The Hubble Space Telescope has discovered something truly unique – a pair of orbiting asteroids that are behaving like a comet.
A group of astronomers used the NASA/ESA telescope to observe the system known as 288P in September 2016, just before it made its closest approach to our Sun. To their surprise, 288P is not a single asteroid, as previously thought, but a pair of orbiting space rocks with very unusual characteristics.
The asteroids are orbiting at a distance of about 100km, much farther than any other known binary pair. But what’s also unusual is that they are exhibiting the features of a comet, including a bright coma and a long tail.
“We detected strong indications of the sublimation of water ice due to the increased solar heating – similar to how the tail of a comet is created,” explained Jessica Agarwal of the Max Planck Institute for Solar System Research in Germany, the team leader and main author of the research paper published in Nature.
Hubble photographed a pair of asteroids orbiting each other that have a tail of dust, which is a comet-like feature. The odd object, called 2006 VW139/288P, is the first known binary asteroid that is also classified as a main-belt comet. Roughly 5,000 years ago, 2006 VW139/288P probably broke into two pieces due to a fast rotation.
(Credits: NASA, ESA, and J. Agarwal, Max Planck Institute for Solar System Research)
This strange behavior makes 288P the first known binary asteroid that is also classified as a main-belt comet. There are other asteroids that orbit each other and those that are releasing vapor, but this is the first time astronomers have seen both characteristics at once.
Astronomers take every chance they can get to study asteroids up close because these space rocks hold vital clues as to how certain planets, like Earth, end up with water, while others get none. The composition of asteroids in the asteroid belt of our Solar System has remained virtually the same since the planets were formed, telling us a lot about the materials that went into making those planets and how they may have been formed.
But asteroids are very difficult to examine because, in cosmic terms, they’re pretty small and dim. Having one pass close by is a great opportunity for study and the fact that these two orbit each other allows the researchers to gather more information, including calculating their masses. The fact that the system is trailing water also proves that it hasn’t been in this binary situation for long.
"Surface ice cannot survive in the asteroid belt for the age of the Solar System but can be protected for billions of years by a refractory dust mantle, only a few metres thick,” said Agarwal.
288P has probably only existed as an orbiting pair for about 5000 years. It probably started as one asteroid that broke up because of how fast it was rotating and then the two large orbiting fragments were pushed further away from each other by the gases and dust they are ejecting. It may just be a coincidence that such an unusual pairing presented for study, it could be quite a unique system. But it nonetheless will be an extremely important system for future studies.
Asteroids are a ripe field for further study, with some citizen projects hoping to be able to mine their riches and agencies like NASA funding further research into them. NASA’s Osiris-Rex mission is currently travelling through space to a nearby asteroid in the hopes of taking a sample from it and returning it to Earth.