| On 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. |
