More than a decade ago, the Hubble Space Telescope spotted a Jupiter-scale planet orbiting Fomalhaut, a star about 25 light years away from our solar system. The discovery marked the first time that an exoplanet, a world that orbits another star system, had ever been directly detected in visible light wavelengths. However, when András Gáspár, an assistant astronomer at the University of Arizona’s Steward Observatory, examined more recent images of the star system, captured by Hubble in 2013 and 2014, he was astonished to find that the exoplanet, known as Fomalhaut b, had vanished.
“To my surprise, it was not present on the latest images,” recalled Gáspár in an email. “So, I went through all the data and started to analyze it and noticed a pattern: it was fading.”
Fomalhaut b, the first optically imaged exoplanet, is not a planet at all. It is likely the explosive fallout of a crash between two icy space rocks, each at least 100 kilometers in radius, according to a study published on Monday in Proceedings of the National Academy of Sciences . A lucky discovery While cataclysmic collisions are common in the universe, especially in young star systems like Fomalhaut, it is extremely rare to capture imagery of them from Earth. “We know of many other directly imaged exoplanets now,” said Gáspár, who led the new study. “We have never seen anything like this before!” The discovery was “pure luck,” he added, as he did not specifically set out to observe Fomalhaut b. Gáspár is helping to develop instruments for the James Webb Space Telescope (JWST), NASA’s next-generation observatory, which will be about 100 times more powerful than Hubble. He was scanning archival Hubble data to calibrate JWST’s optical observations, when he noticed the exoplanet’s absence.