Comet C/2023 A3 (Tsuchinshan-ATLAS) was discovered in January 2023 in China by the Purple Mountain Observatory, and again the following month by the South African ATLAS telescope. Immediately named after the two discovering observatories, the comet had a visual magnitude of 18.
Identity card
C/2023 A3 (Tsuchinshan-ATLAS) is a long-period comet with a highly elongated orbit. Researchers at IMCE (Paris Observatory - PSL) have modelled its trajectory by tracking its progress.
C/2023 A3 (Tsuchinshan-ATLAS) arrives in the inner Solar System from the Oort cloud, after a journey of millions of years.
The trajectory model established by IMCCE at Observatoire de Paris - PSL indicates that comet Tsuchinshan-ATLAS would follow an elliptical orbit, with a maximum distance (or aphelion) of around 400,000 astronomical units (AU). 400,000 AU is the maximum distance at which it could have been. However, this value should be treated with caution, as at this distance from the Sun, it is very difficult to predict what the comet might have encountered in its environment. Its orbit would probably have been disrupted by the gravitational influence of nearby stars or other massive objects in the Oort cloud : a trajectory deviation that would have led it to plunge into the Solar System, to pay us a visit.
Pretender to the title of "comet of the century" ?
Not easy to predict, a comet’s visibility in the sky depends on its composition and the physical characteristics of its surface and interior.
The closer a comet is to the Sun, the brighter and brighter it becomes, and the more it heats up, the more active it becomes.
The visibility of the cloud of ice and dust (the coma) that surrounds the nucleus, as well as that of the dust and gas tails that emanate from it, depends on the comet’s activity, i.e. the rate of production of the various volatiles emitted on its surface.
According to an IMCCE estimate, comet Tsuchinshan-ATLAS could reach a maximum magnitude of 2.4 at its closest approach to Earth on October 12, 2024.
The comet is thus a strong contender for the title of "comet of the century". It could even briefly reach negative magnitude, around its conjunction with the Sun on October 9, when it will be observable with the LASCO coronagraph on the ESA/NASA SOHO satellite.
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Some time marks
◼ Until Monday September 30
Comet Tsuchinshan-ATLAS can be observed at sunrise, just 23° from the Sun.
From the northern hemisphere, observation is limited, as the comet rises in the first light of dawn, which is already too bright.
From the southern and equatorial hemispheres, on the other hand, comet Tsuchinshan-ATLAS rises much earlier : early-morning observers with a clear southeastern horizon can see it for a few days, until September 30, at least an hour before sunrise, located just above the Sun.
▶ On Friday September 27, at 5pm, comet Tsuchinshan-ATLAS reaches its perihelion - its shortest distance from the Sun - at around 59 million kilometers, with a maximum orbital speed of 242,000 km/h (or 67.3 km/s). This is a "critical" passage, with the risk of the comet’s nucleus being too small to survive close to the Sun. Suspenseful...
◼ Until October 12, 2024
If it doesn’t disintegrate as a result of the significant loss of mass following the strong outgassing activity so close to the Sun, comet Tsuchinshan-ATLAS will continue its course between the Sun and Earth. But, in the Sun’s glare, its observation will be almost impossible, from October 3 to 12.
▶ On Saturday, October 12, comet Tsuchinshan-ATLAS will reach the closest point to Earth, at a distance of 71 million km.
◼ From October 13, 2024, visible in the evening
Comet Tsuchinshan-ATLAS will appear on the far side of the Sun. From mid-latitudes in the northern hemisphere, this will be the best time to observe it, in the evening, on a clear western horizon. Day after day, at least an hour after sunset, and just above the Sun, we’ll see the comet with its beautiful tail, higher and higher in the sky.
However, once it has passed its closest point to the Earth, it will shine less and less brightly. It’s hard to say which will be the best evening to observe it...
▶ During the week of October 14, be on the lookout. A pair of binoculars pointed toward a clear western horizon is a good way to take advantage of Tsuchinshan-ATLAS’s "one shot" passage.
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Comet resources
◼ The virtual exhibition "Comets : from myth to reality"
It brings together a wealth of information on comets, particularly those that have made their mark on their time - such as Halley’s comet - because they have been closely studied or because they have particular properties.
◼ Comets in the literature
Read the online article ["What have they written about comets ?"
by Jacques Crovisier, astronomer at Paris Observatory - PSL.