K2-138 planetary system, illustration. These planets are among the many discovered by NASA's Kepler space observatory, which was launched in 2009. Five of the planets were discovered by citizen scientists in 2017 using Kepler data. The sixth was discovered in 2018 by scientists using NASA's Spitzer Space Telescope. One of the planets is seen transiting the parent star. This is the method of detection used by the Kepler space telescope. This planetary system is around 600 light years from Earth, in the constellation of Aquarius. This image was published in 2019.