It is easy to see why understanding planetary evolution, or how planets form, is an important branch of astronomy. If we know that, we can hopefully work our way down to how planets evolved to a point where life as we know it sprouted on them, which in turn could help us find either other planets that have life or can at least support it.
But it is not an easy exercise, since tracing the distant pasts of existing planets is complicated and fraught with uncertainty, and finding newly formed planets is not a common occurrence. Which is precisely why HD 106906b, a massive planet in a solar system about 300 light-years away, is of great importance.
HD 106906b is about 11 times the mass of Jupiter and orbits its star once every 1,500 years. And significantly, it is less than 13 million years old, compared to say, Earth, which is over 4.5 billion years old.
“This is such a young star; we have a snapshot of a baby star that just formed its planetary system — a rare peek at the final stage of planet formation,” Smadar Naoz, an assistant professor of physics and astronomy at University of California, Los Angeles, and a co-author of a recent research paper on the subject, said in a statement Thursday.
The exoplanet is quite unusual in at least one other way: it orbits its star at a distance of over 650 times between Earth and the sun. For context, Neptune, the outer-most planet in our solar system, orbits the sun at about 30 times the Earth-sun distance. Even the erstwhile planet Pluto, which is far beyond Neptune, is less than 50 times that distance at its farthest.
According to current theories of planet formation, they are usually found within a large disk-shaped space that is relatively close to the center of the star system (whose outer edge is the Kuiper Belt, in the case of our solar system). But HD 106906b lies way outside that that disk of debris. The study, titled “HD 106906: A Case Study for External Perturbations of a Debris Disk” and published in the Astrophysical Journal Letters, suggests the planet formed outside the disk, inside of forming inside and then being pushed out.
The study’s lead author Erika Nesvold, a postdoctoral fellow at the Carnegie Institution for Science, wrote a computer program, originally for the Kuiper Belt, to model the planet’s elliptical orbital path. The software allowed the researchers to explain the shape of the debris disk near the planet without needing to introduce other planets into the picture, none of which have been discovered so far.
HD 106906b was discovered in 2013, and the debris disk around it star was photographed in 2016.