Near-infrared spectroscopy of 133P/Elst-Pizarro

Comet 133P/Elst-Pizarro, known to be a main-belt asteroid with a cometary activity, was observed with the near-infrared integral field spectrograph SINFONI at the 8.2-m Very Large Telescope in J, H, and K bands during its 2007 perihelion passage. The goal of these observations was to attempt detection of water ice absorption bands. We present here the details of the data processing, the results of these observations, and our compositional modeling of the final spectrum. No water ice absorptions were detected within the noise of the spectrum but we show that this spectrum is compatible with a reasonable near-infrared albedo value of 7-10% and a mixture of water ice, black carbon, Tholin and silicates. This interpretation, nevertheless, is not unique.     

On the cometary nature of near-Earth asteroid 2003 EH1

Differential evolution of the orbits of near-Earth asteroid (NEA) 2003 EH1 and comet 96P/Machholz 1 under perturbing action of planets was investigated for the time interval of 28000 years. The similarity of the orbits was analyzed with the Southworth–Hawkins criterion D _SH. It has been shown that both the comet and the asteroid can be fragments of a nucleus of the same larger comet being a progenitor of the Quadrantid complex. A break-up of the parent comet apparently occurred approximately 9500 years ago. NEA 2003 EH1 is actually a dormant fragment of a nucleus of the parent comet. It was concluded that comet 96P/Machholz 1, NEA (186256) 2003 EH1 of the Amore group, and the Quadrantid meteorite swarm form a family of related objects.     

Space weathering and the interpretation of asteroid reflectance spectra

Lunar-style space weathering is well understood, but cannot be extended to asteroids in general. The two best studied Asteroids (433 Eros and 243 Ida) exhibit quite different space weathering styles, and neither exhibits lunar-style space weathering. It must be concluded that at this time the diversity and mechanisms of asteroid space weathering are poorly understood. This introduces a significant unconstrained variable into the problem of analyzing asteroid spectral data. The sensitivity of asteroid surface material characterizations to space weathering effects - whatever their nature - is strongly dependent upon the choice of remote sensing methodology. The effects of space weathering on some methodologies such as curve matching are potentially devastating and at the present time essentially unmitigated. On other methodologies such as parametric analysis (e.g., analyses based on band centers and band area ratios) the effects are minimal. By choosing the appropriate methodology(ies) applied to high quality spectral data, robust characterizations of asteroid surface mineralogy can be obtained almost irrespective of space weathering. This permits sophisticated assessments of the geologic history of the asteroid parent bodies and of their relationships to the meteorites. Investigations of the diversity of space weathering processes on asteroid surfaces should be a fruitful area for future efforts.     

Spectral observations of 19 weathered and 23 fresh NEAs and their correlations with orbital parameters

Results of our visible to near-infrared spectrophotometric observations of 41 near-Earth asteroids (NEAs) are reported. These moderate-resolution spectra, along with 14 previously published spectra from our earlier survey [Hicks, M.D., Fink, U., Grundy, W.M., 1998. Icarus 133, 69-78] show a preponderance of spectra consistent with ordinary chondrites (23 NEAs with this type of spectrum, along with 19 S-types and 13 in other taxonomic groups). There exists statistically significant evidence for orbit-dependent trends in our data. While S-type NEAs from our survey reside primarily in (1) Amor orbits or (2) Aten or Apollo orbits which do not cross the asteroid main-belt, the majority of objects with spectra consistent with ordinary chondrites in our survey are in highly eccentric Apollo orbits which enter the asteroid main-belt. This trend toward fresh, relatively unweathered NEAs with ordinary chondrite type spectra in highly eccentric Apollo orbits is attributed to one or a combination of three possible causes: (1) the chaotic nature of NEA orbits can easily result in high eccentricity orbits/large aphelion distances so that they can enter the collisionally enhanced environment in the main-belt, exposing fresh surfaces, (2) they have recently been injected into such orbits after a collision in the main-belt, or (3) such objects cross the orbits of several terrestrial planets, causing tidal disruption events that expose fresh surfaces.     

