Interstellar Object 3I/ATLAS CO2-rich With Smaller Nucleus

A fast-moving interstellar object now cataloged as 3I/ATLAS is revealing an unexpectedly carbon dioxide rich composition and a much smaller nucleus than early scans indicated, astronomers said after a series of telescope campaigns this month. First detected in July by the ATLAS survey, the visitor is currently traversing the inner solar system on a trajectory not bound to the sun and will pass through before heading back into deep space, researchers said.

Detailed spectroscopic observations from the James Webb Space Telescope and NASA surveys including SPHEREx show the object is surrounded by an unusually bright coma dominated by carbon dioxide gas rather than the water vapor typical of most comets. Webb’s Near Infrared Spectrograph measurements in early August yielded a carbon dioxide to water ratio as high as 81 to 1, one of the largest such ratios ever recorded, researchers led by Martin Cordiner of NASA’s Goddard Space Flight Center reported. SPHEREx data indicated a substantial CO2 outgassing rate, on the order of hundreds of trillions of molecules per second, while also detecting surface water ice but little free water vapor or carbon monoxide.