The asteroid Ida orbits the Sun between the orbits of Mars and Jupiter. It takes about 4.8 years to complete an orbit. Ida has a moon named Dactyl, official designation (243) Ida I Dactyl, discovered in images taken by the Galileo spacecraft during its flyby in 1993. These images provided the first direct confirmation of an asteroid moon. Dactyl is heavily cratered, like Ida, and consists of similar materials, suggesting they are fragments of the same parent body. Ida is the dot on the right side of the image above. The image on the left is our best closeup of Dactyl to date. Dactyl is about 1.6 x 1.4 x 1.2 km across.
The large space rock that whizzed past Earth yesterday is most likely a dead comet. It bears an odd resemblance to a skull—fitting for Halloween. This image of the asteroid known as 2015 TB145 was generated from radar data collected by the National Science Foundation’s 305-m Arecibo Observatory in Puerto Rico on 30 October.
This collage of radar images of near-Earth asteroid 2005 WK4 was assembled from data taken by the (70-meter) Deep Space Network antenna at Goldstone, California, on 8 August, 2013.
The data were obtained between 12:40 and 7:10 am PT when the asteroid was about 3.1 million km from Earth (that’s a bit more than 8X the distance to the Moon). The asteroid completed almost 2-1/2 rotations while the data were taken. As it rotated, the images seem to show some flat regions and a bulge near the equator. The asteroid is between 200 and 300 meters in diameter with rounded, asymmetric shape. Resolution of the images is around 4 meters per pixel. (Click the image to embiggen it.)
This radar image of asteroid 2005 YU55 was obtained on 7 Nov., 2011, at 11:45 a.m. PST (2:45 p.m. EST/1945 UTC), when the space rock was at 3.6 lunar distances, which is about 860,000 miles, or 1.38 million kilometers, from Earth. Image credit: NASA/JPL-Caltech
The asteroid safely will safely fly past our planet slightly closer than the moon’s orbit on 8 Nov.. The last time a space rock this large came as close to Earth was in 1976, although astronomers did not know about the flyby at the time. The next known approach of an asteroid this size will be in 2028.