Dynamics of rotationally fissioned asteroids: Source of observed small asteroid systems

We present a model of near-Earth asteroid (NEA) rotational fission and ensuing dynamics that describes the creation of synchronous binaries and all other observed NEA systems including: doubly synchronous binaries, high-e binaries, ternary systems, and contact binaries. Our model only presupposes the Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) effect, “rubble pile” asteroid geophysics, and gravitational interactions. The YORP effect torques a “rubble pile” asteroid until the asteroid reaches its fission spin limit and the components enter orbit about each other (Scheeres, D.J. [2007]. Icarus 189, 370-385). Non-spherical gravitational potentials couple the spin states to the orbit state and chaotically drive the system towards the observed asteroid classes along two evolutionary tracks primarily distinguished by mass ratio. Related to this is a new binary process termed secondary fission - the secondary asteroid of the binary system is rotationally accelerated via gravitational torques until it fissions, thus creating a chaotic ternary system. The initially chaotic binary can be stabilized to create a synchronous binary by components of the fissioned secondary asteroid impacting the primary asteroid, solar gravitational perturbations, and mutual body tides. These results emphasize the importance of the initial component size distribution and configuration within the parent asteroid. NEAs may go through multiple binary cycles and many YORP-induced rotational fissions during their approximately 10 Myr lifetime in the inner Solar System. Rotational fission and the ensuing dynamics are responsible for all NEA systems including the most commonly observed synchronous binaries.     

Dynamical parameters of spacecraft motion near small celestial body

The paper considers how a spacecraft can be put into orbit around a small asteroid to function as its artificial moon. We study the general behavior of perturbations that affect the current coordinates of an orbiting spacecraft and estimate the perturbations caused by the main perturbing factors, i.e., (1) the irregular shape of an asteroid and (2) celestial bodies of the Solar System. With specific orbital parameters, a long-term targeted operation of a spacecraft can be actualized in a mission to the asteroid Apophis where the spacecraft will carry a radio beacon transponder.     

On the bulk density of the M-type asteroid 16 Psyche

Recent estimates of the bulk density of the largest M-type asteroid 16 Psyche (1.4 and 1.8 g/cm³) seem to be too low for asteroids of this type. The interpretation of such low densities for the asteroid 16 Psyche with its increased metal content led to estimates of its macroporosity of 70%. In the present paper, it has been shown that the extremely low density estimates are caused primarily by the usage of a very high value of the IRAS diameter of the asteroid (D = 264 km, which corresponds to an IRAS albedo of 0.10). The application of the more accurate polarimetric albedo (0.170) and diameter (213 km) of Psyche results in a bulk density of the asteroid of 3.3 ± 0.7 g/cm³. For a moderate asteroid macroporosity of 30–40%, this density even agrees with the 50% metal content and, therefore, removes both the contradiction with the radar data and the problems of the very low density and unlikely high porosity of the asteroid 16 Psyche.     

Results of Photometric Observations of Comet P/2019 LD2 at the Sanglokh Observatory

Solar System Research - The short-period comet P/2019 LD2 (Atlas) was discovered in June 2019. The object was originally classified as a Trojan asteroid, but was later included in the Jupiter...     

Physical studies of asteroids XXX: the asteroid 153 Hilda

The asteroid 153 Hilda was studied by photometric, spectroscopic and polarimetric observations during the apparition in 1992. The rotation period was determined to 5.11 hours with a lightcurve amplitude of 0.05 magnitudes. From our spectrum we find 153 Hilda to be of taxonomic type P. The polarization value of -0.23 at a phase angle of 3.2 degrees seems normal for a P-type asteroid. Long term integrations of the orbit shows that it is stable over time intervals of several million years.Partly based on observations collected at the European Southern Observatory, La Silla, Chile     

Search for the 3.4-μm C-H Spectral Bands on Low-Albedo Asteroids

A report of the detection of the C-H hydrocarbon band complex at 3.4 μm in an asteroid spectrum, by D. P. Cruikshank and R. H. Brown (1987, Science238, 183-184) is not confirmed by recent data of higher quality. Spectra of the same asteroid and six other low-albedo asteroids do not show this feature, which if present would indicate the presence of hydrocarbons and might link these asteroids with certain classes of carbonaceous meteorites.     

