Isaac Schultz
Astronomers in Poland have discovered a nearby exoplanet more than 11 times the mass of Jupiter, comfortably putting it in the pantheon of the most massive known worlds.
The object is a cold super-Jupiter; simply put, that means it is cold and larger than Jupiter, the measuring stick by which the largest planets are measured. The characteristics of the oversized exoplanet—as well as the star system in which it resides—were described in a paper published last month in Astronomy & Astrophysics.
The huge world sits in a multi-planet system a little over 300 light-years from Earth in the Great Bear constellation. The host star in the system, HD 118203, is about 20 percent more massive and twice as large as our Sun, but is older than our star. One of the other planets in the system—a hot Jupiter just twice the size of Earth—was spotted by the Transiting Exoplanet Survey Satellite (or TESS) back in 2005.
“Doppler observations, however, indicated that this was not the end of the story, that there might be another planet out there,” said Andrzej Niedzielski, an astronomer at Nicolaus Copernicus University in Poland, in a university release. “Therefore, we immediately included this system in our observational programs.”
Using TESS data and measurements from the 12-foot (3.6-meter) Telescopio Nazionale Galileo and Texas’ roughly 30-foot (9 meter) Hobby-Eberly telescope, the team scrutinized the system and realized there was another object orbiting the star. Though the planet itself is not visible—the star is too bright for the planet to be seen—the team deduced its presence through radial velocity data that caused the star’s brightness to slightly change over time.
In an eccentric twist, the hot Jupiter spotted in 2005 was found to be in an orbit just over six days long. The recently described cold super-Jupiter has a much more leisurely orbit: It takes the exoplanet about 14 years to complete its circumnavigation of its star.
The huge exoplanet is not the largest known to astronomers. That title belongs to TrES-4b, which sits about 1,430 light-years away in the constellation Hercules. TrES-4b is 142,915 miles across (230,000 kilometers), compared to Jupiter’s mere 88,670-mile (142,700 km) radius. But TrES-4b is a little less massive than Jupiter—so the newly described world is definitely denser.
The line between “most massive exoplanet” and “least massive brown dwarf” tends to blur, but at roughly 11 Jupiter masses, the cold super-Jupiter is in the same wheelhouse as the huge Beta Pictoris b, which is about 12 times the mass of Jupiter and 63 light-years away from Earth.