FINDING planets with a mass similar to Earth鈥檚 in habitable zones around other stars is a top priority for astronomers on the lookout for extraterrestrial life. But Marc Kuchner of Princeton University Observatory warns that not all such planets will be rocky worlds like Earth or Mars.
In the cold outer regions of a planetary system, planets that are up to 10 times the mass of Earth and made mainly of water ice and frozen ammonia can form. Even if such a body migrated inwards to a warm spot near their star like Earth鈥檚 in relation to the sun, it would retain most of its ice for billions of years, Kuchner calculates.
These ice balls might be mistaken for Earth-like planets in telescope surveys, Kuchner told an American Astronomical Society meeting in California this week.
Advertisement