Is There a Giant Planet Lurking Beyond Pluto?

As faint as the tiniest moons of Pluto, Planet Nine would be barely two pixels wide on the Hubble Space Telescope’s camera. Searchers could easily miss it among random speckles of sensor noise and the twinkling of distant and variable stars. And because the planet is so far from Earth, near the far end of a highly elliptical path that takes at least 15,000 years to complete, astronomers have to wait a day or more between successive photographs of the right patch of sky to see the planet shift its apparent position relative to the much more distant stars.