July 6, 2005-
GLAST Optical Robotic Telescope (GORT) Images the Deep Impact Probe on Impact


On July 3 at 10:52 p.m. Pacific time, the NASA Deep Impact probe slammed into comet P/9 Tempel 1 at 23,000 miles per hour. The collision not only blew a crater into the comet but also ejected many tons of material off the comet's surface. This material reflected the sunlight, making the comet more than double in brightness.

SSU NASA E/PO team members Dr. Phil Plait, Dr. Kevin McLin, Tim Graves, and Logan Hill spent their July 3rd evening taking images of the celestial collision. Below are the images from the event.

This animation is made of 53 separate images taken over the course of 42 minutes, from 18 minutes before the impact to 24 minutes after. Each image is a 30-second exposure (except for two 60-second exposures shortly before impact). As the comet orbits the Sun, it appears to move against the background stars from the lower right to upper left. The comet appears to jump in the middle of the sequence because of a time gap between images-- the telescope was being prepared to take the impact images, which took a minute or two. So the jump is not real! Note how the comet appears to brighten about halfway through the sequence when the 800 pound impactor slammed into the comet.
Note: other bright points of light appear to move in the sequence, as well as a faint fuzzy blob above the comet. These are not real; they are artifacts of the digital detector used to make the images.
Image of Comet Temple 1 This image is a composite of the same 53 images as in the animation, but this time they were aligned to keep the comet in the same spot, making the stars appear as streaks. Note the fuzz around the comet; that is the gas being expelled by the comet as it is heated by the Sun, as well as the ejecta thrown out by the collision of the Deep Impact probe. The gap in the star streaks is caused by a gap in the sequence of images.
This image is once again the same 53 individual images, but aligned so that the stars do not move. As the comet moved between images, it appears to leave a streak (the gap is due to the imaging technique mentioned above). In this image, the brightening of the comet is very obvious. According to our measurements, it got brighter by about 2.5 times. Interestingly, it got brighter by a few percent before the impact. Comets sometimes emit jets of material which reflect sunlight, making them brighter. Tempel 1 has undergone several such outbursts, and one may have been happening right before the impact. Image of Comet Temple 1 - movement across the sky