Scientists discover asteroid's moon
By Sid Perkins
UPI Science News
WASHINGTON, July 25 (UPI) -- Scientists have found an asteroid with its
own moon.
This discovery, the second of its kind, strengthens the belief among many
astronomers that such objects could be relatively common.
German astronomers discovered the satellite orbiting the asteroid Dionysus
from observations made at a telescope in Chile in May and June of this
year. Initial observations of the asteroid's changing brightness showed
Dionysus has a "day" that is 2.7 hours long. On later nights, the
astronomers noticed an additional dimming and proposed it was caused by
the "eclipse" of an object in orbit around the asteroid.
The scientists from the European Southern Observatory made predictions of
the time of subsequent "eclipses." Further observations from Chile and
from a telescope in the Czech republic confirmed the discovery.
Dionysus's orbit brings it close to the Earth every 13 years. On July 6 it
passed within 10.6 million miles (17 million km) of the Earth. This year's
close approach was the first since the asteroid's discovery that was
favorable for extensive observations.
This is only the second discovery of a satellite orbiting an asteroid. In
August, 1993, a NASA spacecraft passing the asteroid Ida found a small
moon that has since been named Dactyl.
Astronomers have suspected the existence of such objects because of double
impact craters on the Moon and on other planets. Also, some observations
of asteroids passing in front of relatively bright stars have hinted at
the presence of a satellite.
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