Three Planets That Should Have Been Swallowed by Their Star Survive — and a Chinese Team Found Them
Stars swell as they age and swallow the planets orbiting too close — or so astronomers believed. A team at Yunnan University has found three planets that survived, and published the result in PNAS.
Astronomers have long understood what happens to a planet whose star is dying: the star, having exhausted the hydrogen at its core, swells into a red giant, and anything orbiting too close simply gets swallowed. Mercury will meet that end when our own Sun ages. The Sun will stop before reaching Earth, but close-in planets are not expected to survive the expansion.
A team at Yunnan University in Kunming says it has found three that did. Professor Qian Shengbang's group, publishing in the Proceedings of the National Academy of Sciences, announced the discovery of three planets that should have been engulfed by their expanding star but survived — a finding Xinhua framed as overturning a long-standing assumption: "When a star grows old it expands, and a planet orbiting too close gets swallowed — that has been astronomy's understanding. But our astronomers' latest discovery overturns it" (恒星变"老"会膨胀，靠得太近的行星会被它"吞掉"…但我国天文学家的一项最新发现，颠覆了这个认知).
The discovery was trending on Baidu's board under the phrase "three planets that should not have existed" (三颗"本不该存在"的行星被发现), with 6.5 million searches, and picked up on Weibo through provincial media relaying Xinhua's report.
The value of the finding is not just the three worlds themselves but the mechanism. A planet surviving a red giant's expansion means it was either farther out than standard models assumed, it migrated in after the star's violent phase, or the engulfment was less total than theory predicts — and each of those possibilities revises the models used to forecast the fate of planetary systems everywhere, including our own.
The finding also lands at a moment when Chinese institutions are publishing at a new scale in fundamental astronomy — and the Baidu board's ranking suggests the domestic audience has caught on to the significance. Qian's team is part of a decades-long Chinese effort in binary-star research; the PNAS paper is the field's mainstream recognizing it.
What the three planets are actually made of, and how precisely they threaded the expansion, will take follow-up observation to pin down — the sort of question the next generation of telescopes is designed to answer.