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EmergingPeer-reviewed

Interstellar comet 3I/ATLAS: discovery and physical description

Photometry from three observatories in the days after its discovery measures the colours, coma and dust of an interstellar comet.

ByBryce Bolin, Matthew Belyakov, C. Fremling, M. J. Graham, A.M. Abdelaziz, E. G. Elhosseiny and 2 others

Eureka Scientific · California Institute of Technology · National Research Institute of Astronomy and Geophysics · New Mexico State University and 4 more

27th of 28 in Space & Astronomy on Frontier, by Frontier Score.

Read the paper in Monthly Notices of the Royal Astronomical Society LettersSign in to watch

What it is

The authors present the characteristics of interstellar comet 3I/ATLAS, discovered on 2025 July 1 by the Asteroid Terrestrial-impact Last Alert System (ATLAS). The comet has an eccentricity of about 6.1 and a velocity at infinity of about 57 km/s, indicating an interstellar origin. They obtained B, V, R, I, g, r, i and z photometry at Kottamia Astronomical Observatory, Palomar Observatory and Apache Point Observatory on 2025 July 2, 3 and 6, and measured the comet's colour indices and a spectral slope of 16.0 ± 1.9% per 100 nm. They estimate its dust cross-section within 10,000 km at 184.6 ± 4.6 km², assuming an albedo of 0.1; its coma has a full width at half-maximum of about 2.2 arcsec and an A(0°)fρ of 280.8 ± 3.2 cm. They estimate that 3I/ATLAS is ejecting micrometre to millimetre dust at about 0.01 to 1 m/s, with a mass loss of about 0.1 to 1.0 kg per second.

Why it matters

An eccentricity of about 6.1 and a speed far from the Sun of about 57 km/s indicate that comet 3I/ATLAS came from outside the solar system. The paper's arXiv version calls it the third known macroscopic interstellar object, after 1I/ʻOumuamua and 2I/Borisov. Within days of its discovery this paper measured its colours and a dusty coma, and estimated that it was losing about 0.1 to 1.0 kg of dust per second.

Underlined numbers link to their source. Every metric and quoted figure is listed under Sources and data below.

Filed underinterstellar object, comet, 3I/ATLAS, solar system, astronomy

Scored 2026-11-12How scoring works

The Frontier Score, in full

How this entry's score is built, term by term. Open any pillar to see each sub-metric's raw value, how it maps to 0 to 100, and a link to its source (OpenAlex for most sub-metrics that combine several sources, NIH iCite where its ratio is part of field-normalized impact).
Evidence 87Impact 74Novelty 38
The three pillars as one shape: a result strong on every axis fills the triangle.
How the Frontier Score is calculated for this breakthrough
TermScoreWeightPoints
EvidenceHow established and verifiable the result is.87× 0.2521.9
ImpactHow much the result matters, judged field-relative and by current momentum.74× 0.2518.4
NoveltyHow genuinely new the result is, and how fast-moving.38× 0.5018.8
Weighted pillars59.1
Frontier recency17 months since publication× 0.61
IntegrityNot retracted× 1
Frontier Score36
Confidence: Settled. Established evidence: about 54 citations across 4 independent indices. Corroborated beyond citations (cited on Wikipedia).Established evidence: about 54 citations across 4 independent indices. Corroborated beyond citations (cited on Wikipedia).

