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<\/picture><\/div>\n<\/div>A few seconds before my flight to Copenhagen lifted off the ground at Boston\u2019s Logan airport, I received an email with the paper reporting the first Webb telescope data from August 6, 2025 on 3I\/ATLAS (accessible\u00a0here<\/a>). The 15 minutes of wait for the onboard WiFi connectivity to show up felt like eternity. But the wait was worth it. The stunning Webb data from a 6.5-meter infrared telescope with unprecedented spectral sensitivity was worth the wait.<\/p>\n In short, the Webb data confirms the existence of a carbon dioxide (CO2) gas plume around 3I\/ATLAS with significantly lower levels of water (H2O) and carbon monoxide (CO), as reported a few days earlier by the SPHEREx space observatory team (in a paper accessible\u00a0here<\/a>). Whereas the Webb telescope has much better spectral and spatial resolution, SPHEREx mapped the spherically symmetric CO2 plume a hundred times farther from 3I\/ATLAS and demonstrated that it extends beyond 348,000 kilometers.<\/p>\n 3I\/ATLAS does not feature a cometary tail that extends beyond the width of its coma, as was already evident from the higher resolution image taken by the Hubble Space Telescope (reported\u00a0here<\/a>). That this tail is not seen suggests that 3I\/ATLAS does not shed a lot of dust particles with a size comparable to the wavelength of sunlight, ~0.5 micrometer, and that the reflected sunlight originates from the surface of 3I\/ATLAS. This implies a diameter of up to 46 kilometers for an albedo of 5% according to the SPHEREx data.<\/p>\n Infrared spectroscopy of 3I\/ATLAS at a heliocentric distance of 3.32 Earth-Sun separations was taken with the NIRSpec instrument onboard the Webb telescope. The spectral images at wavelengths in the range of 0.6\u20135.3 micrometers reveal a prominent carbon dioxide (CO2) dominated coma, with enhanced outgassing in the direction of the Sun, as well as the presence of much less water vapor (H2O), carbon monoxide (CO), water ice and dust. The derived ratio of CO2 to H2O output by number of molecules is 8, among the highest ever observed. The data implies an intrinsically CO2-rich nucleus. The low abundance of H2O vapor is surprising at the object\u2019s distance from the Sun.<\/p>\n The spectrum of 3I\/ATLAS shows a prominent CO2 gas emission feature along with weak H2O and CO emission features and a prominent water ice absorption feature.<\/p>\n The inferred mass loss rates from 3I\/ATLAS are 129 kilograms per second for CO2, 6.6 kilograms per second for H2O and 14 kilograms per second of CO. The H2O mass loss rate is only 5% of the CO2 output. This is 16 times more extreme than expected for a typical comet at the same distance from the Sun.<\/p>\n Join Medium for free to get updates from\u00a0this\u00a0writer.<\/p>\n<\/div>\n<\/picture><\/div>\n<\/div>Get\u00a0Avi Loeb\u2019s stories in\u00a0your\u00a0inbox<\/h2>\n<\/div>\n