First post-upgrade image of
an asteroid. This delay-Doppler image of asteroid 1998 ML14 was
taken on UTC 1998 August 15 12:45. This image is stretched to
show detail.
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Asteroid 1998 ML14 was discovered on 1998 June 24 by the Lincoln Near Earth Asteroid Research (LINEAR) project at the Lincoln Laboratories Experimental Test Site. It was discovered that it would pass about 0.02 AU (about 3 million miles) from the Earth on 1998 August 11 --- close enough to be observed by the Arecibo Planetary Radar and (at much lower S/N) by the Goldstone Solar System Radar. It was within the part of the sky visible with the Arecibo observatory from August 15 through 18, when it was still less than 10 million miles away. Even at this distance, the Arecibo Planetary Radar can obtain images at up to 7 meter resolution. The highest resolution in these experiments was 30 meters.
Before the radar observations, 1998 ML14 was estimated to be about 1 km in diameter. Hicks and Weissman (IAUC 6987) measured a rotation period of about 15 hours --- relatively long, but not unusually so.
In the images, the asteroid appears to be approximately round, with some lumps and large craters. As the data are processed, we should be able to distinguish more detail.
First post-upgrade image of
an asteroid. This delay-Doppler image of asteroid 1998 ML14 was
taken on UTC 1998 August 15 12:45. This image is stretched to
show detail.
The illumination is from above, and the vertical scale is
45m/pixel (300 ns). The horizontal scale is 0.12
Hz/pixel (increasing towards the right), or 63m / cosine(delta),
where delta is the (unknown) sub-radar latitude.
The same image, but linearly
stretched. Gray levels correspond to 0.5 standard deviations of
the noise (approximately). The image was clipped at 128 sigma.
This mosaic shows smoothed,
logarithmically stretched 5-image sums from 1998 August 15.
Theses images are spaced 6 minutes 15 seconds apart (incrasing
towards the right, then up from the bottom).
A
higher-resolution image taken on Aug 16. This image was taken
at 30m (200 ns) range resolution, and is one whole run
transformed, then smoothed with a 5-element boxcar filter in the
Doppler direction so that the resolution appears about the
same in both directions. The maximum value is about 70-sigma.
The first run (of 80-something) taken on 1998 August 18. This
image was taken at 45m range resolution, and is one run
transformed in 2 looks and smoothed with a 3-element boxcar
filter in the Doppler direction. The maximum value is about 135
sigma.
A mosaic of 9-image sums obtained on 1998 August 17. The range
(vertical) resolution is 30m (200 ns). These images were taken
about 13 minutes apart, increasing towards the right, then down
from the top.
Mike Nolan (nolan@naic.edu)
Last modified 1998 August 19 20:40 UTC
The Arecibo Observatory