Orbital, spin state and thermophysical characterization of near-Earth asteroid (3200) Phaethon

The near-Earth asteroid (3200) Phaethon is an intriguing object: its perihelion is only at 0.14 au and is associated with the Geminid meteor stream. We aim to use all available disk-integrated optical data to derive reliable convex shape model of Phaethon. By interpreting the available space- and ground-based thermal infrared data and Spitzer spectra using a thermophysical model, we also aim to further constrain its size, thermal inertia, and visible geometric albedo. We apply the convex inversion method to the new optical data obtained by six instruments together with the already existing observations. The convex shape model is then used as an input for the thermophysical modeling. We also study the long-term stability of Phaethon’s orbit and spin axis by a numerical orbital and rotation-state integrator We present a new convex shape model and rotational state of Phaethon – sidereal rotation period of 3.603958(2) h and ecliptic coordinates of the preferred pole orientation of (319◦ , −39◦) with a 5◦ uncertainty. Moreover, we derive its size (D=5.1±0.2 km), thermal inertia (Γ=600±200 J m-2s -1/2K -1), geometric visible albedo (pV=0.122±0.008), and estimate the macroscopic surface roughness. We also find that the Sun illumination at the perihelion passage during past thousands of years is not connected to a specific area on the surface implying non-preferential heating

Shape model and spin state of non-principal axis rotator (5247) Krylov

Context. The study of non-principal axis (NPA) rotators can provide important clues to the evolution of the spin state of asteroids. However, very few studies to date have focused on NPA-rotating main belt asteroids (MBAs). One MBA known to be in an excited rotation state is asteroid (5247) Krylov. Aims. By using disk-integrated photometric data, we construct a physical model of (5247) Krylov including shape and spin state. Methods. We applied the light curve convex inversion method employing optical light curves obtained by using ground-based telescopes in three apparitions during 2006, 2016, and 2017, along with infrared light curves obtained by the Wide-field Infrared Survey Explorer satellite in 2010. Results. Asteroid (5247) Krylov is spinning in a short axis mode characterized by rotation and precession periods of 368.7 and 67.27 h, respectively. The angular momentum vector orientation of Krylov is found to be λL = 298° and βL = −58°. The ratio of the rotational kinetic energy to the basic spin-state energy E∕E0 ≃ 1.02 shows that the (5247) Krylov is about 2% excited state compared to the principal axis rotation state. The shape of (5247) Krylov can be approximated by an elongated prolate ellipsoid with a ratio of moments of inertia of Ia : Ib : Ic = 0.36 : 0.96 : 1. This is the first physical model of an NPA rotator among MBAs. The physical processes that led to the current NPA rotation cannot be unambiguously reconstructed

Spin rates of V-type asteroids

Context. Basaltic V-type asteroids play a crucial role in studies of Solar System evolution and planetesimal formation. Comprehensive studies of their physical, dynamical, and statistical properties provide insight into these processes. Thanks to wide surveys, currently there are numerous known V-type and putative V-type asteroids, allowing a detailed statistical analysis. Aims. Our main goal is to analyze I corrected for US language conventions in this paper the currently available large sample of V-type spin rates, to find signatures of the non-gravitational Yarkovsky–O’Keefe–Radzievskii–Paddack (YORP) effect among the different V-type populations, and to estimate the spin barrier and critical density for V-type asteroids. Our intention is to increase the pool of information about the intriguing V-types. Methods. We collected rotational periods from the literature for spectrally confirmed V-types, putative V-types, and Vesta family members. Through spectroscopic observations we confirmed their taxonomic type and verified the high confirmation rates of the putative V-types. We combined the collected periods with periods estimated in this manuscript and produced rotational frequency distributions. We determined the spin barrier in the frequency–light curve amplitude space for V-type asteroids. Results. We analyzed rotational periods of 536 asteroids in our sample. As expected, due to the small size of the objects analyzed, the frequency distributions for the Vesta family and the V-types outside the family are inconsistent with a Maxwellian shape. The Vesta family shows an excess of slow-rotators. V-types outside the family show an excess of both slow and fast rotators. Interestingly, we found that the population of V-types outside the Vesta family shows a significant excess of fast rotators compared to the Vesta family. The estimated critical density for V-type asteroids exceeds ρc = 2.0 g cm−3, which surpasses the previous estimates. Conclusions. We demonstrated that V-type asteroids have been influenced by the thermal radiation YORP effect and that their critical spin rate is higher than for C-type asteroids. The population of V-types outside the Vesta family shows a significant excess of fast rotators compared to the Vesta family. We hypothesize that the objects that evolved from the Vesta family though the Yarkovsky drift are also more susceptible to the YORP effect. Objects for which YORP has not yet had enough time to act and those that are more YORP resistant will be left in the family, which explains the relatively small proportion of fast rotators being left. The YORP timescale must thus be similar to the migration timescale for those objects

The EURONEAR Lightcurve Survey of Near Earth Asteroids

International audienc

Physical modeling of triple near-Earth asteroid (153591) 2001 SN 263 from radar and optical light curve observations

We report radar observations (2380-MHz, 13-cm) by the Arecibo Observatory and optical light curves observed from eight different observatories and collected at the Ondrejov Observatory of the triple near-Earth asteroid system (153591) 2001 SN263. The radar observations were obtained over the course of ten nights spanning February 12-26, 2008 and the light curve observations were made throughout January 12 - March 31, 2008. Both data sets include observations during the object's close approach of 0.06558 AU on February 20th, 2008. The delay-Doppler images revealed the asteroid to be comprised of three components, making it the first known triple near-Earth asteroid. Only one other object, (136617) 1994 CC is a confirmed triple near-Earth asteroid.We present physical models of the three components of the asteroid system. We constrain the primary's pole direction to an ecliptic longitude and latitude of (309 °, - 80 °) ± 15 ° . We find that the primary rotates with a period 3.4256 ± 0.0002 h and that the larger satellite has a rotation period of 13.43 ± 0.01 h , considerably shorter than its orbital period of approximately 6 days. We find that the rotation period of the smaller satellite is consistent with a tidally locked state and therefore rotates with a period of 0.686 ± 0.002 days (Fang et al. [2011]. Astron. J. 141, 154-168). The primary, the larger satellite, and the smaller satellite have equivalent diameters of 2.5 ± 0.3 km , 0.77 ± 0.12 km , 0.43 ± 0.14 km and densities of 1.1 ± 0.2 g /cm3, 1.0 ± 0.4 g /cm3, 2.3 ± 1.3 g /cm3 , respectively