This artist’s conception illustrates a Jupiter-like planet alone in the dark of space, floating freely without a parent star.
Thousands of planets have been discovered by exoplanet hunters, the majority of which circle close to their host stars, but only a small number of alien worlds have been found to drift aimlessly across the galaxy as so-called rogue planets, unattached to any star. Many astronomers think that these planets are more prevalent than we realize, but that current methods for detecting planets haven’t been effective enough to locate them.
A planet survey, called the Microlensing Observations in Astrophysics (MOA), scanned the central bulge of our Milky Way galaxy from 2006 to 2007. It used a 5.9-foot (1.8-meter) telescope at Mount John University Observatory in New Zealand, and a technique called gravitational microlensing. In this method, a planet-sized body is identified indirectly as it just happens to pass in front of a more distant star, causing the star to brighten. The effect is like a cosmic funhouse mirror, or magnifying lens – light from the background star is warped and amplified, becoming brighter.