An international team of astronomers has found that a little-known exoplanet called K2-18b could be a scaled-up version of Earth, and also discovered the planet has a massive neighbor, K2-18c. This artist’s concept shows two super-Earth exoplanets, K2-18b and c, orbiting the red dwarf star K2-18. Image credit: Alex Boersma. “Being able to measure the mass and density of K2-18b was tremendous, but to discover a new exoplanet was lucky and equally...