Distant Planets

The two most distant planets that are easily visible to the unaided eye bracket the sky late this evening. Jupiter — the brightest object in the sky at that time — is in the west around 10 or 11, with golden Saturn low in the east-southeast.

Both planets are easy to see even though they’re quite far from the Sun. But planets at similar distances from other stars have been much more challenging to find. Of the more than a thousand confirmed planets in other star systems, only a few percent are as far from their stars as Jupiter or Saturn are from the Sun.

That doesn’t mean that distant planets aren’t common — only that they’re difficult to find.

One technique looks for a planet to cross in front of its star, briefly making the star look dimmer. This technique works best for close-in planets. For one thing, a close planet is more likely to pass in front of its star as seen from Earth. And it takes many years for a distant planet to make enough crossings for astronomers to confirm it.