Modeling Instrument Observations
|What will the Medium Resolution Instrument see?
|What will the High Resolution Instrument see?
In July of 2005, the Deep Impact spacecraft will release a small, 370 kg (820 lb) Impactor directly into the path of comet Tempel 1 (estimated to be 14 km X 4 km X 4km /9 miles X 2 miles X 2 miles in size). With a closing speed of about 10.2 km/sec (22,800 miles/hour), the resulting collision is expected to produce a small impact crater on the surface of the comet's nucleus. It should be a few hundred meters in diameter and will take a few minutes to form. The crater and its corresponding ejecta curtain (the material thrown out of the forming crater) will be observed in detail by the flyby spacecraft for a period of about 13 1/3 minutes as the comet nucleus approaches. The comet will come approximately within 500 km (310 miles) of the spacecraft.
The flyby spacecraft carries two instruments for observing the impact and its effects within visible light wavelengths. There is a Medium Resolution Instrument (MRI), which produces "the big picture" of the comet and has a field of view of 0.587 degrees or about the diameter of the moon as seen from Earth. It will have a maximum predicted resolution of about 10 meters/pixel.
In addition, there is a High Resolution Instrument (HRI) to give a closer and more detailed look at the comet. It has a field of view of 0.118 degrees or one-fifth the diameter of the moon as seen from Earth. The HRI has a maximum predicted resolution of about 2 meters/pixel. Both instruments will be pointed at the impact site on the comet nucleus, recording the expansion of the impact ejecta curtain and peering inside of the freshly formed crater.
Both sequences shown here are computer simulations of what impact may look like, as viewed from the flyby spacecraft's MRI and HRI instruments. The animations show the predicted impact crater (depicted simply as a black disk), ejecta curtain (a semi-transparent, white, expanding cone), and a few randomly ejected fragments (white dots) resulting from impact on the surface of this model. The comet's coma is not depicted in these animations.
These animations show the view from the flyby spacecraft's Medium and High Resolution Instruments from 30 minutes before to 30 minutes after the time of impact. The actual image sequences during the mission include only the first 13 1/3 minutes (13:20) after the time of impact. Following that, the flyby spacecraft will be placed into a "safe mode" as it passes through the plane of the comet's orbit (where the majority of the cometary dust lies). Therefore, the spacecraft instruments will not actually see the last 17 minutes of time depicted in these animations. Note that these are time-lapse animations, and show the comet flyby at much faster than actual speed (watch the clock in the bottom left of the screen).
CREDIT: Jim Richardson, University of Arizona, Lunar and Planetary Laboratory
And What Did We See?