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3I/ATLAS: The Complete Data File

The most current and comprehensive scientific data available for the interstellar object 3I/ATLAS (C/2025 N1). Data is sourced from NASA/JPL, the Minor Planet Center (MPC), the European Space Agency (ESA), and peer-reviewed astronomical research utilising major observatories.

Note: Values may be refined as observations continue.

Current Status & Visibility

As of 22 October 2025

Position

Currently behind the Sun as seen from Earth (solar conjunction), making it unobservable from ground-based telescopes.

Activity

Presumed to be near peak activity (outgassing, coma/tail development) due to its proximity to the Sun.

Perihelion

Closest to Sun approaching on 29 October 2025.

Next Observation Window (Earth)

Expected late November / early December 2025 in the morning sky (constellation Virgo).

Apparent Magnitude

Currently unobservable. Predicted peak brightness post-conjunction: ~ Magnitude +11.5 to +12 (requiring a moderate-to-large amateur telescope). Will not be visible to the naked eye.

Discovery

Date

1 July 2025

Facility

Asteroid Terrestrial-impact Last Alert System (ATLAS) telescope, Río Hurtado, Chile.

Initial Designation

A11pl3Z

Orbital Characteristics

Hyperbolic Trajectory from Interstellar Space

  • Object Type: Interstellar Comet
  • Designations: 3I/ATLAS, C/2025 N1
  • Origin: Interstellar Space (Trajectory suggests origin from the Milky Way's "thick disk" – implying ancient age, potentially 7+ billion years).
  • Orbit Type: Hyperbolic (unbound to the Sun).
  • Eccentricity (e): ~6.137 (Values > 1 confirm interstellar origin and escape trajectory).
  • Perihelion (q): ~1.356 AU (Approx. 203 million km / 126 million mi).
  • Date: 29 October 2025 (~11:47 UT).
  • Location: Between the orbits of Earth and Mars.
  • Inclination (i): ~175.1° (Retrograde orbit, nearly aligned with the ecliptic plane).
  • Longitude of Ascending Node (Ω): ~322.1°
  • Argument of Periapsis (ω): ~128.0°
58

Hyperbolic Excess Velocity (v∞)

km/s – Original speed relative to the Sun before entering the system

68

Maximum Orbital Speed

km/s – Expected at perihelion

Key Encounter Dates & Distances

Physical Characteristics

Size & Structure

Nucleus Diameter

Highly uncertain due to coma. Hubble Space Telescope (HST) data suggests an upper limit of ~5.6 km (3.5 miles). Could be significantly smaller.

Rotation Period

~16.16 hours (derived from light curve photometry).

Density

Inferred to be anomalously high for a comet. Calculated based on minimal non-gravitational acceleration despite extremely high outgassing rates. Suggests a denser composition than typical ice/rock aggregates (~0.5 g/cm³).

Composition from Coma Spectroscopy

Highly Unusual Chemical Signature

Ices

Rich in Carbon Dioxide (COâ‚‚) & Carbon Monoxide (CO) relative to water (Hâ‚‚O). JWST NIRSpec measured a COâ‚‚/Hâ‚‚O production ratio of ~8:1, among the highest recorded. Contains water ice, likely amorphous.

Metals

Strong Nickel (Ni) emission detected with weak or absent Iron (Fe) (Keck KCWI, VLT UVES). This ratio is highly unusual and deviates significantly from solar system abundances.

Other Gases

Cyanide (CN), Carbonyl Sulphide (OCS) also detected (JWST NIRSpec). Appears relatively depleted in complex carbon-chain molecules (like Câ‚‚) compared to CN (Keck KCWI).

Activity & Morphology

Exceptionally Active Far from the Sun

Water Detection

Water detected (as OH via NASA Swift UVOT) at ~2.9 AU.

Outgassing Rates

Outgassing rates of hundreds of kg/second observed.

Activity Driver

Activity likely driven by sublimation of supervolatiles (CO, COâ‚‚) and ejected icy grains containing amorphous water ice.

Morphology

Exhibits a sunward jet / anti-tail structure in addition to a developing traditional tail. Coma observed to be extensive.

Comparison with Previous Interstellar Objects

3I/ATLAS Stands Apart

The fastest and most hyperbolic interstellar visitor yet observed

With a hyperbolic excess velocity of ~58 km/s and an eccentricity of ~6.1, 3I/ATLAS is moving significantly faster than both 'Oumuamua and Borisov. Its unusual composition – dominated by CO₂/CO with a Ni-rich/Fe-poor metal signature – makes it chemically distinct from any previously studied object.

Observational Notes & Resources

Key Observing Instruments

Key data provided by instruments including JWST (NIRSpec), HST (WFC3), Keck (KCWI), VLT (UVES, X-shooter), NASA Swift (UVOT), Gemini Observatory.

NASA/JPL Horizons System

Real-time orbital data tracking

Minor Planet Center

Official designation and orbital elements

NASA's Eyes on the Solar System

Interactive 3D visualisation tools

A Unique Interstellar Messenger

This page provides a snapshot based on current understanding. Follow 3iatlas.watch for news updates as scientists continue to analyse this unique interstellar messenger.

"3I/ATLAS offers an unprecedented opportunity to study material from another star system, potentially 7+ billion years old, carrying clues about planetary system formation across the galaxy."

3

Interstellar Objects

Confirmed visitors from beyond our solar system

7B+

Estimated Age

Years – potentially older than our Sun

58

Speed

km/s – fastest interstellar object observed

The journey of discovery continues.

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