Hubble Telescope Snaps Best Image Yet of First Interstellar Comet

The Hubble Space Telescope—operated by NASA and the European Space Agency—has snapped an image of the first confirmed interstellar comet, providing astronomers with the sharpest view to date of the mysterious object.

The image indicates that the properties of the comet—known as 2I/Borisov—are very similar to those found in the building blocks of our own solar system.

The comet is only the second known interstellar object to have passed through the solar system. it was discovered by amateur astronomer, Gennady Borisov in August this year.

The only previous interstellar visitor—dubbed 'Oumuamua by scientists—was spotted in 2017 speeding through our cosmic neighborhood before it passed beyond the borders of the solar system.

"Whereas 'Oumuamua appeared to be a rock, Borisov is really active, more like a normal comet. It's a puzzle why these two are so different," David Jewitt, leader of the team that observed the comet from the University of California, Los Angeles, said in a statement.

"['Oumuamua] was inactive but Borisov is ejecting dust, visible in the image as tail to the upper right. Even weirder, comets are normally more active the closer they are to the sun. But Borisov is active even though it's still far from the sun," Jewitt told Newsweek.

The comet's unusual speed and trajectory indicate that it came from interstellar space and will return there again, but not before passing within 190 million miles of Earth in December this year.

"Borisov is currently about three times more distant from us than is the sun. It will come in to a closest approach at twice the Earth-sun distance in early December. After that, Borisov will head back into the darkness, never to be seen again." Jewitt said.

"So we only have a few months to find out everything we can about it. Just as we don't know where it came from, we don't know where it will go. All we can say is that it will leave to go back into the interstellar medium to continue its long, cold journey into darkness," he said.

Astronomers estimate that the object is travelling at a staggering 110,000 miles per hour—roughly 50 times faster than a bullet fired from a rifle.

"It's traveling so fast it almost doesn't care that the sun is there," Jewitt said. "It's past is also very mysterious; we don't know where how long it has been drifting among the stars. It could have been out there for a billion years, conceivably more, all the time at temperatures near absolute zero (-273 degrees Centigrade.) And, because the stars are so far apart, this is likely the first time Borisov has been near any star—our sun—since it left it's home."

On October 12, astronomers used Hubble to take a better look at the comet when it was located around 260 million miles from Earth. To capture a picture of it, astronomers had to track the fast-moving object with precision.

The image revealed that the comet features a central concentration of dust around its nucleus, and that its composition was not unusual for an object which likely formed in a distant star system.

"The data shows that 2I/Borisov is losing a few kilograms per second, probably because ices on its surface are evaporating in the heat of the sun. We see a bright dot in the middle that we think is the main nucleus," Jewitt said.

"Though another star system could be quite different from our own, the fact that the comet's properties appear to be very similar to those of the solar system's building blocks is very remarkable," Amaya Moro-Martin from the Space Telescope Science Institute in Baltimore said in a statement.

Up until the the discovery of 2I/Borisov, the only comets which astronomers knew about have come from the Kuiper belt—a vast disc of small bodies that circle the sun from roughly the orbit of Neptune and beyond—and the hypothetical Oort Cloud which astronomers think marks the limits of the sun's gravitational influence.

"We're interested because this is only the second object from outside the solar system ever to be observed inside the solar system. It's a little piece of some other star's planetary system moving too fast for the sun's gravity to hold it back, and this is our one chance to have a look," Jewitt said.

interstellar comet
As the second known interstellar object to enter our solar system, 2I/Borisov is moving along at a breakneck speed of 110,000 miles per hour. NASA, ESA and J. DePasquale

Identifying interstellar objects in the solar system is extremely difficult because the majority are not bright enough to be detected with currently-available technology.

Even though astronomers have only ever detected two, research suggests that there may actually be thousands of these mysterious visitors passing through our neighborhood at any one time, and dramatically more when you take the whole galaxy into account.

"We're already sure the answer is staggering. In our galaxy, we probably have a trillion trillion things like this," Jewitt said. "That's 10 trillion for every star. Sometimes you have to sit back and just say 'wow' when you find a number like that."

Scientists are now rushing to learn more about 2I/Borisov before it passes beyond our ability to observe it.

"What we are going to do is use the Hubble Space Telescope data to try to figure out how big the nucleus is," Jewitt said. "We can't do that using telescopes on the Earth because they don't have enough resolution to cleanly separate the nucleus from the dust around it."

"We want to know the size because that will help us to figure out how many similar objects are drifting in interstellar space," he said. "And we want to know why the first two interstellar objects look so different, one like a rock and the other like a cosmic fuzz ball. Are they really both members of a common population? Then why are they so different? Is our general picture of their origin and history correct? We can only find out by looking."

This article was updated to include additional comments from David Jewitt.