximtrp/scikit-posthocs: scikit-posthocs: v0.8.1

<p>This release fixes Conover's post hoc test for unreplicated blocked data (#63, thanks to @liborak).</p&gt

maximtrp/scikit-posthocs: scikit-posthocs: v0.8.0

<p>This release includes a number of features, enhancements and fixes:</p> <ul> <li>critical difference diagrams (see <a href="https://scikit-posthocs.readthedocs.io/en/latest/generated/scikit_posthocs.critical_difference_diagram.html"><code>critical_difference_diagram</code></a>) are implemented (thanks to @pedroilidio and @chengmingbo)</li> <li><code>outliers_gesd</code> code improved (thanks to @ysBach)</li> <li>increased abs tolerance for wilcoxon test (<code>test_posthoc_wilcoxon</code>)</li> <li>minor updates and fixes</li> </ul&gt

A polarimetric study of asteroids in comet-like orbits

International audienceContext. Asteroids in comet-like orbits (ACOs) consist of asteroids and dormant comets. Due to their similar appearance, it is challenging to distinguish dormant comets from ACOs via general telescopic observations. Surveys for discriminating dormant comets from the ACO population have been conducted via spectroscopy or optical and mid-infrared photometry. However, they have not been conducted through polarimetry. Aims: We conducted the first polarimetric research of ACOs. Methods: We conducted a linear polarimetric pilot survey for three ACOs: (944) Hidalgo, (3552) Don Quixote, and (331471) 1984 QY1. These objects are unambiguously classified into ACOs in terms of their orbital elements (i.e., the Tisserand parameters with respect to Jupiter TJ significantly less than 3). Three ACOs were observed by the 1.6 m Pirka Telescope from UT 2016 May 25 to UT 2019 July 22 (13 nights). Results: We found that Don Quixote and Hidalgo have polarimetric properties similar to comet nuclei and D-type asteroids (optical analogs of comet nuclei). However, 1984 QY1 exhibited a polarimetric property consistent with S-type asteroids. We conducted a backward orbital integration to determine the origin of 1984 QY1, and found that this object was transported from the main belt into the current comet-like orbit via the 3:1 mean motion resonance with Jupiter. Conclusions: We conclude that the origins of ACOs can be more reliably identified by adding polarimetric data to the color and spectral information. This study would be valuable for investigating how the ice-bearing small bodies distribute in the inner Solar System. Processed data (FITS) and lightcurves (data under Fig. B.1) are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/658/A158</A