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Hubble image of 3I/ATLAS, 30 November 2025
Hubble image of 3I/ATLAS, 30 November 2025. Image: NASA, ESA, STScI, D. Jewitt (UCLA), M.-T. Hui; processing J. DePasquale (STScI) · Public domain · via Wikimedia Commons
Open cases · Discovered 1 July 2025 · now leaving the solar system

3I/ATLAS: The Third Interstellar Visitor

Established2025 CE – 2026 CEDiscovered by ATLAS, Río Hurtado, Chile

A comet from another star system, possibly older than the Sun — and the subject of a viral alien-probe rumor.

Research draft · editor review pending. Every claim below is linked to a checked source, but this dossier has not yet been reviewed by a human editor. Spot an error? Corrections are logged.

On 1 July 2025, the NASA-funded ATLAS survey telescope in Chile spotted a faint object moving too fast to be bound to the Sun. It was only the third interstellar object ever found, after 'Oumuamua in 2017 and comet Borisov in 2019, and was named 3I/ATLAS. It reached its closest point to the Sun around 29–30 October 2025, at about 1.4 astronomical units, and never came closer to Earth than about 1.8 AU.

More than a dozen NASA missions, along with ESA spacecraft and major ground observatories, observed it. The comet turned out to be chemically strange: very rich in carbon dioxide, with methane detected for the first time on an interstellar object and water carrying at least 30 times more deuterium than Solar System comets. Speculation that it might be alien technology spread widely, but radio searches found no artificial signals, and the scientific consensus is that it is a natural comet.

Case log

An open case. Dated developments, oldest first, each with its source.

  1. ATLAS survey telescope in Chile reports the object; it is confirmed as the third interstellar object.

    Sources: 1

  2. A preprint asks whether 3I/ATLAS could be alien technology, sparking viral coverage.

    Sources: 11

  3. Closest approach to the Sun, about 1.4 AU.

    Sources: 1

  4. Webb observes the outbound comet and detects methane.

    Sources: 4

  5. ALMA result published: water deuterium at least 30× Solar System comets.

    Sources: 6

  6. SETI Institute publishes its radio search: no technosignatures.

    Sources: 8

Why it matters

It is a rare physical sample from another planetary system, and a live case study in how science handles a viral claim.

What the evidence says

  1. Established

    3I/ATLAS was discovered on 1 July 2025 by the NASA-funded ATLAS survey telescope in Chile and is the third known interstellar object.

    Basis: NASA mission page.

    Sources: 1
  2. Established

    It came closest to the Sun around 30 October 2025 at about 1.4 AU, and never came closer than about 1.8 AU to Earth.

    Basis: NASA mission page.

    Sources: 12
  3. Established

    Its coma is unusually rich in carbon dioxide compared with water.

    Basis: JWST near-infrared spectroscopy (ApJ Letters, 2025).

    Sources: 3
  4. Established

    Webb detected methane on 3I/ATLAS, the first direct detection of methane on an interstellar visitor.

    Basis: JWST/MIRI observations in December 2025 (ApJ Letters, 2026).

    Sources: 45
  5. Established

    Its water is enriched in deuterium by at least 30 times relative to Solar System comets, pointing to formation in a very cold environment.

    Basis: ALMA measurement (Nature Astronomy, 2026).

    Sources: 67
  6. Established

    Radio searches found no technosignatures; the Allen Telescope Array ruled out transmitters stronger than about 10–110 watts.

    Basis: SETI Institute (Astronomical Journal, 2026); Breakthrough Listen.

    Sources: 8910
  7. Speculative

    3I/ATLAS could be alien technology.

    Basis: Proposed in a July 2025 preprint citing 'anomalous' properties.

    Counterpoint: Not peer reviewed; radio searches and its comet-like chemistry contradict it.

    Sources: 11

Competing interpretations

Natural comet from an ancient, cold system

A comet ejected from the outer reaches of another star system, possibly billions of years old.

Standing: Scientific consensus, supported by chemistry and behavior.
Sources: 64

Artificial object

A probe or spacecraft built by another civilization.

Standing: Speculative; no radio signals detected and its behavior matches a comet.
Sources: 89

Weigh the evidence

Having read the claims and sources, which explanation do you find most convincing?

