Comet 3I/ATLAS astronomy Ask the Chatbot a Question More Actions Share Share Share to social media Facebook X URL https://www.britannica.com/topic/Comet-3I-ATLAS Feedback Corrections? Updates? Omissions? Let us know if you have suggestions to improve this article (requires login). Feedback Type Select a type (Required) Factual Correction Spelling/Grammar Correction Link Correction Additional Information Other Your Feedback Submit Feedback Thank you for your feedback Our editors will review what you’ve submitted and determine whether to revise the article.

　　External Websites Ask the Chatbot a Question Written by Erik Gregersen Erik Gregersen is a senior editor at Encyclopaedia Britannica, specializing in the physical sciences and technology. Before joining Britannica in 2007, he worked at the University of Chicago Press on the... Erik Gregersen Fact-checked by The Editors of Encyclopaedia Britannica Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree.... The Editors of Encyclopaedia Britannica Last Updated: Aug 21, 2025 • Article History Table of Contents Table of Contents Ask the Chatbot { "@context": "https://schema.org", "@type": "FAQPage", "mainEntity": [ { "@type" : "Question", "name" : " What is Comet 3I/ATLAS? ", "acceptedAnswer" : { "@type" : "Answer", "text" : "Comet 3I/ATLAS is the third known interstellar object, discovered by the robotic survey project ATLAS on July 1, 2025. It is possibly the oldest known comet, originating from the Milky Way Galaxyu2019s thick disk, and it may be as old as 11 billion years." } } , { "@type" : "Question", "name" : " How fast is Comet 3I/ATLAS moving relative to the Sun? ", "acceptedAnswer" : { "@type" : "Answer", "text" : "Comet 3I/ATLAS has a velocity of 58 km (36 miles) per second relative to the Sun." } } , { "@type" : "Question", "name" : " When will Comet 3I/ATLAS have its closest approach to the Sun? ", "acceptedAnswer" : { "@type" : "Answer", "text" : "Comet 3I/ATLAS will have its closest approach to the Sun on October 29, 2025. It will be between the orbits of Earth and Mars on that date." } } , { "@type" : "Question", "name" : " What is the estimated size range of Comet 3I/ATLAS? ", "acceptedAnswer" : { "@type" : "Answer", "text" : "The estimated diameter of Comet 3I/ATLAS is between 320 meters and 5.6 km (1,050 feet and 3.5 miles)." } } , { "@type" : "Question", "name" : " Are there any plans to send spacecraft to Comet 3I/ATLAS? ", "acceptedAnswer" : { "@type" : "Answer", "text" : "There are no plans to send spacecraft to rendezvous with Comet 3I/ATLAS." } } ] } Top Questions What is Comet 3I/ATLAS? Comet 3I/ATLAS is the third known interstellar object, discovered by the robotic survey project ATLAS on July 1, 2025. It is possibly the oldest known comet, originating from the Milky Way Galaxy’s thick disk, and it may be as old as 11 billion years.

　　How fast is Comet 3I/ATLAS moving relative to the Sun? Comet 3I/ATLAS has a velocity of 58 km (36 miles) per second relative to the Sun.

　　When will Comet 3I/ATLAS have its closest approach to the Sun? Comet 3I/ATLAS will have its closest approach to the Sun on October 29, 2025. It will be between the orbits of Earth and Mars on that date.

　　What is the estimated size range of Comet 3I/ATLAS? The estimated diameter of Comet 3I/ATLAS is between 320 meters and 5.6 km (1,050 feet and 3.5 miles).

　　Are there any plans to send spacecraft to Comet 3I/ATLAS? There are no plans to send spacecraft to rendezvous with Comet 3I/ATLAS.

　　Comet 3I/ATLAS, interstellar object and possibly the oldest known comet. It was discovered by the robotic survey project Asteroid Terrestrial-impact Last Alert System (ATLAS) on July 1, 2025. Comet 3I/ATLAS is the third known interstellar object, that is, an object that has entered the solar system from interstellar space. Such objects have been scattered through gravitational interaction from where they originated in a planetary system around other stars. These objects give astronomers a rare chance to study conditions in other planetary systems up close. Comet 3I/ATLAS has a velocity relative to the Sun of 58 km (36 miles) per second, ...(100 of 262 words)

　　Continue reading with Britannica Premium The trusted destination for facts and information 7-Day Free Trial, No Ads, Unlimited Access Subscribe Today