Earthlike alien planet. Artwork of an Earthlike alien planet (upper left). A planets orbit and its size have to fit within a narrow range for it to have a surface temperature suitable for liquid water, and for it to retain an atmosphere. Also seen here are nebulae (red), clouds of gas and dust where new stars may form, such as those of the star cluster at centre right. As of 2010, hundreds of planets have been detected around other stars.
