3I/ATLAS: The Complete Data File

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 (CO₂) & Carbon Monoxide (CO) relative to water (H₂O). JWST NIRSpec measured a CO₂/H₂O 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 C₂) 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, CO₂) 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
3I/ATLAS poses no impact threat to Earth.
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.