Deep Space Target
On July 4, NASA's Deep Impact spacecraft will attempt an extraordinarily daring encounter with the far-flung comet Tempel 1 hurtling through space at tens of thousands of miles per hour. As if that is not challenging enough, the comet's size, shape and other characteristics are not entirely known.
Two of NASA's eyes in the sky, the Spitzer and Hubble Space Telescopes, helped scientists prepare for the comet encounter. From their orbits high above Earth, the telescopes watched Tempel 1 in early 2004. Together they came up with the best estimates of the comet's size, shape, reflectivity and rotation rate. The data may help Deep Impact snap pictures of the dramatic rendezvous and increase the probability of making contact with the comet.
These artist's concepts of Tempel 1 simulate an optical view of the comet (left), next to the simulated infrared view (right). The images illustrate the comet's shape, reflectivity, rotation rate and surface temperature, based on information from NASA's Hubble Space Telescope and Spitzer Space Telescope.
Measurements from the Great Observatories indicate that the comet is a matte black object roughly 14 by 4 kilometers (8.7 by 2.5 miles), or about one-half the size of Manhattan.
Spitzer detects the comet's infrared energy or heat, depicted by the reddish glow. The sunlit side of the nucleus is glowing warmly, and the nightside is about the temperature of deep space.