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The asteroid Hermes was re-discovered last week after being lost for 66 years. Using Now planetary scientists are analyzing new radar measurements from the Arecibo Observatory, Puerto Rico, the world's largest single-dish radio telescope, have determined that the asteroid is in fact two objects orbiting each other. The two objects together would cover an area approximately the size of a small city.
Hermes makes frequent close approaches to Earth, Venus, Mars, as well as Vesta, the third largest asteroid in the main asteroid belt between Mars and Jupiter. While several other asteroids have satellites, they normally consist of a large asteroid orbited by a much smaller one. Hermes becomes a unique exception to this rule.
"Hermes is the first asteroid ever discovered in the near-Earth population where the two components are essentially equal in size," Margot said. "It's a very unusual binary, a puzzle. It may have formed when it swung so close to a planet that it was ripped apart by gravitational forces, but we don't know for sure. One of our goals is to learn more about the two components and how they rotate about each other in the hopes that we may be able to deduce how Hermes became a double asteroid.” said Brian Marsden, of the Minor Planet Center in Cambridge, Massachusetts, USA.
"Because the components are close to each other, they raise appreciable tides in each other and each has slowed down the other's spin significantly. They are now likely in a doubly synchronous state, where their spin period is equal to their orbital period. This means they constantly present the same face to each other, just like Pluto and its satellite, Charon. Hermes, was first observed in 1937 as a fast-moving bright object and then went undetected until last week, although it had circled the sun almost exactly 31 times since then,” Brain concluded.
On 15 October, Brian Skiff of the Lowell Observatory Near-Earth-Object Search sighted a mysterious object; Timothy Spahr at the Minor Planet Center in Cambridge identified similarities with the 1937 observations, and Steven Chesley and Paul Chodas at NASA's Jet Propulsion Laboratory (JPL) linked the observations to Hermes.
The same day, the Arecibo Observatory's team proposed to observe the asteroid with their high-powered radar system, a proposal that was accepted within hours. The goals of the proposal were to measure precisely the distance and velocity of this object, to improve the knowledge of its trajectory and help trace back its history, to characterize Hermes' physical properties, and to search for satellites.
Hermes gets as close as 378 000 miles from Earth, which, in astronomical terms, is quite close, about 1.6 times the distance between Earth and the moon. Orbits can change over time due to gravitational influences of the planets. Hermes travels on an elliptical orbit and reaches deep into the inner solar system, crossing Venus' orbit. The new research has made it possible to extend the time interval over which the trajectory can be computed reliably.
More info: Arecibo Observatory
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