Every sub-metric, traced to its source

Evidence87
Evidence sub-metrics
Sub-metricRaw value0 to 100WeightPointsSource
Peer review & venueWhether the work has cleared peer review, and how selective its venue is. Peer review is necessary but not sufficient: before citations accrue, a fresh result in one of the five general flagships (Nature, Science, Cell, NEJM, the Lancet) is a stronger evidence signal than one in a selective specialist or society journal, which in turn outranks one in a legitimate but very high-volume mega-journal, and any of them outranks a preprint that has not been reviewed at all.Maps to 0 to 100: Peer-reviewed article graded by venue tier: flagship journal (Nature, Science, Cell, NEJM, the Lancet) 100; selective journal (every other journal the index admits: the specialist journals of those families, JAMA, PNAS, Physical Review Letters and X) 90; high-volume mega-journal (Nature Communications, Science Advances) 78; venue not recorded 88. Other records: review 90, book 70, dataset 60, preprint 45, an article that has not been peer reviewed 45, other 55.Peer-reviewed, selective journal900.3027.0OpenAlex type / primary_location / source
CorroborationIndependent corroboration that the result is on the record and reaching beyond a single source, read as the BREADTH of independent records rather than the size of the citation pile. Counts how many of the five independent citation indices (OpenAlex, Crossref, Semantic Scholar, OpenCitations, Europe PMC) report a citation count for the work at all, zero included, plus orthogonal, non-citation lines of corroboration: citation in Wikipedia, registered clinical trials or clinical citations, released datasets or software or a repository copy, public funding on record, and technical-community discussion. Citation MAGNITUDE is deliberately judged under Impact, not here, so Evidence and Impact measure genuinely different things instead of both rewarding the same citation pile twice.Maps to 0 to 100: Starts at 28 and rises by 9 for each of the five independent citation indices that returns a citation count for the work (zero counts; OpenCitations returns zero even for a DOI it does not hold) and by 6 for each orthogonal non-citation line (Wikipedia, clinical trials or clinical citations, open datasets, software or a repository copy, public funding, community discussion), up to the top of the 0-100 scale.4 of 5 citation indices report a count, 2 independent non-citation lines760.3022.8OpenAlex, Crossref, Semantic Scholar, OpenCitations, Europe PMC, DataCite, NIH RePORTER, Wikipedia, Hacker News count of indices that report a count for the work + orthogonal reach
VerifiabilityHow openly the result can be read, reused, and reproduced. Rewards open access, a Creative Commons BY or CC0 license, a green repository copy anyone can archive, openly minable full text, and released datasets or software a reader can actually run. Cross-checked across OpenAlex, Unpaywall, Europe PMC, and DataCite.Maps to 0 to 100: Closed access 45; open access 88; any Creative Commons BY license (including the NC, ND and SA variants) or CC0 100. A repository copy raises the floor to 85, openly minable full text to 90, and released data or software to 92.Open access (hybrid), repository copy880.2017.6OpenAlex, Unpaywall, Europe PMC, DataCite is_oa / license / has_repository_copy / open datasets
IntegrityRetraction and post-publication correction status. A retracted result is not evidence of anything and collapses the whole Frontier Score; a correction or expression of concern is a softer flag. A correction the publisher labels as its own error (a Publisher Correction) is not a flag on the work. Read across OpenAlex and Crossref (both update-to and updated-by notices).Maps to 0 to 100: Clean 100 (also when the only notice is a Publisher Correction); a correction or expression of concern 75; retracted 0. Flagged if OpenAlex OR Crossref records the notice.No retraction or concern on record1000.2020.0OpenAlex, Crossref is_retracted / update-to / updated-by
Impact74
Impact sub-metrics
Sub-metricRaw value0 to 100WeightPointsSource
Field-normalized impactImpact relative to the world average for the same field, year, and type, so a small field and a large field are judged fairly. Triangulates three independent field-normalized measures: OpenAlex's Field-Weighted Citation Impact, its citation percentile within the exact field-and-year cohort, and the NIH iCite Relative Citation Ratio. 1.0x is average; the percentile is the share of same-field, same-year work it out-cites.Maps to 0 to 100: Each ratio (1.0 = field average) maps 1.0 to 50, 3.0 to 75, 9.0 to 90; the field+year percentile maps directly (top 1% -> ~99). The available measures are averaged. When none is available yet (very recent work), this sub-metric is left out and Impact is computed from the others.43.2x FWCI, top 0.0% of field-year vs field990.4544.5OpenAlex, NIH iCite fwci / citation_normalized_percentile / relative_citation_ratio
Influential citationsCitations that genuinely build on the work rather than mention it in passing (Semantic Scholar's influential-citation measure). A sharper signal of real impact than a raw count.Maps to 0 to 100: Saturating: 15 influential citations maps to 50, and none maps to 0. When Semantic Scholar has no measure for the work, this sub-metric is left out and Impact is computed from the others.7 influential320.206.4Semantic Scholar influentialCitationCount
Citation velocityCitations received in the trailing twelve months (estimated from yearly citation counts: this year's so far plus the share of last year's that falls inside the window), judged as a rate rather than a lifetime total. Momentum is what a frontier index cares about: a result being taken up fast right now is landing, whether its lifetime pile is large or still small. Where an expected field citation rate is known, the momentum is also read relative to it, so a fast-moving result in a quiet field is not overlooked.Maps to 0 to 100: Saturating: 30 citations in the last twelve months maps to 50. When NIH iCite provides the field's expected rate, this is blended evenly with the ratio of observed to expected momentum.56 in last 12 months650.3522.8OpenAlex, NIH iCite counts_by_year / field_citation_rate
Novelty38
Novelty sub-metrics
Sub-metricRaw value0 to 100WeightPointsSource
Conceptual noveltyHow genuinely new the contribution is, measured at publication from the work's OWN content, not its date: how atypical its combination of research areas is versus all prior work, and whether it builds on a broad, deep base rather than only the newest papers in a fast-moving area. This is what separates a real advance from a recent-but-commodity result, and it needs no forward citations, so it is stable for brand-new work. An honestly noisy proxy (even state-of-the-art novelty measures agree only moderately with expert judgment), so it carries bounded weight and never drives the ranking alone.Maps to 0 to 100: Two publication-time signals, each 0-100. The primary one is atypical combination: how unusual the work's median pairing of research topics is versus the prior literature, by pointwise mutual information (a pairing made far more often than chance scores low). The second, foundational reach (the median age of the work's references and the share older than five years), can only lift it: when reach is higher, the score rises by 35% of the gap, and it is never lowered. When only one signal is measurable it is used alone; when neither is (a work too thin in topics or references), this sub-metric is left out and Novelty is computed from the other three. A review is damped to 60%.Median topic pairing Astro and Planetary Science x Astrophysics and Star Formation Studies (70,623 prior works made this pairing)150.456.5OpenAlex topics + referenced_works (publication-time)
RecencyHow recently the work appeared. The frontier is now, so newer scores higher.Maps to 0 to 100: Exponential decay with a 12-month half-life from the publication date.17 months old380.3011.3OpenAlex publication_date
Attention accelerationWhether attention is rising: citations in the latest full year versus the year before. Accelerating interest signals an active, opening frontier.Maps to 0 to 100: Latest/prior-year ratio: 1x maps to 50, 2x to 75, 4x to 100. The prior year counts as at least 3 citations, so a jump from one citation to a few is not read as explosive growth. With no citations in the latest full year it reads as unknown, and unknown is neutral (50).10.0x rising1000.1010.0OpenAlex counts_by_year
Edge of reviewPreprints sit ahead of the peer-review process and brand-new papers have only just cleared it. Both earn novelty here (while a preprint is discounted under Evidence), because that is where the frontier forms first.Maps to 0 to 100: Preprint 95; any other record 80 when under 6 months old, 65 under 18 months, 45 after that.Peer-reviewed record650.159.8OpenAlex type / publication_date
ProvenanceAll sources

