Near-Earth Asteroid Hermes Is Redetected

An asteroid that has been missing for 66 years was rediscovered last week and found to be an unusual pair of objects traveling together in an orbit that comes much closer to Earth than other large asteroids.

The fast-moving object was first observed in 1937 and named Hermes, but it quickly disappeared and was not seen again until Oct. 15, even though it had circled the sun nearly 31 times since then.

It was redetected by Brian Skiff of the Lowell Observatory Near-Earth Object Search. Steven Chesley and Paul Chodas of Caltech’s Jet Propulsion Laboratory later identified it as Hermes.

As soon as it was detected, Jean-Luc Margot and his colleagues at UCLA sought permission to study Hermes using the high-powered radar telescope at the Arecibo Observatory in Puerto Rico, a request that was granted within hours.

They discovered that Hermes is actually two objects -- with a total size about that of Disneyland -- orbiting each other, an unusual occurrence.

Many asteroids have a much smaller companion orbiting them, but “Hermes is the first asteroid ever discovered in the near-Earth population where the two components are essentially equal in size,” Margot said.

The pair are in a doubly synchronous state, in which their spin period is equal to their orbital period, so that they constantly present the same face to each other.

Using the new observations, researchers have been able to map Hermes’ orbit around the sun from the year 1561 to 2103. The team found that it comes within 378,000 miles of Earth, about 1.6 times the distance from Earth to the moon.

Its last close approach was in 1942, but astronomers did not notice it at the time.