Earth and nearby planets rotate around the sun’s equator through circular orbits. Other dwarf planets like Pluto revolve around the sun through more elongated, tilted orbits. Scientists believe that the distorted orbits were the result of a passing star during the infant stages of the solar system.
Astronomer Paul Kalas from the University of California, Berkeley told Space.com that distant objects in our solar system, like comets and the hypothetical Planet Nine, could have been influenced by these stellar flybys.
While studying exoplanets, Kalas noticed that, in some systems, planets are misaligned even though they were born from a flat, circular disc. He believed that at some point during the development of a planetary system, it was hit by a cosmic tsunami which rearranged everything. (Related: Experts: More than 100 giant exoplanets may have potentially life-hosting moons.)
With the help of his research team, Kalas now has proof to support his theory that stellar flybys, despite wreaking havoc on planetary systems, could help in reshaping them as well.
They focused their study on HD 106906, a pair of yellow-white dwarf stars. These stars are located in the constellation of Crux, about 300 light-years from Earth. They found that this binary star is 15 million years old, relatively young compared to our solar system, which is about 4.6 billion years old. Kalas and his colleagues found that a giant planet was circling HD 106906 on an orbit tilted at 21 degrees. They named this giant planet, which is 11 times bigger than Jupiter, HD 106906 b. Their studies also showed that HD 109609 comes with an asymmetrical disk of dust and a lopsided comet, suggesting that this system experienced a stellar flyby.
Past studies suggest that HD 106906 b was thrown into an eccentric orbit while passing close to its parent stars, while the research Kalas and his team did suggests that HD 106906 b was rescued by the gravitational pull of a passing binary system.
Analyzing data gathered from the European Space Agency’s Gaia space observatory, Kalas and his team are looking for concrete evidence of the flyby. The Gaia space observatory is currently creating a highly precise 3D map of over a billion stars across the galaxy. Using data for 461 stars located in the same cluster, they found that an HD 106906 may have been approached by another binary system some three million years ago. Kalas said that passing stars need to be close to a planetary system to have a major effect. In the case of HD 106906 b, they found that the passing star provided just enough pull to prevent it from flying off into deep space. These new findings may explain the evolution of our solar system. “It’s like going back in time to watch the Oort cloud of comets forming around our young sun,” Kalas said. Just like what they observed with HD 106906, the gravitational pull of our solar system’s giant planets influenced countless comets, kicking them out to eventually become interstellar objects. Others were influenced by the pull of passing stars, which detached them from their orbit, preventing them from being ejected into deep space.
For future studies, Kalas and his team began collaborating with a group of French scientists. They are hoping to measure the movement of stars more accurately to determine if flyby stars exerted more influence on our planet. Kalas is hopeful that this collaboration will give them the data they are looking for.