A staggering 250,000 kilometers per hour was the speed at which the comet had rushed through the inner solar system near the Sun–a reminder of how extreme velocities set interstellar visitors apart from homegrown comets. That velocity set the stage for NASA’s newly released close‑up views of 3I/ATLAS, captured by three spacecraft at Mars as the object swept just 18 million miles from the planet, a very unusually intimate pass for an object born around another star.
The sharpest imaging came from the HiRISE camera aboard the Mars Reconnaissance Orbiter, which resolved a compact coma appearing as a bright, pixelated sphere at about 19 miles per pixel. While modest in appearance, these data provided crucial constraints on both nucleus size and dust environment. MAVEN’s ultraviolet instrument added a layer of chemical insight to the campaign, as its design for probing tenuous atmospheric gases lent itself to detecting hydrogen signatures tied to water breakdown, thus providing an upper limit on the comet’s deuterium‑to‑hydrogen ratio, an important tracer of the comet’s formation region. Composition-sensitive ultraviolet data of this sort are extremely rare for interstellar objects.
This multi‑spacecraft campaign corresponds to an unprecedented solar system–wide effort. Per ESA, twelve NASA assets have imaged 3I/ATLAS since July, including heliophysics missions that could observe the comet near the Sun when Earth-based telescopes couldn’t track it through the intense glare. Those vantage points allowed for continuous monitoring as 3I/ATLAS passed behind the Sun, enabling high‑cadence studies of its evolving tail geometry. Newly processed images from SOHO and NASA’s PUNCH mission showed the dust tail in late September and early October, capturing distinct jets that intensified after perihelion in late October.
The pace of the observations then quickened when the James Webb Space Telescope joined the campaign. Its infrared spectrograph measured an unexpected chemical signature: the coma contains nearly eight times as much CO₂ as water vapor. This inversion of the typical cometary ratio is unlike almost every well‑studied solar system comet. “I have never seen such a strong CO2 peak in a comet spectrum,” said Martin Cordiner of NASA Goddard. Because Earth’s atmosphere blocks the relevant infrared wavelengths, only Webb could uncover this composition, hinting that 3I/ATLAS may preserve ice chemistry inherited from a star-forming environment very different from the Sun’s.
Such chemical fingerprints are complemented by orbital analyses that suggest great age. As NASA’s Tom Statler pointed out, the comet may have originated in a system older than the solar system itself: “gives me goose bumps to think about.” Its hyperbolic trajectory confirms that it is indeed an interstellar visitor, and integrations backward in time of its motion indicate it approached from the constellation Sagittarius with a heliocentric velocity in excess of 58 km/s. Investigations using the stellar data from the European Space Agency’s Gaia spacecraft demonstrate that the distribution of the velocity of the comet is indicative of objects that have been ejected from the Milky Way thin disk-a stellar population which contains long‑lived, moderately metal‑poor systems. These results support early theoretical predictions that 3I/ATLAS may have formed billions of years ago.
Amateur astronomers have seized the moment as the comet moves through the predawn sky. Observers say small telescopes can capture a faint, fuzzy glow-an accessible signpost of cosmic material that spent eons drifting between stars before its brief appearance near Earth. Indeed, as NASA’s acting astrophysics director Shawn Domagal‑Goldman put it, “Everyone that is in control of a telescope wants to look at it because it’s a fascinating and rare opportunity.”
Meanwhile, the scientific race goes on, as ESA’s Juice spacecraft conducts its own observations. The main antenna is now serving as a heat shield near the Sun, delaying data return until February, but its unusual geometry also means it will provide some of the highest‑quality post-perihelion measurements. When those data do arrive, they will be joining a rapidly growing archive of multi-wavelength studies and form the most complete portrait ever assembled of an interstellar comet during one solar system passage.
