Just how do you find an exoplanet?

Astronomers deploy several techniques to find planets beyond our solar system


I'd be more excited about the exoplanet scientists recently found that appears to be in a "habitable zone" if it were a bit closer than 42 light years away. It's not as if Earthlings will be visiting that planet any time soon, given that a light year is about 6 trillion miles. To put things in perspective, NASA's excited about sending astronauts to Mars by the mid-2030s, and the Red Planet is a mere 140 million miles from Earth (on average, depending on where the planets are in their respective orbits). So using that average, you'd have to travel back and forth to Mars 21,429 times to equal just one trillion miles, by my possibly incorrect space division. Multiply that by 42 and it's just science fiction. But stepping back from that reality, the fact that we have technology to find anything 42 light years away is mind-boggling. Believe it or not, the first planet discovered outside our solar system was found in 1992, and it was 980 light years from Earth! Since then another 845 exoplanets have been discovered, according to Exoplanet.eu, an online database of, well, exoplanets. The latest discovered exoplanet, in the constellation Pictor, was found by analyzing changes in light, a technique known as radial velocity. As Discovery's Irene Klotz explains:

The new findings are based on a re-analysis and refinement of data collected by Europe's High Accuracy Radial velocity Planet Searcher (HARPS) instrument, a light-splitting spectrograph installed on Europe's La Silla Observatory in Chile. Planets beyond the solar system can be detected by tiny gravitational tugs they exert of the light coming from their parent stars.

HARPS also was credited last month with finding the closest-known exoplanet to Earth -- Alpha Centauri Bb, just 4.37 light years from Earth. Radial velocity is the most successful technique for discovering exoplanets, credited with finding 494 total. But there are others. The "transit method" can be used if an exoplanet crosses in front of its star, slightly diminishing its brightness. This technique is credited by Exoplanet.eu with discovering 288 planets outside our solar system. Gravitational microlensing measures anomalies in the magnification of a star's light caused by its gravitational field. Sixteen exoplanets have been found using this technique. Another lesser-used technique is called pulsar timing, which measures radio waves emitting from pulsars (neutron stars). Just 17 exoplanets have been found this way, including the first. All of the above are indirect techniques for discovering exoplanets. Astronomers also have found 31 exoplanets through direct imaging -- using computer-enhanced images taken through powerful telescopes trained on the stars. Of these, 23 have been discovered since 2008. Now read this:

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