Astrophysicists are busy studying an ancient comet from another star system that entered our solar system this year and has already passed Mars.
The comet, called 3I/ATLAS, poses no threat to Earth or its neighboring planets, but it is of great interest as space agencies train to monitor what is just one of three interstellar objects detected by scientists.
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Here’s what we know about this astronomical object that intrigues scientists.
What is 3I/ATLAS?
This comet is only the third interstellar object ever recorded to have passed through Earth’s solar system from another star. A comet is a celestial body made of ice, dust, and gas that orbits the sun. They are thought to be remnants of the solar system’s formation about 4.6 billion years ago.
3I/ATLAS was first discovered in July by scientist Larry Denau of the Asteroid Earth Impact Final Alert System (ATLAS) telescope team in Rio Hurtado, Chile. The project is funded by NASA and operated by researchers at the University of Hawaii Institute for Astronomy.
Prior to this, the cigar-shaped rocky object “1I/’Oumuamua” was discovered in October 2017 by Canadian Robert Werick using the Pan-STARRS telescope at Haleakala Observatory in Hawaii.
In August 2019, Gennady Borisov, a Crimean astronomer and telescope manufacturer, discovered a “rogue comet” 2I/Borisov at the Margo Observatory in Crimea, which travels freely through space without being bound by gravity to any particular star system.
Comets are usually named after humans or the station’s founder. The “I” in their name stands for “Interstellar”, meaning they are from another solar system.
Where is 3I/ATLAS moving?
It passed Mars in early October, moving at a speed of 310,000 kilometers (193,000 miles) per hour, bringing it within 29 million kilometers (18 million miles) of the planet.
According to NASA, the comet is expected to make its closest approach to the sun at the end of October and to Earth, about 270 million kilometers away, in December. It would still be farther from Earth than the Sun, which is 150 million kilometers (93 million miles) away.
Who studies comets?
A number of spacecraft and other assets have already set their sights on this celestial visitor, especially since its current orbit obscures the Sun, making it impossible to track from Earth for now. NASA notes that it will reappear on the opposite side of the sun by early December 2025.
Scientists want to understand more about the actual size and physical properties of comets.
Besides the Hubble Telescope, other NASA-owned space assets track or are already tracking comets and relay information on:
The Mars rovers “Perseverance” and “Curiosity” have been exploring Mars since 2021. The Mars Reconnaissance Orbiter was designed to search for water on Mars. The Europa Clipper mission, a space probe bound for Jupiter’s icy moon Europa, was launched on October 14, 2024. The Lucy and Psyche missions are two robotic spacecraft launched in 2017 to visit eight different asteroids that share Jupiter’s orbit around the sun. The Parker Solar Probe was launched in 2018 to observe the sun’s outer corona. The Polarimeter Unifying Corona and Heliosphere (PUNCH) mission, launched in March 2025, is studying the Sun’s outermost atmosphere. NASA describes the mission as “four suitcase-sized spacecraft” that will “spread along Earth’s day/night boundary, providing the mission with a continuous, unobstructed view of the Sun.” The Solar Heliosphere Observatory (SOHO) is operated by NASA and the European Space Agency (ESA). It was launched in 1995, and according to the project, it is currently orbiting the Sun-Earth Lagrangian point L1, about 1.5 million km from Earth, and can be continuously observed from there.
Separately, ESA’s Juice spacecraft, scheduled to launch in 2023 and bound for Jupiter and its icy moons, will also monitor the high-speed intruder throughout November.
What has been discovered so far?
Using these multiple resources, researchers were able to capture images of the object that were clear enough to determine that the object was actually a comet, as indicated by the hyperbolic shape of its orbital path, meaning the object did not follow a closed orbit around the sun, according to NASA.
NASA’s Hubble Space Telescope announced in July that it had captured the first images of the comet showing a teardrop-shaped cocoon of dust emerging from its solid, icy core.
Observations by the Hubble Space Telescope show that the comet’s core is only 5.6 km (3.5 miles) in diameter. According to NASA, it could be as small as 440 meters (1,444 feet).
3I/Atlas’ coma (the vague halo that appears around the comet) is filled with carbon dioxide, meaning it must have formed somewhere very cold and therefore quite far from its star, planetary scientist Darryl Seligman of Michigan State University told Scientific American.
