Different Methods of Detecting Exoplanets in Our Galaxy Exoplanets, or extrasolar planets, are planets that revolve around other stars. While astronomers had for centuries believed that many exoplanets existed in our galaxy (and beyond), it was not proven until the early 1990s, when, in 1992, several terrestrial-mass planets were found orbiting a pulsar known as PSR B1257+12. To date, more than a thousand confirmed exoplanets have been discovered, including 175 multi-planetary systems. The Kepler mission space telescope, launched in 2009, has discovered more than 3,500 additional candidate planets, as of November 2013. Approximately 11 percent of these may be false positives, however. Which leads to the question of how scientists find exoplanets at all—what methods do they use to detect planets orbiting stars many light years away? Despite the availability of advanced telescopic equipment like the Hubble Space Telescope, scientists are generally unable to detect exoplanets directly. This is because stars like our Sun are roughly one billion times brighter than the reflected light of the planets orbiting them. Exoplanets are so close (relatively speaking) to their suns that any light the planets give off is essentially drowned out. Astronomers have had much better success detecting exoplanets indirectly, and, below, Lab Roots highlights three such indirect detection methods. Transit Method The transit method looks for dimming on the sun’s surface indicating that a planet is passing in front of the sun from the vantage point of the observer (or instrument). This method is only effective when the planet’s orbit is perfectly aligned from the vantage point of the observer, which is infrequently the case, thus limiting the usefulness of this detection method. One of the advantages of the transit method, however, is that it can help astronomers determine the radius of a planet. Radial Velocity The gravitational force of a planet “tugs” on the star it orbits, thus giving the star its own small orbit. This causes variations in the speed with which a star moves toward or away from Earth. This variation can be deduced from the Doppler shifts in the star’s spectral lines as its center of mass shifts. Also known as Doppler spectroscopy, this method has been the most productive in finding extrasolar planets. Orbital Light Variations Similar to the moon, planets that closely orbit their parent star go through phases because of the close proximity between the planet and star, and these phases can be detected. Additionally, planets in close proximity to a star are superheated and give off potentially detectable thermal emissions. While the planet cannot be distinguished from the star through a telescope, the brightness of a star’s surface is increased by the planet, creating a pattern that is detectable over time. As with the transit method, it is easier to see larger planets orbiting a star, than smaller ones, as larger planets reflect more light from their parent star. The last two decades have been a remarkable time in exoplanet discovery. Scientists now estimate that there are 20-40 billion planets in our galaxy, alone, orbiting stars in the “habitable” zone conducive to life as we know it. Perhaps the most exciting aspect of the search for extrasolar planets is how new

discoveries will lead astronomers to prove and disprove previously held theories, and, as they do, come closer to understanding how rare or how common planets like Earth are in our galaxy and beyond. About Lab Roots LabRoots is the leading networking site for science news connecting professionals in the scientific world across fields of expertise. Our site features over 30,000,000 documents of publication metadata and allows subscribers to watch and post videos, images, files and links, post publication and product reviews, access hundreds of live scientific news feeds, and much more. Learn more about LabRoots on our website.