Free Astronomy Magazine November-December 2019

10 NOVEMBER-DECEMBER 2019 EXOPLANETS to have been a bit excessive. As often hap- pens when a scientific discovery becomes a media event, journalists lost control and K2- 18 b soon became “the planet most similar to Earth yet discovered,” despite the au- thors of the discovery being quick to point out that it is actually quite a bit different. To understand how different it is, it is suffi- cient to consider the main characteristics of the system that hosts it. K2-18 is a dwarf M3-type star almost 111 light-years away from Earth. Its mass is 40% that of the Sun, it has a diameter equivalent to four times that of Jupiter, a temperature of 3460 Kelvin (K), and a brightness that is just 2.7% that of the Sun. In 2015, the Kepler Space Telescope discovered the first known planet of this system, K2-18 b, the super-Earth in I f super-Earth K2-18 b has a rocky surface, an atmosphere not too thick, and maybe even a moon, its nights might resemble this imaginative view.