Photometric observation of (4660)Nereus Original Research Article

The Apollo type asteroid (4660)Nereus (1982DB) is recognized as one of the most accessible asteroid, and it is a candidate for the target of MUSES-C project, i.e. the first asteroid sample return mission by the Institute of Space and Astronautical Science (ISAS). Information on the size, shape, and rotational period of the asteroid is necessary for the planning of mission scenario, but available data on these properties are very limited. From our photometric observations in R band on the nights of August 2/3 and 3/4, 1997, we have found that the rotational period is 15.1 ± 1.2 hours, the amplitude of brightness variation is about 0.9 mag, and the mean of the absolute magnitude is +18.3 mag. Our results suggest that the size of Nereus is nearly 1.1 km in diameter when the geometric albedo is 0.05. Although the slow rotation is preferable to the mission scenario, the large light variation results the highly elongated shape of Nereus. It is also appeared that comet nuclei is more preferred for the origin of Nereus than main-belt asteroids.