Two Earth-size worlds orbiting perilously close to their dying star may be the fractured remnants of a Jupiter-like gas giant, a new study suggests. The planetary pair—discovered using NASA's Kepler space telescope and announced in the journal Nature last December—are just under Earth's radius. Both orbit a so-called subdwarf B star dubbed KIC 05807616, which sits about 4,000 light-years away.
When sunlike stars run out of hydrogen fuel, they enter a red giant phase, in which their gas envelopes can swell to several hundred times their original size.
Eventually a red giant's gas envelope will slough off entirely, leaving behind a dense stellar corpse known as a white dwarf. Sometimes, however, a red giant will lose its gas envelope prematurely to form a subdwarf B star, like KIC 05807616.
The scientists who discovered the roughly Earth-size planets in Kepler's data had proposed that both worlds were once gas giants, like Jupiter or Saturn, that had been pulled nearer to their star when it ballooned during the red giant phase.
Plowing through the dying star's swollen atmosphere burned away the planets' liquids and gases, that team suggested, leaving behind the two rocky pits that Kepler sees as Earth-size worlds.
But a new study, by astrophysicists Ealeal Bear and Noam Soker of the Israel Institute of Technology, offers an alternate explanation.
It's possible that both worlds actually come from a single gas giant planet at least five times more massive than Jupiter that was stripped naked by the dying star, the researchers say.
The lone planet's rocky core was then ripped apart by the star's gravity into several Earth-size chunks.
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