DALLAS – Go out after dark and look above the southern horizon, near the red star Antares in the constellation Scorpius. There, invisibly ensconced in a cluster of old stars, lies a planet that has existed since nearly the beginning of time.

Astronomers announced Thursday that they had discovered a planet almost 13 billion years old, placing it within 1 billion years of the big bang that created the universe. Had life ever arisen on the planet – an unlikely event, scientists say – it would have witnessed most of the universe’s history, including the birth of Earth about 5 billion years ago.

The discovery is “a stunning revelation,” astronomer Alan Boss said during a NASA news briefing in Washington, D.C. A report on the finding appears in Friday’s issue of the journal Science.

At 7,200 light-years (40 million billion miles) from Earth, the planet is also the farthest known.

Scientists have found 117 other planets outside the solar system, but most of those orbit ordinary sunlike stars in the cosmic neighborhood. The newfound planet orbits a bizarre pair of burned-out stars known as a white dwarf and a pulsar.

For the last decade, astronomers suspected that the system also must contain a third object. But only now have they been able to calculate its mass – two or three times that of Jupiter.

New observations from the Hubble Space Telescope pinned down the planet’s identity, said Steinn Sigurdsson, an astronomer at Pennsylvania State University who led the research team.

Hubble helpful

“There were a lot of little pieces missing, and the Hubble data just snapped them into place,” he said.

For the first time, the Hubble pictures revealed the color and temperature of the white dwarf star. Astronomers then calculated its mass and the tilt of its orbit, which in turn pinned down the planet’s orbit and mass.

The planet is far too faint to photograph directly, said Harvey Richer, an astronomer at the University of British Columbia in Vancouver. But its discovery suggests that planets could be abundant elsewhere.

“It would be nice to say the universe is full of very old planets, and it very well may be,” said Richer, another member of the team.

Surprisingly, the planet resides in a clump of old stars, a globular cluster known as Messier 4 or M4. If the planet is the same age as the stars, that places it back in a time when stars had yet to produce elements heavier than hydrogen and helium.

Each later generation of stars forged elements like iron, silicon and carbon, spewing them into space and providing the raw ingredients for planets to form.

But if the M4 planet were born 13 billion years ago, only hydrogen and helium would have been present, said Boss, of the Carnegie Institution of Washington. Scientists may now have to revise their ideas about what conditions are needed for planets to form, he said.

Mario Livio, of the Space Telescope Science Institute in Baltimore, added that the planet isn’t necessarily as old as the stars in M4.

“Being a theorist,” he said, “I can think of scenarios how the planet could have formed at a much later stage in the life of this cluster.”

In that case, he said, the important factor is not the age of the planet but that it managed to form and survive in such a rough-and-tumble environment.

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