{"id":279201,"date":"2025-11-08T11:34:10","date_gmt":"2025-11-08T11:34:10","guid":{"rendered":"https:\/\/www.newsbeep.com\/us\/279201\/"},"modified":"2025-11-08T11:34:10","modified_gmt":"2025-11-08T11:34:10","slug":"first-radio-signal-from-3i-atlas-absorption-by-hydroxyl-radicals-oh-molecules-by-avi-loeb-nov-2025","status":"publish","type":"post","link":"https:\/\/www.newsbeep.com\/us\/279201\/","title":{"rendered":"First Radio Signal from 3I\/ATLAS: Absorption by Hydroxyl Radicals (OH Molecules) | by Avi Loeb | Nov, 2025"},"content":{"rendered":"

\"Avi<\/a>Press enter or click to view image in full size\"\"The MeerKAT Radio Telescope in South Africa. (Credit: Wikimedia<\/a>)<\/p>\n

MeerKAT<\/a>, a radio telescope with a diameter of 13.5 meters operated by the South African Radio Astronomy Observatory, announced that they detected radio absorption lines by hydroxyl radicals, namely OH molecules, from the interstellar object 3I\/ATLAS<\/a>.<\/p>\n

MeerKAT observed 3I\/ATLAS on October 24, 2025 when the angular separation of 3I\/ATLAS from the Sun was 3.76 degrees, just 7 times the diameter of the Sun in the sky. The OH absorption signal was detected in two spectral lines at radio frequencies of 1.665 and 1.667 gigahertz. The two lines revealed absorption at Doppler velocity shifts of -15.59 (+\/-0.16) and -15.65(+\/-0.17) kilometers per second, respectively. The full-width-at-half-maximum of the absorption lines were 0.88(+\/-0.37) and 1.26(+\/-0.40) kilometers per second, respectively. Previous attempts to detect these lines with MeerKAT on September 20 and 28, 2025 were not successful.<\/p>\n

The solar conjunction of 3I\/ATLAS relative to Earth occurred a few days earlier, on October 21, 2025, when the object was traveling very close to the orbital plane of the Earth around the Sun. Given that the velocity vector of 3I\/ATLAS was nearly perpendicular to MeerKAT\u2019s line-of-sight, the Doppler shift of the OH absorption results from the full speed of 3I\/ATLAS relative to Earth of (30+68)=98 kilometers per second, times the sine of the angle between the direction of relative motion and MeerKAT\u2019s line-of-sight to 3I\/ATLAS on October 24. This angle was apparently 9.2 degrees.<\/p>\n

Given that 3I\/ATLAS was separated from the Sun by 1.38 times the Earth-Sun separation, its surface temperature was smaller than that of Earth by roughly the square root of 1.38. This is because the solar heating rate scales inversely with separation squared, whereas surface cooling scales as temperature to the 4th power. The resulting thermal speed of the OH molecules shed from the surface of 3I\/ATLAS at a temperature of ~230 degrees Kelvin, yields thermal broadening of the OH lines by a full-width at half maximum of ~0.8 kilometers per second \u2014 in agreement with the observed widths. Coincidentally, I taught thermal broadening in my class \u201cRadiative Processes in Astrophysics\u201d at the Harvard Astronomy department a month ago.<\/p>\n

This absorption signal constitutes the first radio detection of 3I\/ATLAS. Five weeks ago, I encouraged radio observatories like MeerKAT to search for radio emission from 3I\/ATLAS given that the arrival direction of 3I\/ATLAS coincided to within 9 degrees with the arrival direction of the Wow! Signal<\/a> detected in 1977 at a frequency of 1.4204556 gigahertz (as discussed here<\/a>). In response, I was assured that 3I\/ATLAS will be monitored by radio observatories like MeerKAT. So far there was no report on a radio detection of 3I\/ATLAS other than the OH absorption signal.<\/p>\n

On March 16, 2026, 3I\/ATLAS is expected to pass within 53 million kilometers from Jupiter. At that time, the Juno spacecraft will use its dipole antenna to search for a radio signal from 3I\/ATLAS at low frequencies ranging from 50 hertz to 40 megahertz.<\/p>\n

ABOUT THE AUTHOR<\/p>\n

Press enter or click to view image in full size\"\"(Image Credit: Chris Michel, National Academy of Sciences, 2023)<\/p>\n

Avi Loeb is the head of the Galileo Project, founding director of Harvard University\u2019s \u2014 Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011\u20132020). He is a former member of the President\u2019s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of \u201cExtraterrestrial:<\/a> The First Sign of Intelligent Life Beyond Earth<\/a>\u201d and a co-author of the textbook \u201cLife in the Cosmos<\/a>\u201d, both published in 2021. The paperback edition of his new book, titled \u201cInterstellar<\/a>\u201d, was published in August 2024.<\/p>\n","protected":false},"excerpt":{"rendered":"Press enter or click to view image in full sizeThe MeerKAT Radio Telescope in South Africa. (Credit: Wikimedia)…\n","protected":false},"author":2,"featured_media":279202,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[49],"tags":[199,79],"class_list":{"0":"post-279201","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-physics","8":"tag-physics","9":"tag-science"},"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/posts\/279201","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/comments?post=279201"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/posts\/279201\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/media\/279202"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/media?parent=279201"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/categories?post=279201"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/tags?post=279201"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}