Gaby
Astronomers at NASA and MIT have found an exoplanet so close to its star that its surface has turned to magma and is evaporating into space. NASA’s Transiting Exoplanet Survey Satellite (TESS) detected the planet, and researchers say it’s literally falling apart as it races around its star. Located about 140 light-years away in the constellation Pegasus, the doomed world BD+05 4868 Ab completes an orbit every 30.5 hours. With each orbit, BD+05 4868 Ab leaves behind a blazing trail of molten rock, like a comet. Scientists call it an “exoplanet in the final stages of its destruction.”
Each time the planet rotates its surface heats to about 1,600 °C, and it sheds molten rock in chunks as massive as Mount Everest. The team also reported that the planet’s tail is enormous. “The length of the tail is colossal: it stretches for 9 million kilometers, which is about half of the planet’s entire orbit,” said Mark Hon, a postdoctoral researcher at MIT. He called it an epic disintegration unfolding in real time. Scientists estimate the planet could finish breaking apart in one to two million years. “We are fortunate to have discovered it just as it is disappearing. It’s as if it’s on its last breath,” said Avi Shporer, a co-author on the TESS discovery team.
Previously, researchers had identified only three disintegrating planets among more than 6,000 known exoplanets. Each of those planets leaves behind a comet-like tail of debris. However, BD+05 4868 Ab has the longest tail of the three, according to Live Science. “This means its evaporation will be the most catastrophic, and it will vanish much faster than the other planets,” Hon explained.
Because BD+05 4868 Ab orbits so close to its star, its transit—a dip in starlight when the planet passes in front of the star—is unusually deep and asymmetric. That makes the planet an ideal target for the James Webb Space Telescope (JWST); Webb’s sensitive instruments can pick up subtle changes in starlight and help determine the chemical composition of the evaporating rock. “The shape of the transit is typical for a comet with a long tail,” Hon said. “Except that this tail is unlikely to contain volatile gases and ices like a normal comet—those wouldn’t survive so close to the host star. Instead, mineral grains evaporating from the planet’s surface can persist long enough to form such a tail.”
Shporer suggested the disintegration is driven by the planet’s tiny mass. “This is a very small object—between the size of Mercury and the Moon—with very weak gravity, so it easily loses mass, which further weakens its gravity,” he said. The process is runaway and growing more dramatic. The team plans follow-up JWST observations this summer. “This will be a unique opportunity to directly measure the internal composition of a rocky planet,” Hon said. “That could tell us a lot about the diversity and potential habitability of Earth-like worlds beyond our solar system.”
For now, researchers are searching for more examples like this in TESS data. “We’re trying to start a search for such objects,” Shporer said. “They are odd, and their signals change over time, which makes them hard to detect, but we’re actively working on it.” The study’s findings were published by Space.
