Hubble Close-up of Bright Nucleus in Comet P/Shoemaker-Levy 9 
 
This is an enlargement of a NASA Hubble Space Telescope image 
of the "brightest nucleus" in a string of approximately 20 objects 
that comprise comet P/Shoemaker-Levy 9. The comet is hurtling 
toward a July 1994 collision with the giant planet Jupiter. 
Hubble's high resolution shows that this bright region is 
actually a group of at least four separate pieces. The HST 
images allow for the best separation of the individual nuclei 
and their surrounding halo of dust (comae), which results in a 
better estimate of the nuclear sizes. The image was taken with 
the Wide Field and Planetary Camera (WFPC), in PC mode, on 
July 1, 1993. The Hubble observations show that the cometary 
nuclei are probably less than three miles (5 km) across, as 
opposed to earlier estimates of nine miles (14 km). The new 
Hubble data show that the impacts will unleash only 1/10th 
to 1/100th as much energy as thought previously. However, 
even with these new size estimates, the total energy of the 
July 1994 collisions will be equivalent to 100 million 
megatons of TNT. 

credit: Dr. H. A. Weaver and Mr. T. E. Smith, STScI 
NASA Photo Caption STScI-PR93-22c