Astronomers have learned a lot about space over the years, and one thing that they know for certain is that there is still a lot that they don’t understand.

Until recently, scientists assumed that planets could not form around binary star systems. The gravitation of the two stars and their constant motion would make it impossible, they thought. This, of course, was proven wrong.

And according to a study published in the journal Nature, they were even more wrong than they previously understood. The study looked at a binary star system called ʋ Octantis, which is pronounced nu Octantis. This system consists of one star that is 57% heavier than our sun and another that is 43% lighter. Unexpectedly, this system also contains at least one planet, and it is about twice as massive as Jupiter.

Finding a planet in this system was very surprising, but that is not where the unexpected stops. The planet is orbiting the two stars in retrograde. This means that while the stars are orbiting each other in one direction, the planet is orbiting them both in the opposite direction, which is rare even in this already very rare scenario.

You can see the path of the orbit in this brief video:

Professor Man Hoi Lee from the University of Hong Kong talked with IFLScience about this, saying:

“This planet is retrograde in the sense that the planet goes around the primary star (nu Oct A) in the opposite direction as the two stars go around each other. The existence of this planet has been controversial, because there were no observational precedents and we expect planets to form in prograde orbit if they form at the same time as the stars.”

Data has been collected about this system for nearly two decades, and the researchers say that it first formed around 2.9 billion years ago. The smaller star in the system, which is a white dwarf now, used to be much larger than our sun. It evolved quickly due to its size. During that time period, there likely was no planet here at all. Instead, the planet may have formed due to the materials that were ejected from the large star as it evolved into the white dwarf we see today.

Professor Lee explained:

“The discovery that the secondary star (nu Oct B) is a white dwarf means that the binary has evolved significantly in terms of the mass of nu Oct B and the orbit of the binary. When nu Oct B evolved into a white dwarf about 2 billion years ago, the planet could have formed in a retrograde disc of material around nu Oct A accreted from the mass ejected by nu Oct B, or it could [have been] captured from a prograde orbit around the binary into a retrograde orbit around nu Oct A.”

While it was very unexpected to find a planet forming billions of years after the stars that it orbits, it just goes to show that the universe still holds many secrets and surprises.

If you thought that was interesting, you might like to read about a second giant hole has opened up on the sun’s surface. Here’s what it means.