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J.S. Lambert, D.J. Tholen (IFA, U. Hawaii)
The Apollo-type near-Earth asteroid (25143) 1998 SF36 has been selected as the target for the Japanese MUSES-C sample return mission. To assist with mission planning, we participated in a world-wide effort to acquire physical observations of this asteroid during its close approach to the Earth in 2001. The work being presented here deals with observations to determine the rotational state and shape of the asteroid. The 2001 apparition was particularly well-suited for the determination of the orientation of the spin axis, because the asteroid swung through 180 degrees of geocentric ecliptic longitude, though our observations will need to be combined with similar ones from other observatories made at different times during the apparition to realize the full potential of the data. Our observations do show a 12-hour rotation period, which is slower than average for asteroids. The brightness variation exceeds 0.7 mag, indicating an elongated shape with an axial ratio of at least 2 to 1. This research was conducted through a Research Experience for Undergraduates (REU) position at the University of Hawaii's Institute for Astronomy.