Sources and data

The source figures behind this entry, grouped by the source that holds them: up to five citation indices cross-checked, field-normalized impact, then real-world reach (Wikipedia, community discussion, clinical trials, released data and public funding) where it exists. Each value links to its record.

OpenAlex

Primary record
Total citations
82
Field-weighted citation impact
43.2x field average
Citation percentile
Top 0.1% of its field-year
Citations, recent 12 months
56
Publication date
2025-06-14
Access
Open access (hybrid)

Crossref

Citations
61
Works it builds on
56
Funders on record
8

Semantic Scholar

Citations, all versions
47
Influential citations
7

OpenCitations

Citations
45

Unpaywall

Reuse license
PUBLIC-DOMAIN

arXiv

arXiv preprint
v3

Wikipedia

Wikipedia articles citing it
1
OpenAlex recordRead it in Monthly Notices of the Royal Astronomical Society Letters

Figures quoted in the write-up

FigureValueSource
Orbital eccentricity (With the velocity at infinity, indicates an interstellar origin)≃6.1Monthly Notices of the Royal Astronomical Society: Letters
Velocity at infinity (Speed relative to the Sun far from the solar system)≃57 km s⁻¹Monthly Notices of the Royal Astronomical Society: Letters
Spectral slope (From B, V, R, I, g, r, i and z photometry)16.0 ± 1.9 per cent/100 nmMonthly Notices of the Royal Astronomical Society: Letters
Dust cross-section (Within 10 000 km of the comet, assuming a 0.1 albedo)184.6 ± 4.6 km²Monthly Notices of the Royal Astronomical Society: Letters
Radius for the dust cross-section (Abstract)10 000 kmMonthly Notices of the Royal Astronomical Society: Letters
Albedo assumed for the dust cross-section (An assumption, not a measurement)0.1Monthly Notices of the Royal Astronomical Society: Letters
Width of the coma (Abstract)full width at half-maximum ≃ 2.2 arcsecMonthly Notices of the Royal Astronomical Society: Letters
Dust activity measure A(0°)fρ (Abstract)280.8 ± 3.2 cmMonthly Notices of the Royal Astronomical Society: Letters
Speed of the ejected dust (Micrometre to millimetre dust, estimated)∼0.01–1 m s⁻¹Monthly Notices of the Royal Astronomical Society: Letters
Mass-loss rate (Estimated)∼0.1–1.0 kg s⁻¹Monthly Notices of the Royal Astronomical Society: Letters
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