CAPE CANAVERAL, Fla. (AP) — A comet is heading back our way after 50,000 years.
The dirty snowball was last visited in Neanderthal times, according to NASA. It will come within 26 million miles (42 million kilometers) of Earth on Wednesday before speeding off again, unlikely to return for millions of years.
So look at the opposite of the killer-comet movie title “Don’t Look Up.”
Discovered less than a year ago, this innocuous green comet is already visible in the northern night sky with binoculars and small telescopes, and perhaps with the naked eye in the dark corners of the Northern Hemisphere.
It is expected to get brighter and brighter as it rises above the horizon by the end of January, best seen in the early morning hours. On February 10, it will be close to Mars, a good landmark. Southern Hemisphere skygazers will have to wait until next month for a glimpse.
Although a lot of comets have graced the sky in the past year, “this one probably seems a little bigger and therefore a little brighter and it’s coming a little closer to Earth’s orbit,” said Paul Chodas, NASA’s comet and asteroid-tracking guru.
Green from all the carbon in the gas cloud or coma surrounding the nucleus, this long-lived comet was discovered last March by astronomers using the Zwicky Transient Facility, a wide-field camera at Caltech’s Palomar Observatory.
This explains its official, cumbersome name: Comet C/2022 E3 (ZTF).
On Wednesday, it will strike between the orbits of Earth and Mars at a relative speed of 128,500 miles (207,000 kilometers). Its nucleus is thought to be about a mile (1.6 km) across, with its tail stretching millions of miles (km).
The comet is not expected to be nearly as bright as Neowise in 2020 or Hale-Bopp and Hyakutake in the mid-to-late 1990s.
But “it will be brighter because of Earth’s close passage … allowing scientists to do more experiments and enable the public to see a beautiful comet,” University of Hawaii astronomer Karen Meech said in an email.
Scientists are confident in their orbital calculations, placing the comet’s last swing through the vicinity of the Solar System’s planets 50,000 years ago.
But they don’t know how close it came to Earth or whether it was even visible to Neanderthals, said Chodas, director of the Center for Near Earth Object Studies at NASA’s Jet Propulsion Laboratory in California.
When it comes back, though, he’s hard to judge.
Every time comets skirt the Sun and planets, their gravitational tugs alter the iceball’s path ever so slightly, leading to large trajectory changes over time. Another wild card: Jets of dust and gas flow from comets as they heat up near the Sun.
“We don’t really know exactly how much they’re pushing this comet around,” Chodas said.
The comet — a time capsule of the emerging solar system 4.5 billion years ago — came from beyond Pluto in what’s known as the Oort Cloud. This deep-submerged shelter for the comet is thought to extend more than a quarter of the way to the next star.
When comet ZTF originated in our solar system, we couldn’t be sure it would stay there, Chodas said. If it gets booted out of the solar system, it will never return, he added.
Don’t worry if you miss it.
“In the comet business, you just wait for the next one because there are dozens of them,” Chodas said. “And the next one may be bigger, brighter, closer.”
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