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April 13, 2029, the ~300-meter diameter near-Earth asteroid 2004 MN4
will make a very close approach to Earth. During this close pass (about
5.7 Earth radii, within geostationary distance!), tidal torques will
measurably alter the asteroid´s spin state (Scheeres et al. 2005,
Icarus) and may well cause surface and/or internal structural
deformations that would be detectable by seismometers emplaced on or
within the object (Richardson and Walsh 2005, personal communication).
Such measurements could reveal important clues to the internal
structure and mechanical properties of an object representative of
those we wish to explore for resource utilization and may one day need
to deflect from an impacting trajectory. The potential exists (roughly
1 chance in 10000) for a subsequent impact by 2004 MN4 with Earth in
2036 if the asteroid passes through a keyhole during the 2029 pass. If
the accuracy of our knowledge of the asteroid´s trajectory using
passive optical and radar tracking proves to be inadequate to make a
timely deflection decision then serious consideration should be given
to flying a mission to the asteroid in order to emplace a radar
transponder on it. This mission should be launched in the near future
in order to provide adequately accurate trajectory information about
the asteroid by 2014, the approximate date by which a deflection
mission decision would have to be made (the time to deflect the object
is *before* 2029, when the object only need miss the small keyhole,
rather than afterwards, when the object would have to be deflected to
miss the entire Earth). A pre-2014 combined seismic-sounder/transponder
mission could provide a useful baseline against which to compare
observations in the 2029 or post-2029 timeframe.
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