Astronomers have discovered an extrasolar planet only 5 times larger than the Earth orbiting a star in the Sagittarius constellation. They used a technique called microlensing, where a star briefly passes in front of a more distant star, acting as a lens that magnifies its brightness. In this case, the planet passed in front of the star as well and created a second brightening that allowed astronomers to measure its mass. The planet is likely very cold, as it orbits about three times the distance of the Earth to the Sun, and its parent star is a colder red dwarf.