Astronomers this week announced they have directly imaged the smallest planet yet found around a sun-like star. The planet, GJ 504b, is about four times the mass of Jupiter. It orbits its star at around 43 times the distance from Earth to the sun and has a dark pink color. The star GJ 504 is a main sequence (G0 stellar classification) star that is slightly hotter than the sun and located 57 light-years away from our solar system. It can be faintly seen near the constellation Virgo.

“If we could travel to this giant planet, we would see a world still glowing from the heat of its formation with a color reminiscent of a dark cherry blossom, a dull magenta,” said Michael McElwain, a team member on the discovery and an astronomer at NASA’s Goddard Space Flight Center. “Our near-infrared camera reveals that its color is much more blue than other imaged planets, which may indicate that its atmosphere has fewer clouds.”

GJ 504b was spotted using the infrared Subaru Telescope, located in Hawaii. It was found as part of the Strategic Exploration of Exoplanets and Disks with Subaru (SEEDS) project, which began in 2009. A new paper describing the planet will soon be published in The Astrophysical Journal.

Apart from its interesting size, the distance of GJ 504b from its star could call into question current hypotheses about the formation of gas giants like Jupiter. The current model has solid material coalescing into a core, which attracts gas from a star’s accretion disc. Such a process would be hard to explain at GJ 504b’s distant orbit.

“This is among the hardest planets to explain in a traditional planet-formation framework,” said Markus Janson, another team member and a Hubble postdoctoral fellow at Princeton University. “Its discovery implies that we need to seriously consider alternative formation theories, or perhaps to reassess some of the basic assumptions in the core-accretion theory.”

(Image courtesy Goddard Space Flight Center/S. Wiessinger)