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Giant comet is already active – Comet Bernardinelli-Bernstein is already in a coma beyond Uranus

Giant outgassing: Recently discovered comet Bernardinelli-Bernstein is not only the largest of its kind — it’s also active very early on, as images from the TESS space telescope now reveal. Although it is farther from the Sun than Uranus, its core is actually surrounded by a crust of carbon monoxide ice gases. This makes this comet one of the most active comets in the solar system.

Usually it would be comets Active when approaching the inner solar system. Because then solar radiation heats up its icy surface and water ice and other frozen materials begin to emit gases. As a result, the comet’s envelope – the coma – and the typical tail are formed. When a comet becomes active depends, among other things, on its size and the composition of its ice.

A dark energy survey image from October 2017. At this time, the comet was still about 25 astronomical units from the sun. © Dark Energy Survey, DOE / FNAL / DECam / CTIO, NOIRLab / NSF / AURA / P. Bernardinelli & G. Bernstein (UPenn) / DESI Legacy Imaging Surveys

Zombie chase with Tess

Observations now show that it was only discovered in the summer of 2021 Comet Bernardinelli – Bernstein He is also special in this regard. With a size of about 150 kilometers, it is by far the largest comet ever observed in the Solar System. It could even be a thousand times more massive than a typical “tail star”. Due to its size, even at a distance of 29 AU from the Sun, it can already be seen on old telescope images – the comet was at the height of Neptune’s orbit at that time.

The comet is now approaching the orbit of Uranus and is still a good 20 AU from the Sun. To find out if the giant comet was indeed active despite such a huge distance, Tony Farnam and his team at the University of Maryland examined images from NASA’s TESS space telescope in 2018 and 2020. During this time, the telescope mistakenly searched regions of the sky that were The culprit is walking in it.

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In their study, the astronomers used several thousand images showing the comet and physically stacked them to increase the light output. To ensure that this procedure did not lead to visual effects that could be confused with a comet comet, they performed the same method for some similarly distant non-comet bodies.

Clear evidence of outgassing

The result: While the objects of comparison can be viewed as sharply defined, clear points of light, this was different with Comet Bernardinelli-Bernstein: its point of light was surrounded by a hazy glow in both images from 2020 and 2018. Farnham and colleagues wrote: “This proves that the comet is He was already in a coma, at a distance of 21.2 and 23.8 AU from the Sun.” “It is one of the more distant comets in which such activity has already been detected.”

In fact, so far only two comets have already been detected in a coma at a similar distance – Comet C/2010 U3 Boattini and Comet C/2017 K2 PanSTARRS. However, both are ten times smaller than the giant comet. “The detection of a coma around Bernardinelli-Bernstein at 23.8 AU makes it only the third body actually active at such an extreme distance,” the astronomers say.

Comet shell made of carbon monoxide

From analyzing the TESS images, Farnham and his team concluded that the comet may have been active for some time: according to their calculations, it may have been in a coma as early as 2016, perhaps even earlier. “This changes the maximum distances of active comets dramatically,” Farnham says. “So far we don’t even know if there is an absolute limit to cometary activity anywhere.”

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With the help of comparisons and model calculations, astronomers were also able to determine what the Bernardinelli-Bernstein coma consists of. “At these distances, the sublimation of water ice is too slow to explain the coma of a comet,” they wrote. However, it is known from studies of other comets that frozen carbon monoxide (CO) can degas under these conditions. Based on TESS images, researchers estimate that the giant comet will already be 2 x 10 in 202028 Carbon dioxide molecules are pumped into space every second – that’s 10,000 quadrillion.

Perigee only in 2031

From the previous trajectory of Comet Bernardinelli-Bernstein, astronomers have concluded that it will approach the Sun by January 2031. The comet will reach its closest point to the Sun on January 31, 2031 at 10.95 AU – just outside Saturn’s orbit. The giant comet will approach Earth in April 2031, and it will approach it within 10.11 AU. (Journal of Planetary Science, 2021; doi: 10.3847/psj/ac323d)

Coyle: University of Maryland