An international team of astronomers discovered a planet several times the mass of Jupiter and orbits its sun at about nine times the distance, according to a NASA press release.
Named GJ 504b, it is the lowest-mass planet ever detected around a star like the sun using direct imaging techniques. Using infrared data from the Subaru Telescope in Hawaii, the team also discovered the planet's unique deep magenta color.
"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 member of the discovery team at NASA's Goddard Space Flight Center in Greenbelt, Md. "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."
Planets like Jupiter start in gas-rich debris disks surrounding a young star and get their core from the collisions of asteroids and comets. When the core's mass reaches a high enough level, its gravitational pull attracts gas from the disk to form the planet.
While this model is effective for planets in our solar system, it poses a problem with determining how a planet as far away from its sun as GJ 504b forms. On the outer rim of our solar system, Neptune lies at average distance of 30 astronomical units (AU) away. GJ 504b is estimated at 43.5 AU, but our line of sight with the system has not been determined.
"This is among the hardest planets to explain in a traditional planet-formation framework," explained team member Markus Janson, a Hubble postdoctoral fellow at Princeton University in New Jersey. "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 part of a project to image extrasolar and protoplanetary disks around hundreds of nearby stars. The Strategic Explorations of Exoplanets and Disks with Subaru (SEEDS), based in Mauna Kea, Hawaii, is a five-year project started in 2009 and led by Motohide Tamura at the National Astronomical Observatory of Japan (NAOJ).
A paper with the team's results will be in a future edition of the Astrophysical Journal. GJ 504b is about four times as massive as Jupiter and is about 460 degrees Fahrenheit. GJ 504, the star it orbits, is slightly hotter than the sun and just barely visibile in the Virgo constellation.
Young stars and solar systems are more attractive for astronomers to image because the heat and evidence of their formation is still fresh, enhancing their infrared brightness.
"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."
