Article published in Science:
Direct Detection of the Yarkovsky Effect via Radar Ranging to Asteroid 6489 Golevka.
S. R. Chesley, S. J. Ostro, D. Vokrouhlicky, D. Capek, J. D. Giorgini, M. C. Nolan,
J. L. Margot, A. A. Hine, L. A. M. Benner, and A. B. Chamberlin.
Science 302, 1739-1742 (2003).
Electronic reprint is available.
Abstract:
Radar ranging from Arecibo, Puerto Rico, to the 0.5-kilometer near-Earth asteroid 6489 Golevka unambiguously reveals a small nongravitational acceleration caused by the anisotropic thermal emission of absorbed sunlight. The magnitude of this perturbation, known as the Yarkovsky effect, is a function of the asteroid's mass and surface thermal characteristics. Direct detection of the Yarkovsky effect on asteroids will help constrain their physical properties, such as bulk density, and refine their orbital paths. Based on the strength of the detected perturbation, we estimate the bulk density of Golevka to be 2.7 (+0.4, -0.6) grams per cubic centimeter.
Press reports:
Radar images of Golevka reveal a half-kilometer object whose shape is extraordinarily angular, with flat sides, sharp edges and corners, and peculiar concavities. Extremely large gravitational slopes in some areas indicate the presence of exposed, solid, monolithic rock. This asteroid, the first sub-kilometer object studied in this much detail, probably is a monolithic collision fragment rather than a rubble pile.
Click here to see collages of delay-Doppler images made at Goldstone during June 8-10, 1991, during Golevka's closest approach to Earth (0.034 AU, about 13 Earth-Moon distances)) until 2374. The resolution of the images is about 30 meters.
6489 Golevka (1991 JX) was discovered by E. F. Helin at Palomar on May 10, 1991. It is named to honor the success of the multinational radar observations of it in June 1995. The Goldstone 70-m antenna provided the transmission and echoes were received by the Russian 70-m antenna in Evpatoria and also by the Japanese 34-m antenna in Kashima. This experiment produced the first intercontinental radar observations and also initiated planetary radar astronomy in Japan. The asteroid's name is made from leading letters of the antennas GOLdstone-EVpatoria-KAshima.
Reference:
Radar Observations and Physical Modeling of Asteroid 6489 Golevka.
R. S. Hudson, S. J. Ostro, R. F. Jurgens, K. D. Rosema,
J. D. Giorgini, R. Winkler, R. Rose, D. Choate, R. A. Cormier,
C. R. Franck, R. Frye, D. Howard, D. Kelley, R. Littlefair,
M. A. Slade, L. A. M. Benner, M. L. Thomas, D. L. Mitchell,
P. W. Chodas, D. K. Yeomans, D. J. Scheeres, P. Palmer, A. Zaitsev,
Y. Koyama, A. Nakamura, A. W. Harris, and M. N. Meshkov.
Icarus 148, 37-51 (2000). download pdf
Click here for a rotational sequence of the radar-derived shape model, color-coded for gravitational slope. Surfaces with gravitational slopes as large as about 40 degrees are likely to be exposed, solid rock.
Click here for a Quicktime animation of Golevka rotating.
Here are an animation of Golevka rotating in mov and avi formats.
