In Photos: Interstellar Comet 3I/ATLAS’s Journey Through the Solar System

A mysterious interstellar visitor, designated 3I/ATLAS, has been traversing our solar system in recent months, drawing intense interest from astronomers and space enthusiasts worldwide. A rare object from another part of the galaxy, 3I/ATLAS has been photographed by ground-based telescopes, space observatories and spacecraft from both NASA and the European Space Agency.

Discovery and Early Observations

ATLAS (Asteroid Terrestrial-Impact Last Alert System) first detected the object in July from its Rio Hurtado, Chile site when it was roughly 420 million miles away. ATLAS is a NASA-funded survey network designed to spot near-Earth asteroids and other transient objects.

What Telescopes and Spacecraft Have Seen

NASA’s SPHEREx observatory observed 3I/ATLAS from Aug. 7–15 when the comet was about 290 million miles from the Sun. SPHEREx detected a coma — the diffuse cloud of gas and dust surrounding the nucleus — rich in water ice and carbon dioxide, a composition similar to many comets formed within our own solar system.

In late August, Gemini South in Chile produced some of the most detailed ground-based images to date, showing an expanding coma and an increasingly elongated tail as the object became more active while approaching the Sun.

The European Space Agency’s ExoMars Trace Gas Orbiter (TGO) observed 3I/ATLAS for about a week beginning Oct. 1. In those frames the comet appears as a fuzzy white point moving against a starry background; at that time it was roughly 18.6 million miles from the orbiter.

Spacecraft Imaging and Hubble Observations

NASA released a collection of images captured by several missions — including the PUNCH constellation, SOHO (Solar and Heliospheric Observatory), the Lucy probe, MAVEN (Mars Atmosphere and Volatile EvolutioN) and the Perseverance rover on Mars — taken from late September through mid-October. Many of these show the comet as a bright dot, while higher-resolution shots reveal a faint, extended tail.

Late last month, the Hubble Space Telescope tracked 3I/ATLAS from about 178 million miles away, recording the moving comet as a luminous point while background stars appeared as streaks. NASA plans additional Hubble observations as the object departs the solar system.

Juice Close Approach and Tail Structure

ESA’s Jupiter Icy Moons Explorer (JUICE), en route to Jupiter, made observations shortly before its closest approach to the comet on Nov. 4, when the spacecraft passed within roughly 41 million miles. JUICE’s images revealed a glowing coma and evidence for two distinct tails: a plasma tail of ionized gas and a dust tail composed of gas and small solid particles. ESA expects to release more instrument data from JUICE in February.

Current Status and Flyby Timing

3I/ATLAS reached perihelion (its closest point to the Sun) at the end of October and is scheduled to pass Earth on Dec. 19 at a safe distance of about 170 million miles. There is no evidence the object is artificial; all observations to date are consistent with a natural comet from outside our solar system. Scientists continue to collect data as the object leaves our neighborhood.

Why This Matters: Every interstellar visitor provides a rare opportunity to compare materials formed around other stars with those formed in our own solar system, improving our understanding of planetary formation and the diversity of small bodies in the galaxy.