Planetary Exploration Research Center

This paper is a summary from the results of the first systematic survey of small Main-Belt Asteroids (MBAs) using 8.2 m Subaru telescope. We searched about 3 square-degree sky area near opposition and near the ecliptic. About 1100 moving objects down to R∼26 mag (including very slow Kuiper Belt Objects) were detected. In this survey, the observational arc for each moving object was only 2 hours, so that only their semi-major axis (a) and inclination (I) were estimated statistically based on their apparent motions. We found that (1) the sky number density of MBAs is about 290 per square-degree down to R∼24.4 mag (for MBAs), (2) the slope of the cumulative size distribution for detected MBAs ranging from 0.5 to 1 km in diameter is considerably shallower (about 1.2) than that for large MBAs (about 1.8) and (3) the shallowness of the size distribution slope for sub-km MBAs is more conspicuous in the outer part of the main-belt than in the inner part. These findings suggest that the number of small MBAs is much more depleted than an estimate extrapolated from the existing statistics of large asteroids. We also propose a new form of the power-law distribution with a size-dependent slope to express the observed sub-km MBA distribution.

... Dermawan, B., Nakamura, T., Fukushima, H., Sato, H., Yoshida, F., & Sato, Y. 2002, PASJ, 54, 635. Harris, AW & Lupishko, DF 1989, in Asteroids II, ed. RP Binzel, T. Gehrels, & MS Matthews (Tucson: The University of Arizona Press), 39. Landolt, AU 1992, AJ, 340, 436. ...

This paper describes scientific rationale for Trojan asteroid exploration to contribute planetary science research as clues of the origin and evolution of the Jovian System. JAXA is aiming to launch the solar power sail engineering demonstrator to the outer planet region of the solar system like Jupiter and the Jovian Trojan asteroids in 2010's. Its interplanetary cruise is a relevant and rare opportunity to monitor physical properties that may be varied by heliocentric distances continuously such as solar wind, solar magnetosphere and micrometeoroid flux.

The near-Earth Asteroid 25143 Itokawa, the target of the Japanese space mission Hayabusa, was observed in June, 2004 with the Torino photopolarimeter attached at the 2.15 m telescope of the El Leoncito Observatory (Argentina). The degree of linear polarization ...

Abstract—We obtained color images of near-Earth asteroid 25143 Itokawa by the Hayabusa multiband imaging camera to characterize the regional color properties. Images were obtained for the whole disk from the gate position (GP) and home position (HP) at a spatial ...

Because of their young age (~ 5.8 million years) the Karin Family asteroids provide a unique opportunity to study the impact fragmentation, collisional evolution and surface weathering effects of the main belt asteroids and near-Earth objects. We are also interested in knowing the internal structures and chemical composition of the member asteroids. For example, would anyone of them carry a certain amount of volatile material or would anyone of them be spun up to the condition of rotational breakup? Both effects would possibly lead to the formation of a dust halo of dust trail near an asteroid similar to the dust feature of (7968) or 133 P/Elst-Pizzaro observed by Elst (1996) and Hsieh, Jewitt and Fernandez (2003). In this work, we present the results for the search of such dust comas around several Karin Family member asteroids.

Abstract Here, we report on results of statistical analyses on spin periods and shapes of main-belt asteroids (MBAs) smaller than 1 km in diameter, which were derived from lightcurve observations of a single night with the 8.2 m Subaru telescope. It is shown that, ...

Near-Earth asteroid (25143) 1998 SF36 is now planned as the target for the Japanese MUSES-C sample return mission. We conducted extensive photometric observations at NAO-Mitaka from 2001 February 15 until March 19 to obtain its physical properties, such as asteroid's colors, rotation period, phase curve, and light curves. The colors of this asteroid were found to be S-type and in agreement with the spectroscopic result by Binzel et al. (2001,Meteor. Planet. Sci., 36, 1167). From the phase curve of this object, the visual absolute magnitude is obtained to be 18.61 +/- 0.18; we suggest that the albedo may be higher than that for typical S-type asteroids, after applying a known empirical relation between phase curve slope and geometric albedo. We also reveal that the synodic rotation period of this asteroid is 12.13 +/- 0.02 hr and the peak-to-peak light variation amplitude at zero phase angle has been shown to be ~ 0.49 mag, which implies the ra tio of the longest and intermediate ellipsoidal axes for the asteroid >~ 1.6.

ABSTRACT We constructed a new surface number density distribution model for Jovian Trojans around the L4 or L5 libration point of Jupiter. This is an empirical asymmetric model of the Maxwellian-Gaussian type, derived from numerical integrations of orbital motions for actual Trojan asteroids around the L4 point. With this model, in combination with the observed surface number densities obtained by Yoshida and Nakamura (2005, AJ, 130, 2900; 2008, PASJ, 60, 297), we estimate that the total populations of L4 and L5 Trojans with diameters (D)>2km are (6.3±1.0)×104 and (3.4±0.5) ×104, respectively. These results indicate that the L4 total populations (D> 2km) calculated previously by Jewitt, Trujillo, and Luu (2000, AJ, 120, 1140) and by Yoshida and Nakamura (2005, ibid.) using the former's isotropic Gaussian model are overestimated by a factor of 3-4.