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Super-Earths may form in two ways

Contrast in star composition hints at two categories for large rocky planets

12:12pm, March 13, 2015
Super Earth vs. Earth

BULKING UP   The formation of super-Earths like Gliese 832c, a potentially habitable planet roughly 5 times as massive as Earth (illustrated here), puzzles astronomers. New research suggests that not all super-Earths form the same way.

Super-Earths, rocky planets that are several times as massive as Earth, form in two different ways, a new study suggests.

Stars with super-Earths huddled up close are enriched in heavy elements such as iron, while stars where the super-Earths keep their distance are slightly deficient in those elements. Since planets form from the same reservoir of gas and dust as their stars, astronomers use the chemical makeup of a star to see what material was available to the growing planets. Wei Zhu, an astronomy graduate student at Ohio State University, suggests that the contrasting stellar environments are a clue that these planets formed in different ways. The research appeared online March 8 at

Super-Earths are super baffling, and astronomers struggle to understand how these rocky heavyweights formed. Zhu suggests that close-in super-Earths might have formed near where we see them today in disks brimming with planet

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