Comet Tsuchinshan-ATLAS risks its life on Friday by passing as close as possible to the Sun, on a journey that began millions of years ago, which promises a remarkable spectacle for Earthlings in October if it survives.
The small body of rock and ice was detected in January 2023 by China’s Purple Mountain Observatory (Tsuchinshan), giving it the first half of its name. He owes the second to the confirmation of his existence by a telescope from the South African ATLAS program.
Since then, for astronomers, who like more rigorous nomenclatures, C/2023 A3 continues its journey towards the Sun. The study of its course is too short, “barely a year of hindsight”, to know precisely the path it has followed until now, explains to AFP Lucie Maquet, astronomer at the Institute of Celestial Mechanics and of ephemeris calculation (IMCCE), located within the Paris-PSL Observatory.
It follows an orbit “which is not closed”, with models suggesting that it could have been up to 400,000 times the Earth-Sun distance before reaching us.
A journey counting in millions of years for this comet which probably saw the light of day in the Oort cloud, a hypothetical and gigantic assembly of tiny planets and celestial bodies, at the edge of the solar system.
Until now, you had to be in the Southern Hemisphere to hope to see it with the naked eye. Friday around 5:00 p.m. Paris time, it will have crossed as close as possible to the Sun, before returning close to the Earth.
In the Northern Hemisphere, it will be visible from October 13, and if the weather is right “it will be obvious” every evening when looking “in the direction of the setting sun”, according to Ms. Maquet.
– “A bright comet” –
On condition of having survived its passage near the Sun. Because when comets approach our star, the ice contained in their core sublimates and lets out a long trail of dust, reflecting the solar light.
This characteristic hair, the coma, is also a sign that the object is “degassing”. The whole question is whether this degassing will not be too great, at the risk of disintegrating the unwary visitor.
A catastrophe “always possible”, according to the astronomer, because the assembly of ice and stones “may very well not resist the force of gravity of the Sun”. The good news is that C/2023 A3 appears to have a very massive core, and therefore “there is a good chance that it will survive” this passage.
The first forecasts, revised downwards since, suggested that it would have exceptional brightness as it passed near the Earth. “It’s a bit of a surprise at the last moment, but in any case it’s going to be a bright comet, that’s for sure,” according to Ms. Maquet.
As for its future course, it is unpredictable. Her solar odyssey will not be without consequences on her orbit, disrupted by the gravity of the stars she will have encountered and by the weight loss cure inflicted by the Sun.
The models used predict, without any commitment, that it could be “ejected from the solar system, to get lost between the stars”, according to the September IMCCE bulletin.
Everything will ultimately depend on the encounters that C/2023 A3 will make during its journey through the Oort cloud, a few thousand years from now. It would be enough, notes the astronomer, for it to “encounter a body which deflects it enough for it to return for a trip through the solar system”.
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