Wrong-way driver comes from a different solar system

More than a year ago, the asteroid 2015 BZ509 made headlines among astronomers, because it is circling our Sun as a wrong-way driver – its direction of motion is opposite that of all the planets and most other objects. To make this work, this asteroid selected an especially clever orbit, a trisectrix, which is apparently stable over the long term.

Even a year ago, the following was being still said: “Nobody knows exactly where 2015 BZ509 comes from. It might be a former comet that, however, is no longer active.” That wasn’t enough for two astronomers. The researchers simulated the motion of the asteroid over a very long time, namely over the entire existence of the Solar System.

In a paper, they now describe their surprising findings: 2015 BZ509 could never have originated from within the Solar System, because it has never moved in the normal direction. Therefore, the asteroid must have migrated at some point in the far, distant past. Different than Omuamua, which only passed through as a visitor, 2015 BZ509 has settled among us as a migrant. At the time shortly after the creation of the Solar System, the likelihood for such immigration was much greater than it is today, because there were far more young stars in our immediate vicinity.

Image of 2015 BZ509 in the Large Binocular Telescope Observatory (LBTO). This is a negative image, bright stars and the asteroid (with yellow marking) appear black (picture: C. Veillet / Large Binocular Telescope Observatory)

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