The system was discovered by a group of researchers led by Maria Hjorth and Simon Albrecht from the Stellar Astrophysics Centre, Aarhus University Credit: Representational image

Two planets were recently discovered orbiting backwards around their star in a very fascinating planetary system found by scientists. Because of a second star in this system, the newfound orbital architecture is working in reverse, unlike our own solar system.

The system was discovered by a group of researchers led by Maria Hjorth and Simon Albrecht from the Stellar Astrophysics Centre, Aarhus University. Their findings have been published in the journal Proceedings of the National Academy of Sciences. The study, titled “A backward-spinning star with two coplanar planets”, mentions two planets that orbit around the star in nearly the opposite direction as the star rotates around its own axis.

“Here, we show that the star K2-290 A is tilted by 124 ± 6 degrees compared to the orbits of both of its known planets, and has a wide-orbiting stellar companion that is capable of having tilted the protoplanetary disk,” the study explains.

Co-author Rebekah Dawson of Pennsylvania State University, US, says, “In any planetary system, the planets are thought to form in a spinning, circular disk of material that swirls around a young star for a few million years after the star itself is born, the so-called protoplanetary disk. Usually, the disk and the star are spinning the same way. However, if there is a neighboring star, the gravitational force from the neighboring star might tilt the disk.”

Interestingly, the theory explaining the existence of such a planetary system follows the same laws of physics as a spinning top. As the rotation of a spinning top slows down, its axis starts to rotate in a cone-like manner. This is exactly what is happening with the K2-290 system, wherein the planets are being pulled by the gravitational force of another star and hence are skewed from a regular protoplanetary disk.

A report by explains that the theory was first put forward in 2012. The K2-290 system is the first one in which this process has played out.

The scenario was first theorised in 2012, and now this research team has found the first system in which this process has played out.

Teruyuki Hirano of the Tokyo Institute of Technology says, “After we discovered the K2-290 system, we realized this system is ideally suited to test this theory, as it is not only orbited by two planets but also contains two stars. So logically, the next step would be to study the system in finer detail, and indeed we have hit the jackpot.”

One implication of the discovery is that astronomers can no longer assume that the initial conditions of planet formation exhibit alignment between stellar rotation and planetary orbits.

While other theories that aim at explaining misalignments in exoplanet systems tend to work best on large, Jupiter-like planets, in short period orbits the disk-tilting mechanism applies to planets of any size. There may be another Earth-like world, for example, that travels over the north and south poles of its home star.

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