3I/ATLAS is an interstellar comet confirmed in July 2025 and traveling at about 137,000 mph. Hubble and other observations estimate its nucleus at roughly 1,400 feet to 3.5 miles across, with a Nov. 30 sighting placing it ~178 million miles from Earth. NASA projects a closest approach of about 170 million miles on Dec. 19; the comet poses no threat and can be seen with small telescopes through spring 2026.
Countdown: Interstellar Comet 3I/ATLAS to Fly Past Earth on Dec. 19 — What You Need to Know
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Ever since astronomers confirmed the object known as 3I/ATLAS in July 2025, public interest has been intense. The interstellar visitor has drawn attention from scientists, the media and the public — even sparking celebrity buzz and online speculation. Below is a clear, fact-based guide to what 3I/ATLAS is, when it will pass by Earth and how you can observe it safely.
What Is 3I/ATLAS?
3I/ATLAS is the third confirmed object discovered that originated outside our solar system. When first observed in July 2025 it was traveling at roughly 137,000 miles per hour, and its speed and incoming trajectory convinced astronomers it was ejected from another star system. Its inbound direction traces roughly toward the constellation Sagittarius, near the center of the Milky Way.
Orbit and Long-Term Path
Unlike comets bound to the Sun, 3I/ATLAS follows a hyperbolic trajectory, meaning it will pass through the inner solar system and continue back into interstellar space. This is a one-time visit on human timescales — the comet is not captured by the Sun’s gravity and will not remain in our system.
Size and Observations
Estimates of 3I/ATLAS’s nucleus vary. Early data from the European Space Agency and Hubble Space Telescope place the icy, solid nucleus at about 1,400 feet to 3.5 miles across. Hubble imaged the object again on Nov. 30, at which time it was roughly 178 million miles from Earth. Because the telescope tracked the comet’s motion, background stars in those images appear as streaks.
When and How Close Will It Come?
NASA projects that 3I/ATLAS will make its closest approach to Earth on Dec. 19, passing at about 170 million miles — roughly twice the distance between Earth and the Sun. Scientists emphasize the comet poses no threat to Earth.
Can I See It?
The comet won’t be bright enough for the unaided eye, but observers with small telescopes should be able to spot 3I/ATLAS in the pre-dawn sky through spring 2026. For an accurate, real-time view of the comet’s position and trajectory, use NASA’s free online simulation "Eyes on the Solar System."
Why It Matters
Interstellar objects like 3I/ATLAS offer rare, direct samples of material from other star systems. Studying their composition, structure and behavior helps astronomers learn about planet formation and the diversity of small bodies across the galaxy.
Quick Note: Although the comet has generated viral theories and celebrity commentary, scientists rely on telescopic data and orbital calculations — all of which indicate a safe, scientifically rich visit.
Reported by Eric Lagatta; contributed by Kim Luciani. For live tracking, visit NASA’s "Eyes on the Solar System."
