First Impressions: Peter Schultz
The impact experiment on comet Tempel 1 provided incredible details about the nature of the upper surface of the comet. The following comments are first impressions and are not necessarily the view of the entire team. There's simply much more work to do. The first sequences revealed a double flash: a faint initial flash at contact and then a delay before a brilliant flash saturated the images. A bright plume left the comet at high speed and formed an arc, like an eyebrow. This represents the vapor phase and is very similar to what has been observed in experiments at the NASA Ames Vertical Gun Range (AVGR). Its rapid expansion indicates both the effect of hot gases and the downrange motion of the hot gases released. Experiments at the AVGR previously allowed estimating the amount of energy in the vapor cloud. Even though the dust and vapor blocked the field of view, we could see the shadow of the ejecta coming out of the crater. This shadow rapidly grew across the surface, initially like a column and then eventually, into a conical curtain that gradually expanded. Even in the look-back image we were able to see the conical curtain and the vertical plume extending from the point of impact. This first look suggests that the crater was large although more processing will require nailing down the actual images. Prior to the encounter in a paper published in Space Science Reviews, estimates for the crater size for loose particulate targets ranged from ~90m to as large as ~140m if the cratering was controlled by gravity. But certain predictions also suggested a crater as large as ~ 240m if the impact transferred its energy explosively.
(QuickTime, closed captioned)