A fleet of spacecraft and telescopes – from Hubble and James Webb to spacecraft orbiting Mars – tracked comet 3I/ATLAS, the third to reach us from outside the solar system, and discovered a composition and geometry different from local comets but without any sign of alien technology.
NASA this week (November 19, 2025) revealed the first images and data on interstellar comet 3I/ATLAS – a “frozen fossil” from another solar system, perhaps even older than our own. At a press conference at the Goddard Center, the agency’s scientists showed how a fleet of spacecraft and telescopes – from Hubble and the James Webb Space Telescope to probes around Mars and around the orbit of Jupiter – tracked the comet during its passage through the solar system, confirming unequivocally: It is a natural comet, not an alien spacecraft.
3I/ATLAS is only the third object ever to be classified as an “interstellar body” – that is, an object that comes from outside the Sun’s gravitational frame. It was preceded by the strange object 1I/ʻOumuamua, which behaved more like an asteroid, and comet 2I/Borisov, which was observed in 2019. The name 3I stands for “interstellar” and the serial number is the third, and ATLAS is the name of the system of telescopes in Hawaii and Chile that are funded by NASA as part of the Earth Defense Network and are designed to detect approaching small bodies. The comet was first detected on July 1, 2025, when it was already inside the orbit of Jupiter, about 670 million kilometers from the Sun.
3I/ATLAS's orbit is hyperbolic – an “open” orbit indicating that the object is not bound to the Sun and will continue into interstellar space after passing its closest approach. Upon entering the solar system, it is traveling at a speed of about 221 kilometers per hour relative to the Sun, and its speed is expected to peak at about 246 kilometers per hour near perihelion (the point of closest approach to the Sun). The comet crossed the orbit of the planet Mars on October 30, 2025, and its closest approach to the Sun was just inside the orbit of Mars, at a distance of about 230 million kilometers from the Sun. NASA emphasizes that there is no danger to Earth: on December 19, 2025, it will pass “closely” at only about 270 million kilometers – about twice the distance between the Earth and the Sun.
The exact size of the comet's nucleus is still unknown, but images from the Hubble Space Telescope, which observed it in July, allow us to estimate a diameter of between about 0.44 and 5.6 kilometers. Hubble saw a nucleus surrounded by a "coma" – a teardrop-shaped cloud of dust and gas – and a dust trail that was ejected from the comet at a rate similar to "normal" comets bound to the Sun. Measurements of the brightness of the comet also indicate that the nucleus is close to spherical in shape, and not a particularly elongated body like ʻOumuamua.
Once 3I/ATLAS was determined to be interstellar, a sort of “scientific emergency” was activated: multiple NASA mission teams synchronized observations to follow it throughout almost its entire transit through the solar system. The Hubble and James Webb telescopes observed changes in elevation in a combination of visible and infrared light, the new SPHEREx mission added a broad infrared spectrum, and satellites like Swift and TESS searched for early appearances of the comet before it was officially detected. Together with ground-based telescopes, this data allowed its trajectory to be refined and more focused observations to be planned by planetary and heliophysics missions.
A notable advantage of NASA was the dispersion of the spacecraft throughout the solar system. The Psyche probe, which was on its way to study a metallic asteroid in the asteroid belt, photographed the comet on September 8–9 from a distance of about 53 million kilometers. A week later, the Lucy probe – designed to study Jupiter’s Trojan asteroids – photographed it from a distance of about 386 million kilometers, at a completely different angle of illumination. In this image, the dome and the dust trail extending far away in the direction away from the Sun are clearly visible. Comparing the density and dispersion of the dust at different angles of illumination should allow scientists to reconstruct the structure of the dust and the size of the grains ejected from the comet.
The closest approach was to Mars: in early October, 3I/ATLAS passed within 30 million kilometers of the Red Planet. The HiRISE camera on the Mars Reconnaissance Orbiter captured the comet as a “blurry spot” – the floor – in an image where each pixel represents hundreds of kilometers. At the same time, the MAVEN spacecraft’s ultraviolet spectrograph measured the hydrogen emission from the comet, using a clever comparison between hydrogen in the Martian atmosphere, hydrogen in interplanetary space, and hydrogen originating from the comet itself. Combining these measurements with infrared observations makes it possible to estimate the rate of water vapor emission from the comet – a key piece of information for understanding its composition and the history of its orbit in the galaxy.
