Asteroid With Three Moons: Astronomers From Thailand Discover First Known Quadruple
Astronomers have found 3 bodies orbiting Elektra, making it the 1st quadruple asteroid system. They previously knew of the outer 2 moons (shown in orange and green orbits). The fainter, inner body (in blue) is the newly discovered 4th body.
(ESO)
If you have been under the impression that planets are the only cosmic bodies that have moons, here’s some news for you: they’re not. It is, in fact, quite common for even asteroids to have moons, with some space-rocks even possessing more than one!
One prime example of such a system is the asteroid Didymos and its moonlet Dimorphos, which also happen to be the targets for NASA’s DART mission. Such structures aren’t uncommon in our cosmic neighbourhood; even (130) Elektra from the main asteroid belt — located approximately 179.5 million kilometres away from Earth — was thought to be a similar system, with the existence of two of its moonlets already known.
But on February 14, the European Southern Observatory reported that the asteroid (130) Elektra had not two, but three moonlet companions!
Dr Anthony Berdeu, a postdoctoral researcher from the National Astronomical Research Institute of Thailand (NARIT), made the discovery, effectively transforming Elektra into the first quadruple system to ever be detected in the vast space.
How was the third moon discovered?
Elektra, having a 5.5-year-long orbit, spans a width of 200 kilometres. Although not gigantic as per asteroid standards, it is large enough to have been discovered in 1873 and then be tracked.
Its first moon was discovered in 2003 and its second in 2014. However, the discovery of the second moon didn’t particularly create any waves, as the slightly larger asteroid Sylvia had already been found to possess two moons nine years before.
Very recently, a team of researchers from NARIT decided to reanalyse the data acquired three days after the discovery of the second moon. And that is when the presence of the third moonlet, provisionally named S/2014 (130) 2, was discovered.
Dr Berdeu had developed the data processing system used to find the third moonlet for his PhD and applied it to Jupiter’s moons, when he noticed the same telescope had been observing Elektra around the same time.
Why its discovery took so long
S/2003 (130) 1, the first moon, measures 6 kilometres in diameter and orbits Elektra at a distance of roughly 1,300 kilometres. Despite being in a close orbit, it is at a distance that makes it easy to spot. The sizes of the second and third satellites are comparable at 2.0 and 1.6 kilometres wide, respectively.
Now, the second moonlet S/2014 (130) 1 was discovered instantly from the 2014 data. And since the third and second had similar dimensions, you might be wondering why it took another seven years for researchers to figure out that there was a third moon.
That is because the third moon orbits even closer to Elektra, at just 344 kilometres on average. And since it’s 15,000 times fainter than the asteroid it orbits, its light is readily lost in Elektra’s brightness.
Furthermore, S/2014 (130) 2 is so close to Elektra that irregularities in the parent body’s shape distort its already eccentric orbit.
Why does Elektra have three moons?
Sometimes, asteroid moons form when collisions break off chunks of the parent body that never get far enough to escape its gravity. And that’s likely what happened with moon numbers 2 and 3, as the two have overlapping orbits and similar spectra and, therefore, composition.
Given the success of this new data analysis technique, it could probably be employed to find more moons around other asteroids.
“This new detection nonetheless shows that dedicated data reduction and processing algorithms modelling the physics of the instruments can push their contrast limits further,” the team wrote in their research paper.
The findings of this research were published in Astronomy & Astrophysics earlier this month and can be accessed here.
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