D. Choate

INTERCONTINENTAL BISTATIC RADAR OBSERVATIONS OF 6489 GOLEVKA (1991 JX)

Abstract Unlike the major planets and main belt asteroids, some near-Earth objects (NEOs) make their closest approaches to Earth at high northern declinations and therefore are visible simultaneously from North America, Europe and/or Asia, providing occasional opportunities for intercontinental radar experiments. The first celestial target of intercontinental radar was the Earth-crossing asteroid 6489 Golevka (1991 JX), which in June 1995 passed 0.034AU from Earth at a declination of ∼40deg. High power (∼0.5MW), continuous-wave signals at 3.5cm wavelength were transmitted toward the asteroid from the 70m antenna at the JPL/NASA Goldstone Deep Space Communication Complex (DSCC) in California on 13, 14 and 15 June 1995 during several hours on each date. This illumination of the asteroid created an artificial radio source for astronomers anywhere on the asteroid-facing side of Earth. Five astronomical groups tried to detect the radar echoes and two succeeded. Detections were obtained on each of the three days by the 70m antenna at Evpatoria DSCC in Crimea and on June 15 by the 34m antenna at Kashima Space Research Center in Japan. The Goldstone 34m antenna monitored echoes throughout all the observations. From the results of the Goldstone-Evpatoria experiment it can be inferred that the asteroid is about 0.5km across, is not very elongated, possesses considerable surface irregularity and is very reflective presumably due to a large near-surface bulk density. This first intercontinental radar astronomy experiment can be considered as an initial step toward a global radar network for routine NEO investigations.