Comet Tsuchinshan-ATLAS is approaching Earth and will not return for another 800 centuries

An ancient celestial traveler from afar Oort cloudwhich may have been seen during the time of the Neanderthals, occurs in mid-October near our planet. Those who want to enjoy the spectacle will have to take advantage of the moment, because it will not return for another 800 centuries.

This is Comet C/2023 A3 Tsuchinshan-ATLAS, as officially stated in Minor Planet Centerthe body of the National Astronomical Union responsible for naming small bodies in the Solar System.

Its name refers to the fact that it was discovered in early 2023 by the Tzuchinshan (Purple Mountain) Observatory in China, and a month later also by the Asteroid Impact Last Alert System (ATLAS) in South Africa.

On September 27, the comet successfully approached the Sun, reaching just 58 million km at perihelion, or the point in its orbit closest to our star.

The images were taken from different parts of the world, for example by researchers at the Institute of Astrophysics of the Canary Islands and astrophotographers at the Teide Observatory in Tenerife.

Passed the test by fire

Scientists did not exclude that the comet disintegrated as it approached the Sun, since its volatile and icy composition may not have withstood the intense heat of our star, but it remained more or less intact.

This was confirmed by photographs taken in the following days, e.g. TAO project Institute of Astronomy of the University of Tokyo (Japan) since its foundingAtacama Observatory in Chile, the highest in the world.

“Comets are more fragile than people think because of the effects of their passage close to the Sun on their internal water ice and volatiles such as carbon monoxide and carbon dioxide,” explains astronomer Bill Cook of NASA’s Marshall Space Flight Center in the US. . States.

“Comet Kohoutek – he gives an example – it reached the inner solar system in 1973, broke up, passing too close to the Sun; and similarly comet Ison could not survive the intense heat and gravity of the Sun during perihelion in 2013.”

Closest approach to Earth

But this time, Comet Tsuchinshan-ATLAS survived its transit around the Sun. In fact, on October 12, it comes within about 44 million miles (almost 71 million kilometers) of Earth.

Although observers in the southern hemisphere will be in an ideal position to observe from the southern hemisphere, observers in the northern hemisphere will also be well positioned. Maximum visibility will be on October 9 and 10, when the sickle begins to move away from the comet, although it will be closest to us a couple of days later.

Cook recommends choosing a dark spot to observe just after dark. Looking southwest, about 10 degrees above the horizon, we identify the constellations Sagittarius and Scorpio. The Tsutingshan-ATLAS should be visible between them. By October 14, the comet may remain visible at the midpoint between the bright star Arthur and the planet Venus.

The National Astronomical Observatory (OAN-National Geographic Institute) also recommends viewing this western region at dusk, as opposed to early October when the comet was seen eastward at dawn. “You need binoculars, but brightness is expected to increase,” they note from their quantity.

“And enjoy the view,” advises Cook, because in early November the comet will disappear again for the next 80,000 years.

How bright will the comet be?

Tzuchinshan-ATLAS is unlikely to be visible during the day, except perhaps at dusk, Cook said. Over the past 300 years of astronomical observations, only nine comets have been bright enough to be seen during the day. The last were comets West in 1976 and in ideal conditions the comet Hale-Bopp in 1997.

The brightness of comets is measured on the same scale we use for stars, which has been in use since about 150 BC. e., when it was invented by the ancient scientist Hipparchus and improved by the astronomer Ptolemy. Magnitude is measured on a logarithmic scale, so a 1st magnitude star is exactly 100 times brighter than a 6th magnitude star.

The lower the number, the brighter the object and therefore the more likely it is to be clearly visible both through a telescope and to the naked eye. “Typically, a comet must be between magnitude -6 and -10 to be visible in daylight,” Cook explains, “and this is extremely rare.”

The latest data estimates the brightness of Tzuchinshan-ATLAS to be between 2 and 4. By comparison, the brightest visible star in the night sky, Sirius, has a magnitude of -1.46. At its brightest, Venus’s solar reflection is magnitude -4. The International Space Station sometimes reaches a relative brightness of -6.

Comet C/2023 A3 Tsuchinshan-ATLAS, as seen from the Atacama Observatory (Chile) of the University of Tokyo. / TAO Project, University of Tokyo/Akio Nakanishi

Comets are often difficult to predict because they are elongated or elongated objects, the NASA astronomer recalls, their brightness spread out and often dimmer than their magnitude suggests.

The phenomenon of “forward scattering”

At the same time, they can benefit from a phenomenon called “forward spread“, which causes sunlight to reflect more intensely off all the gas and debris in the comet’s tail and its coma – the bright nebula that develops around it in close stellar orbit – and causes a brighter glow effect that is intense to observers.

“With strong forward scattering, the comet can be as bright as -1 magnitude,” Cook notes. This could make it “visible to the naked eye or really spectacular through binoculars or a small telescope.”

Terminus Tsuchinshan-ATLAS

What will ultimately happen to Comet Tsuchinshan-ATLAS? Cook notes that it is not expected to get too close to the planetary giants in our solar system, but that over time it could eventually be thrown out of the solar system – like a rock from a slingshot – due to the gravitational influence of other planets. worlds and its subtle connection with the Sun.

But the hardy hiker probably still has a few miles to go. “I learned a long time ago not to bet on comets,” Cook concludes with a laugh, “so we’ll just have to wait and see.”