Astronomers discover a planet so massive it defies classification

Scientists using the Subaru Telescope in Hawaii have discovered a "super-Jupiter" orbiting around the bright star Kappa Andromedae. The planet, which is about 13 times the size of Jupiter, glows with a reddish color and skirts the line between planet and star on account of its tremendous mass. Moreover, its parent star now holds the record for the most massive sun known to host a directly imaged planet or lightweight brown dwarf companion.

Called Kappa Andromedae b (or 'Kappa And b,' for short), it is 170 light-years away and sits in an orbit about 1.8 times farther than Neptune's. It's also quite young, as its parent star is only 30 million years old (compared to our sun's 5 billion years).

But more interestingly, the object is sitting on the dividing line that separates the most massive planets from the lowest-mass brown dwarfs — a so-called "failed star" that's not big enough to sustain nuclear fusion in its core. Because the astronomers are not sure how to classify it, they're dubbing it a "super-Jupiter." Subsequently, it could represent a celestial "bridge" between planets and stars.

Astronomers discover a planet so massive it defies classification

"According to conventional models of planetary formation, Kappa And b falls just shy of being able to generate energy by fusion, at which point it would be considered a brown dwarf rather than a planet," noted NASA's Michael McElwain through their official release. "But this isn't definitive, and other considerations could nudge the object across the line into brown dwarf territory."

Massive planets like this one radiate the heat that's left over from their own formation, what gives them their star-like attributes. They are teetering on the edge of being a full-blown star. Even Jupiter radiates energy — about twice the amount it receives from our Sun.

But for those objects the size of Kappa And b, they're able to generate energy internally by fusing a heavy form of hydrogen called deuterium. And interestingly, this super-Jupiter is situated at the exact theoretical minimum for this to happen — about 13 Jupiters worth of mass. Consequently, it could very well be a brown dwarf.

And indeed, the massive planet is in fact releasing the heat trapped within it as infrared radiation. It may even be generating some heat from low levels of deuterium fusion in its core. Further analysis with the infrared camera will help to confirm these suspicions.

The discovery also shows that large stars are capable of producing exceptionally large planets. That said, the astronomers believe that this stellar scaling can only extend so far — perhaps to objects only a few times the mass of our sun. Interestingly, the Kappa Andromedae star fits the bill at 2.5 times the size of our sun.

The scientists made the discovery by using the High Contrast Instrument for the Subaru Next Generation Adaptive Optics (HiCIAO) and the Infrared Camera and Spectrograph (IRCS) mounted on the Japanese Subaru Telescope atop Mauna Kea, Hawaii.

You can read the entire study here.

All images via NASA/JPL/NASA's Goddard Space Flight Center/S. Wiessinger