Folks, it’s official: the object that astronomers recently spotted blowing through the outer solar system came from interstellar space.
Yesterday, the intriguing stranger was named A11pl3Z. Now, it’s earned the esteemed designation 3I/ATLAS — that “I” standing for “interstellar.”
3I/ATLAS is currently located between the orbits of the asteroid belt and Jupiter, the New York Times reports, where it‘s about 416 million miles away from the Sun, NASA said. That’s equal to four and a half times the distance between the Earth and our star.
But it’s approaching fast. As we speak, 3I/ATLAS is hurtling toward the inner solar system at a speed of about 130,000 miles per hour — a “thousand times over the speed limit on a highway,” Harvard’s Avi Loeb quipped.
“This thing is traveling pretty fast,” Paul Chodas, director of the Center for Near Earth Object Studies at NASA’s Jet Propulsion Laboratory in California, told the NYT.
“If you trace its orbit backward, it seems to be coming from the center of the galaxy, more or less,” Chodas added. “It definitely came from another solar system. We don’t know which one.”
3I/ATLAS is only the third confirmed interstellar object to reach our Sun’s domain — hence the “3.” The first was ‘Oumuamua, spotted in 2017, which became famed for its unusually elongated shape. The second, dubbed Borisov, was a comet that spectacularly began to break apart.
Provisionally, this latest visitor also appears to be a comet, making it the second known “rogue” comet in history.
Its discovery and confirmation as an extrasolar visitor were a collaborative effort. What initially appeared to be an asteroid was first flagged Tuesday by a telescope in Chile that’s part of the Asteroid Terrestrial-impact Last Alert System (ATLAS). The International Astronomical Union’s Minor Planet Center quickly added the intriguing object to its list of confirmed near-Earth objects. So did NASA and its Jet Propulsion Laboratory.
Soon, more than 100 observations from telescopes across the globe poured in, including “tentative reports of cometary activity,” the Minor Planet Center said Wednesday, providing enough data to designate it 3I/ATLAS.
“There’s no uncertainty” about its interstellar origins, Chodas told the NYT, because it’s moving too fast to come from our own solar system.
We can only speculate how it got here. Per the NYT, it probably formed as a comet around another star, before a gravitational interaction, perhaps a passing star, booted it out of its home system.
How large 3I/ATLAS is is also a matter of some debate. If it were a rocky asteroid, the interstellar interloper would have to be about 12 miles wide to reflect the levels of light we’re seeing, according to the NYT, which is what astronomers initially estimated.
But since it’s a comet, it’s much harder to say. Comets owe their luminous appearance to a halo of gas and dust known as a coma, which is released when the object is heated up by sunlight. These comas appear much larger than the solid object at their center, and their tails even more so; Borisov’s was nearly 100,000 miles long, astronomers estimated, or about 14 times the size of the Earth.
“You can’t infer the size of the solid object from the brightness of the coma,” Chodas told the NYT. “So it’s too early to say how big this object is.”
The good news is that there will be plenty of time to study 3I/ATLAS, which hasn’t always been the case in our limited encounters with interstellar visitors; ‘Oumuaua, for instance, vanished after just a few weeks.
“It’ll be easily observable for astronomers around the world,” Chodas told the NYT. “It should be visible well into next year to large telescopes.”
3I/ATLAS is expected to reach its closest approach to the Sun around October 30, NASA said, at a distance of about 130 million miles, putting it inside the orbit of Mars.
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