The flyby of Tempel 1 will give scientists an opportunity to look for changes on the comet's surface since it was visited by NASA's Deep Impact spacecraft in July 2005. Since then, Tempel 1 has completed one orbit of the sun, and scientists are looking forward to discovering any differences in the comet.
The closest approach is expected tonight at approximately 8:40 p.m. PST (11:40 p.m. EST).
During the encounter phase, the spacecraft will carry out many important milestones in short order and automatically, as the spacecraft is too far away to receive timely updates from Earth. These milestones include turning the spacecraft to point its protective shields between it and the anticipated direction from which cometary particles would approach. Another milestone will occur at about four minutes to closest approach, when the spacecraft will begin science imaging of the comet's nucleus.