Abstract
We present the size distribution for the Hilda asteroid group using optical survey data obtained by the 8.2 m Subaru Telescope with the Hyper Suprime-Cam. Our unbiased sample consists of 91 ...Hilda asteroids (Hildas) down to 1 km in diameter. We found that the Hildas’ size distribution can be approximated by a single-slope power law in the ∼1−10 km diameter range with the best-fit power-law slope of
α
= 0.38 ± 0.02 in the differential absolute magnitude distribution. Directly comparing the size distribution of Hildas with that of the Jupiter Trojans measured from the same data set indicates that the two size distributions are similar to each other within a diameter of ∼10 km, while these shapes are distinguishable from that of main-belt asteroids. The results suggest that Hildas and Jupiter Trojans share a common origin and have a different formation environment from main-belt asteroids. The total number of the Hilda population larger than 2 km in diameter is estimated to be ∼1 × 10
4
based on the size distribution, which is less than that of the Jupiter Trojan population by a factor of about five.
We present an analysis of survey observations of the trailing L5 Jupiter Trojan swarm using the wide-field Hyper Suprime-Cam CCD camera on the 8.2 m Subaru Telescope. We detected 189 L5 Trojans from ...our survey that covered about 15 deg2 of sky with a detection limit of mr = 24.1 mag, and selected an unbiased sample consisting of 87 objects with absolute magnitude 14 ≲ Hr ≤ 17 corresponding to diameter 2 km ≲ D ≲ 10 km for analysis of size distribution. We fit their differential magnitude distribution to a single-slope power law with an index α = 0.37 ± 0.01, which corresponds to a cumulative size distribution with an index of b = 1.85 ± 0.05. Combining our results with data for known asteroids, we obtained the size distribution of L5 Jupiter Trojans over the entire size range for 9 ≲ HV ≤ 17, and found that the size distributions of the L4 and L5 swarms agree well with each other for a wide range of sizes. This is consistent with the scenario that asteroids in the two swarms originated from the same primordial population. Based on the above results, the ratio of the total number of asteroids with D ≥ 2 km in the two swarms is estimated to be NL4/NL5 = 1.40 ± 0.15, and the total number of L5 Jupiter Trojans with D ≥ 1 km is estimated to be 1.1 × 105 by extrapolating the obtained distribution.
Abstract
We performed a wide-field survey observation of small asteroids using the Hyper Suprime-Cam installed on the 8.2 m Subaru Telescope. We detected more than 3000 main-belt asteroids with a ...detection limit of 24.2 mag in the
r
-band, which were classified into two groups (bluish C-like and reddish S-like) by the
g
–
r
color of each asteroid and obtained size distributions of each group. We found that the shapes of the size distributions of asteroids with C-like and S-like colors agree with each other in the size range of 0.4–5 km in diameter. Assuming the asteroid population in this size range is under collision equilibrium, our results indicate that compositional difference hardly affects the size dependence of impact strength, at least for the size range between several hundred meters and several kilometers. This size range corresponds to the size range of “spin barrier,” an upper limit observed in the rotation rate distribution. Our results are consistent with the view that most asteroids in this size range have a rubble-pile structure.
ABSTRACT
Beyond the snow line of protoplanetary discs and inside the dense core of molecular clouds, the temperature of gas is low enough for water vapour to condense into amorphous ices on the ...surface of pre-existing refractory dust particles. Recent numerical simulations and laboratory experiments suggest that condensation of the vapour promotes dust coagulation in such a cold region. However, in the numerical simulations, cohesion of refractory materials is often underestimated, while in the laboratory experiments, water vapour collides with surfaces at more frequent intervals compared to the real conditions. Therefore, to re-examine the role of water ice in dust coagulation, we carry out systematic investigation of available data on coagulation of water-ice particles by making full use of appropriate theories in contact mechanics and tribology. We find that the majority of experimental data are reasonably well explained by lubrication theories, owing to the presence of a quasi-liquid layer (QLL). Only exceptions are the results of dynamic collisions between particles at low temperatures, which are, instead, consistent with the JKR theory, because QLLs are too thin to dissipate their kinetic energies. By considering the vacuum conditions in protoplanetary discs and molecular clouds, the formation of amorphous water ice on the surface of refractory particles does not necessarily aid their collisional growth as currently expected. While crystallization of water ice around but outside the snow line eases coagulation of ice-coated particles, sublimation of water ice inside the snow line is deemed to facilitate coagulation of bare refractory particles.
This study investigates the influence of surface treatment of contaminated lithium disilicate and leucite glass ceramic restorations on the bonding efficacy of universal adhesives. Lithium disilicate ...and leucite glass ceramics were contaminated with saliva, and then cleaned using distilled water (SC), or 37% phosphoric acid (TE), or hydrofluoric acid (CE). Specimens without contamination served as controls. The surface free energy was determined by measuring the contact angles formed when the three test liquids were placed on the specimens. Bond strengths of the universal adhesives were also measured. Saliva contamination and surface treatment of ceramic surfaces significantly influenced the surface free energy. The bond strengths of universal adhesives were also affected by surface treatment and the choice of adhesive materials. Our data suggest that saliva contamination of lithum disilicate and leucite glass ceramics significantly impaired the bonding of the universal adhesives, and reduced the surface free energy of the ceramics.
