Astronomers have discovered an unusual planet that challenges several widely held assumptions about the way solar systems work. The planet, about 2,000 light-years away from us, is orbiting an unlikely star at an unlikely distance.
The find, reported Thursday in the online edition of the journal Science, also indicates that planets may be more common outside our own Milky Way galaxy than had been thought.
When astronomer Rainer Klement of the Max Planck Institute for Astronomy in Heidelberg, Germany, began observing the planet, his expectations were low.
"To be honest, it started as kind of a fun project," he said.
The star, known as HIP 13044, originated in a small neighboring galaxy that merged with the Milky Way 6 billion to 9 billion years ago. It is one of 33 intergalactic interlopers astronomers have traced to this small galaxy.
The planet, called HIP 13044 b, appears to be a gas giant about 25% more massive than Jupiter. Its orbit is closer to its star than even Mercury is to the sun, and it circles the star in a mere 16 days.
The most noteworthy thing about the planet, however, is that it exists at all.
First off, its star is remarkably poor in heavier elements — although scientists have long theorized that only a star rich in such chemical building blocks would be able to seed a surrounding solar system.
Second, the aging star has already expanded into a red giant, the stage in which its outer shell expands and engulfs everything in its path before it runs out of fuel and shrinks back down. A planet so close shouldn't stand a chance — and yet there was HIP 13044 b, still intact.
Klement said the discovery gives him some hope that Jupiter might survive when the sun becomes a red giant 5 billion to 6 billion years from now. "The Earth will not be so lucky," he added.
Alex Wolszczan, an astronomer at Pennsylvania State University who wasn't involved in the study, said he always welcomed reports indicating that planets are more common than previously believed.
"It keeps on making us less and less important in the universe, but I am not saddened by this — I think it's comforting," he said. "Do you like to be alone for long periods of time?"