Astronomers Say Small Planets Can Form Around Many Different Types of Stars
Posted on June 14, 2012
The formation of small worlds like Earth previously was thought to occur mostly around stars rich in heavy elements such as iron and silicon. However, new ground-based observations, combined with data collected by NASA's Kepler space telescope, shows small planets form around stars with a wide range of heavy element content. The finding, published here in Nature, significantly increases the likelihood that Earth-like planets are widespread in the universe.
A research team led by Lars A. Buchhave, astrophysicist at the Niels Bohr Institute and Centre for Star and Planet formation at the University of Copenhagen, studied the elemental composition of more than 150 stars harboring 226 planet candidates smaller than Neptune.
Buchhave says, "I wanted to investigate whether planets only form around certain types of stars and whether there is a correlation between the size of the planets and the type of host star it is orbiting. This study shows that small planets do not discriminate and form around stars with a wide range of heavy metal content, including stars with only 25 percent of the sun's metallicity."
NASA says astronomers refer to all chemical elements heavier than hydrogen and helium as metals. Astronomers define metallicity as "the metal content of heavier elements in a star." Stars with a higher fraction of heavy elements than the sun are considered metal-rich. Stars with a lower fraction of heavy elements are considered metal-poor.
Natalie Batalha, Kepler mission scientist at NASA's Ames Research Center at Moffett Field, Calif, says, "Kepler has identified thousands of planet candidates, making it possible to study big-picture questions like the one posed by Lars. Does nature require special environments to form Earth-size planets? The data suggest that small planets may form around stars with a wide range of metallicities -- that nature is opportunistic and prolific, finding pathways we might otherwise have thought difficult."
An interesting interview with astronomer Lars Buchhave can be found here. Buchhave says "small planets seem to be rule, not the exception" in the Universe.