Asteroid systems such as binaries and pairs are indicative of the physical properties and dynamical histories of small solar system bodies. Although numerous observational and theoretical studies ...have been carried out, the formation mechanism of asteroid pairs is still unclear, especially for near-Earth asteroid (NEA) pairs. We conducted a series of optical photometric and polarimetric observations of a small NEA 2010 XC15 in 2022 December to investigate its surface properties. The rotation period of 2010 XC15 is possibly a few to several dozen hours and the color indices of 2010 XC15 are derived as g − r = 0.435 ± 0.008, r − i = 0.158 ± 0.017, and r − z = 0.186 ± 0.009 in the Pan-STARRS system. The linear polarization degrees of 2010 XC15 are a few percent at the phase angle range of 58°–114°. We found that 2010 XC15 is a rare E-type NEA on the basis of its photometric and polarimetric properties. Taking the similarity of not only physical properties but also dynamical integrals and the rarity of E-type NEAs into account, we suppose that 2010 XC15 and 1998 WT24 are of common origin (i.e., an asteroid pair). These two NEAs are the sixth NEA pair and first E-type NEA pair ever confirmed, possibly formed by rotational fission. We conjecture that the parent body of 2010 XC15 and 1998 WT24 was transported from the main belt through the ν6 resonance or Hungaria region.
ABSTRACT
We report on the first polarimetric study of (3200) Phaethon, the target of JAXA’s DESTINY+ mission, in the negative branch to ensure its anhydrous nature and to derive an accurate geometric ...albedo. We conducted observations at low phase angles (Sun-target-observer angle, α = 8.8–32.4°) from 2021 October to 2022 January and found that Phaethon has a minimum polarization degree Pmin = −1.3 ± 0.1 per cent, a polarimetric slope h = 0.22 ± 0.02 per cent deg−1, and an inversion angle α0 = 19.9 ± 0.3°. The derived geometric albedo is pV = 0.11 (in the range of 0.08–0.13). These polarimetric properties are consistent with anhydrous chondrites, contradict hydrous chondrites, and typical cometary nuclei.
Origin of Planetary Impactors in the Inner Solar System Strom, Robert G; Malhotra, Renu; Ito, Takashi ...
Science (American Association for the Advancement of Science),
09/2005, Letnik:
309, Številka:
5742
Journal Article
Recenzirano
Odprti dostop
Insights into the history of the inner solar system can be derived from the impact cratering record of the Moon, Mars, Venus, and Mercury and from the size distributions of asteroid populations. Old ...craters from a unique period of heavy bombardment that ended approximately3.8 billion years ago were made by asteroids that were dynamically ejected from the main asteroid belt, possibly due to the orbital migration of the giant planets. The impactors of the past approximately3.8 billion years have a size distribution quite different from that of the main belt asteroids but very similar to that of near-Earth asteroids.
Abstract
Accurate estimations of the brightness of (3200) Phaethon up to lower phase angles are essential for the planning of the on-board camera for the DESTINY+ mission. We carried out intensive ...observations of Phaethon in the optical wavelength (g, r, and i) with the TriCCS camera on the Seimei 3.8 m telescope in 2021 October and November. We derived the absolute magnitude HV and the slope parameter G of Phaethon as HV = 14.23 ± 0.02 and G = 0.040 ± 0.008 from multiple photometric observations including lower phase angles down to ∼9° with the H–G model. Using the HV value and the geometric albedo of Phaethon derived in previous polarimetric studies, we estimated that Phaethon’s diameter is within a range of 5.22–6.74 km, which is consistent with radar and occultation observations. With the linear model, we derived HV = 14.65 ± 0.02, which corresponds to a diameter range of 4.30–5.56 km. Our simultaneous tricolor light curves of Phaethon indicate that no rotational spectral variations larger than 0.018 and 0.020 mag in the g − r and r − i colors, possibly related to inhomogeneity of the surface material and/or structure, are seen at the 2021 apparition.
Abstract
We observed the L4 Jupiter Trojans (JTs) swarm using the Hyper Suprime-Cam attached to the 8.2 m Subaru Telescope on 2015 March 30 (UT). The survey covered ∼26 deg
2
of sky area near the ...opposition and around the ecliptic plane with a 240 s exposure time in the
r
-band filter through the entire survey. We detected 631 L4 JTs in the survey field with a detection limit of
m
r
= 24.4 mag. We selected 481 objects with absolute magnitude
H
r
< 17.4 mag and heliocentric distance
r
< 5.5 au as an unbiased sample and then used them to estimate the size distribution. Assuming a geometric albedo of 0.07, the size range of our unbiased sample is ∼2–20 km in diameter (
D
). We fit a single-slope power law to the cumulative size distribution and found that the best-fit index (
b
) is
b
= 1.84 ± 0.05 in
. The slope value (
α
) of the corresponding absolute magnitude distribution (
) is 0.37 ± 0.01. This
α
is consistent with that of the faint-end slope presented by Wong & Brown. The size distribution obtained from this survey is slightly different from the results of previous surveys with a similar size range, which reported broken power-law or double power-law slopes in their cumulative size distribution. Our results insist that the slope of
b
= 1.84 continues from
H
= 14.0 to at least
H
= 17.4. Since this work contains the largest L4 JT samples and is 1 mag deeper than the study by Wong & Brown, we believe that our study has obtained the most robust size distribution of small JTs so far. Combining the cataloged L4 JTs and our survey, we show the entire size distribution of L4 JTs up to
H
r
= 17.4 mag.
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