Astronomers surprised to find planet 'too massive for its star'

By Will Dunham

WASHINGTON (Reuters) - Our Milky Way galaxy's most common type of star is called a red dwarf - much smaller and less luminous than our sun. These stars - or so it was thought - simply are not big enough to host planets much larger than Earth.

But the discovery of a planet at least 13 times Earth's mass orbiting very close to a red dwarf only 11% of the sun's mass has astronomers going back to the drawing board on planetary formation theory involving this prevalent type of star. The mass ratio of this planet with its star is more than 100 times greater than that of Earth and the sun.

"We discovered a planet that is too massive for its star," said Penn State astronomer Suvrath Mahadevan, one of the leaders of the study published this week in the journal Science.

The star, called LHS 3154, is relatively close to us, about 50 light years from Earth. A light year is the distance light travels in a year, 5.9 trillion miles (9.5 trillion km).

The sun is about a thousand times more luminous than this star.