Construction is expected to begin later this year, with completion anticipated in late 2026. Thursday's event was akin to a kickoff for the expansion.

Explore This Section 1. … 2. Comets 3. Comet 3I/ATLAS * Comets Home * Facts * Featured Comets * Hartley * Swift-Tuttle * Borrelly * Halley * Churyumov-Gerasimenko * Borisov * Encke * Wild 2 * Tempel 1 * Hale-Bopp * Siding Spring * ISON * 'Oumuamua * Shoemaker-Levy 9 * Resources * Solar System Home # Comet 3I/ATLAS NASA missions are working together to track and study this rare, interstellar comet as it passes through our solar system. ## Overview, Discovery, and Observing Video: Cruising Toward a Mars Flyby Follow Comet 3I/ATLAS's Journey News about Comet 3I/ATLAS FAQs Image: The First Sighting Multimedia Gallery ## Comet 3I/ATLAS * ### Overview Comet 3I/ATLAS is the third known object from outside our solar system to be discovered passing through our celestial neighborhood. Astronomers have categorized this object as interstellar because of the hyperbolic shape of its orbital path. (It does not follow a closed orbital path about the Sun.) When the orbit of 3I/ATLAS is traced into the past, the comet clearly originates from outside our solar system. Comet 3I/ATLAS poses no threat to Earth and will remain far away. The closest it will approach our planet is about 1.8 astronomical units (about 170 million miles, or 270 million kilometers). 3I/ATLAS will reach its closest point to the Sun around Oct. 30, 2025, at a distance of about 1.4 au (130 million miles, or 210 million kilometers) — just inside the orbit of Mars. The interstellar comet’s size and physical properties are being investigated by astronomers around the world. 3I/ATLAS should remain visible to ground-based telescopes through September 2025, after which it will pass too close to the Sun to observe. It will reappear on the other side of the Sun by early December 2025, allowing for renewed observations _._ Animation of comet 3I/ATLAS's trajectory through our solar system. NASA/JPL * ### Discovery The NASA-funded ATLAS (Asteroid Terrestrial-impact Last Alert System) survey telescope in Rio Hurtado, Chile, first reported observations to the Minor Planet Center of comet 3I/ATLAS on July 1, 2025. Since the first report, observations made before the discovery were gathered from the archives of three different ATLAS telescopes around the world and Caltech’s Zwicky Transient Facility at the Palomar Observatory in San Diego County, California. These “pre-discovery” observations extend back to June 14, 2025. **How this comet got its name:** Comets are generally named for their discoverer(s), in this case the ATLAS survey team. The letter “I” is for “interstellar,” indicating that this object came from outside our solar system. It’s the third known interstellar object, hence the “3” in the name. Read more about NASA's discovery of comet 3I/ATLAS This animation shows the observations 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/NASA * ### NASA Assets Observing Comet 3I/ATLAS NASA's Hubble Space Telescope captured this image of interstellar comet 3I/ATLAS on July 21, 2025, when the comet was 277 million miles from Earth. Hubble revealed a teardrop-shaped cocoon of dust coming off of the comet's solid, icy nucleus. Because Hubble was tracking the comet moving along a hyperbolic trajectory, the stationary background stars are streaked in the exposure. Hubble’s continuing observations allow astronomers to more accurately estimate the size of the comet’s nucleus. Observations as of Aug. 20, 2025, indicate that the upper limit on its diameter is 3.5 miles (5.6 kilometers), though it could be as small as 1,444 feet (440 meters) across. NASA assets that are planning to gather observations of 3I/ATLAS include: Hubble, Webb, TESS, Swift, SPHEREx, Perseverance Mars rover, Mars Reconnaissance Orbiter, Curiosity rover, Europa Clipper, Lucy, Psyche, Parker Solar Probe, PUNCH, and ESA/NASA’s SOHO and Juice. Check back here for observations, schedules, or any additional NASA assets, as that information becomes available. Read more about the Hubble image Hubble captured this image of the interstellar comet 3I/ATLAS on July 21, 2025, when the comet was 277 million miles from Earth. Hubble shows that the comet has a teardrop-shaped cocoon of dust coming off its solid, icy nucleus. Image: NASA, ESA, David