![]() It was used in the notable discovery of the TRAPPIST-1 system. NASA’s Spitzer Space Telescope (2013-2020) was not designed to search for exoplanets, but its infrared instruments made it an excellent exoplanet explorer. The spacecraft was retired in 2018, but Kepler data are still being used to find exoplanets (more than 2,700 confirmed so far). After the second of Kepler’s four gyroscope-like wheels failed in 2013, Kepler completed its prime mission that November and began its extended mission, K2. The Kepler mission was specifically designed to survey our region of the Milky Way galaxy to discover hundreds of Earth-size and smaller planets in or near the habitable zone (also called the “Godilocks zone,” the area around a star where rocky planets could have liquid water on the surface) and determine the fraction of stars that might have such planets around them. The discovery of exoplanets grew exponentially in the years to follow with the launch of the Kepler Space Telescope. The first evidence of exoplanets dates to 1917 when Van Maanen identified the first polluted white dwarf, however, the first confirmed detection of an exoplanet would not come until the 1990s. Thousands of exoplanets have been discovered and confirmed orbiting other stars. Observing this is known as the radial velocity method. ![]() If it is moving away from the observer, it will shift toward the red. If the star moves in the direction of the observer it will appear to be shifted toward blue. Stars are affected by the gravitational tug of their orbiting planets and, when observed through a telescope, this affects the star's light spectrum. Orbiting planets cause stars to wobble in space, changing the color of light astronomers see when observing a star. It's a tiny change, but it's enough to clue astronomers in to the presence of an exoplanet around a distant star. For a brief period of time, that star’s light actually gets dimmer. When a planet passes directly between an observer and the star it orbits, it blocks some of that starlight. The two main techniques are the transit and radial velocity methods. ![]() There are five methods scientists commonly use to discover exoplanets. At only four light-years away, Proxima b is our closest known exoplanet neighbor.
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