NASA has unveiled close-up pictures of an interstellar comet that's making a quick dash around the solar system.
Discovered in July this year, the comet known as 3I/Atlas is only the third confirmed object to visit our corner of the cosmos from another star.
It zipped harmlessly past Mars last month.
The comet is visible from Earth in the pre-dawn sky by using binoculars or a telescope.
Several NASA spacecraft at and near the red planet zoomed in on the comet as it passed at 29 million kilometres away.
The European Space Agency's two satellites around Mars also made observations.
Astronomers are aiming their ground telescopes at the approaching comet, which is about 307 million kilometres from Earth.
Italian astronomer and physicist Gianluca Masi, at the Virtual Telescope Project, zoomed in on it on Wednesday local time from Italy.
The closest the comet will come to Earth is 269 million kilometres in mid-December.
From that point, it will hightail it back into interstellar space, never to return.
Named for the telescope in Chile that first spotted it, the comet is believed to be anywhere from 440 metres across but not greater than 5.6 kilometres across.
The European Space Agency's Juice spacecraft, bound for Jupiter, has been training its cameras and scientific instruments on the comet all month, particularly after it made its closest pass to the sun.
But scientists won't get any of these observations back until February.
Scientist suggests anomalies
NASA said it was conducting an "unprecedented solar system-wide observation campaign" of the comet.
"NASA has an opportunity to learn about the ways that 3I/ATLAS differs from our solar system's home-grown comets and give scientists a new window into how the compositions of other systems may differ from our own," it said in a statement.
However, one scientist is not truly convinced it could be a comet. Enter Avi Loeb, an astrophysicist and professor of science at Harvard University.
He said this space object was "at least a thousand times more massive" than any previous interstellar objects that had been discovered.
That is just one of the 12 anomalies he has spotted with this comet.
"There is an alignment of its trajectory with the orbital plane of the planets around the sun, to within 5 degrees; the chance of that happening at random is a fraction of a per cent," he told The Radio National Hour.
"The object showed a jet of evaporated materials towards the sun that is 10 times longer than it is wide, in the Hubble telescope image.
"That is difficult to explain. It has never been seen before."
At the outset of the briefing for the latest images, NASA Associate Administrator Amit Kshatriya said he would like to "address the rumours" about the nature of 3I/ATLAS.
"I think it's important that we talk about that. This object is a comet," he said.
"We certainly haven't seen any techno signatures or anything from it that would lead us to believe it was anything other than a comet," Nicola Fox, associate administrator of NASA's Science Mission Directorate added.
And NASA's lead scientist for solar system bodies, Tom Statler, believes it's definitely a comet.
"It very, very strongly resembles, in just about every way, the comets that we know," he said.
"It has some interesting properties that are a little bit different from our solar system comets, but it behaves like a comet, and so the evidence is overwhelmingly pointing to this object being a natural body. It's a comet."
Meanwhile, NASA assured the public that the object "is no threat to Earth".
