Astronomers have spotted something that’s only been hinted at once before, an interstellar comet that likely originated in another star system making its way to our Solar System:
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.
To astronomers, the comet is a care package from the cosmos — a piece of a place they will never be able to visit, a key to all the worlds they cannot directly observe.
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.
As the sun sinks behind the Tennessee mountains, and stars wink into view, astronomer Doug Durig climbs onto the roof of his observatory, powers up his three telescopes and angles them skyward.
Every night, the comet grows bigger and brighter in the sky, expelling streams of gas and dust that may offer up clues to its history. On Dec. 8, it will make its nearest approach to Earth, offering researchers an up-close glimpse before it zooms back into the freezing, featureless void.
Ordinarily, of course, the comets we are familiar with come from within our own Solar System, with most of them originating in a region far beyond Pluto and, when conditions are right, being sent on a journey toward the sun that either result in their ultimate destruction or sets them in an orbit that causes them to reappear on what generally becomes a predictable basis. The most famous of these reappearing comets, of course, is Halley’s Comet, which was first recorded as appearing in 1066 A.D., but which may have been recorded as far back as the 400 B.C. time period. Like clockwork, Halley’s Comet reappears every 75-76 years. It was last in the neighborhood of Earth in 1986 and is scheduled to reappear in 2061, According to calculations, it will make its closest known approach to Earth in 2134 when it will be 13 million kilometers of our planet. These comets are of particular interest because they are made up of some of the same material as the early planets were when the Solar System was first formed.
The comet that was spotted in this case, though, is of a different vintage. It appears to have drifted from a completely different star system, which one we cannot tell at this point apparently, and its composition is likely completely different from the comets we’re familiar with. As such, it is of particular interest to people studying planets orbiting stars other than our sun:
Scientists’ best hope for closely examining another solar system was to wait for a piece of one to come to us.
It was Aug. 30, in the quiet moments before dawn, when a self-taught astronomer in a Crimean mountain village spotted a faint smudge low on the horizon, barely distinguishable against the glittering background of stars.
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.”
But ‘Oumuamua was already on its way out of the system when it was discovered in October 2017, and it was so faint that scientists were never able to view it as more than a single pixel of light. They were not quite sure what they had seen — was it a metallic, rocky asteroid or an icy,dusty comet? And they were unsure whether the detection was just a lucky fluke, never to be repeated, or a harbinger of things to come.
So researchers were thrilled when, less than two years later, another interstellar traveler arrived.
The new comet, which has been named 2I/Borisov (indicating its discoverer and its status as the second known interstellar object), is expected to be within reach of telescopes until fall 2020. At its closest approach, next month, it will be twice as far from Earth as Earth is from the sun.
Though it entered the solar system from the direction of the constellation Cassiopeia, scientists do not know yet where 2I/Borisov came from, or how long it has flown through the desolation of interstellar space. Given its current speed, it has certainly been traveling for millions, if not billions, of years.
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.”
So this visitor in our night sky could tell us something about what exoplanets, planets from outside our Solar System, are like and what they are composed of. It’s even possible that the comet, like those that have existed in our own Solar System, could carry some form of evidence of the building blocks of life in another star system. Quite fascinating, really.
Photo via Space.com
