First quadruple asteroid discovered in the solar system
Astronomers have discovered the first known quadruple asteroid system. A team from Thailand and France spotted a third moon orbiting the main-belt asteroid Elektra, moving the object into the record books.
Most asteroids are solo travelers, but some are gravitationally bound in pairs – usually with one small object orbiting a larger one. On rare occasions, triple asteroid systems have been found, with two moons orbiting a bigger primary body. That was as complex as asteroid systems got, until now.
The asteroid Elektra, orbiting the Sun in the outer region of the main asteroid belt, was first discovered in 1873, with a sizeable diameter of around 200 km (124 miles). However, its first moon wasn’t spotted until 2003, when a 6-km (3.7-mile) rock was detected orbiting around it every five days, at a distance of about 1,300 km (808 miles). Moon number two turned up in 2014 – a smaller rock of just 2 km (1.2 miles) orbiting 500 km (310 miles) from Elektra every 1.2 days.
And now a third moon has been found, making Elektra a quadruple asteroid system. This one measures just 1.6 km (1 mile) wide, orbiting the main body every 16 hours at a distance of 344 km (214 miles). 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 the Very Large Telescope (VLT) in Chile. These algorithms reduce the glare of light from the main asteroid and remove it from the image, allowing fainter objects to become visible. When this was applied to the 2014 dataset in which the second moon was discovered, Berdeu found the third. To confirm, the team applied the algorithms to two other datasets of Elektra, and sure enough, the third moon was visible in each.
It may be the first quadruple asteroid discovered, but Elektra likely won't be the last. The team says that this method could be used to image other asteroids and solar system objects, to potentially find other hidden moons.
The research was published in the journal Astronomy & Astrophysics.