A team of astronomers used the Subaru Prime Focus Camera (Suprime-Cam) mounted on the Subaru Telescope to observe faint asteroids with highly inclined orbits. They found that a smaller fraction of tiny bodies occur among high-inclination asteroids than those near the ecliptic plane. This means that large asteroids in high velocity collisions between asteroids probably have a greater increase of strength in resisting disruption than those in the present mean-velocity collisions. Clarification of the relationship between collisional velocity and asteroids’ disruptive strength is helpful in understanding the collisional evolution of asteroids in the early Solar System.

Figure 1
(Left and Center) Optical images from the Subaru Telescope’s Suprime-Cam, obtained in the same field at 20-minute intervals on August 24, 2008. (Right) Processed Image from the two optical images. Only the moving asteroid remains after the background stars and galaxies were masked. It appears to be elongated, because it moved during the 4-minute exposures.
Figure 2
Relationship between the diameter and cumulative number of bodies larger than the size obtained from the observed asteroids. The orange dotted line shows the detection limit for asteroids. The red circles show the diameter range used for evaluation of the distribution slope, which indicates the asteroid population. The crosses show the excluded range. The slope changes at one kilometer, a shift that asteroids near the ecliptic plane also show. The blue and green lines show the estimated slope of asteroids in diameter ranges smaller and larger than one kilometer, respectively. The former provides a basis for comparison with that of asteroids smaller than one kilometer near the ecliptic plane. A difference in the near and far ecliptic populations’ slopes indicates that the collisional evolutions were different.

The scientific paper on which this article is based appears in the Astronomical Journal published on November 5th. (Terai et al. 2013, “High Ecliptic Latitude Survey for Small Main-belt Asteroids”, Astronomical Journal, Volume 146, Issue 5, article id. 111)

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