The shape of asteroids: Theoretical considerations

Theoretical consideration and observations by other authors indicate that small asteroids are capable of maintaining irregular shapes, notably the shape of a cigar and even of a dumb-bell. This paper presents a model which describes the changes in the shape of an asteroid due to collisions of smaller objects (meteoroids) with the asteroid. The following assumptions must be approximately valid: (1) collisions are not uncommon; (2) collisions between a (relatively) large asteroid and small objects (meteroids) are more common than collisions between asteroids; (3) the cumulative probability of the collision of a meteoroid on a point on the surface of an asteroid is proportional to the zenith angle of the horizon as seen by that point; (4) obliquities of all but the major asteroids are random, so that there is not a preferred side on which collisions occur; (5) a considerable percentage of collision ejecta achieves escape velocity; and (6) the rate of erosion of each point on the surface of an asteroid is proportional to the cumulative probability of collision.Generalized conclusions that are obtained from the computer running of the model indicate that both cigars and dumb-bells are possible outcomes. Sharp corners are smoothed away, the radius of curvature of rounded surfaces increases to the point of going from convexity to concavity, and flat surfaces develop into gentle concavities.Collisions of an asteroid with an object of sufficient size such that the impact causes the breakage of the asteroid or the formation of a large crater, are not discussed in this paper. Previous work, however, suggests that the crater will undergo geomorphological changes of different geometry than a similar crater on the Moon.     

The light curve of asteroid 2867 Steins measured by VIRTIS-M during the Rosetta fly-by

On 5 September 2008, the Rosetta spacecraft encountered the asteroid 2867 Steins on its way to the comet 67P/Churyumov-Gerasimenko. This was the first of two planned asteroid fly-bys performed by the probe, the second fly-by being with the much larger asteroid 21 Lutetia in July 2010. The VIRTIS imaging spectrometer (IFOV 0.250 mrad, overall spectral range 0.25-5.1 μm) onboard Rosetta acquired data of Steins already before the closest approach phase, when the target was spatially unresolved, in order to obtain a light curve of the asteroid in the infrared spectral range extending up to 5 μm, that was never explored before. The VIRTIS light curve campaign started at 11:30 UTC onboard time, when the spacecraft was about 221,377 km away from the target, and ended at 17:58 UTC, at a distance of 20,741 km away from Steins. During this timeframe, the solar phase angle of the asteroid was roughly constant, ranging from 38.2° to 36.3°.Assuming the most recent value derived for the rotational period of Steins (Lamy et al., 2008), the VIRTIS observations covered slightly more than one rotation of the asteroid. In this interval, VIRTIS collected 8 hyperspectral cubes where Steins was captured 119 times, both in the visual and in the infrared range. Given the low signal and the unresolved appearance of the source, for which the instrument was not designed, only a small subset of wavelengths turned out to be suitable to sample the light curve. Nevertheless, in both the VIS and NIR ranges we find a similar trend, with two different maxima and minima during one rotational period, and amplitudes consistent with the results in the visual range obtained in previous works, including the data set acquired by the OSIRIS camera onboard Rosetta. We also report the presence of a new broad feature centered at approximately 0.81-0.82 μm, which is seen in the visual data throughout the rotation of the asteroid.     

Asteroid spectroscopy: Progress and perspectives

Abstract The following discussion is divided into seven major sections. The first section outlines the scientific background and justification for asteroid studies in the context of understanding the formation and early evolution of the solar system. The second section briefly reviews the nature and distribution of the asteroid population. The third section discusses several major unresolved issues in asteroid and meteorite science which can potentially be addressed by asteroid remote sensing investigations. The fourth section outlines the nature and definition of the asteroid taxonomic classes. The fifth section summarizes the existing asteroidal spectral (and other remote sensing) data sets which are used to determine compositions and the techniques employed in the interpretation of such data. The sixth section explores the compositional meaning and diversity of these taxonomic classes and suggests meteoritic analogues for the taxonomic types. The seventh section describes the conclusions—or preliminary results—of several recent asteroid investigations which have focused on particular unsolved issues of the asteroid-meteorite relationship and of the early solar system properties. The final section discusses the overall conclusions and future directions.     

Rosetta target asteroid 2867 Steins: An unusual E‐type asteroid

Abstract— ESA's Rosetta spacecraft will fly by main‐belt asteroid 2867 Steins on September 5, 2008. We obtained new visible wavelength spectra of 2867 Steins on December 19, 2006 (UT), using the Palomar 5 m telescope and the facility Double Spectrograph. Two sets of spectra, taken ～3 h apart, one half of the rotation period for 2867 Steins, show it to be an E‐type asteroid. The asteroid displays a 0.50 μm feature that is considered diagnostic of the E(II) sub‐class, but is deeper than any previously observed E‐type. This feature is most likely due to the presence of oldhamite (CaS) on the asteroid's surface. Also, the observed Steins spectra are far redder than any other known E‐types. There is potential evidence for heterogeneity on hemispheric scales, one side of the asteroid appearing to be significantly redder than the other. No known recovered meteorite sample matches the unusual spectra of 2867 Steins, but the closest analog would be similar to an enstatite achondrite (aubrite).     

