Slightly larger than the size of Jupiter, the largest in our solar system, the newly discovered exoplanet is orbiting a star 2,000 light years from Earth that has found its way into the Milky Way.
The pair of bodies is believed to be part of the Helmi stream, a group of stars that remains after its mini-galaxy was devoured by the Milky Way some six to nine billion years ago, said the study, published Thursday in the journal Science Express.
The planet and star are thought to have originally belonged to a dwarf galaxy that was devoured by the Milky Way in what the astronomers called "an act of galactic cannibalism."
"As far as I know this is the first time a planet like this has been discovered," said Johny Setiawan at the Max Planck Institute for Astronomy in Heidelberg, in an interview with Reuters. "It came to our galaxy about six to nine billion years ago,"
Astronomers located the planet, named HIP 13044 b, by focusing on the "tiny telltale wobbles of the star caused by the gravitational tug of an orbiting companion," the study said.
They found the planet and star by using a high-resolution spectrograph attached to a 2.2-meter telescope (7.2-foot) at the European Southern Laboratory at La Silla Observatory in Chile.
"This discovery is very exciting," said Rainer Klement, also of the Max Planck Institute for Astronomy, in a statement. "Because of the great distances involved, there are no confirmed detections of planets in other galaxies. But this cosmic merger has brought an extragalactic planet within our reach."
A view of Earth's fate?
Scientists said the planet could offer a look at the future of the Earth's planetary system as it survived the "red giant" stage of stellar evolution in which the host star grew massively after depleting its core hydrogen fuel supply.
"This discovery is particularly intriguing when we consider the distant future of our own planetary system, as the Sun is also expected to become a red giant in about five billion years," added Setiawan in the same statement.
The exoplanet is likely to be quite hot because it is orbiting so close to its star, completing each orbit in just over 16 days, and is probably near the end of its life, astronomers said.
Astronomers were mystified as to how the planet might have formed, since the star contained few elements heavier than hydrogen and helium and planets typically form out of a complex cloud of spinning space rubble.
The astronomers said it would be impossible to draw any certain conclusions about the planet's formation from the single data point, adding that they would continue trying to find more planets orbiting late-type stars.
"It is a puzzle for the widely accepted model of planet formation to explain how such a star, which contains hardly any heavy elements at all, could have formed a planet," Setiawan noted.
Author: Sean Sinico (AFP, Reuters)
Editor: Cyrus Farivar