Figure 1. Old World First Asteroid Radar Echo.
Poster presentation at the IAU Symposium 160: "Asteroids, Comets, Meteors", Belgirate, Italy, June 14 – 18, 1993. Abstract Book, p. 325.
Six-Centimeter Radar Observations of 4179 Toutatis
Alexander L. Zaytsev, Alexander S. Vyshlov, Oleg N. Rzhiga, Vladimir A. Shubin, Alexander H. Krivtsov, Olga S. Zaytseva, and Alexander S. Nabatov
Institute of Radio Engineering and Electronics, Russian Academy of Science, Vedensky Square 1, 141190 Fryazino, Russia
Richard Wielebinski, and Wilhelm J. Altenhoff
Max-Planck-Institut fur Radioastronomie, Auf dem Hugel 69, 53121 Bonn, Germany
Vladimir A. Grishmanovsky
Russian Institute of Space Device Engineering, Aviamotornaia 53, 111024 Moscow, Russia
Yury F. Kolyuka, and Oleg K. Margorin
Mission Control Center, Pionerskaia 4, 141070 Korolev, Russia
Andrey Sokolsky, and Victor A. Shor
Institute of Theoretical Astronomy, Kutuzova Quay 10, 191187 St. Peterburg, Russia
A radar signal was transmitted from Evpatoria Deep Space Station (Crimea) and after reflection from asteroid was received at Effelsberg (Germany). The 70-m antenna and 50 kW transmitter were used at Evpatoria, and 100-m antenna and 90 K noise temperature two-channel receiver at Effelsberg. When transmitting, the predicted Doppler shift was compensated. Continuous wave and periodic linear frequency modulated radar signals were used.
The observations were carried on 8 and 9 December 1992. Spectrum analysis of echo signals was made with 0.02 Hz frequency resolution. An echo bandwidth B, which depends on synodic rotation period and aspect angle, was determined by three different methods. The values of B are (1.8 – 2.2) Hz. After correction for fast apparent motion, preliminary estimations of proper rotation period of Toutatis give values within interval from 9.9 to 11.7 days (if the rotation was orthogonal to the line of sight and taking the asteroid diameter to be equal to 6.0 km).
Two orthogonal circular polarizations have been received simultaneously. Polarization ratios are equaled to 0.24 – 0.28. This fact gives evidence of high degree roughness of the asteroid surface at the wavelength scale. The most interesting result is a bimodal distribution of power spectra for both polarizations, Fig. 2. The depth of a gap is as much as Pmax / 2. It testifies that 4179 Toutatis is a double object like asteroid 4769 Castalia. The preliminary estimation of radar cross section for 9 December gives the value 0.26 square kilometer. The time delay and frequency shift was obtained with the precision that permits their use for more precise determination of the Toutatis orbit.
Figure 2. Dual polarization echo power spectra obtained for Toutatis at the beginning and the end of each observational day.
1) Zaitsev, A. L., A. G. Sokolsky, O. R. Rzhiga, A. S. Vyshlov, A. P. Krivtsov, and V. A. Shubin. Radar investigation of asteroid 4179 Toutatis with 6 cm waves. Radiotekhnika Elektronika 38, 1842-1850 (1993). (in Russian). Translation: Zaytsev, A. L., A. G. Sokol'skiy, O. R. Rzhiga, A. S. Vyshlov, A. P. Krivtsov, and V. A. Shubin (1993) "Radar Investigations of the Asteroid 4179 Tautatis at Wavelength of 6 cm", Journal of Communications Technology and Electronics 38:16, 135-143 (in English, by Scripta Technica, Inc., 1994).
2) Zaitsev, A. L., W. Altenhoff, R. Wielebinski, A. S. Vyshlov, A. Jessner, A. P. Krivtsov, and V. A. Shubin. Interference of Radar Echo from the Binary Asteroid 4179 Toutatis. Doklady Akademii Nauk, v. 342, No 4, pp. 480-483, 1995.
Abstract. An analysis of the 6-cm radar data revealed quasi-harmonic oscillation of the echo’s “central” Doppler frequency with a period of about 14 sec and a deviation of about (0.7*B) Hz, where B is the echo bandwidth, which for 4179 Toutatis was equal to 2.1 Hz and 1.9 Hz for 1992 Dec 8 and 9, respectively. We explain this effect by the interference of echoes from the binary asteroid when it was oriented so that some contours of constant Doppler frequency shift are crossing both parts of binary system. A computer model of this phenomenon shows that interference may cause both quasi-harmonic and more complex oscillation modes, which depend on rotation phase and aspect angle between the line of sight and the apparent spin vector. Probably, similar effect may take place for other compound objects, such as 4769 Castalia, 216 Kleopatra, or for comet IRAS-Araki-Alcock 1983d. Also, the presence of interference oscillations may help to detect binary or more complex objects.