Astronomers Image Giant, Lowest-mass Exoplanet GJ 504b Around Sun-Like Star

Astronomers have discovered the lowest-mass exoplanet around a sun-like star. The planet, called GJ 504b, is several times the mass of Jupiter.

The planet orbits around its star- GJ 504- at nearly nine times the distance between Sun and Jupiter and was imaged using data from Subaru Telescope in Hawaii.

GJ 504b orbits around a G0-type star GJ 504, which is slightly hotter than the Sun and can be seen with the naked eye in the Virgo constellation. GJ 504b is four times the mass of Jupiter and has a temperature of about 460 degrees Fahrenheit (237 Celsius).

"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. 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," said Michael McElwain, a member of the discovery team at NASA's Goddard Space Flight Center in Greenbelt, Md.

The discovery shows that models describing giant-planet formation need to be revaluated.

The core accretion model is most widely accepted to understand the formation of huge Jupiter-like planets. The model claims that massive planets are formed from the gas-rich debris disk of young stars. The rocks form asteroid collisions provide the seed for the planet. When this seed gathers sufficient mass, it attracts gas from the disk. There are many drawbacks in this model.

One issue with the model is that it only explains the formation of planets present at a certain distance from their stars. Neptune, for example, has an orbit of about 30 times the average distance between earth and sun (30 astronomical units, or AU). However, the new planet GJ 504b orbits at an estimated 43.5 AU from its star, NASA said.

"This is among the hardest planets to explain in a traditional planet-formation framework," said team member Markus Janson, a Hubble postdoctoral fellow at Princeton University in New Jersey, according to a news release from NASA "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."

The research is a part of Strategic Explorations of Exoplanets and Disks with Subaru (SEEDS) and a paper describing the research is accepted for publication in The Astrophysical Journal.

"Our sun is about halfway through its energy-producing life, but GJ504 is only one-thirtieth its age," added McElwain. "Studying these systems is a little like seeing our own planetary system in its youth."