One vote per browser. Results appear after you vote.

Open questions

Connected dossiers

ʻOumuamua: The First Interstellar ObjectComparable case · The first and third interstellar visitors.The Wow! SignalSame open question · A viral 'alien' claim tested by radio searches.Webb's First Deep FieldInfluence · Webb measured its unusual chemistry.

See 3I/ATLAS in the discovery universe →

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Sources

  1. “Comet 3I/ATLAS.” NASA Science (2025) Open source ↗
    INSTITUTION · CHECKED 2026-10-22 · HTTP 200 LINK CHECK
  2. “IAU combats misinformation on interstellar object Comet 3I/ATLAS.” International Astronomical Union (2026) Open source ↗
    INSTITUTION · CHECKED 2026-10-22 · HTTP 200 LINK CHECK
  3. Cordiner, Roth, Kelley et al.. “JWST Detection of a Carbon-dioxide-dominated Gas Coma Surrounding Interstellar Object 3I/ATLAS.” The Astrophysical Journal Letters (2025) DOI 10.3847/2041-8213/ae0647
    PEER-REVIEWED · CHECKED 2026-10-22 · CROSSREF DOI METADATA
  4. “NASA's Webb Detects Methane on Interstellar Comet 3I/ATLAS.” NASA Science (2026) Open source ↗
    INSTITUTION · CHECKED 2026-10-22 · HTTP 200 LINK CHECK
  5. Belyakov, Wong, Bolin et al.. “The Volatile Inventory of 3I/ATLAS as Seen with JWST/MIRI.” The Astrophysical Journal Letters (2026) DOI 10.3847/2041-8213/ae5700
    PEER-REVIEWED · CHECKED 2026-10-22 · CROSSREF DOI METADATA
  6. “ALMA reveals interstellar comet 3I/ATLAS formed in a far colder world than our own.” ALMA Observatory (2026) Open source ↗
    INSTITUTION · CHECKED 2026-10-22 · HTTP 200 LINK CHECK
  7. Salazar Manzano, Paneque-Carreño, Cordiner et al.. “Water D/H in 3I/ATLAS as a probe of formation conditions in another planetary system.” Nature Astronomy (2026) DOI 10.1038/s41550-026-02850-5
    PEER-REVIEWED · CHECKED 2026-10-22 · CROSSREF DOI METADATA
  8. “SETI Institute looks for signs of technology in interstellar visitor 3I/ATLAS.” SETI Institute (2026) Open source ↗
    INSTITUTION · CHECKED 2026-10-22 · HTTP 200 LINK CHECK
  9. “Breakthrough Listen observations of interstellar object 3I/ATLAS.” SETI Institute / Breakthrough Listen (2026) Open source ↗
    INSTITUTION · CHECKED 2026-10-22 · HTTP 200 LINK CHECK
  10. Sheikh, Garcia Lopez, Gerrard et al.. “A Search for Radio Technosignatures from Interstellar Object 3I/ATLAS with the Allen Telescope Array.” The Astronomical Journal (2026) DOI 10.3847/1538-3881/ae6651
    PEER-REVIEWED · CHECKED 2026-10-22 · CROSSREF DOI METADATA
  11. Hibberd, Adam; Crowl, Adam; Loeb, Abraham. “Is the Interstellar Object 3I/ATLAS Alien Technology?.” arXiv preprint 2403.00040 (2025) Open source ↗
    REFERENCE WORK · CHECKED 2026-10-22 · HTTP 200 LINK CHECK

How to read the labels

EstablishedSupported by strong, converging evidence.
ContestedEvidence exists but qualified scholars disagree.
UnresolvedThe question is open; evidence does not settle it.
LegendComes from myth, literature or tradition, not physical evidence.
SpeculativeA hypothesis with little direct evidence so far.

Hero image: Hubble image of 3I/ATLAS, 30 November 2025. Image: NASA, ESA, STScI, D. Jewitt (UCLA), M.-T. Hui; processing J. DePasquale (STScI) · Public domain · via Wikimedia Commons. Evidence labels describe the written claims, not the image. Version 1 · updated 2026-10-22.