SEWANEE, Tenn. — Something strange is sailing toward us. Something small and cold and extraordinarily fast. No one knows where it came from, or where it is going. But it's not from around here.

This is an interstellar comet - an ancient ball of ice and gas and dust, formed on the frozen outskirts of a distant star, which some lucky quirk of gravity has tossed into our path.


It is only the second interstellar interloper scientists have seen in our solar system. And it's the first one they've been able to get a good look at. By tracking the comet's movement, measuring its composition and monitoring its behavior, researchers are seeking clues about the place it came from and the space it crossed to get here. They have already found a carbon-based molecule and possibly water - two familiar chemicals in such an alien object.


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Far below in the darkness, Durig will be waiting.



Yet even when viewed through the most powerful telescopes, exoplanets are not discernible as anything more than specks of light. And no human alive has a hope of traveling to another star - merely approaching the nearest one would take 40,000 years.



Gennady Borisov submitted his observations to the Minor Planet Center, the astronomers' clearinghouse for information about small bodies in the solar system, so other scientists could take a look.

One night later, halfway across the planet, the strange report caught Durig's eye.

"I was the second person to observe it," Durig said. "That confirmed the comet was real."

Within a couple of weeks, scientists had collected enough observations to calculate the comet's orbit. But they did not find the oval path that comets typically make around the sun. Instead, the orbit was hyperbolic - it did not close in on itself. The object was also traveling at the blistering speed of 93,000 miles per hour, far faster than any comets, asteroids or planets orbiting our sun.

"Wow," said Davide Farnocchia, a navigation engineer at NASA's Jet Propulsion Laboratory, who was among the first people to determine that the comet came from another star. "I was not expecting to see anything like that."

There has been only one other interstellar object spotted in our solar system: a cigar-shaped rock named 'Oumuamua, a Hawaiian word that translates to "messenger from afar."

Interstellar Interloper 2I/Borisov. Courtesy of NASA, ESA, and D. Jewitt (UCLA) et al





As the object gets closer to the sun's warmth, ices on its surface turn into gas. This creates the characteristic halo-like "coma," which scientists can scrutinize to determine what the comet is made of. Already, 2I/Borisov has been observed more than 2,000 times.

"That's going to be fun, in terms of looking at this object . . . as it comes in from the deep freeze for the very first time," said Michele Bannister, an astronomer at Queen's University Belfast. "Let's open it up and see what we have with this particular present from another star."

Exoplanet discoveries revealed we live in a crowded cosmos. But they also awakened Earthlings to how lonely we are. Mostplanetary systems discovered in recent decades are wildly unfamiliar, and the most common type of exoplanet - a body larger than Earth but smaller than Neptune - doesn't exist near our home.

When astronomers had only our own solar system to go by, "it used to seem like planet formation was solved,"said Malena Rice, an astrophysicist at Yale University. "And then all of a sudden there are all these strange systems that don't fit our picture."


Comets in our own solar system have been found to contain some of the basic ingredients for life: water, carbon, even complex organic compounds. Now 2I/Borisov could tell us whether life's essential molecules were among the building blocks of a world beyond our own.


"When I saw that, I shouted in my office . . . something not repeatable in a respectable newspaper," Fitzsimmons recalled.


"Even in these other systems where their architectures are very different, maybe the underlying physics and chemistry is still pretty similar," said McKay, a research scientist at NASA's Goddard Space Flight Center.

The path of comet 21/Borisov through our Solar System. The panel at left shows the comet's straight path across interstellar space slightly deflected by the sun's gravitational pull. The panel at right shows the comet's position relative to Earth when the NASA/ESA Hubble Space Telescope observed it on Oct. 12, 2019, when it was almost 261 million miles (420 million kilometers) from Earth. Courtesy of NASA, ESA, J. Olmsted, F. Summers (STScI)



"There's a universality to that, which is amazing," Bannister said. "Our planetary system is woven together with another planetary system by these little wanderers roving across the galaxy."

With just an hour to go until daybreak, 2I/Borisov is due to appear above the horizon and make its way across the eastern sky. Durig's long night is almost over.



It is tiring and often tedious work. Unlike discoverers, follow-up observers do not get to put their names on anything. And unlike researchers working at the world's largest observatories, someone such as Durig faces real hurdles in achieving the findings that get published in prestigious journals.


Here in Sewanee's cramped observatory, cluttered with stacks of observation records and piles of broken equipment he hopes to one day refashion into something usable, "we're doing essential science," Durig says. "We're filling in all the gaps."




Durig sends his images and a record of the comet's location to the Minor Planet Center - another drop of data in the bucket of scientific knowledge.

Consistent observations like this, conducted by the same people using the same instruments every night, will be even more important once the comet becomes visible in the Southern Hemisphere, where many of the world's biggest telescopes are positioned. They need to be pointed with extreme precision, so astronomers must have a firm handle on the comet's trajectory and things that might subtly alter it, such as outbursts of gas.

An accurate orbit is also key to astronomers' most ambitious plan for the comet.

"If we can get the best possible trajectory, so we can trace it back with the exact direction it's coming in . . . maybe we can find out what the origin system is," said Farnocchia, the Jet Propulsion Laboratory engineer.




This article was written by Sarah Kaplan, a reporter for The Washington Post.