What Will the Deep Impact Mission See? (2004)
by James Richardson and H. Jay Melosh
Contents:
Introduction
In July of 2005, the
Deep Impact
spacecraft will release a small, 370 kg
Impactor
directly into the path of the nucleus of comet
Tempel 1
(approximately 6 km X 3 km in size).
With a closing speed of about 10.2 km/sec (22,800 miles/hour),
the resulting collision will probably produce a small impact crater on the surface of the nucleus,
perhaps a few hundred meters in diameter and taking 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 it flies by the comet nucleus, coming within
about 500 km (310 miles).
The flyby spacecraft carries with it two instruments for observing the impact and
its effects within visible light wavelengths. These are a
Medium Resolution Instrument (MRI),
having a field of view of 0.587 degrees and a maximum predicted resolution of about 10 meters/pixel, and a
High Resolution Instrument (HRI),
having a field of view of 0.118 degrees and 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.
Below we present computer simulations of what this flyby may look like, as viewed from the flyby spacecraft's
MRI and HRI instruments. These simulations show the predicted impact crater area (depicted simply as a black disk),
ejecta curtain (a semi-transparent, white, expanding cone), and a few random ejecta blocks (white dots) resulting
from this impact on the surface of a digital comet nucleus model. Note that the comet's coma is not depicted.
Because we currently do not know the actual shape and orientation of comet Tempel 1, only its crude
dimensions, these simulations can only give a general idea of what the real images from the mission will truly show.
What will the Medium Resolution Instrument See?
Below are two example flyby animations, using a modified-Borelly comet model to
represent the nucleus of Tempel 1 and shown at two different encounter
orientations. These animations show the view from the flyby spacecraft's Medium
Resolution Instrument over
a one hour period, from 30 minutes before to 30 minutes after the time of impact.
Note that the actual image sequences for Deep Impact will only include the first
13 1/3 minutes (13:20) after the time of impact, following which 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). Thus, the last 17 minutes
of time depicted in these animations will not actually be seen by the instrument.
MPEG and AVI files for these animations are provided below. Note that these are time-lapse animations, and therefore show the comet flyby at much faster than actual speed (watch the clock in the bottom left).
Flyby 1
Medium Resolution Instrument (MRI)
|
 |
Flyby 2
Medium Resolution Instrument (MRI)
|
 |
What will the High Resolution Instrument See?
Below are two example flyby animations, using a modified-Borelly comet model to
represent the nucleus of Tempel 1 and shown at two different encounter
orientations. These animations show the view from the flyby spacecraft's
High Resolution Instrument over
a one hour period, from 30 minutes before to 30 minutes after the time of impact.
Note that the actual image sequences for Deep Impact will only include the first
13 1/3 minutes (13:20) after the time of impact, following which 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). Thus, the last 17 minutes
of time depicted in these animations will not actually be seen by the instrument.
MPEG and AVI files for these animations are provided below. Note that these are time-lapse animations, and therefore show the comet flyby at much faster than actual speed (watch the clock in the bottom left).
Flyby 1
High Resolution Instrument (HRI)
|
 |
Flyby 2
High Resolution Instrument (HRI)
|
 |
