Behold! Astronomers Discover First-Ever Asteroid With Three Moons

An asteroid discovered in the nineteenth century has now been classified as the most crowded object ever discovered.

Elektra and its three moons. (ESO/Berdeu et al., Yang et al.)

It's known as 130 Elektra, or just Elektra, and scientists have recently found that it has three smaller satellite companions or moons. This not only makes it the most numerous asteroid system discovered to date, but it also indicates how we can locate more dim, difficult-to-see asteroid moons in the future.

Anthony Berdeu, one of the authors of the research paper, said: "Elektra is the first quadruple system ever detected. This new detection … shows that dedicated data reduction and processing algorithms modeling the physics of the instruments can push their contrast limits further."

Although it is not unheard of for asteroids to have smaller partners, seeing them is extremely rare. Approximately 150 of the over 1,100,000 asteroids found so far have at least one moon. 

Elektra, which is about 260 kilometres wide, was found in the asteroid belt between Mars and Jupiter in 1873, but its first moon, S/2003 (130) 1, was identified 130 years later in 2003. S/2014 (130) 1, its second moon, was found in 2014.

There's a reason why it takes so long to locate these satellites. Asteroids are tiny and, at best, weakly illuminated. Anything even smaller than an asteroid will be darker, fainter, and potentially significantly outshone by its parent asteroid.

The smaller and closer the moon is to the asteroid, the more difficult it will be to view. It's comparable to the reason why it's difficult to observe exoplanets orbiting other stars.

S/2003 (130) 1 is just 6 kilometres wide and orbits Elektra at a distance of roughly 1,300 kilometres on average; S/2014 (130) 1 is only 2 kilometres across and orbits Elektra at a distance of 500 kilometres on average.

S/2014 (130) 2 is the newest found moon, and it is even smaller and closer: only 1.6 kilometres wide, with an average orbital distance of 340 kilometres. It's also 15,000 times less bright than Elektra.

Berdeu and his colleagues discovered it by running archival data from the SPHERE instrument attached to the European Southern Observatory's Very Large Telescope through a newly built data reduction pipeline to efficiently eliminate noise from raw data.

Although the scientists were able to collect some basic information about S/2014 (103) 2, there is still a great deal of mystery regarding its motion around Elektra. Furthermore, we don't know a lot about how these systems form.