In new observations of a distant region of primitive stars, the Hubble Space Telescope has found tantalizing evidence that planets began appearing much earlier in cosmic history and therefore may be more abundant than previously suspected.
Astronomers reported today that measurements showing that a giant gaseous object, orbiting a pair of burned-out stars, is the most distant and oldest planet known in the universe. It appears to have formed 12.7 billion years ago, within a billion years of the explosive origin of the universe in the theorized Big Bang.
Advertisement
"What we think we have found is an example of the first generation of planets formed in the universe," said Dr. Steinn Sigurdsson of Pennsylvania State University, a member of the discovery team.
The observations challenged a widely held view among astrophysicists that planets could not have formed that early because the universe had yet to generate the enough heavy elements as raw material needed to make them. Planet-making ingredients include silicon, iron and other elements heavier than hydrogen and helium. These so-called metallic elements are cooked in the nuclear furnaces of stars and accumulate in the ashes of dying stars that are recycled in new stars and their families of planets.
If a planet has now been detected from a time when heavy elements were extremely rare, the astronomers reasoned, the discovery shows that theories of planetary formation may have to be revised.
The findings were described at a news conference at the National Aeronautics and Space Administration in Washington. A more detailed report by Dr. Sigurdsson and his colleagues is to be published on Friday in the journal Science.
The planet, more than twice as massive as Jupiter, was found in the heart of a group of extremely ancient stars, known as a globular star cluster. The M4 cluster is 7,200 light-years from Earth in the summer constellation Scorpius. The stars there are estimated to have formed almost 13 billion years ago, so early that the region is deficient in heavy elements.
Astronomers had assumed that such primitive stars could not have planets, and observations of other globular clusters appeared to support that view.
The research began in 1988 when a pulsar, a rapidly rotating stellar remnant, was discovered in the M4 cluster. Further observations revealed that the pulsar was linked gravitationally with a white dwarf star, on object that has exhausted its nuclear fuel.
Later, astronomers noticed irregularities in the pulsar signals that implied a third object was orbiting the other two. The recent Hubble telescope studies determined the mass of the object was that of a planet.
Finding a planet in an unlikely place from the early universe, Dr. Sigurdsson said, "implies that planet formation happened very early in the universe and that planet formation processes are quite robust and efficient at making use of small amounts of heavier elements."
Dr. Alan P. Boss, an astrophysical theorist at the Carnegie Institution in Washington, called the discovery "a stunning revelation" that would prompt new studies of planetary evolution.