47 Ursa Majoris Solar System

47 Ursa Majoris Solar System, solar system made up of a star similar to Earth’s Sun and two known planets that orbit the star. The solar system is about 46 light-years from Earth in the constellation Ursa Major (see Big Dipper). The star, 47 Ursa Majoris, is slightly more massive and slightly hotter than the Sun.

American astronomers Geoffrey Marcy and Paul Butler announced the discovery of the first planet to be found circling 47 Ursa Majoris, which they called 47 Ursa Majoris B, on January 17, 1996. 47 Ursa Majoris B is too dim to be visible from Earth, so Marcy and Butler used an indirect method to discover it. As 47 Ursa Majoris B orbits 47 Ursa Majoris, its gravity tugs at the star from different directions. When the planet pulls 47 Ursa Majoris away from the Earth, the star’s light appears to redden slightly (see Redshift). The star’s light becomes slightly bluer when 47 Ursa Majoris B pulls the star toward Earth. The color change is so small that only sensitive instruments can detect it.

47 Ursa Majoris B is about 2.5 times as massive as Jupiter. It orbits 47 Ursa Majoris at a distance of 314 million km (195 million mi) in a nearly circular orbit, less than half the distance at which Jupiter orbits the Sun. If 47 Ursa Majoris were located the same distance from the Sun, it would orbit in the asteroid belt just beyond Mars. The time it takes for 47 Ursa Majoris B to circle 47 Ursa Majoris, known as the planet’s year, is the equivalent of three Earth years.

Marcy, Butler, and a team of scientists based at the University of California at Berkeley used similar techniques to detect a second planet, Ursa Majoris C, circling Ursa Majoris 47 in 2001. Ursa Majoris C is slightly less massive than Jupiter and orbits its star in a circular orbit at a distance of 560 million km (348 million mi), a bit less than the distance at which Jupiter orbits the Sun. The planet takes just over seven Earth years to complete one orbit.

Most extrasolar systems discovered so far contain planets much larger than Jupiter orbiting very close to their parent stars or in highly elliptical orbits. Of all the confirmed solar systems, 47 Ursa Majoris appears to most closely resemble Earth’s solar system. Astronomers believe it is a likely candidate to contain small rocky worlds similar to the planets Mars, Earth, Venus, and Mercury that are found between the Sun and Jupiter.