If at first you don’t succeed, keep looking.

That’s a lesson from planet searches being conducted at the McDonald and Keck observatories. Two decades of observing scores of stars have yielded a special discovery: a planet that takes an especially long time to orbit its star. The discovery will help scientists test theories of how planets form, and help them figure out how unusual planetary systems like our own really are.

The planet orbits HR 5183, a star in Virgo, which is in the southwest at nightfall. The star is a bit bigger and heavier than the Sun, and a few billion years older. It’s about a hundred light-years away.

Astronomers have been watching the star with the Keck Telescope in Hawaii, and the Harlan Smith Telescope at McDonald Observatory, since the late ’90s. They’ve looked for a slight “wobble” in the star’s light as the star is tugged by the gravity of an orbiting planet.

Early last year, they saw such a tug. They calculated that it’s produced by a planet about three times the mass of Jupiter, the giant of our own solar system. It orbits the star every 75 years — longer than any other planet discovered with this technique.

The planet’s orbit is lopsided, so its distance from the star varies by billions of miles. The planet was at its closest last year — which is one reason it was discovered. As the planet moves away, it should be possible to take its picture — showing us a world that took a long time to find.

Script by Damond Benningfield

TODAY'S PROGRAM WAS SUPPORTED BY A GRANT FROM THE NATIONAL SCIENCE FOUNDATION.