HR 1988 Orionis

(The Planet Project)


The circle shows the location of the class G star HR 1988, found in the constellation Orion, is orbited by not one, but two planets. The inner of the pair has mass at least 0.78 times the mass of Jupiter. Like so many other planets of nearby stars, it is tucked up close to its parent at a distance of only 0.13 Astronomical Units (19 million kilometers, or 33% the distance between the Sun and Mercury), causing it to orbit in a mere 14.3 days (16% of Mercury's orbital period). Even though close to its star, its orbital eccentricity is fairly high, the planet going as far from the star as 0.17 AU and as close as 0.09 AU. The outer of the two planets has a much larger mass of 12.7 Jupiters, which makes it close to being a deuterium (heavy hydrogen) fusing brown dwarf and perhaps not a planet at all. The big one orbits in 5.95 years at a mean distance from the star of 3.68 AU (going from 2.4 to 5.0 AU over its "year").


HR 1988, also called HD 38529, is a sixth magnitude (5.95) star in the constellation Orion. Too faint to have a proper or Greek letter name, it is known best by its numbers in the Bright Star(HR) and the Henry Draper (HD) Catalogues. Classed G4 and somewhat cooler than the Sun (5675 Kelvin), the star was originally catalogued as a dwarf (G4 V), but is now considered a subgiant (G4 IV). HR 1988's distance of 138 light years reveals a luminosity 6.5 times that of the Sun, placing it squarely in the subgiant realm, in which stars have either used up their internal hydrogen fuel or will soon begin to do so, the star's mass 1.4 times solar. Like so many of the stars that have orbiting planets, HR 1988 is metal-rich, its iron abundance estimated to be about 70% greater than the Sun's.
Written by Jim Kaler. Return to The Planet Project or go to STARS.