comets solar system asteroids interstellar objects earth oumuamua asteroid comet Atlas comet 67P/Churyumov-Gerasimenko Comet Bernardinelli-Bernstein comet C/2023 A3 NASA meteorite Oort Cloud near earth objects dark comets more tags universe DNA life asteroid belt binary asteroid breakthrough listen Phaethon 21/Borisov MARGO Comet 21/Borisov bacteria viruses bacteria in space Chandra Wickramasinghe Hubble Comet 153P/Ikeya-Zhang comet tail rosetta mission aurora comet aurora