mountain profile Institute for Astronomy University of Hawaii


Maintained by WW

Near-Earth Asteroids.

David Tholen is tracking near-Earth asteroids to help determine which of them may represent an impact hazard to Earth, observing them until they are removed as impact threats. Special attention is being given to (99942) Apophis (rright), with the goal being to detect the Yarkovsky acceleration on this object, which is the largest source of uncertainty of its future impact threat.

Tholen’s group has also measured the density of a small near-Earth asteroid, 2009 BD, via the detection of radiation pressure effects acting on the object. The results indicate a nominal density that is less than that of water, suggesting a very porous internal structure, which has also been seen in a couple of other smallasteroids. If these results can be shown to apply to larger near-Earth asteroids, the potential impact energy estimates could be revised downward, making them less of a threat.

Robert Jedicke also studies Near-Earth Objects and has provided evidence that some small, dark objects catastrophically self-destruct when they approach too close to the Sun



Some near-Earth asteroids can be temporarily captured by the Earth's gravity if they have a slow relative speed while passing through the Earth-Sun Lagrangian points. Robert Jedicke has been calculating the population characteristics of these irregular natural Earth satellites.

He finds that any given time there should be at least one such object of at least 1 meter diameter orbiting Earth. His results are consistent with the single known natural minimoon, 2006 RH120, a few-meter diameter object that was captured for about a year starting in June 2006.  Jedicke estimates that about 0.1% of all meteors impacting the Earth were once minimoons.





Asteroid spectrum

Main-Belt Asteroids


Some of the oldest materials in the solar system are the refractory minerals contained in calcium, aluminum-rich inclusions that are found in chondritic meteorites.  

Bobby Bus has been using infrared spectroscopy to estimate the concentration of these minerals in a number of main-belt asteroids.  He has found several asteroids with concentrations of these minerals 2-3 times higher than in any meteorite. These asteroids must therefore be older than any known sample in our meteorite collections, making them prime candidates for future sample return missions.



Three main-belt, calcium-aIuminum-rich asteroids showing the 2-micron absorption band diagnostic of aluminous spinel.