It’s not every day that NASA uses the term “Planet Nine” in a press release, so when it did in a recent one about new Hubble telescope observations of a massive exoplanet orbiting a nearby young binary star system, it garnered a lot of attention from Planet Nine proponents. Why is NASA interested in HD 106906 b and why have they linked it with the potential existence of Planet Nine in our solar system?
"This system draws a potentially unique comparison with our solar system. It's very widely separated from its host stars on an eccentric and highly misaligned orbit, just like the prediction for Planet Nine. This begs the question of how these planets formed and evolved to end up in their current configuration."
Meiji Nguyen of the University of California, Berkeley, is the lead author of a paper in The Astronomical Journal describing the strange orbit of HD 106906 b, an exoplanet 11 times the size of Jupiter orbiting binary stars a mere 336 light years from Earth. Discovered in 2013 by astronomers using the Magellan Telescopes in Chile, its orbit was unknown until the more powerful Hubble telescope picked it up. The HD 106906 binary system is only 15 million years old – a newborn when compared to 4.5 billion-year age of our solar system. That means whatever happened to put HD 106906 b in its current weird and far-flung orbit happened recently. Could the same thing have happened to our own rumored Planet Nine shortly after its birth?
“The prevailing theory is that it formed much closer to its stars, about three times the distance that Earth is from the Sun. But drag within the system's gas disk caused the planet's orbit to decay, forcing it to migrate inward toward its stellar pair. The gravitational effects from the whirling twin stars then kicked it out onto an eccentric orbit that almost threw it out of the system and into the void of interstellar space. Then a passing star from outside the system stabilized the exoplanet's orbit and prevented it from leaving its home system.”
Paul Kalas, another Berkeley professor and co-author, explains in the university's press release how HD 106906 b started out in a tight orbit around its two stars before being flung like an Olympic hammer throw on a path that would take it out of the system completely. However, a passing star’s gravity caught it and pushed it back into a new orbit more than 730 times the distance of Earth from the Sun. In addition, this new extreme orbit is misaligned, elongated and external to the debris disk of the twin host stars – a disk similar to our own solar system’s Kuiper Belt. That disk itself is distorted, which helped the team define HD 106906 b’s orbit.
“The idea is that every time the planet comes to its closest approach to the binary star, it stirs up the material in the disk. So, every time the planet comes through, it truncates the disk and pushes it up on one side. This scenario has been tested with simulations of this system with the planet on a similar orbit — this was before we knew what the orbit of the planet was.”
Team member Robert De Rosa describes why this phenomena made the astronomers think of Planet Nine – not only do some scientists believe it was violently kicked out of a close solar orbit early in its life and saved by a passing star, this could explain the strange clusterings of space rocks in the Kuiper Belt.
“What I really think makes HD 106906 unique is that it is the only exoplanet that we know that is directly imaged, surrounded by a debris disk, misaligned relative to its system and is widely separated. This is what makes it the sole candidate we have found thus far whose orbit is analogous to the hypothetical Planet Nine.”
Meiji Nguyen says HD 106906 b is real and makes the connection to Planet Nine. As we’re finding so often when it comes to new discoveries in astronomy – if there’s one, there’s more. Knowing how HD 106906 b came into existence and moved to its current eccentric location and orbit gives astronomers a better roadmap to proving the existence of Planet Nine and finding it. NASA scientists are already planning to use the James Webb Space Telescope, scheduled to be launched in 2021, to further observe HD 106906 b and also look for other similar oddball exoplanets.
Look out, Planet Nine – they’re coming for you!