A comet visiting the sky for the first time in 50,000 years: it will pass close to the Sun and could be visible to the naked eye in late January!

Steph Deschamps / January 8, 2023

Its last visit was 50,000 years ago: the comet "C/2022 E3 (ZTF)", from the farthest reaches of the solar system and recently discovered, will pass close to the Sun this week and could be visible to the naked eye in late January.
The small, rocky, icy body, estimated to be about 1 km in diameter, was discovered in March 2022 by the Zwicky Transient Facility (ZTF) astronomical sky survey program operating the Samuel-Oschin Telescope at Palomar Observatory in California.
Detected as it passed through Jupiter's orbit, the comet is currently heading toward the Sun and will reach its perihelion, or closest point to the Sun, on Jan. 12, astronomers calculate.
The celestial object will then be "10% farther" from the Sun than the Earth is (about 150 million km), said Nicolas Biver, of the Observatoire de Paris-PSL.
When a comet gets closer to the Sun, the ice contained in its nucleus sublimes and lets escape a long trail of dust reflecting the light of the Sun.
It is this bright hair that will be seen from Earth as C/2022 E3 (ZTF) comes toward us.
The comet will reach the peak of its brilliance "when it's closest to Earth," says Thomas Prince, a physics professor at the California Institute of Technology who is working on ZTF.
However, the phenomenon will be less spectacular than during the passage of its congeners Hale-Bopp (1997) or Neowise (2020), much larger.
The star will be easy to spot with a good pair of binoculars, and maybe even with the naked eye during a part of the night, under a sky without too much Moon and free of light pollution.
The best viewing window should be the weekend of January 21-22 and the week following.
During this period, the comet will pass between the constellations of the Little Dipper and the Big Dipper. Before plunging into the Southern Hemisphere and heading back to the outer reaches of the solar system, its probable birthplace.
According to current models, comets come from two reservoirs: the Kuiper belt, beyond Neptune's orbit, or the Oort cloud, a vast theoretical area located up to one light year from the Sun, at the limit of its gravity field.
"Based on the inclination of the plane of its orbit, it would be a long-period comet originally from the Oort cloud," according to Biver.
This is not the first time that the icy visitor has passed close to the Sun: a previous journey had already propelled it towards our lands, about 50,000 years ago.
The comet then went back in the other direction, but without going as far as the Oort cloud. This time, it will probably end up being "definitely ejected from the solar system ».
Its final visit will be an opportunity for scientists to understand a little more about the composition of comets, especially through observations from the James Webb Space Telescope.
"We're going to observe it from every angle. It's not the comet of the century, but we're happy to be able to observe comets like this every one or two years, because we consider them to be remnants of the formation of the solar system," explains Biver.
This "rare visitor" will bring "information on the 'inhabitants' of our solar system far beyond the most distant planets", adds Thomas Prince.
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