Hubble's Advanced Camera for Surveys snapped the latest photos from a distance of 120 million kilometers on June 14, 2005. The jet extends some 2,200 kilometers from the comet's nucleus in the direction of the sun. Similar jets have been observed coming from other comets, but astronomers are still unsure as to exactly why they occur. Proximity to the sun could have caused a crack in Tempel 1's outer crust, allowing trapped dust and gas to escape, or the ejected material could be comprised of crumbled bits of crust thrown off by mounting pressure from underlying heated gas.
The NASA team hopes the close encounter next week will provide new insight into Tempel 1's core, as well as "lead to a better understanding of both the solar system's formation and the implications of comets colliding with Earth." The crash landing on Tempel 1 will not change the comet's orbital path, but it should leave a crater that is between two and 14 stories deep and at least as wide as a house. Deep Impact will closely monitor the resulting ejecta curtain for about 14 minutes, and other space- and ground-based observatories will be trained on the event as well. The collision is scheduled for 1:52 a.m. EST on July 4.