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(meteorobs) Deep Impact mission



Hello all,

I am currently a graduate student working for one of the members of the 
mission planning team for Deep Impact, and thought I might respond to this 
thread.  This mission seems a little "ripe for hype," especially from the 
press, so here are a few points to keep in mind.

(1)  The goal of the mission is NOT, repeat NOT to destroy the target 
comet, 9P/comet Tempel 1.  The comet is currently estimated to have a 
diameter of about 2-3 km and a mass on the order of 10^12  to 10^13 
kg.  The impactor has a planned mass of 350 kg, and is a hemisphere of 
radius 0.35 meter; striking the comet at about 10 km/sec.  My current 
estimates for the resulting crater size is 200-400 meters in diameter and 
50-100 meters deep.

(2)  The goal of the mission IS to produce a crater on the surface of the 
comet large enough to punch through the crustal layer of the comet and 
reveal the more pristine material in the comet's interior.  The size of the 
impact is designed such that (1) the instrumentation on the flyby 
spacecraft can gather detailed data on the resulting ejecta plume and 
crater interior through the coma of the active comet, and (2) Earth-based 
instrumentation can also detect the impact and collect data on its effects 
on the comet's coma, dust, and gas tails.

(3)  This mission mimics a natural process which has been occurring on this 
particular comet and ALL solar system bodies for billions of years.  Recent 
flybys of asteroids reveal VERY scared and altered surfaces due to impact 
cratering, and there is no reason to believe that comets do not undergo the 
same types of collisions with other objects.  In this case, we may be 
artificially creating the impact and collecting data on it as it occurs, 
but this is (in all likelihood) something which has happened to this comet 
before,  and is something which will happen again (especially as one looks 
on smaller and smaller scales).

(4)  Although I don't personally consider it a primary goal, for those 
interested in the NEA hazard area, this mission is also a good test of the 
navigation and logistics involved in delivering a payload to a near-earth 
object in an attempt to change its orbital path.  In this particular case, 
everything is rather small-scale, and the comet's orbit will be changed by 
a barely perceptible amount (if all goes well).  However, much can still be 
learned from a proof-of-concept standpoint.

(5)  While I will readily admit that there are several instances where, in 
the end, the mainstream of scientific thought proved to be wrong and a 
fringe idea proved to be right (the idea of "continental drift" is perhaps 
the best modern example), the *current* mainstream idea with regard to life 
in our solar system outside of the earth is that three things are 
required:  organic molecular and atomic building blocks, liquid water, and 
a source of energy.  Comets contain water ice and organic molecules, but 
lack an energy source for life or sufficient temperatures for stable areas 
of liquid water.  From what I know at this time, most of their 4.5 billion 
year life-times have been spent far away from the sun (making it an 
unusable energy source).  After being perturbed into an orbit which swings 
them near the sun, the sun might become an intermittent source of heating, 
but it also spells the death of the comet after a few tens of thousands of 
years, especially if the comet is perturbed again by Jupiter into an even 
shorter period orbit.  While comets and carbonaceous chondrite bodies do 
carry both water and organic molecules, it is highly, highly unlikely that 
any sort of life could actually evolve on them.  The ingredients for the 
cake are there, but this isn't an oven.

While one might argue against Deep Impact's "destructive testing" procedure 
-- as opposed to non-destructive, passive data collection -- I don't 
believe that the evidence is there to argue that the comet represents an 
"ecosystem."

For more information on Deep Impact, see:

http://www.ss.astro.umd.edu/deepimpact/


Best regards,

      Jim


------------------------------------------------------------------------
James Richardson                         (graduate student)
Department of Planetary Sciences
Lunar and Planetary Laboratory (LPL)
The University of Arizona
Tucson, AZ  85721

LPL email:  jrich@lpl.arizona.edu
LPL phone:  (520) 621-6960
Home phone:  (520) 877-2715
Home page:  http://www.lpl.arizona.edu/~jrich/

Operations Manager
American Meteor Society (AMS)
AMS email:  richardson@amsmeteors.org
AMS website:  http://www.amsmeteors.org
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