Unbound by gravity, an icy comet formed some 7 to 10 billion years ago has been traveling through space at breakneck speed ever since.
Originating from outside our solar system, this visitor was detected in July. On Oct. 29, it will pass behind the sun. Then, in March of next year, it will soar past Mars on its way out of our solar system.
Astronomers around the world are taking note, including in Vermont.
Alain Brizard is an astrophysicist and professor at St. Michael’s College in Colchester. He said this comet is distinct from the other two interstellar comets from the past decade and from periodic comets — like Halley's Comet — that are visible every 80 years or so.
Plus, this icy chunk has a one-way ticket.
And though casual observers with binoculars can't readily see Comet 3I/ATLAS, there is much to be learned from it.
"Here is this visitor," Brizard said, "knocking on our door."
Its name is a nod to its potential origins as well as the enormous Chilean telescope used to detect it. The "3" denotes its status as the third comet from beyond our solar system, "I" stands for interstellar, and "ATLAS" is an acronym for the "Asteroid Terrestrial-impact Last Alert System," based in Chile.
In the last decade, two other visitors came from other star systems: Oumuamua in 2017 and Borisov in 2019. And as with then, Brizard said there is no need for Dr. Who-level speculation about comet 3I/ATLAS' trajectory.
"We're in no danger of being collided with," Brizard said. Instead, Brizard said he sees it as a great opportunity to find out more about the origins of our own solar system as well as others.
While Oumuamua was described as cigar-shaped, 3I/ATLAS is more of a teardrop. And scientists have been able to surmise what makes up its emissions as it hurtles through space — a mixture that includes carbon dioxide and water vapor.
While casual comet-chasers won’t be able to see this one, Brizard said that large telescopes, such as the Hubble Space Telescope, have already captured photos and video.
And the comet’s astronomic measurements — including eccentricity and speed — are making scientists take note. NASA categorizes its speed as "very fast," or traveling about 137,000 miles per hour.
Eccentricity in astronomy measures how much something's orbit deviates from a perfect circle. To compare it to known planets and moons, Brizard said the eccentricity of our moon is almost zero, because it is nearly circle-shaped. The earth, as well, has a small eccentricity. "Any eccentricity below one is gravitationally bound to the sun," Brizard said.
When an interstellar comet has an eccentricity greater than one, it's known as having a hyperbolic or an escape trajectory, which means the object is moving too fast to be bound by another body.
"Oumuamua had an eccentricity of 1.22. Borisov had an eccentricity of 3.4. And this one," Brizard said, "is estimated to be above six."
"Before we developed the technology, it's reasonable to assume that we've had such visitors in the past," Brizard said. He plans to take this opportunity to find out all he can about this new visitor and its chemical composition.
"It would be boring if it was the same," he said. "And it would be interesting to see if it was markedly different, right?"
These measurements help scientists put data points in our understanding of the formation of a solar system that's not our own.
