► Limits on the physical properties of Asteroid 2008
TC
3 are presented based on its shape model and Almahata Sitta meteorite measurements. ► Results indicate the mass of Asteroid 2008 TC
3 to be ...probably below 20
×
10
3
kg. ► This estimate is significantly lower compared to previous studies.
The density measurements of Almahata Sitta ureilites reveal a bulk density of ∼3.1
g/cm
3. This value, together with the 2008 TC
3 asteroid shape model and albedo, was used to estimate the asteroid’s mass. Based on the study of recovered meteorites and atmospheric entry observations Asteroid 2008 TC
3 is compositionally heterogeneous and of low mechanical strength. Thus we consider the presence of significant macroporosity likely, lowering asteroid’s bulk density compared to that of the Almahata Sitta ureilites. Most realistic albedos lie in a range of 0.09-0.2 and the presence of significant macroporosity leads to mass estimates below 20
×
10
3
kg, which is lower than previously estimated. The presence of a non-ureilitic fraction and space weathering may affect the albedo and also influence the mass estimates. However, from current data it is not possible to quantify this effect.
Aims. This paper reports on a search for new classical nova candidates in the M 81 galaxy based on archival, as well as recent, new images. Methods. We used images from 1999–2007 to search for ...optical transients in M 81. The positions of the identified classical nova candidates were used to study their spatial distribution. Kolmogorov-Smirnov test (KS) and bottom-to-top (BTR) ratio diagnostic were used to analyze the nova candidate distribution and differentiate between the disk and the bulge populations. Results. In total, 49 classical nova candidates were discovered. In this study, we present the precise positions and photometry of these objects, plus the photometry of an additional 9 classical nova candidates found by Neill & Shara (2004, AJ, 127, 816). With our large sample, we find a different spatial distribution of classical nova candidates when compared to the results of earlier studies. Also, an extraordinarily bright nova was found and studied in detail.
We explore the effects of the 2029 Earth encounter on asteroid (99942) Apophis' non-principal axis spin state, leveraging refined orbit, spin state, and inertia information provided by more recent ...optical and radar observations. Propagating the asteroids' coupled orbit and rigid body attitude dynamics through the flyby, we present the range of possible post-flyby spin states. These spin state distributions will be valuable for planning Apophis observation campaigns and spacecraft missions, most notably OSIRIS-APEX. The simulations indicate that gravitationally induced changes to the asteroid's tumbling periods and rotational angular momentum direction (pole) will likely be significant and measurable. For the current spin state and inertia estimates and their uncertainties, Apophis is likely to remain in a short axis mode (SAM) tumbling state but its effective spin rate could halve or double. Its pole is likely to shift by 10 degrees or more and increase in longitude while moving closer to the ecliptic plane. These spin state changes are very sensitive to the asteroid's close approach attitude and mass distribution. With ground-based tracking of the asteroid's spin state through the encounter, this sensitivity will help refine mass distribution knowledge. We also discuss the implications of this abrupt spin state alteration for Apophis' Yarkovsky acceleration and geophysical properties, identifying possible pathways for surface and internal changes, most notably if Apophis is a contact binary. Comparison of the pre and post-flyby inertia estimates obtained from the ground-based observations will help assess the extent of possible geophysical changes.
Dynamical simulations of the coupled rotational and orbital dynamics of binary near-Earth asteroid 66391 (1999 KW4) suggest that it is excited as a result of perturbations from the Sun during ...perihelion passages. Excitation of the mutual orbit will stimulate complex fluctuations in the orbit and rotation of both components, inducing the attitude of the smaller component to have large variation within some orbits and to hardly vary within others. The primary's proximity to its rotational stability limit suggests an origin from spin-up and disruption of a loosely bound precursor within the past million years.
