"Five Out of Five Researchers Agree: Earth's Solar System Special", Sara Goudarzi, space.com, 31 March 2005 Paul Butler's homepage at the Carnegie Institution for Science
"Five Out of Five Researchers Agree: Earth's Solar System Special", Sara Goudarzi, space.com, 2005-03-31 ポール・バトラーのホームページ（カーネギー研究所）