German astronomers have found the oldest planets on record in a solar system 375 light-years away that is 12.8 billion years old, according to a new study. The findings call into question the theory of planet formation.
Astronomers identified the planets from flickers in the star's light caused by the gravitational pull of the planets. They estimated the star to be 12.8 billion years old, which would mean it was created less than a billion years after the Big Bang, and said the planets are likely of similar age.
Usually planets form just shortly after the star formation, Johny Setiawan, coauthor of the study and astronomer at Max-Planck Institute for Astronomy, told National Geographic. Second-generation planets might also form after a star has died, but this is still under debate.
The star lacks heavy metals; its iron content is only 1 percent that of our sun, researchers said. The findings indicate that planet formation was possible in the early universe despite a lack of elements heavier than hydrogen and helium, researchers said. The observation counters the current theory of planet formation, called the accretion model, which says heavy elements are needed to form planets.
In 2010 we found the first example of such a metal-poor system, Veronica Roccatagliata, coauthor of the study and astronomer at the University Observatory Munich, said in a statement. Back then, we thought it might be a unique case; now, it seems as if there might be more planets around metal-poor stars than expected.
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Heavy elements did not exist in the early universe; they were formed over time inside stars and then released into space when stars exploded in supernovae. Known planets are relatively young and even gas giants like Jupiter and Saturn have a core of heavy elements, but that theory could be the result of observational bias, the researchers said.
Astronomers looking for planets have concentrated on young, sun-like stars, Setiawan told National Geographic. To verify this issue, it is necessary to do a planet-search survey around [older] metal-poor stars, he said.
The planets will likely be destroyed relatively soon, researchers said. The star is turning into a red giant, one of the last stages of its life. As a red giant, the star will enlarge and consume any nearby planets it touches.
The journal Astronomy and Astrophysics published the study in print March 5 and online Monday.