{"id":252858,"date":"2025-10-31T18:28:11","date_gmt":"2025-10-31T18:28:11","guid":{"rendered":"https:\/\/www.newsbeep.com\/ca\/252858\/"},"modified":"2025-10-31T18:28:11","modified_gmt":"2025-10-31T18:28:11","slug":"afterthoughts-on-the-non-gravitational-acceleration-of-3i-atlas-at-perihelion-by-avi-loeb-oct-2025","status":"publish","type":"post","link":"https:\/\/www.newsbeep.com\/ca\/252858\/","title":{"rendered":"Afterthoughts on the Non-Gravitational Acceleration of 3I\/ATLAS at Perihelion | by Avi Loeb | Oct, 2025"},"content":{"rendered":"

\"Avi<\/a>Press enter or click to view image in full size\"\"Trajectory of 3I\/ATLAS with positions of the planets on October 31, 2025. (Credit: NASA\/JPL<\/a>)<\/p>\n

Yesterday\u2019s report on a non-gravitational acceleration of 3I\/ATLAS near perihelion (discussed here<\/a>) stems from data obtained by the Atacama Large Millimeter Array<\/a> (ALMA) which indicated that 3I\/ATLAS was 4 arcseconds away in Right Ascension from where it was supposed to be on October 29, 2025 if its trajectory was dictated by gravity.<\/p>\n

As soon as I heard about the results, I used momentum conservation to calculate that the nucleus of 3I\/ATLAS should have lost at least a sixth of its mass in order to accelerate that much as a result of cometary outgassing. The calculation goes as follows.<\/p>\n

The non-gravitational force acting on 3I\/ATLAS equals its mass times its non-gravitational acceleration:<\/p>\n

M*a=(dM\/dt)*v<\/p>\n

where a is the non-gravitational acceleration, M is the mass, (dM\/dt) is the mass loss rate and v is the ejection speed of the sublimated gas of volatiles from the surface of the nucleus, which I adopted to be lower than a few hundred meters per second \u2014 the thermal speed of related molecules at the perihelion distance. This gives the total evaporation time:<\/p>\n

t=M\/(dM\/dt)=v\/a<\/p>\n

The measured value of the non-gravitational acceleration a~0.02 millimeters per second squared gives t<6 months. It took about a month for 3I\/ATLAS to cross the perihelion distance scale of 203 million kilometers, so it must have lost at least a sixth of its mass during that time.<\/p>\n

The mass loss rate measured by the Webb telescope (reported here<\/a>) of 150 kilograms per second did not yield a detectable non-gravitational acceleration in the five months prior to October 2025. This led me to conclude (as described here<\/a>) that the mass of 3I\/ATLAS is at least 33 billion tons. This means that the dense cloud around it should carry at least 5.5 billion tons.<\/p>\n

This implies that we should detect a massive cloud of gas around 3I\/ATLAS in November and December 2025 if the non-gravitational acceleration resulted from cometary evaporation.<\/p>\n

On December 19, 2025, 3I\/ATLAS will arrive closest to Earth at a separation of 269 million kilometers, when hundreds of ground-based telescopes as well as the Hubble and Webb space telescopes will have the best opportunity to observe it. Between November 27, 2025 and January 27, 2026, 3I\/ATLAS will be monitored by the International Asteroid Warning Network (IAWN) campaign (as described here<\/a>). If the extensive IAWN data will not reveal a massive cloud of gas around 3I\/ATLAS, then cometary evaporation would not constitute a natural explanation for its non-gravitational acceleration.<\/p>\n

If we do not observe a massive cloud of gas around 3I\/ATLAS in December, then the reported non-gravitational acceleration near perihelion might be regarded as a technological signature of a propulsion system.<\/p>\n

A non-detection of an accompanying gas cloud will bring the sensation of D\u00e9j\u00e0 vu. The first interstellar object 1I\/`Oumuamua<\/a> exhibited non-gravitational acceleration without showing any sign of gas or dust around it, even after deep observations by the Spitzer space telescope (as reported here<\/a>). This led comet experts to define 1I\/`Oumuamua as a dark comet, namely a comet which does not show a visible tail. Given that a tail is the defining signature of a comet, the notion of a `dark comet\u2019 is an oxymoron. A spacecraft with a propulsion system could show a non-gravitational acceleration without cometary evaporation. It could be classified by comet experts as a dark comet in the same way that a cave dweller would classify a cell phone as a rare rock.<\/p>\n

A few reporters asked me today about the strong statements made by the science popularizer Brian Cox who argued forcefully that 3I\/ATLAS is definitely a natural comet. I explained that Brian Cox did not write a single scientific paper about 3I\/ATLAS. He acts as a science popularizer rather than a researcher who is engaged with the related science concerning 3I\/ATLAS. In comparison, I wrote 11 scientific papers in recent months about 3I\/ATLAS (accessible here<\/a>). Rather than engage in sweeping statements, Brian should be challenged to explain the 9 anomalies associated with 3I\/ATLAS (with 8 anomalies compiled here<\/a> and the 9th anomaly being its unprecedented recent brightening while being bluer than the Sun, discussed here<\/a>). Scientific truth is not decided by a popularity contest but by attention to data \u2014 especially when it is anomalous.<\/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 sizeTrajectory of 3I\/ATLAS with positions of the planets on…\n","protected":false},"author":2,"featured_media":252859,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[24],"tags":[49,48,314,66],"class_list":{"0":"post-252858","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-physics","8":"tag-ca","9":"tag-canada","10":"tag-physics","11":"tag-science"},"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/posts\/252858","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/comments?post=252858"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/posts\/252858\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/media\/252859"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/media?parent=252858"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/categories?post=252858"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/tags?post=252858"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}