Jewitt (UCLA); Image Processing: Joseph DePasquale (STScI) September 2025 update ### **Interstellar Comet Cruising Toward Mars Flyby** in Early October NASA has been studying the icy visitor 3I/ATLAS with space telescopes including Hubble, Webb, and SPHEREx. When the comet passes Mars on Oct. 3, multiple spacecraft there might catch a glimpse. The comet is on course to pass behind the Sun in late October, and venture past Jupiter in March 2026, on its way out of our solar system. Watch the video ## Follow Comet 3I/ATLAS's Journey With NASA's Eyes on the Solar System interactive app, you can follow comet 3I/ATLAS as it travels through our solar system and see where it's headed next. Unable to render the provided source ## News About Comet 3I/ATLAS NASA’s Webb Space Telescope Observes Interstellar Comet 1 min read NASA’s James Webb Space Telescope observed interstellar comet 3I/ATLAS Aug. 6, with its Near-Infrared Spectrograph instrument. The research team has been analyzing insights from Webb’s data, and a preprint is available online. Webb is one of NASA’s space telescopes observing… Blog NASA’s New SPHEREx Mission Observes Interstellar Comet 1 min read NASA’s SPHEREx (Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer) observed interstellar comet 3I/ATLAS Aug. 7 to Aug. 15. The SPHEREx team has been analyzing insights from this data, and a research note is available… Blog ## FAQs * ### ****Where did this interstellar object come from?**** 3I/ATLAS formed in another star system and was somehow ejected into interstellar space, which is the space between the stars. For millions or even billions of years, it has drifted until it recently arrived at our solar system. It has been approaching from the general direction of the constellation Sagittarius, which is where the central region of our galaxy, the Milky Way, is located. When discovered, 3I/ATLAS was about 410 million miles (670 million kilometers) away from the Sun, within the orbit of Jupiter. * ### **How was it determined that 3I/ATLAS didn’t originate in our solar system?** Observations of the comet’s trajectory show that it is moving too fast to be bound by the Sun’s gravity and that it's on what is known as a hyperbolic trajectory. In other words, it does not follow a closed orbital path around the Sun. It is simply passing through our solar system and will continue its journey into interstellar space, never to be seen again. * ### **How many interstellar objects have been discovered?** This is the third known interstellar object to have been observed passing through our solar system. Discovered in 2017, ‘Oumuamua was the first known interstellar object; the second was 2I/Borisov, which was discovered in 2019. * ### Is 3I/ATLAS an asteroid or a comet? From telescope observations, astronomers can tell that 3I/ATLAS is active, which means it has an icy nucleus and a coma (a bright cloud of gas and dust surrounding a comet as it approaches the Sun). This is why astronomers categorize it as a comet and not an asteroid. * ### **How big is 3I/ATLAS?** Astronomers don’t yet know exactly how big 3I/ATLAS is, but from Hubble Space Telescope observations as of Aug. 20, 2025, they can see that the diameter of its nucleus is not less than 1,444 feet (440 meters) and not greater than 3.5 miles (5.6 kilometers). * ### **How fast is it moving?** Very fast. When it was discovered, the interstellar comet was traveling about 137,000 miles per hour (221,000 kilometers per hour, or 61 kilometers per second), and its speed will increase as it approaches the Sun. * ### **Is there a danger of this interstellar object hitting Earth?** No. Although the trajectory of the object brings it into the inner solar system, it won’t come close to Earth. As the comet 3I/ATLAS journeys through the solar system, it won’t come closer than 1.8 astronomical units (about 170 million miles, or 270 million kilometers) to our planet. ## First Sighting 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/NASA Image and video gallery ## Comet 3I/ATLAS Multimedia Check here for NASA's latest images and graphics of comet 3I/ATLAS as they become available. Multimedia Gallery 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-Caltech Keep Exploring ## Discover More Topics From NASA Asteroids, Comets & Meteors Our Solar System Planetary Defense at NASA Kuiper Belt