HD 47186 Canis Majoris

(The Planet Project)

cma HD 47186, while quite faint and well out of naked-eye range, is a breakthrough star in that it is was of three with "superearths" that were announced in 2008. Of the three, it has the largest "superearth planet" (in addition to a larger one), which comes in at a minimum of 0.0717 Jupiter masses, or 23 Earth-masses. (HR 40307 in Pictor has three planets with minimum masses of 4.2, 6.9, and 9.2 Earth masses in tight orbits with respective periods of 4.31, 9.62, and 20.5 days, while HD 181433 has a planet of 7.6 Earth masses in an orbit of 9.37 days, in addition to a larger, more Jupiter-like planet.)


The upper circle shows the location of the class G7 dwarf star HD 47186 in the constellation Canis Major, which has two planets, one quite small. The planets orbit their star with periods of 4.08 days and 3.7 years with (assuming the star to have a mass of 0.9 times that of the Sun) orbital sizes of 0.05 and 2.3 Astronomical Units. Lower limits to the masses are estimated at 0.0717 and 0.35 times that of Jupiter (23 and 111 times that of Earth. The system thus appears vaguely like our own Solar System, with an inner smaller planet 12 percent Mercury's distance from the Sun and a more Jovian one about where our asteroid belt would be.


HD 47186 is an 8th magnitude (7.8) class G6 older dwarf in Canis Major. Far too faint to have a proper or Greek letter name, it is known best by its number in the Henry Draper Catalogue. From a distance of 123 light years, it shines with a luminosity of only 0.96 times that of the Sun from a surface with a temperature of 5590 Kelvin. From these values, we infer a radius five percent greater than that of the Sun and a mass of 0.9 solar. Like most stars with planets, HD 47186 is rich in metals, with an iron content 50 percent greater than that of the Sun.

HR 2447, toward the bottom of the picture, also has a pair of orbiting planets.
Written by Jim Kaler. Return to The Planet Project or go to STARS.