Comet 3I/ATLAS, spotted earlier this month, is expected to approach the sun Oct. 29, 2025, but won’t come close to EarthPublished Jul 23, 20256 minute readComet 3I/ATLAS streaks across a dense star field in this image captured by the Gemini North telescope’s Gemini Multi-Object Spectrograph (GMOS-N). The left panel captures the comet’s colorful trail as it moves through the solar system. The image was composed of exposures taken through three filters, shown here as red, green, and blue. The right inset zooms in to reveal the comet’s compact coma — a cloud of gas and dust surrounding its icy nucleus. International Gemini ObservatoryArticle contentOn July 1, 2025, the ATLAS telescope in Chile, South America, discovered only the third interstellar object (ISO) to enter our solar system from interstellar space.THIS CONTENT IS RESERVED FOR SUBSCRIBERS ONLY.Subscribe now to access this story and more:Unlimited access to the website and appExclusive access to premium content, newsletters and podcastsFull access to the e-Edition app, an electronic replica of the print edition that you can share, download and comment onEnjoy insights and behind-the-scenes analysis from our award-winning journalistsSupport local journalists and the next generation of journalistsSUBSCRIBE TO UNLOCK MORE ARTICLES.Subscribe or sign in to your account to continue your reading experience.Unlimited access to the website and appExclusive access to premium content, newsletters and podcastsFull access to the e-Edition app, an electronic replica of the print edition that you can share, download and comment onEnjoy insights and behind-the-scenes analysis from our award-winning journalistsSupport local journalists and the next generation of journalistsRegister to unlock more articles.Create an account or sign in to continue your reading experience.Access additional stories every monthShare your thoughts and join the conversation in our commenting communityGet email updates from your favourite authorsSign In or Create an AccountorArticle contentThe two other objects known to have visited our solar system are 1I/’Oumuamua in 2017 and Comet 2I/Borisov in 2019.Article contentArticle contentObservations of Comet 3I/ATLAS in the weeks following its discovery suggest it is larger than either ‘Oumuamua or Borisov, possibly being between 12 and 20 kilometres in diametre, with a bluer surface hue and redder coma (suggesting the presence of organic materials) than in most solar system comets.Article contentArticle contentWhat does the name mean?Article contentWith the classification of ISOs, the first number, such as “one” in the classification, indicates that it was the first interstellar object discovered; a two indicates the second such object discovered, a three indicates it’s the third, and so on.Article contentThe capital letter “I” after the number simply indicates that it is an interstellar object.Article contentIt’s then followed by the name(s) of the person(s) who discovered it, or, as in this case, the telescope or system that found it.Article contentComet 3I/ATLAS is the first comet believed to have possibly come from a completely different region of the Milky Way Galaxy than other comets.Article contentHow was it found?Article contentThe new comet was discovered by astronomers at the observatory in Chile, South America, part of the Asteroid Terrestrial – impact Last Alert System (ATLAS) — an asteroid impact early warning system consisting of four telescopes stationed around the globe. There are two in Hawaii, and one each in South Africa and Chile.Article contentArticle contentIt was discovered using a protocol known as the Otautahi-Oxford interstellar object population model, jointly developed by astronomers in the United Kingdom and New Zealand.Article contentArticle contentUsing this protocol, astronomers have been able to backtrace the trajectory of Comet 3I/ATLAS to a region in the Milky Way Galaxy’s outer “thick disk”.Article content This diagram shows the trajectory of interstellar comet 3I/ATLAS as it passes through the solar system. It will make its closest approach to the sun in October. NASA/JPL-CaltechArticle contentWhere does it come from?Article contentThe outer “thick disk” is the core population of ancient stars that orbit above and below the thin, inner plane of the Milky Way Galaxy in which our sun and most of the Milky Way Galaxy’s stars reside.Article contentHowever, the theory that 3I/ATLAS originated within the thick disk has not yet been verified, as the comet’s current trajectory places it right along the boundary between the thin and thick disks.Article contentThe thick disk of the Milky Way Galaxy is estimated to contain approximately 10 per cent of our galaxy’s total number of stars, most of which are believed to be 10 billion years or more old; thus, the speculation that Comet 3I/ATLAS is a very old comet.Article contentIf further observations and analysis of the trajectory of Comet 3I/ATLAS prove that it is, in fact, from the thick disk region of the Milky Way Galaxy, it could, according to statistical methodology, possibly be the oldest comet discovered to date, with an estimated age of between 7.5 billion and 14 billion years old.Article contentIf that’s the case, it would predate the formation of our solar system. All known non-stellar comets, such as Halley’s Comet, originate from within our solar system’s Oort Cloud, and, as a consequence, are no older than our solar system, which is estimated to be approximately 4.6 billion years old.Article contentWe apologize, but this video