LP 791-18 d, illustrated here, is an Earth-size world about 90 light-years away. The gravitational tug from a more massive planet in the system, shown as a blue disk in the background, may result in internal heating and volcanic eruptions – as much as Jupiter’s moon Io, the most geologically active body in the solar system. Astronomers discovered and studied the planet using data from NASA’s Spitzer Space Telescope and Transiting Exoplanet Survey Satellite along with many other observatories. Credit: NASA’s Goddard Space Flight Center/Chris Smith (KRBwyle)