Astronomers have spotted a third interstellar object passing through our solar system, the fast-moving 3I/ATLAS, the third interstellar visitor caught passing us by since ʻOumuamua was first spotted in 2017.

3I/ATLAS was first spotted on July 1, 2025, by the Asteroid Terrestrial-impact Last Alert System (ATLAS) survey telescope located in Río Hurtado, Chile, when it was still four-and-a-half times further out from the Sun than the Earth. The object, determined to be a comet due to being surrounded by a fuzzy coma of reflective dust, was soon found to be travelling at a whopping 61 kilometers (38 miles) per second, nearly twice as fast as 2I/Borisov’s 32 kilometers per second, speeds that ʻOumuamua didn’t reach until it passed close to the Sun.

This high rate of speed means that 3I/ATLAS is moving way too fast to be bound by the Sun’s gravity, making this the third interstellar visitor to grace our Solar System in the eight years since ʻOumuamua was first spotted. 3I/ATLAS is also estimated to be rather large: although the solid icy nucleus is obscured by the bright halo of its coma, the object is at least 800 meters (0.5 miles) across—and possibly as large as 5 kilometers (3.11 miles); compared to 2I/Borisov’s 500 meters (1,641 feet) and ʻOumuamua’s largest possible dimension of 400 meters (1,312 feet, provided its shape is cylindrical, or about a quarter of that if it’s disk-shaped).

At that speed, even if 3I/ATLAS is at the lower end of its size and mass estimates, an impact with an Earth-like planet would result in a release of energy equivalent to between 50 and 60 billion tons of TNT—a thousand times more powerful than the Tzar Bomba, a 50-megaton nuclear weapon detonated by the Soviet Union in 1961.

Thankfully, 3I/ATLAS isn’t expected to come close to striking any of the Solar System’s bodies. It is expected to make its closest pass to the Sun on October 29 about halfway between the orbits of Earth and Mars, at which point it is expected to have sped up to 68.2 kilometers (42.4 miles) per second. Although it will make a comparatively close 28.4 million-kilometer (17.7 million-mile) pass to Mars on October 3, 3I/ATLAS will be on the opposite side of the Sun from Earth when this happens; its nearest pass to Earth will be no closer than 266 million kilometers (165.5 million miles, or 1.78 astronomical units), occurring on December 19.

“We think that probably these little ice balls get formed associated with star systems,” remarked Jonathan McDowell, an astronomer at the Harvard-Smithsonian Center for Astrophysics. “And then as another star passes by, tugs on the ice ball, frees it out. It goes rogue, wanders through the galaxy, and now this one is just passing us.”