Asteroid 4769 Castalia (1989 PB)

This figure shows the orbits of 1989 PB and some other Earth-crossing asteroids. The yellow band marks the main asteroid belt.

The asteroid's trajectory passed within 0.027 AU, or 11 lunar distances, from Earth on August 25, when the Voyager 2 spacecraft was making its closest approach to Neptune. (The Goldstone 70-meter antenna was occupied with Voyager communications during the Neptune encounter and was unavailable for radar astronomy until Aug. 30.) Arecibo observations were conducted on August 19-22 and were highly successful. All the Arecibo and Goldstone observations were reported by Ostro et al. (1990, Science 248, 1523-1528) ; the following figures are from that paper, copyright 1990 by the AAAS.

Rotational Phase Coverage

Delay-Doppler Images

This diagram shows the rotation phase coverage of Doppler-only (also known as continuous wave or "CW") radar observations on Aug. 20 and 21, and of delay-Doppler observations on Aug. 22. Analysis of the Doppler-frequency extent of the echoes produced the estimate of the convex hull, or envelope, on the asteroid's pole-on silhouette. The most useful observations, on Aug. 22, yielded a 64-frame sequence of images that resolve the asteroid in time delay (range) and Doppler frequency (line-of-sight velocity). Here the images are shown smoothed and color-coded for intensity. These images constitute a movie covering ~60% of the asteroid's 4.07 hour rotation period.

The 64 images may also be viewed at their raw resolution. The equivalent linear dimensions of the radar resolution cells in these images are 150 x ~170 meters.


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