has failed to load.Article contentHow close will it get to Earth?Article contentWhen discovered, Comet 3I/ATLAS was traveling at approximately 220,000 kilometres per hour.Article contentIts orbital path will, unfortunately, not bring it anywhere near Earth, as our planet will be on the opposite side of the sun when the comet reaches perihelion. It will come no closer to Earth than 240 million km (1.6 AU) in December.Article contentInstead, the comet will pass within the orbit of Mars as it heads for its predicted perihelion (its closest approach to the sun) on Oct. 29, 2025.Article contentWith an extreme orbital eccentricity of 6.2 (“0” signifies a perfect circle), one of the clues that this comet was of interstellar origin, 3I/ATLAS will very likely never return to our solar system again.Article contentSurprisingly, the comet, even at its current distance just inside the orbit of Jupiter, is fairly active, with some fuzziness already visible around the comet’s coma, and the suggestion of a diffuse tail already beginning to form. This might indicate, although it is still far too early to be sure, that Comet 3I/ATLAS may become a reasonably bright comet, although it is not expected to reach naked-eye visibility.Article contentArticle contentThat being said, astronomers state that Comet 3I/ATLAS may be visible in moderate-sized telescopes in late 2025 and early 2026, before and after it reaches perihelion, respectively.Article content This image shows the observation of comet 3I/ATLAS when it was discovered on July 1, 2025. The NASA-funded ATLAS survey telescope in Chile first reported that the comet originated from interstellar space. ATLAS/University of Hawaii/NASAArticle contentWhat can we learn from it?Article contentBy studying Comet 3I/ATLAS, astronomers hope to gain evidence of the processes of the formation and evolution of planetesimals — minute planets or bodies which could come together with many others under gravitation to form a planet.Article contentThese studies may also provide astronomers with clues about the role such ancient interstellar comets may have played in seeding “life,” or the basic ingredients of life, on Earth and, possibly, other planets in the universe.Article contentOnce the Vera C. Rubin Observatory in Chile becomes fully operational later this year and begins its Legacy Survey in Space and Time (LSST) program, it is predicted that the survey will discover between five to 10 ISOs over the course of its planned 10-year mission.Article contentArticle contentPerseid meteors comingArticle contentIn the coming weeks, on clear, moonless nights, you may now start to see some early Perseid meteors streaking across the night sky from the northeast.Article contentThe Perseid meteor shower lasts roughly from July 14-Sept. 1, with the shower’s peak expected to occur on Aug. 12.Article contentThe shower’s radiant, or apparent point of origin in the sky, lies in the constellation of Perseus – the Prince (thus the shower’s name), near the famous Double Cluster open star clusters.Article contentAssociated with Comet 109P/Swift-Tuttle, the Perseids are undoubtedly the premier meteor shower of the summer.Article contentMore about the Perseids as we near the shower’s peak.Article content The Perseids meteor shower, photographed early Wednesday morning, Aug. 12, 2020, by Barry Burgess in Cheverie, N.S.Article contentThis week’s skyArticle contentMercury (magnitude +1.4, in Cancer – the Crab), soon to pass in front of the sun (inferior solar conjunction), is not observable this coming week, as it is 16 degrees (13 degrees by Aug. 3) below the western horizon at dusk.Article contentVenus (mag. -4.1, in Taurus – the Bull) is visible in the dawn sky, rising in the east-northeast around 2:50 a.m. ADT, reaching 24 degrees (25 degrees by Aug. 3) above the eastern horizon before fading from view into the brightening dawn by about 5:25 a.m. ADT.Article contentMars (mag. +1.5, in Leo – the Lion) is not observable this coming week, as it is no higher than eight degrees (seven degrees by Aug. 3) above the western horizon at dusk.Article contentJupiter (mag. -1.9, in Gemini – the Twins) rises in the east around 3:45 a.m. ADT, reaching 15 degrees (19 degrees by Aug. 3) above the eastern horizon before fading from view in the brightening dawn around 5:25 a.m. ADT.Article contentArticle contentSaturn (mag. +0.9, in Pisces – the Fish), becomes accessible by about 12:10 a.m. ADT, when it reaches 11 degrees above the eastern horizon before fading into the dawn twilight just as it reaches its highest point in the sky 42 degrees (41 degrees by Aug. 3) around 5 a.m. ADT.Article contentUranus (mag. +5.8, in Taurus) rises in the east around 1:05 a.m. ADT, reaching 30 degrees (36 degrees by Aug. 3) above the eastern horizon before fading with the approaching dawn around 4:15 a.m. ADT.Article contentNeptune (mag. +7.9, in Pisces), rises around 10:55 p.m. ADT, reaching 42 degrees (43 degrees by Aug. 3) above the southern horizon before fading from view in the dawn sky by about 4:15 a.m. ADT.Article contentNote: I inadvertently left the word “wiki” out of last week’s link regarding the relationship between variations in Earth’s rotation rate and the resulting changes in the length of day. My apologies. Go to: en.wikipedia.org/wiki/Day_length_fulucuationsArticle contentUntil next week, clear skies.Article contentEvents: Aug. 1 – First Quarter Moon Aug. 1 – Moon at apogee; farthest point from EarthArticle content
ATLANTIC SKIES: Is the newly-discovered Comet 3I/ATLAS the oldest comet yet?
