Upsilon Andromedae

(The Planet Project)

The circle shows the location of the class F star Upsilon Andromedae (in the constellation Andromeda). Like Mu Arae, it is unusual in having three known planets. It also has a binary companion.

THE PLANETS

*Planet 1 orbits in 4.62 days, has a mass at least 0.71 times that of Jupiter, and is 0.06 astronomical units from the star (8.9 million kilometers, 5.5 million miles, or 15 percent Mercury's distance from the Sun).

*Planet 2 orbits in 241 days, has a mass at least 2.1 times that of Jupiter, and is 0.83 astronomical units from the star (125 million kilometers, 77 million miles, or 83 percent Earth's distance from the Sun).

*Planet 3 orbits in 3.5 years, has a mass at least 4.6 times that of Jupiter, and is 2.5 astronomical units from the star (375 million kilometers, 233 million miles, or 1.64 times Mars's distance from the Sun). The orbit of this third planet is particular eccentric, the ellipse taking the planet from as close as 1.5 astronomical units to the star to as far as 3.5 astronomical units.

THE STAR

Upsilon Andromedae is a fourth magnitude star (magnitude 4.09) class F (F8) ordinary dwarf 44 light years away. Its temperature of 6210 Kelvin and luminosity 3.4 times that of the Sun suggest a mass 1.3 times solar and a radius 60 percent larger than the Sun. Like most stars with planets, Ups And is rich in metals, its iron content (relative to hydrogen) 1.34 times that of the Sun. In addition to its planets, Upsilon Andromedae has a faint 12th or so magnitude class M red dwarf (M4.5) binary companion that is at least 750 AU away and takes at least 17,000 years to orbit. Two other much more distant stars may or may not be real companions.
Written by Jim Kaler. Return to The Planet Project or go to STARS.