Missions originally designed to study the Sun have also contributed to the effort. The SOHO observatory (a joint NASA/ESA mission) was able to "rescue" the comet from the strong sunlight noise in its field of view by stitching together and stacking multiple exposures. The STEREO mission and the Parker Solar Probe, which monitors the solar wind, have also collected data that are still being downloaded and processed. For cosmic dust scientists, this is a rare opportunity to see how an interstellar comet responds to our solar wind environment, and to compare it to comets native to the Solar System.
One of the most intriguing discoveries has to do with the chemical composition of 3I/ATLAS. Infrared observations with the James Webb Space Telescope and SPHEREx have revealed a chamber that is unusually rich in carbon dioxide, in addition to water vapor, carbon monoxide vapor, and other “normal” cometary compounds. The ratio of carbon dioxide to water is higher than is typical for local comets—perhaps because the comet formed in a cold, CO₂-rich environment, or because its icy shell has absorbed intense cosmic radiation over billions of years in interstellar space. Ground-based spectroscopic measurements also showed an unusually high abundance of nickel relative to iron, a feature that has been observed in a few comets but is particularly striking here.
All of this supports the hypothesis that the comet came from an alien planetary system, perhaps older than our own. Its high entry velocity relative to the Sun's local "neighborhood" suggests that it belongs to an old population of stars, where the orbits of the stars have become more random and "messy" over billions of years of gravitational interactions. Researchers using the James Webb data have argued that the composition of the ice near the surface suggests an age of several billion years, possibly even older than the age of our solar system—although the uncertainty is still large, and these are model estimates rather than direct measurements.
As expected, the passage of a new interstellar comet in the middle of a partial shutdown of the US government has given rise to a wave of rumors on the Internet about an “alien spacecraft”. Right at the beginning of the press conference, Amit Kshesthiriyya, the administrator of NASA, emphasized that “this object is a comet. It looks and behaves like a comet, and all the evidence points to a natural comet”. NASA scientists noted that no “signature technologies” – artificial perturbations in the orbit, orderly radio emission or other signs of technology – had been observed and that all changes in the orbit were well explained by the emission of gases and dust, as is the case with many other comets. Independent astronomers emphasized to the Reuters news agency that the idea of an alien spacecraft “is not based on any empirical data”.
Why is there so much excitement about 3I/ATLAS? For science, every comet is a “frozen archive” of the conditions that prevailed in the region where it was born. Local comets have provided important clues in recent years about the original composition of the gas and dust cloud from which the Sun and planets formed. An interstellar comet like 3I/ATLAS is a kind of ice and dust sample from a completely different laboratory—an alien planetary system—that arrives on our doorstep. Systematic comparisons between the composition and microphysics of interstellar comets and “native” comets could change how we understand planet formation, the distribution of elements in the galaxy, and perhaps how water and organic matter arrived on Earth-like worlds.
In the coming months, the comet will continue to move out of Jupiter's orbit, and in the spring of 2026, it will once again retrace its path on its way to interstellar darkness. The James Webb Space Telescope is expected to follow it long after it is too faint to be observed by other telescopes, thanks to its infrared sensitivity. All data, NASA emphasizes, is being uploaded to the agency's open data archives, and is available to teams around the world as well as to amateur astronomers and "citizen science" researchers. For the scientific community, this is just the starting line: It will take years of data analysis to turn the first wave of images and spectra into a solid understanding of what that block of ice and rock went through on its long journey to us - and beyond.
More of the topic in Hayadan:
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Could be a spaceship disguised as a star…
Manny is not in the same plane as the planets ("plane of milk", from the word "eclipse"). Think about the fact that every velocity vector (except the one that is actually perpendicular to the plane) has a *component* in this plane, and that is (probably) what is chosen to be plotted. The perpendicular component cannot be seen – obviously – in a two-dimensional diagram.
Has the "Yadan" heard about the 12 anomalies discovered by Prof. Avi Loeb, or is he content with a translation from the NASA press conference? The agency relies only on the poor data from SOHO and elegantly ignores all the other discoveries, which present a multitude of oddities. No one, including NASA bureaucrats, has an explanation for them and there is no justification for ruling out an alternative explanation other than a mere comet.
If the solar system moves through space at speed around the center of the galaxy, how can a comet from outside our system end up in the same plane as the planets?