More Pegasus

The first planet ever discovered orbiting a Sun-like star is nothing like anything in our own solar system. But it helped astronomers learn more about the history of the solar system. The planet orbits 51 Pegasi. The star is a little bigger, heavier, and brighter than the Sun. The planet is 51 Pegasi b. It’s about half as heavy as Jupiter, the giant of the solar system. But it’s much closer in – just a few million miles from the star. The planet’s gravity causes the star’s light to “wobble” a bit. Precise measurements of that wobble revealed the planet’s details. Astronomers have since discovered hundreds more planets with the same technique, including many planets that are “hot Jupiters” like 51 Pegasi b. There’s no way for such a massive planet to form so close to its star. So it must have been born much farther out, then migrated to its current location. That realization led to theories that the Sun’s giant planets shifted around when the solar system was young. And that could have nudged the small inner planets, including Earth. It might even have pushed closer planets into the Sun – destroying some of Earth’s planetary siblings. Pegasus is in the east at nightfall. Look for four moderately bright stars that form the Great Square, which is tilted on its side. 51 Pegasi is along the top right side of the tilted square. Under dark skies, it’s barely visible to the eye alone. Script by Damond Benningfield