Kappa Coronae Borealis

(The Planet Project)

Kappa Corona Borealis used to be a much hotter class A star, showing that such stars -- which are more massive than the Sun and frequently have surrounding debris disks -- also have real planets to go along with them.


The upper circle shows the location of the class K subgiant Kappa Coronae Borealis (in the constellation Corona Borealis). The planet orbits Kappa Coronae Borealis in 1191 days (3.26 years), averaging 2.7 Astronomical Units from the star, which would place it nicely within our asteroid belt 1.8 times farther than Mars is from the Sun. However, a modest eccentricity of 0.19 makes the planet sweep from as far as 3.2 AU to Kappa to as close as 2.2, a range of a full Astronomical Unit, which would make a fine mess of any asteroid belt that might ever have formed. Since we do not know the planet's orbital tilt, we can measure only a lower limit to its mass, which is at least 1.8 times that of Jupiter.


Kappa Coronae Borealis is a fifth magnitude (4.82) class K (K1) subgiant 102 light years away with a temperature of 4960 Kelvin, a luminosity 14 times solar, and a mass 1.8 times that of the Sun. As a subgiant, it has given up core hydrogen fusion, is just beginning to evolve into a true giant with a current radius 5 times that of our Sun. Though the star will eventually grow in size to near that of the Earth's orbit, its large planet will still be far enough away to escape destruction.

Rho Coronae Borealis, the lower star in the picture, also has an orbiting planet.
Written by Jim Kaler. Return to The Planet Project or go to STARS.