23 Librae

(The Planet Project)


The circle shows the location of the class G dwarf (G4 V) 23 Librae (in the constellation Libra). The planet is in roughly the middle of the mass range of those planets so far discovered, with a minimum mass 1.58 times that of Jupiter. Unlike many of the first planets found, it is also relatively far from its parent star, averaging 0.81 Astronomical Units (122 million kilometers, 12 percent farther than Venus is from the Sun). Like so many extraterrestrial planets, the orbit is relatively eccentric, the planet approaching as closely as 0.62 Astronomical Units, and receding to as far as 1.00 AU, as far as the Earth is from the Sun, the whole course taking 260 days.


At faint sixth magnitude (6.45, almost 7th), 23 Librae is for most of us just under naked-eye visibility, though easily seen in binoculars just to the south of the classic figure of Libra. This class G solar type star (G4 V, possibly G5 V) is just a bit cooler (5700 Kelvin) than the Sun. At a distance of 84 light years, the star is, however, half again as luminous as the Sun (a factor of 1.49). The combination of luminosity and temperature shows that 23 Librae has a mass very nearly that of the Sun (1.05 solar), but is older (age brightening solar-type stars), with an age close to 9 billion years, near the time at which hydrogen fusion inside will shut down and the star will begin to die and become a giant. Like so many stars that have planets, 23 Librae is metal-rich, its iron content 70 percent greater than that seen in the Sun. 23 Librae is also a bit unusual in having a fairly high velocity of 77 kilometers per second relative to the Sun, over 3 times that of most normal stars.
Written by Jim Kaler. Return to The Planet Project or go to STARS.