Earth-Size Planets Come in Two Flavors: Rocky or Gassy
"Super-Earth" planets can be either rocky like Earth or fluffy like Neptune.
Earth-size planets circling nearby stars come in two flavors, either rocky or gassy, astronomers reported on Monday. And more than three-quarters of stars likely host at least one of these alien Earths. (See also: "Earth-Like Worlds 'Very Common.'")
"We are talking about worlds barely larger than our own," says astronomer Geoff Marcy of the University of California, Berkeley, speaking at the American Astronomical Society meeting in Washington, D.C. "That's how far we have come." (See "MacArthur Genius Searching for Signs of Life on Exoplanets.")
When astronomers began reporting the discovery of planets orbiting nearby stars in 1995, the few worlds they detected were as large or larger than Jupiter. Now measurements from NASA's Kepler space telescope—which has discovered
