Three exoplanets orbiting HR8799, a star 120 light-years
away, photographed using the Palomar Observatory’s
Hale Telescope. The light from HR8799 has been
masked with the aid of a coronagraph.
Recent advances in telescope technology allow exoplanets to be seen directly, but it helps if the planet is very large, even larger than Jupiter, for example, and far from the star that it orbits so that it’s not lost in the glare. A relatively hot exoplanet that gives off infrared radiation is also easier to detect.
In 2010, three exoplanets orbiting HR8799, a star 120 light-years away, were photographed using a portion of the Palomar Observatory’s Hale Telescope. This was the first time exoplanets were photographed using a relatively small telescope by attaching a coronagraph to it. A coronagraph blocks out the direct light from a star so that nearby objects—which would otherwise be hidden by the star’s glare—can be seen. The three planets are thought to be gas giants like Jupiter, but more massive.
Most exoplanets, however, are indirectly detected. One method is measuring minute variations in a star’s velocity due to the gravitational tug a planet has on it. Exoplanets that orbit pulsars can be indirectly detected by measuring tiny changes in the pulses of radio waves that are emitted. This is how the first exoplanet was discovered.
Liftoff of NASA’s Kepler Spacecraft
aboard a Delta II Rocket.