OTOH:
Alien Earths Could Form Earlier than ExpectedPrevious studies have shown that Jupiter-sized gas giants tend to form around stars containing more heavy elements than the Sun. However, new research by a team of astronomers found that planets smaller than Neptune are located around a wide variety of stars, including those with fewer heavy elements than the Sun. As a result, rocky worlds like Earth could have formed earlier than expected in the universe's history. "This work suggests that terrestrial worlds could form at almost any time in our galaxy's history," said Smithsonian astronomer David Latham (Harvard-Smithsonian Center for Astrophysics). "You don't need many earlier generations of stars." ...Astronomers call chemical elements heavier than hydrogen and helium "metals." They measure the metal content, or metallicities, of other stars using the Sun as a benchmark. Stars with more heavy elements are considered metal-rich while stars with fewer heavy elements are considered metal-poor... They measured the stars' metallicities and correlated that with the sizes of the associated planets. Large planets tended to orbit stars with solar metallicities or higher. Smaller worlds, though, were found around metal-rich and metal-poor stars alike. "Giant planets prefer metal-rich stars. Little ones don't," explained Latham. They found that terrestrial planets form at a wide range of metallicities, including systems with only one-quarter of the Sun's metal content.
David A. Aguilar & Christine Pulliam
Wednesday, June 13, 2012
Harvard-Smithsonian Center For Astrophysics
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