Mass distribution in the asteroid belt

The dependence of the cumulative number of numbered asteroids (up to 3720) on their absolute magnitude is investigated. The differential mass index k is derived from these relations for fainter asteroids. A steeper slope (2.2 < k < 2.4) is found in the four most populous asteroid familes (Flora, Koronis, Eos and Themis) and a flatter slope (1.3 < k < 1.6) for non-family asteroids. This indicates that there are two different asteroid populations in the asteorid belt. Total masses of the asteroid families may be greater than it is commonly accepted.     

Observations of asteroid occultations by the trailed-image method

The method of trailed CCD images for observations of asteroid occultations is described. This method was used to observe 9 asteroid occupations at the Lisnyky observational station in 2006 with the telescope AZT-8 (D= 0.7m and F= 2.8m) equipped by the CCD ST-8 XME. In the case of occultation of the star TYC 0587-00209-1U by the asteroid 76 Freia in November 4, 2006, the distance between the asteroid center and the star, as well as the time of asteroid occultation were determined. The size of asteroid 76 Freia is determined assuming that its shape is spherically symmetric. In other cases, the minimal distances between the asteroid center and the star are determined. The method makes it possible to observe asteroid occultations with high time resolution.     

On three types of fragmentation processes observed in the asteroid belt

From comparison of the mass ratio and velocity dispersion between the asteroid family members, we find that the fragmentation processes in the asteroid belt could be generally classified into three types: (a) surface cratering; (b) spallation; and (c) complete breakup as observed in the laboratory hypervelocity impact experiments. Whether there is ongoing accretion for large bodies like Ceres, as an additional type of collision process, is still an open question to be answered by further study.     

Astrometry and photometry of asteroid (308635) 2005 YU55

Astrometric and photometric observations of asteroid (308635) 2005 YU55 were carried out at the computer-aided ZA-320M and MTM-500M telescopes of the Pulkovo observatory in the period of its closest approach to the Earth, from November 9 to 20, 2011. The new orbit of the asteroid changed after its close approach to the Earth was determined. From this orbit, a close approach to Venus on January 19, 2029, was precalculated, and the distance at the closest approach—359000 km—was estimated. From the analysis of the acquired photometric data, the axial rotation period of the asteroid was more accurately determined, and it amounted to 16.3 ± 0.4 h. The color indexes of the asteroid, B-V, V-R, and R-I, were estimated, which allowed the taxonomic class of the asteroid, B, to be determined from them. In addition, from our photometric observations of the asteroid, the earlier unknown change in its brightness with a period of 0.9–1.2 h was detected; the cause of this change has not been completely studied yet.     

The Processing and Classification for the Spectra of Six Comets

In order to explore the relationship between comets and asteroids, the spectra of six comets, including 78P, C/2009 P1, 49P, C/2010 G2, C/2010 S1, and C/2011 F1, have been observed with the 2.16 m telescope at the Xinglong Observing Station of National Astronomical Observatories. At the same time, the spectra of some sun-like stars are also observed. The IRAF (Image Reduction and Analysis Facility) software is used to process the obtained spectra, and to obtain the relative re?ectance spectra of the six comets. Then, they are compared with the 24 asteroid spectral types of the Bus-DeMeo taxonomy to derive the spectral distances of these comets. According to the order of the calculated spectral distances, the details of the re?ectance spectra, as well as the results of the K-S test, the asteroid spectral types which are most close to the spectra of these comets are ?nally determined.     

Is 1220 Crocus a precessing,binary asteroid?

Photoelectric observations of asteroid 1220 Crocus (an Eos family member) show evidence for two distinct periods in its light variation: 30.7 days and 7.90 hr. The lightcurve amplitudes are 0.87 and 0.15 mag, respectively. The shorter period variation appears to be modulated over the longer period. Two periods are possible for a rigid body only if it is in a state of precession. The observations are shown to be compatible with a body in a forced precession state. This result leads us to hypothesize the existence of a satellite of Crocus as the source of the external torque. Calculations are presented which show that there are in fact dynamically possible “binary asteroid” solutions consistent with the observations. More photoelectric and perhaps direct (space telescope) observations are needed to resolve the true nature of this asteroid.