Astronomers Observe Interstellar Object Passing Through Solar System

This is the third recorded instance of an object from outside the solar system being observed.

Discovery of Interstellar Object A11pI3Z

Astronomers confirmed the discovery of an interstellar object, designated A11pI3Z, moving through the solar system on June 2, 2025. This object was captured by David Rankin at the Catalina Sky Survey at the University of Arizona. Scientists note that while this is only the third such object detected, it is possible that additional interstellar objects pass through the solar system without being observed.

Detection and Observations

The object, which is likely a comet, was initially detected using data from the Asteroid Terrestrial-impact Last Alert System (ATLAS), an asteroid impact early warning system in Rio Hurtado, Chile. NASA confirmed the discovery on Tuesday.

According to the Minor Planet Center, the object displays characteristics such as a marginal coma and a short tail, indicating cometary activity.

Multiple telescopes have provided further observations since the initial report. Data from three ATLAS telescopes worldwide and the Zwicky Transient Facility at the Palomar Observatory in San Diego County, California, have supported the identification of the comet. These observations date back to June 14.

Trajectory and Characteristics

This diagram shows the trajectory of interstellar comet 3I/ATLAS as it passes through the solar system. It will make its closest approach to the Sun in October. NASA/JPL-Caltech

The object appears to originate from interstellar space, arriving from the direction of the constellation Sagittarius. It is currently approximately 420 million miles from Earth, according to NASA.

Astronomers state that the comet poses no threat to Earth and will remain at least 150 million miles away. It is expected to reach its closest approach to the sun around October 30, at about 130 million miles, just inside the orbit of Mars.

The object, also referred to as "A11pl3Z" or "3I/ATLAS," is estimated to be about 25 miles in diameter, according to Josep Trigo-Rodriguez, an astrophysicist at the Institute of Space Sciences near Barcelona, Spain.

It is traveling at approximately 152,000 mph and is approaching the inner solar system from the bar of the Milky Way. Its trajectory suggests it did not originate in this solar system.

Previous Interstellar Objects

This is the third recorded instance of an interstellar object entering the inner solar system. The first was a cigar-shaped object named 'Oumuamua, detected in 2017. The second, in 2019, was a comet named 21/Borisov, which likely originated from another star system.

Ongoing Research

Astronomers plan to continue studying the size and physical properties of the comet through September, after which it will pass too close to the sun to be observed. The comet is expected to become visible again on the other side of the sun in early December.