Astronomers announced the discovery of a potential interstellar object passing through our solar system, provisionally named A11pl3Z. First detected by the Asteroid Terrestrial-impact Last Alert System (ATLAS) sky survey on July 1, the object was also found in pre-discovery images taken between June 25 and June 29. This finding could mark only the third time an interstellar visitor has been observed traversing our cosmic neighborhood.
If its interstellar origins are confirmed, A11pl3Z would join the ranks of ʻOumuamua, discovered in 2017, and comet 2I/Borisov, spotted in 2019, as the only known interstellar objects to have been seen passing through our solar system. According to Live Science, the object is traveling toward the inner solar system at a speed of about 245,000 km/h (152,000 mph) and could set a new speed record, passing Earth with a relative velocity of around 56 miles per second.
A11pl3Z has captured the attention of astronomers worldwide due to its unusual trajectory. The European Space Agency confirmed the discovery on Blue Sky, stating, "Astronomers may have just discovered the third interstellar object passing through the Solar System!" With an estimated orbital eccentricity near 6.0—the highest observed yet—A11pl3Z's hyperbolic path suggests it is not bound by the Sun's gravity and is passing through our solar system.
David Rankin of the University of Arizona's Catalina Sky Survey explained the significance of this eccentricity. "An eccentricity of 1.0 or lower signifies a closed orbit, indicating an asteroid or comet on an elliptical orbit in our solar system," he said. "This object has an eccentricity of around 6, much higher than both of the previous 'I' objects." This value confirms A11pl3Z's status as an interstellar visitor.
The object is currently around 3.8 times as far from the Sun as Earth is and is moving slowly along the border of the constellations Serpens Cauda and Sagittarius, near the galactic plane. Astronomers believe that A11pl3Z is most likely an asteroid or possibly a comet, with preliminary evaluations suggesting a diameter of about 20 kilometers (up to 12 miles). Observations thus far have not shown any signs of cometary activity, but aspects of its appearance could suggest that it is a comet composed of ice, dust, and small rock particles.
A11pl3Z is projected to make its closest approach to the Sun on October 29, 2025, reaching perihelion at about 1.35 astronomical units (AUs) from the Sun, which is just outside the orbit of Mars. On October 3, 2025, the object will pass approximately 0.2 AU from Mars, with some uncertainty as to whether it will pass inside the orbit of Mars at its closest approach or just outside it. This proximity presents an opportunity for observation.
From its position during this time, A11pl3Z might be captured by the telescope aboard the Mars Reconnaissance Orbiter, which may be able to observe it as an +11th magnitude object. Some researchers have proposed using NASA's Mars rovers to photograph A11pl3Z as it flies close to Mars. Such observations could provide data on the object's composition and origin.
Despite its speed and trajectory, A11pl3Z poses no threat to Earth. It will not come closer than about 284 million kilometers from our planet, and Earth will be on the opposite side of the Sun during the object's solar flyby in late October 2025.
The discovery has prompted a flurry of activity among astronomers. Observatories worldwide are scouring their archives for any overlooked images of A11pl3Z, which could help refine its orbit and provide more precise data. Nearly a hundred astrometric observations have already improved the preliminary orbit calculations, but more observations are necessary to confirm its origin and trajectory.
The European Space Agency's Operations account shared on Blue Sky, "ESA's Planetary Defenders are observing the object, provisionally known as #A11pl3Z, right now using telescopes around the world." This reflects the collaborative international effort to study this interstellar visitor.
Researchers will continue to study A11pl3Z in the coming weeks and months to learn more about its size, shape, and origins. Updates will be provided as more is known about the object. As Rankin noted, "A really neat find."
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