NASA Ames Research Center scientists fired a copper projectile at a bed of pumice to simulate the Deep Impact probe's collision with Comet Tempel 1. The projectile's speed was about 4.5 times the speed of a high-velocity rifle bullet, but only half the expected collision speed with the comet.
Photo credit: (NASA Ames Research Center/Peter H. Schultz, BrownUniversity.)
Though it was a great way to celebrate Independence Day, there's more to Deep Impact than fireworks. Scientists the world over, in fact, view the event as a way to learn more about our universe.
The spacecraft's impactor has now slammed into Comet 9P/Tempel 1 and created a crater. Scientists are now analyzing the process by which it formed to help reveal the makeup of the comet's nucleus, giving clues as to how the comet formed. Many scientists currently theorize that comet nuclei are accretions of pristine dust, ice and debris left over from formation of the solar system. Detailed analysis of the Deep Impact blast will help test this theory.
The impact has also given scientists their first look inside a comet. Though there have been comet flybys in the past (most notably of Halley's Comet in 1988), and cometary debris and tails have been subject to spectroscopic analysis, only materials on the comet's surface could be analyzed. There has been no way to get at the core, a situation that Deep Impact has now remedied.
In addition, scientists want to know whether comets go dormant or extinct. They believe up to half the near-Earth "asteroids" are either dormant or extinct comets, and analysis of Tempel 1's behavior after impact should help them test this belief.
In all, the Deep Impact science mission focuses on these main questions:
- What are some basic properties of the nucleus, for example: what does it's landscape look like, how dense is it, how strongly is it held together and how massive is it?
- How has the comet changed during its lifetime?
- What kinds of ice remain unchanged from the comet's early days?
- Can the heat of the sun finally drive all the ice out of a comet so that it becomes extinct or will it only go to sleep perhaps to wake again?
- Do smaller comets collide and form larger comets?
- Are there impact craters on comets like there are on moons and asteroids?
- Can the course of a comet be altered to reduce the effect of, or avoid, a collision with Earth?
Stay tuned to see what develops. We'll be tracking results of the experiments and will have current Deep Impact mission data posted on our Web site.