Best of both worlds

摘要

One sure bet for 2017 is that astronomers will find more of the alien worlds called super-Earths. The existence of these planets, with masses greater than Earth's and less than Neptune's, was largely unanticipated by science. The first found around a star similar to ours was Gliese 876 d, in 2005. They are now thought to be the most common planet type, making our solar system a bit of an oddity.