Water in Trappist-1 system, illustration. Trappist-1 is a red-dwarf star the most common variety located some 40 light-years away in Aquarius. In 2015, astronomers discovered that Trappist-1 was host to three earth-sized planets. Then it came under the spotlight again in 2017 when NASA scientists found an additional four planets, taking the total up to seven. This is the most terrestrial planets that have ever been found to orbit a single star, including our own Solar System. Trappist-1 is only fractionally larger than Jupiter in diameter.