Photometric observations of 1999 HF sub(1) reveal that its lightcurve has two components of low amplitudes (0.10-0.12 mag) and different periods (2.3191 and 14.02 h). It is likely another binary ...near-Earth asteroid; its lower limit on the secondary-to-primary-diameter ratio is approximately 0.2, the radius of the mutual orbit is (2.0 plus or minus 0.3) x the effective primary diameter, the primary's bulk density is >2.0 g/cm super(3), and it belongs to the E/M/P taxonomic class.
Photometric observations of 1999 HF(1) reveal that its light curve has two components of low amplitudes (0.10-0.12 mag) and different periods (2.3191 and 14.02 h). It is likely another binary ...near-Earth asteroid; its lower limit on the secondary-to-primary-diameter ratio is = 0.2, the radius of the mutual orbit is (2.0 +/- 0.3) x the effective primary diameter, the primary's bulk density is > 2.0 g/cubic cm, and it belongs to the E/M/P taxonomic class. (Author)
We obtained thorough photometric observations of two binary near-Earth asteroids (66391) Moshup = 1999 KW4 and (88710) 2001 SL9 taken from 2000 to 2019 and derived physical and dynamical properties ...of the binary systems. We found that the data for 1999 KW4 are inconsistent with a constant orbital period and we obtained unique solution with a quadratic drift of the mean anomaly of the satellite of -0.65 +/- 0.16 deg/yr2 (all quoted uncertainties are 3sigma). This means that the semimajor axis of the mutual orbit of the components of this binary system increases in time with a mean rate of 1.2 +/- 0.3 cm/yr. The data for 2001 SL9 are also inconsistent with a constant orbital period and we obtained two solutions for the quadratic drift of the mean anomaly: 2.8 +/- 0.2 and 5.2 +/- 0.2 deg/yr2, implying that the semimajor axis of the mutual orbit of the components decreases in time with a mean rate of -2.8 +/- 0.2 or -5.1 +/- 0.2 cm/yr for the two solutions, respectively. The expanding orbit of 1999 KW4 may be explained by mutual tides interplaying with binary YORP (BYORP) effect (McMahon and Scheeres, 2010). However, a modeling of the BYORP drift using radar-derived shapes of the binary components predicted a much higher value of the orbital drift than the observed one. It suggests that either the radar-derived shape model of the secondary is inadequate for computing the BYORP effect, or the present theory of BYORP overestimates it. It is possible that the BYORP coefficient has instead an opposite sign than predicted; in that case, the system may be moving into an equilibrium between the BYORP and the tides. In the case of 2001 SL9, the BYORP effect is the only known physical mechanism that can cause the inward drift of its mutual orbit.
We studied 93 asteroid pairs. We estimated times elapsed since separation of pair members that are between 7*10^3 and a few 10^6 yr. We derived the rotation periods for all the primaries and a sample ...of secondaries. We derived the absolute magnitude differences of the asteroid pairs that provide their mass ratios. We refined their WISE geometric albedos and estimated their taxonomic classifications. For 17 pairs, we determined their pole positions. In 2 pairs where we obtained the spin poles for both components, we saw the same sense of rotation for both components and constrained the angles between their original spin vectors at the time of their separation. We found that the primaries of 13 pairs are actually binary or triple systems, i.e., they have one or two bound secondaries (satellites). As by-product, we found 3 new young asteroid clusters (each of them consisting of three known asteroids on highly similar orbits). We compared the obtained asteroid pair data with theoretical predictions and discussed their implications. We found that 86 of the 93 studied pairs follow the trend of primary rotation period vs mass ratio that was found by Pravec et al. (2010). Of the 7 outliers, 3 appear insignificant (may be due to our uncertain or incomplete knowledge), but 4 are high mass ratio pairs that were unpredicted by the theory of asteroid pair formation by rotational fission. We discuss a (remotely) possible way that they could be created by rotational fission of flattened parent bodies followed by re-shaping of the formed components. The 13 pairs with binary primaries are particularly interesting systems that place important constraints on formation and evolution of asteroid pairs. We present two hypotheses for their formation: The pairs having both bound and unbound secondaries could be `failed asteroid clusters', or they could be formed by a cascade primary spin fission process.
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