3I/ATLAS Interstellar Object Overview
3I/ATLAS C/2025 N1 is the third confirmed interstellar object to visit our solar system, following 1I/ʻOumuamua and 2I/Borisov. This page highlights key points emphasized by Professor Avi Loeb and the Galileo Project. It explains why the object matters, when it comes closest to Earth, how fast it moves, and what it is likely made of.
The model below assumes constant radial speed near closest approach for illustration. At closest approach the distance is set to about 1.8 AU which is about 269 million kilometers.
This tracker uses an illustrative constant speed model around the closest approach date. For precise real time ephemeris, a data service such as JPL Horizons would be required.
Countdown to closest approach
Nominal closest approach is on 19 December 2025.
Why 3I/ATLAS Matters
3I/ATLAS is a rare chance to study material that was born around another star and is now passing through our solar system. Its unbound, interstellar path confirms it does not belong here, making it a natural sample from a distant planetary system. By observing its motion and behavior near the Sun, scientists can test their assumptions, compare theory with real data, and learn how common objects like this might be in the galaxy. 3I/ATLAS gives us direct insight into worlds beyond our own and helps define our place in a much larger cosmic environment.
- Third known interstellar visitor. After 1I/ʻOumuamua and 2I/Borisov, 3I/ATLAS is only the third confirmed object from outside the solar system. That rarity gives it high scientific value.
- Direct material from another star system. Its ices, dust, and outgassing behavior carry chemical fingerprints of the environment where it formed. This lets us compare its parent system to our own.
- Trajectory and possible anomalies. Its hyperbolic and unbound orbit allows tests for non gravitational acceleration, similar to the questions that came up with the motion of 1I/ʻOumuamua.
- Unique observation opportunity. No spacecraft is required. Ground based and space based telescopes can still extract spectra, light curves, and precise orbital data during its passage.
- Natural and non natural hypotheses. Professor Loeb emphasizes that data and not assumptions should decide whether an object is fully natural, unusual, or in an extreme case engineered.
- Mapping interstellar debris. Each new interstellar visitor refines estimates of how much material other planetary systems eject and how common objects like this are.
- Improving future searches. 3I/ATLAS helps optimize survey strategies, detection pipelines, and early warning systems for the next generation of interstellar detections.
Timeline and closest approaches
These are key dates in the 3I/ATLAS passage through the inner solar system. Each entry lists an approximate closest approach distance. One astronomical unit AU is about 149.6 million kilometers.
| Date | Event | Distance |
|---|---|---|
| 3 October 2025 | Closest to Mars | About 0.19 AU about 29 million kilometers |
| 29 October 2025 | Closest to the Sun perihelion | About 1.36 AU about 203 million kilometers |
| 19 December 2025 | Closest to Earth | About 1.8 AU about 270 million kilometers |
| 16 March 2026 | Closest to Jupiter | About 0.36 AU about 54 million kilometers |
Sources:
• Perihelion distance (q ≈ 1.3564 AU), inclination (i ≈ 175.113°) and eccentricity (e ≈ 6.1390) reflect published orbital solutions from the COBS Comet Database.
• Orbital values including Ω ≈ 322.155° and ω ≈ 128.009° are consistent with compiled data from G. van Buitenen's Comet Orbit Catalog.
• Epoch and perihelion time (T ≈ 2025‑10‑29 11:35 UT) are based on current predicted perihelion passage estimates.
• These values may be refined as updated orbital solutions are published.
Even at closest approach to Earth on 19 December 2025, 3I/ATLAS remains almost twice as far away as the Sun is from Earth. It has no impact risk and it will appear relatively faint.
Live ephemeris snapshot
This section is designed to show a live snapshot of 3I/ATLAS in the sky and in the solar system. You can connect it to a service such as JPL Horizons or the Minor Planet Center so that the values update automatically.
- Right ascension (RA): –
- Declination (Dec): –
- Distance from Sun: –
- Distance from Earth: –
- Space velocity: –
- Last updated: –
Orbital elements for 3I/ATLAS
| Element | Symbol | Value |
|---|---|---|
| Semi major axis | a | — |
| Eccentricity | e | 6.1390 |
| Inclination | i | 175.113° |
| Argument of perihelion | ω | 128.009° |
| Longitude of ascending node | Ω | 322.155° |
| Epoch | t₀ | Perihelion T ≈ 2025-10-29 11:35 UT |
Interactive solar system view
This interactive view shows a simplified map of the inner solar system and a stylized path for 3I/ATLAS. It is not a precise ephemeris and it is meant for intuition and explanation. You can play the animation or drag the slider to move through time. The panel also lists the current approximate distance from the comet to the planets.
Planet paths are drawn as circles and the 3I/ATLAS path is a curved line that passes through the inner solar system. The geometry is stylized. The goal is to show that this object enters from deep space, passes near the orbits of Mars and Earth, and then heads back out.
How fast 3I/ATLAS moves
Like other interstellar objects, 3I/ATLAS arrived already moving very fast. The gravity of the Sun accelerates it further as it swings through the inner solar system.
- About 221000 kilometers per hour at discovery when it was within the orbit of Jupiter.
- About 246000 kilometers per hour at perihelion which is its closest approach to the Sun on 29 October 2025.
- As it leaves the influence of the Sun, its speed relaxes back toward its original interstellar velocity.
Likely composition of 3I/ATLAS
Spectroscopic observations and comparisons to 2I/Borisov and solar system comets suggest that 3I/ATLAS is most likely a natural icy comet. From Professor Loeb and the Galileo Project perspective, the key question is whether any detail in its composition or motion deviates from what we expect of such objects.
Ingredients that are likely present include the following.
- Volatile ices such as water, carbon dioxide, and carbon monoxide. There may also be traces of methane and ammonia. These ices sublimate and form a coma as the comet is heated by the Sun.
- Carbon rich dust and silicate grains that build the coma and tail. This is similar to many comets in our own solar system.
- Trace metals such as nickel and iron in the gas and dust phase. Scientists watch the nickel to iron balance and any unusual ratios.
- Complex organic molecules which are carbon bearing compounds at low concentrations. These are consistent with what has been seen in many icy bodies.
The broader point from Professor Loeb is that these ingredients are compatible with a natural comet. Careful measurements of brightness, polarization, composition, and any non gravitational acceleration are still essential. Only then can we fully characterize this visitor from another star.
Sources and references
- Orbital elements (q, e, i, Ω, ω, T) are based on published solutions for 3I/ATLAS from comet databases such as COBS and compilations by G. van Buitenen.
- The perihelion distance q ≈ 1.3564 AU, eccentricity e ≈ 6.1390, inclination i ≈ 175.113°, longitude of ascending node Ω ≈ 322.155°, and argument of perihelion ω ≈ 128.009° reflect current best-fit interstellar orbit parameters.
- The “Live ephemeris snapshot” values shown above are illustrative placeholders. For scientific use, connect this page to a live ephemeris source such as JPL Horizons or the Minor Planet Center.