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Unique Asteroid Search Strategy by University of Hawaii Astronomers Pays Off
A hunt for hazardous asteroids by University of Hawaii astronomers who use a unique search strategy has paid off. Last Thursday, NASA announced that asteroid 2004 MN4, discovered in June by University of Hawaii astronomers David Tholen and Fabrizio Bernardi, and Roy Tucker of the University of Arizona, reached the highest level on the hazard scale of any asteroid found to date. For a while, it looked as though it might hit Earth in the year 2029, but additional observations ruled out an impact in that year.
"There are several near-Earth asteroid search programs funded by NASA, but they all tend to look away from the sun," explained Tholen. "As a result, we have fairly extensive monitoring of the solar system beyond Earth's orbit. However, some asteroids orbit closer to the sun than the Earth does for most, if not all, of their orbits. The best way to find those is to look in the direction of the sun." Of course, daytime observing is not practical, so Tholen and Bernardi have been looking low in the western sky after evening twilight or low in the eastern sky before morning twilight to catch a glimpse of the heavens between Earth's orbit and the sun.
Those efforts paid off on June 19, when they discovered 2004 MN4 low in the evening sky with a University of Arizona telescope on Kitt Peak. "We had the opportunity to try out a new camera on a large telescope that covers five times the area of the full moon," Tholen recalled. His team followed the object for two nights before uncharacteristically early summer rainstorms wiped out the last two scheduled nights on the telescope. After that, bright moonlight made seeing the asteroid difficult. The object then moved farther south and even closer to the sun, so it remained hidden from view.
In December, an observer in Australia recovered the asteroid in the evening sky. Now it is moving both northward and away from the sun, and will remain observable until the middle of 2005. Ongoing observations continued to raise the 2029 impact probability, which reached a high of 1 in 37 on Monday. However, Jeff Larsen and Anne Descour of the Spacewatch Observatory near Tucson, Arizona, were able to detect and measure very faint images of asteroid 2004 MN4 on archival images dating back to March 15. The improved orbit calculated with these observations rules out the possibility of an impact in 2029.
UH astronomers are looking forward to using the soon-to-be-built Pan-STARRS telescopes to search the skies for hazardous asteroids. Pan-STARRS (short for Panoramic Survey Telescope and Rapid Response System) will employ four automated telescopes with unique CCD cameras to observe the entire available sky several times each month. A single prototype telescope, PS1, is being constructed on Haleakala and is scheduled to attain first light in January 2006. The complete four-telescope system, which will be the most powerful asteroid survey telescope ever, will become operational in late 2007. It will be built on Haleakala or on Mauna Kea, where it would be placed within the footprint of the existing UH 88-inch telescope.
The search strategy being developed for Pan-STARRS will build on the successful strategy that led to the detection of asteroid 2004 MN4 and will include the same regions of sky being explored by Tholen and Bernardi now. This will drastically increase the rate at which near-Earth asteroids are discovered and thus provide a much more accurate assessment of whether Earth is threatened by a future impact. The system is being designed to produce positional information with increased accuracy, which in turn will reduce the frequency of false impact predictions.
The Institute for Astronomy at the University of Hawaii conducts research into galaxies, cosmology, stars, planets, and the sun. Its faculty and staff are also involved in astronomy education, deep space missions, and in the development and management of the observatories on Haleakala and Mauna Kea.
Additional information on the Pan-STARRS project can be
2004MN4.jpg: Asteroid 2004 MN4 (inside circle). The streaks in the picture are star trails created because the telescope was following the motion of another asteroid. (credit: David Tholen, Roy Tucker and Fabrizio Bernardi)
plotorb.eps, plotorb.jpg: Diagram showing the positions of Earth, asteroid 2004 MN4, and the sun on June 19, 2004, the day the asteroid was first discovered by UH astronomers David Tholen and Fabrizio Bernardi. Most of the asteroid's orbit is inside that of Earth. (credit: David Tholen)
tholen.tif: David Tholen (credit: Institute for Astronomy)