Literally, look who's back: A comet that last swung by Earth 50,000 years ago

Get a look while you can: a comet that last graced Earth's sky tens of thousands of years ago is back, and may now be visible to the naked eye – or at least those with binoculars – later this month and into February.

And not only has C/2022 E3 (ZTF) been away for quite some time, it may never come this way again, astronomers said. Those who want to see the green-tailed chunk of space ice should clear their early-morning calendars for late January and early February, depending on their hemisphere of residence, and hope it maintains its current level of brightness.

E3 will make its closest approach to the Sun on January 12, and will make its closest pass of Earth on February 1, NASA said. Comets are hard to predict, the Americans added, but if E3's brightness trends hold, "it'll be easy to spot with binoculars, and it's just possible it could become visible to the unaided eye under dark skies."

A return visit tens of thousands of years in the making

Astronomers identified E3 in March last year, and tagged it as a long-period comet believed to originate from the Oort cloud, a shell of comet-like objects, planetoids, and icy bodies that boffins said can be "as large as mountains – and sometimes larger."

The Oort Cloud, evidence of which is theoretical and largely extrapolated from the existence of long-period comets, is incredibly distant to the point that it really lies in interstellar space. 

Voyager 1, the most distant human-made object from Earth, still has another 300 years to go before it reaches the theorized inner edge of the cloud, and it'll take the probe an additional 30,000 years to exit its estimated outer reaches, according to NASA. 

In short, if E3 came from the Oort, it traveled a really long way to get here.

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NASA's Jet Propulsion Laboratory believes E3 has an orbital period of around 50,000 years, meaning potentially the last time it came this close was the earliest days of the Upper Paleolithic Era, around the time humans began organizing into early settlements. 

Jessica Lee, astronomer at the Royal Observatory Greenwich, London, told Newsweek that astronomers haven't determined how far E3 will get from Earth, but said it's unlikely to return in less than 50,000 more years, if it returns at all.

"Some predictions suggest that the orbit of this comet is so eccentric it's no longer in an orbit — so it's not going to return at all and will just keep going," Lee said.   

When it makes its close pass of Earth later this month, E3 will come within 0.29 astronomical units, or about 27 million miles (43 million km), of Earth. NASA said it's unlikely to be as good a show as 2020's NEOWISE comet, "but it's still an awesome opportunity to make a personal connection with an icy visitor from the distant outer solar system." ®