Astronomers have discovered what they think may be an interstellar object passing through the solar system. At twice as wide as Mount Everest is tall, A11pl3Z would be the third interstellar object — an object that originates from outside the solar system — ever to be found, after ‘Oumuamua in 2017 and a comet called 2I/Borisov in 2019. Telescopes around the world are now scrambling to observe it — including a virtual telescope that plans to share real-time images online.
A11pl3Z could be similar to Oumuamua, the first confirmed interstellar object observed passing ... More
Thought to be around 12 miles (20 kilometers) in diameter, A11pl3Z’s eccentric trajectory suggests that it’s from outside the solar system.
“Astronomers may have just discovered the third interstellar object passing through the Solar System!” wrote the European Space Agency Operations on X (Twitter). “ESA’s Planetary Defenders are observing the object, provisionally known as A11pl3Z, right now using telescopes around the world.”
A11pl3Z was added to a list of Near-Earth Objects on July 1 by the International Astronomical Union’s Minor Planet Center. It’s thought to be a large asteroid or a comet, but more observations will be needed to confirm.
At magnitude 18.8, A11pl3Z is far too dim to see with the naked eye or even with backyard telescopes. However, the Virtual Telescope Project will host an online observation on YouTube of A11pl3Z at 6:00 p.m. EDT on July 3, 2025.
A11pl3Z poses no danger to Earth, but it will pass relatively close to Mars. It will reach its perihelion — the closest it will get to the sun — in October but will only get about as half as close to the sun as Earth is. According to EarthSky, at perihelion, it will be traveling at around 42 miles (68 kilometers) per second/second or about 152,000 miles (245,000 kilometers) per hour.
Not only will it not get near Earth, but during its perihelion, it will be difficult for astronomers to study because it will be lost in the sun’s glare as seen from Earth. After October, A11pl3Z will travel out of the solar system.
If A11pl3Z is an interstellar object, it joins a very select group. The first known interstellar object ever identified was ’Oumuamua (also known as 1I/2017 U1) on Oct. 19, 2017, by the Pan-STARRS1 Near-Earth Object survey. Challenging astronomers’ assumptions about how small bodies from another star system would look, ’Oumuamua — meaning “a messenger from afar arriving first” in Hawaiian, according to NASA — displayed some strange behavior, moving too quickly to be an asteroid (and even accelerating) and leaving no trail of debris behind it, as comets do. It also varied in brightness, probably because it was sausage-shaped and spinning. All of this led some to speculate that ’Oumuamua was, in fact, an artificial creation of an advanced civilization. It wasn’t — but since it was only discovered on its way out of the solar system, it was faint and frustrating for observers — which prompted plans for a 22-year mission to visit it.
A second interstellar interloper, 2I/Borisov, was discovered in Crimea on Aug. 30, 2019, by Gennady Borisov, an amateur astronomer. It was way more impressive. While ’Oumuamua was estimated to have a diameter of 0.19 miles (0.3 kilometers), Borisov’s was 3.7 miles (6 kilometers). It looked and behaved like a regular comet but with a very eccentric path that underlined its interstellar origin.
As telescopes and sky surveys continue to improve, more interstellar objects will be discovered. About seven objects like ’Oumuamua should pass within one Earth-sun distance of the sun each year, according to a paper published in 2021 using data from the Gaia satellite. However, it calculated that interstellar comets like 2I/Borisov could occur once every decade. It went further, predicting that three objects per century could come from other galaxies.