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Science Objectives and Encounter Strategy
A. Harch, J. Veverka, J.F. Bell, C. Chapman, M. Malin, L.A. McFadden, S. Murchie, M. Robinson, P.C. Thomas, D.K. Yeomans, B.G. Williams, S. Squyres, R.W. Farquhar, A. Cheng, D.W. Dunham
On June 27, 1997 the NEAR spacecraft passed within 1200 km of main
belt asteroid 253 Mathilde. Complementing the
Galileo flybys of S-asteroids
Gaspra and Ida, this was the first ever close observation of a C-asteroid.
Mathilde has attracted recent attention due to its extremely slow rotation
period of 17.5 days.
Primary science objectives during this 10 km/sec flyby
include high- resolution imaging, as well as albedo and spectral mapping
of the illuminated surface of the large (50x50x70 km) asteroid. The best
monochrome images achieved resolutions of 200 meters/pixel. Global
imaging in seven colors between 0.4 and 1.1 micron were carried out at
resolutions of 400-500 m/pixel. On departure a satellite search was made
in which bodies as small as 100 meters across could be detected. A determination
of the mass of Mathilde to about ±10% are being conducted by the
Radio Science experiment.
Due to the encounter geometry (approach phase angle 139°, departure
at 39°) the best imaging of Mathilde occurred around closest approach.
Locating Mathilde with sufficient accuracy to insure
the highest resolution observations are obtained near closest approach
requires optical navigation updates of Mathilde's position as late as 12
hours before encounter. This was the first ever fast flyby of an
asteroid with a spacecraft, which unlike Galileo, does not have a scan
platform.
Reprinted with permission from Eos, Trans. AGU, 77, F449.
visitors since 6-24-97.