You may have recently heard about HD 106906b, the latest of many oddballs in the rapidly growing exoplanet family. This planet orbits far away from its star, far enough that it is not lost in the glare, and can be seen with some of our best telescopes. In fact, it orbits farther from its star than any other known planet: an astounding 650 times the distance from Earth to the Sun. That’s 30 times the distances to Neptune.
We have no idea how this planet got there. Planets are supposed to form from a disk of gas and debris surrounding a young star, but there shouldn’t be enough gas that far out to form a planet this big. After all, it’s 11 times the mass of Jupiter. More likely, it collapsed directly out of the protostellar nebula along with the star itself. However, we’re still not sure how to make objects that small that way.
But its weird location is not this planet’s only claim to fame. A few planets have been directly imaged by telescopes before, but they’re usually in infrared light, where stars are dimmer and planets are brighter. Only two planets have ever been imaged in wavelengths of light that our eyes can see. The first was Fomalhaut b. The second is HD 106906b.
This planet was spotted in red light by the Hubble Space Telescope. It was possible because it not only orbits very far from its star, but it is also very young–only 13 million years. At that age, the planet is still glowing red hot from its formation, making it possible for Hubble to see it. Seeing smaller, more Earth-like planets is a much more difficult problem that we don’t yet have the technology to do…but we’re working on it. However, that is a story for another day.