A visitor from another galaxy swooped into our solar system earlier this year, and now Hubble has the footage to prove it.
NASA's Hubble Space Telescope took snapshots of 2I/Borisov, which you can see in the video above provided by Goddard Space Flight Center. It's the sharpest view of the comet to date.
Hubble captured comet 2I/Borisov streaking through our solar system about three weeks before it reached its closest point to the sun. (Photo: NASA, ESA, and D. Jewitt (UCLA))
An amateur astronomer from Crimea named Gennady Borisov first spotted the fast-moving fleck in the night sky in August. Soon after, several telescopes confirmed a trajectory that would take it within 190 million miles of our sun. The photo above was taken as the comet was traveling at 175,000 kilometres per hour (roughly 109,000 miles per hour) as it was headed for a rendezvous with the sun.
The photos and video are significant because while this comet won't be staying with us long, it still reveal clues about the solar system it came from.
2I/Borisov was known as C/2019 Q4 before it became official. (Photo: Gemini Observatory/NSF/AURA)
The Gemini Observatory snapped an earlier full-color picture of the celestial body as it streaked through the heavens. Its woolly white halo and telltale tail were the first hints that we were entertaining our first interstellar comet.
The Polish researchers who analyzed the data proudly dubbed the visitor C/2019 Q4 (Borisov), publishing their findings in the journal ArXiv.
"Both orbital and morphological properties of this body show that this is the first certain case of an interstellar comet," the authors noted in the study.
Scientists at the International Astronomers Union (IAU) concurred with their findings, designating it the second interstellar object; it was crowned 2I/Borisov to honor that status.
From another world
It's only the second time we've detected an interstellar object. (In fact those first few letters of its official name stand for second interstellar.) The comets that typically blaze through our neighborhood hail from within the solar system — either from that icy outermost region known as the Oort Cloud or the Kuiper Belt, a veritable comet factory just beyond Neptune's orbit.
And while some of these celestial objects don't come around here very often — Comet West, for example, has an orbital period of about 250,000 years — they all call our solar neighborhood home. In all, there are likely more than 6,000 comets sailing around our space, all eventually brought to heel by our sun's gravitational leash.
But 2I/Borisov has made the longest journey of all. Researchers say it won't loop around our sun, like its domestic counterparts. It's also traveling at a torrid 110,000 miles per hour — a speed that's far faster than any of the local spaceballs could muster. At that pace, not even the sun will be able to reel it in.
"It's traveling so fast it almost doesn't care that the Sun is there," said David Jewitt of the University of California, Los Angeles (UCLA), leader of the Hubble team who observed the comet.
Strangely enough, this is the second time we've had an interstellar visitor in as many years. In 2017, a very strange object known as 'Oumuamua graced our solar system. Its unwieldy, cigar-like dimensions, unknown origin point and blazing speed sparked a frenzy of scientific speculation. While some scientists suggested it's a hobbled, tail-less comet that has been wandering the galaxy for billions of years, others just came right out and said what many of us were thinking: alien spaceship.
2I/Borisov is a little less ambiguous. Even though it was born in an incomprehensibly foreign space, it bears all the telltale trappings of comethood — specifically a lustrous tail of glitter likely caused by outgassing from its ice-cold heart.
"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," said Jewitt.
In any case, we'll get a chance to scrutinize 2I/Borisov a lot more closely as it brightens our doorstep over the coming weeks. While 'Oumuamua didn't stick around long enough for us to unfurl the "Welcome to Earth" banner, Borisov should make its nearest pass to Earth in December. It won't be quite as intimate as 'Oumuamua's visit, which scraped within 180 million miles of Earth. But it will light up the night sky a lot longer. The flyby will be closest to Earth on Dec. 7 — when the comet will be 190 million miles away — but will be present through April, when it finally bids our solar system a fond farewell. Hubble observations are planned through January 2020.
Editor's note: This story has been updated since it was first published in September 2019.