Hubble pins down weird exoplanet with far-flung orbit that behaves like the long-sought 'Planet Nine'

A planet in an unlikely orbit around a double star 336 light-years away may offer a clue to a mystery much closer to home: A hypothesized, distant body in our solar system dubbed "Planet Nine."

This is the first time that astronomers have been able to measure the motion of a massive Jupiter-like planet that is orbiting very far away from its host stars and visible debris disk. This disk is similar to our Kuiper Belt of small, icy bodies beyond Neptune. In our own , the suspected Planet Nine would also lie far outside of the Kuiper Belt on a similarly strange orbit. Though the search for a Planet Nine continues, this exoplanet discovery is evidence that such oddball orbits are possible.

"This system draws a potentially unique comparison with our solar system," explained the paper's lead author, Meiji Nguyen of the University of California, Berkeley. "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."

The system where this gas giant resides is only 15 million years old. This suggests that our Planet Nine—if it does exist—could have formed very early on in the evolution of our 4.6-billion-year-old solar system.

An extreme orbit

The 11-Jupiter-mass exoplanet called HD 106906 b was discovered in 2013 with the Magellan Telescopes at the Las Campanas Observatory in the Atacama Desert of Chile. However, astronomers did not know anything about the planet's orbit. This required something only the Hubble Space Telescope could do: Collect very accurate measurements of the vagabond's motion over 14 years with extraordinary precision. The team used data from the Hubble archive that provided evidence for this motion.

The exoplanet resides extremely far from its host pair of bright, young stars—more than 730 times the distance of Earth from the Sun, or nearly 6.8 billion miles. This wide separation made it enormously challenging to determine the 15,000-year-long orbit in such a relatively short time span of Hubble observations. The planet is creeping very slowly along its orbit, given the weak gravitational pull of its very distant parent stars.