Giant Planet In Baby Stellar System Hints At Unusual Planet Formation

Artist's impression of an exoplanet orbiting outside a debris disk. ESO/ESA/Lynette R. Cook/L. Calcada/IFLScience

HD 106906b is a remarkable and puzzling exoplanet. New observations suggest it formed where it couldn't, farther from its star than one would expect.

The exoplanet is 11 times the mass of Jupiter and located 300 light-years away. It’s 650 times farther from its star than Earth is from the Sun, and that’s the main issue. According to astronomers, it must have formed outside the debris disk, which is odd since most planets usually form within it. These observations are reported in Astrophysical Journal letters.

“Our current planet formation theories do not account for a planet beyond its debris disk,” co-author Smadar Naoz, an assistant professor from UCLA, said in a statement. 

The system is young, not more than 13 million years. It is so young that the star is still surrounded by a large disk of rocky planet-forming material. While several young systems have been observed, for example TW Hydrae, in those cases the planets were forming inside the debris disk.

“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," added Naoz.

While this external formation is mysterious, the effect of this exoplanet on the disk is well understood. HD 106906b's orbit is very elliptical and its gravity has been warping the debris disk. They show via computer simulations that there’s no need for any more planets to recreate the shape of the disk.

These findings suggest that external planets might be just as important as internal planets when it comes to shaping debris disks, and that the shape is crucial for the orbits of planets.

It is a very exciting time to study planetary formation. We have discovered over 3,450 exoplanets and more are added every week. Each one gives us a piece of a large and complicated puzzle. HD 106906b is the latest piece we have, but there are still a lot more to find before we have an idea of what the full picture looks like.

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