Astronomers have discovered the first known quadruple asteroid system. A team from Thailand and France have discovered a third moon orbiting the main-belt asteroid Elektra, putting the object in the record books.
Most asteroids travel alone, but some are gravitationally bound in pairs, usually with a small object orbiting a larger one (imagine planet Earth and the Moon as a small asteroid orbiting them).
Triple asteroid systems, with two moons orbiting a larger primary body, have been found on rare occasions. Until now, asteroid systems were no more complex.
The asteroid Elektra, which orbits the Sun in the outer region of the main asteroid belt, was discovered in 1873, with a considerable diameter of about 200 km.
However, its first moon was not seen until 2003, when a 6 km rock was detected orbiting it every five days, at a distance of about 1,300 km. Moon number two appeared in 2014: a smaller rock just 2 km long that orbits 500 km from Elektra every 1.2 days.
And now a third moon has been found, making Elektra a quadruple asteroid system. It is only 1.6 km wide and orbits the main body every 16 hours at a distance of 344 km.
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While the other two moons orbit in roughly circular paths, the third follows an eccentric egg-shaped orbit.
The discovery was made by Dr. Anthony Berdeu, applying new algorithms he developed to archival data from Chile’s Very Large Telescope (VLT).
These algorithms reduce the glare of light from the main asteroid and remove it from the image, allowing objects weakest are visible. When this was applied to the 2014 dataset in which the second moon was discovered, Berdeu found the third.
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To confirm this, the team applied the algorithms to two other Elektra data sets, and sure enough, the third moon was visible in each of them.
It may be the first quadruple asteroid discovered, but Elektra probably won’t be the last. The team says this method could be used to image other asteroids and solar system objects, to potentially find other hidden moons.