For only the third time, astronomers have found something passing through our solar system that came from outside the solar system.

This interstellar object, known as 3I/ATLAS, is still pretty far from the sun, currently located between the orbits of the asteroid belt and Jupiter but heading toward the inner solar system.

“This thing is traveling pretty fast” said Paul Chodas, director of the Center for Near Earth Object Studies at NASA’s Jet Propulsion Laboratory in California.

Relative to the sun, it is currently moving at about 130,000 miles per hour and it will continue to accelerate as the sun’s gravity pulls on it.

The first known interstellar object was Oumuamua, which traveled through the solar system in 2017. In 2019, Borisov, a comet of interstellar origin, passed by.

On Tuesday, a telescope in Chile spotted what initially looked like an unknown asteroid on a highly eccentric path that might come close to Earth’s orbit. The telescope is one of five around the world that are part of the Asteroid Terrestrial-impact Last Alert System, or ATLAS, which is a NASA-funded project that watches for space rocks that might be on a collision course with our planet.

The observation was submitted to the International Astronomical Union’s Minor Planet Center, which maintains a catalog of small space bodies in the solar system. Other skywatchers quickly took a look.

“Follow-up observations on July 1 and 2 began to reveal that its orbit might be unusual, possibly interstellar,” said Larry Denneau, a co-principal investigator for ATLAS, which was developed by the University of Hawaii.

Then, an amateur astronomer, Sam Deen, spotted the object in photos that ATLAS had taken in late June. The additional sightings allowed more precise calculations of the trajectory.

An update issued by the Minor Planet Center on Wednesday evening listed more than 100 observations by telescopes around the world, and the center said it had received “tentative reports of cometary activity” from some observers. That led to the center issuing a name for the object: 3I/ATLAS (Earlier in the day, it was referred to as A11pI3Z, a label used by ATLAS for candidate asteroids.)

With all the observations, “There’s no uncertainty” that the comet came from interstellar space. Dr. Chodas said. The speed is too fast to be something that originated within the solar system.

Most likely, it formed as a comet around another star. Then a passing star or some other gravitational interaction provided a kick that sent the comet into interstellar space on a path that, by chance, happened to intersect with our solar neighborhood.

“If you trace its orbit backward, it seems to be coming from the center of the galaxy, more or less,” Dr. Chodas said. “It definitely came from another solar system. We don’t know which one.”

Although it cannot be seen by the naked eye, modest-size telescopes can spot this interstellar object, which is bright compared to Oumuamua and Borisov.

“This is the most interesting question in my mind right now,” Avi Loeb, an astrophysicist at Harvard who had speculated that Oumuamua was an alien artifact, said during an interview Wednesday morning. “What accounts for its very significant brightness?”

If the surface had been dark like that of a rocky asteroid, the object would have to be big, about 12 miles wide, to reflect the amount of light observed.

But now 3I/ATLAS appears to be a comet like Borisov, the second interstellar object observed. For a comet, the brightness comes from sunlight bouncing off a plume of gas and dust known as a coma that surrounds a considerably smaller nucleus.

“You can’t infer the size of the solid object from the brightness of the coma,” Dr. Chodas said. “So it’s too early to say how big this object is.”

Astronomers will also have months to study it. “It’ll be easily observable for astronomers around the world,” Dr. Chodas said. “It should be visible well into next year to large telescopes.”

Analysis of specific colors emitted could identify elements and molecules on its surface and in the cloud of gas and dust. Dr. Loeb said infrared measurements by the James Webb Space Telescope could measure how much heat is coming off the surface.

In contrast, the smaller Oumuamua faded out of view after only a few weeks, leaving many of its mysteries unsolved.

The Vera C. Rubin Observatory in Chile, which will soon begin scanning the full sky every three to four days, should find more interstellar objects, even farther away. This will provide a more complete view of the interstellar objects passing through our solar system and how puzzling it is that no one saw any extrasolar visitors before 2017.

Something that no one will need to worry about is the comet hitting Earth. According to NASA’s trajectory calculations, in late October, when it makes its closest pass to the sun, 3I/ATLAS will be just inside the orbit of Mars. Its closest approach to Earth will occur in December, at a distance of 160 million miles.

“It never gets close to the Earth,” Dr. Chodas said.