Which makes them approximately eight-billion years older than Earth. The two huge Jupiter-sized planets found orbiting a star 375 light-years away, that will soon transform into a red giant (image above), are the oldest alien worlds yet discovered, according to scientists at the Max-Planck Institute for Astronomy.
"The Milky Way itself was not completely formed yet," said study leader Johny Setiawan. During a survey using radial velocity, in which astronomers watch for periodic wobbles in a star's light due to the gravitational tugs of orbiting worlds, Setiawan and colleagues found the signatures of the two planets orbiting the star, dubbed HIP 11952. At an estimated age of 12.8 billion years, the host star—and thus the planets—most likely formed at the dawn of the universe, less than a billion years after the big bang.
Based on the team's calculations, one alien planet is almost as massive as Jupiter and completes an orbit in roughly seven days. The other exo planet is nearly three times Jupiter's mass and has an orbital period of nine and a half months.
"Usually planets form just shortly after the star formation," Setiawan said. "Second-generation planets might also form after a star has died, but this is still under debate."
The discovery indicates that planet formation in the early universe was possible despite the fact that stars in existence back then were lacking in elements heavier than hydrogen and helium, which runs counter to a widely accepted theory called the accretion model, which says that heavy elements are needed to form planets. In the case of HIP 11952, "its iron abundance is only about one percent that of our sun," Setiawan said.
The accretion theory has so far been backed up by observations: Most of the planet-harboring stars discovered to date are relatively young and have moderate to high amounts of metals, but Setiawan says that "astronomers may think the accretion model is correct because planet hunters using Kepler Mission data have been targeting mostly young, sunlike stars."
"To verify this issue, it is necessary to do a planet-search survey around [older] metal-poor stars," Setiawan said.
Image credit: lcse.umn.edu
Source: The Daily Galaxy via Astronomy & Astrophysics