Visible and infrared investigations of planet-crossing asteroids and outer solar system objects

A major effort was directed toward 951 Gaspra in preparation for the Galileo encounter in October 1991. Most of the observational work involved photometry, for purposes of investigating the rotational state and phase function of the asteroid to help plan the encounter, and for purposes of navigating the spacecraft to the object. Work was also done with radiometric data obtained with the IRTF at NASA's request, for which simultaneous visible photometry was acquired with the University of Hawaii 2.24-m telescope. The results from the observations made during the 1990 opposition were published by Goldader et al. The main results reported include a rotational period of 7.04246 hours, an absolute visual magnitude of 11.8026, a slope parameter of 0.285, an early estimate of a high obliquity, an infrared spectrum indicating an olivine-rich composition, and 13 astrometric positions

First spacecraft encounter with an asteroid approaches

During the course of the Galileo spacecraft's journey to Jupiter it will make two excursions through the steroid belt situated between Mars and Jupiter. The first excursion involves an encounter with the asteroid 951 Gaspra, which will take place on October 29, 1991. Gaspra is a small (about 15 km diameter) asteroid near the outer edge of the main asteroid belt. It's spectral classification is S, suggesting a composition similar to those of stony-iron meteorites. A figure is given showing the brightness of this asteroid as a function of time

The year 1990 marks end of Pluto-Charon mutual event season

From late 1984 until late 1990, the orbit of Pluto's satellite Charon was sufficiently close to an edge-on configuration, as seen from Earth, to produce transit, occultation, and eclipse events involving the two objects. The systematic observation of these events, each of which offers a unique geometry of Pluto, Charon and shadow, has been used to directly measure several parameters of the system. With data now available from the entire mutual event season, reliable values for the radii of Pluto and Charon can be derived. Pluto's radius is 0.05860 plus or minus 0.00031, in units of Chiron's mean orbital radius, and Charon's radius is 0.03019 plus or minus 0.00066, in the same units

Visible and infrared investigations of planet-crossing asteroids and outer solar system objects

The project is supporting lightcurve photometry, colorimetry, thermal radiometry, and astrometry of selected asteroids. Targets include the planet-crossing population, particularly Earth approachers, which are believed to be the immediate source of terrestrial meteorites, future spacecraft targets, and those objects in the outer belt, primarily the Hilda and Trojan populations, that are dynamically isolated from the main asteroid belt. Goals include the determination of population statistics for the planet-crossing objects, the characterization of spacecraft targets to assist in encounter planning and subsequent interpretation of the data, a comparison of the collisional evolution of dynamically isolated Hilda and Trojan populations with the main belt, and the determination of the mechanism driving the activity of the distant object 2060 Chiron