for National Geographic News
Scientists made the find while studying the larger planet, which orbits a small, dim star in the constellation Centaurus.
The planet had puzzled experts, because its brightness and temperature didn't match what is known about how such objects evolve.
"It's either way too dim or it's way too hot," said Eric Mamajek of the Harvard-Smithsonian Center for Astrophysics.
The planet's star system is only eight million years old, an age at which planets are still being formed, he said.
So the world may be glowing with the leftover heat from a mammoth collision with another protoplanet, Mamajek proposed.
Such a collision would leave the planet unusually hot for many years, he explained.
"We're not seeing the actual collision right now," Mamajek said.
"We're seeing this long drawn-out period after the collision, of roughly a hundred thousand years, where this thing would be very hot."
Mamajek discussed his findings yesterday at a meeting of the American Astronomical Society in Austin, Texas.
"This could be the first evidence of this happening to another object in another solar system," Mamajek said.
The theory can't be confirmed, however, until the astronomers can make detailed observations of the distant planet's atmosphere.
"It's really faint," Mamajek said. "So even the biggest telescopes we have now really struggle to gather enough light."
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