If planets could talk, a newly-discovered asteroid belt orbiting a double sun about 1,000 light years from Earth may contain one that might send Luke Skywalker this message, since it’s the first evidence of solid planetary material ever discovered in a binary system.
The discovery is interesting for a number of non-Star Wars reasons, according to the announcement published in Nature Astronomy. The biggest, says study lead author Dr. Jay Farihi of the University College London Physics & Astronomy department, was finding out that the white dwarf the team had been studying actually a brown dwarf partner. The binary system – now named SDSS 1557 – is a white dwarf about the mass of our Sun orbited by a large brown dwarf about 60 times more massive than Jupiter. Until now, the exoplanets discovered orbiting binary systems have been gas giants like Jupiter. The asteroid belt in SDSS 1557 means a solid planet could have formed there. The white dwarf is an old star, which implies the asteroids are also old and the belt is stable. The researchers found that the rocks have a high metal content, predominantly silicon and magnesium, and there are a lot of them. Their composition was determined by analyzing the light created by some loose debris as it hit the white dwarf, and the combined mass was about the size of a 4 km asteroid.
Why have no solid planets been found orbiting binary stars before? Dr. Farihi explains:
Building rocky planets around two suns is a challenge because the gravity of both stars can push and pull tremendously, preventing bits of rock and dust from sticking together and growing into full-fledged planets. With the discovery of asteroid debris in the SDSS 1557 system, we see clear signatures of rocky planet assembly via large asteroids that formed, helping us understand how rocky exoplanets are made in double star systems..