Space Telescope Science
The majority of planets discovered outside our solar system orbit close to their parent stars because these planets are the easiest to find. But to fully understand how distant planetary systems are put together, astronomers must conduct a census of all the planets around a star. So they need to look farther away from the star-from about the distance of Jupiter is from our sun, and beyond.
Now, astronomers using NASA's Hubble Space Telescope and the W. M. Keck Observatory in Hawaii have confirmed the existence of a Uranus-sized exoplanet orbiting far from its central star, discovered through a technique called gravitational microlensing. Microlensing occurs when a foreground star magnifies the light of a background star that momentarily aligns with it. The unique signature of the event, which is influenced by the relative motion of the stars across space, can reveal clues to the nature of the foreground star and any associated planets. Gravitational microlensing can find cold planets in long-period orbits that other methods cannot detect. This finding opens a new piece of discovery space in the extrasolar planet hunt: to uncover planets as far from their central stars as Jupiter and Saturn are from our sun.