Exoplanets

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.

We’re all familiar with the eight planets in our solar system, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune, but did you know that since 1992 there have been hundreds of planets discovered outside our solar system? And that number is rapidly increasing with thousands of new planets waiting to be confirmed. Planets outside our solar system are called exoplanets. 

   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.

   Astronomers can also detect planets by observing a drop in a star’s brightness as a planet crosses directly in front of it. In 2009 NASA launched the Kepler Mission in an attempt to discover Earth-like planets using this method. Kepler’s space telescope will continuously monitor 145,000 stars looking for periodic changes in brightness that would indicate an exoplanet moving across the face of the star. Kepler’s goal is to find an Earth twin—similar in size and distance from its star so that water could exist in liquid form on its surface—thought to be essential for the formation of life. James Fanson, Kepler Project Manager at JPL in Pasadena, had this to say of the Kepler Mission: “Our team is thrilled to be a part of something so meaningful to the human race—Kepler will help us understand if our Earth is unique or if others like it are out there.”