|Main page||Projects page||CV page||Preprints||DASOP Meudon|
This series of radar images of the asteroid
4769 Castalia were taken at approximately 2 minute intervals
on Aug. 22, 1989, at the Arecibo Observatory.
The horizontal axis is Doppler frequency, and the vertical axis
is the time the echo was received (delay). These two scales map
differently onto distance, which has been approximately
compensated by replicating the pixels in the vertical
dimension, yielding a resolution of approximately 150 m
(horizontal) by 300 m (vertical).
The images are fainter at the beginning and the end of the
sequence because the antenna gain was a fairly strong function
of zenith angle when these images were taken.
Each image is the sum of 27 separately reduced (Fourier transformed)
data sets, or "looks". The sampling frequency was 16 ms,
and there are 64 complex samples in each look, giving a resolution
of 0.95 Hz (corresponding 150m), and allowing 27 looks to be summed.
The total time of each observation is about 30 s.
Goldstone recording of the asteroid Toutatis on Dec. 8, 9,10 and 13, 1992
(on the left). All eight days of Toutatis observations (on the right).
A 400 kW coded radio transmission was beamed at Toutatis from the
Goldstone main 70-meter antenna when the asteroid was about 4 million
km from the Earth. The echoes, which took 24 seconds
to travel to Toutatis and back, were received by the new 34-meter
antenna and relayed back to the 70-meter station, where they were
decoded and processed into images. The time required to obtain the
images were 55, 14, 37, and 85 minutes, respectively. In these
images the radar illumination comes from the top of the page, so parts
of each component facing towards the bottom are not seen. The two
irregularly shaped, cratered objects are about 4 and 2.5 km in average
diameter and they are probably in contact with each other. The large
grater seen in the Dec. 9 image is about 700 m in diameter.
(From "http://22.214.171.124/solarsys/toutatis.htm" and Public Information Office, JPL)
Asteroid Geographos viewed from above its north pole.
The radar images were obtained with the Deep Space Network's facility
at Goldstone on August 30, 1994, when the asteroid was 7.2 million km
from Earth. The tick marks on the borders are 1 kilometer apart. The
central white pixel locates the asteroid's pole. The gray scale is
arbitrary and no meaning is attached to brightness variations inside
the silhouette. (Dr. S. Ostro, JPL/NASA, "http://126.96.36.199/solarsys/geograph.htm")
The first radar detection of Comet Hyakutake.
The Goldstone X-band radar operates at a frequency of 8510 MHz
($\lambda$=3.5 cm). One Hertz is equivalent to a radial
velocity of one half wavelength per second.
And finally, for future target determination :-), the Hubble Space Telescope
view of the asteroid Vesta. The images show the full 5.34-hour
rotation of the 525 km diameter asteroid.
Hubble resolves features as small as 80 km across, allowing
astronomers to map Vesta's geologically diverse terrain. Features include
ancient lava flows and a gigantic impact basin. This sequence was taken
with Hubble's Wide Field Planetary Camera 2 between November 28 and
December 1, 1994, when Vesta was at a distance of 252 million km
(1.7 AU) from Earth. When combined with ground-based data, astronomers will
be able to make the first geochemical map of Vesta's surface.
(Photo release no. STScI-PRC95-20A)