“The largest comet ever observed” presents a strange surprise!

Comet Bernardinelli-Bernstein (BB) – the largest ever observed by our telescopes – appears to be on a journey from the outer reaches of our solar system and we will watch it fly relatively close to Saturn’s orbit.

Now, a new analysis of the data has revealed something somewhat surprising. By looking at readings recorded by the Transiting Exoplanet Survey Satellite (TESS) between 2018 and 2020, the researchers discovered that BB became active earlier, and farther from the Sun, than previously thought.

A comet becomes active when light from the sun heats its icy surface, turning the ice into steam and releasing trapped dust and pebbles. The resulting haze could be useful to astronomers in determining exactly what a particular comet is made of.

Based on studies of comets at similar distances, the emerging haze was likely driven by a slow release of carbon monoxide. Only one active comet was previously observed at a greater distance from the Sun, and it was much smaller than Comet BB.

“These observations push the distances of active comets significantly further than we previously knew,” says astronomer Tony Farnham, from the University of Maryland (UMD).

And some clever imagery layers were needed to detect fog around the BB: the researchers had to combine multiple shots of TESS, which use 28-day long exposures, with the comet’s position aligned each time to get a better look at it.

The comet’s size – about 100 kilometers or 62 miles – and its distance from the sun when it became active are the main clues to the presence of carbon monoxide. In fact, based on what we know about carbon monoxide, it’s possible that BB was already producing clouds before it appeared in plain view of our telescopes.

“We’re assuming that Comet BB was most likely active farther away, but we haven’t seen it before,” Farnham says. “What we don’t know yet is whether there’s a stopping point where we can start seeing these things in cold storage before they become active.” .

By replicating the image stacking technique on Kuiper Belt objects, the researchers were able to confirm that their methods were indeed sound – and that the activity they observed around the BB wasn’t just a blurring effect of placing several images on top of each other.

All of these precise calculations are useful to astronomers in determining the source of individual comets, and from there tracing the history of our solar system. This is certainly the case for BB.

And as our telescopes and sensors get more powerful, so will comet discoveries – whether that’s finding the rarest types of comets in space, or finding comets with chemical makeups far from the norm.

The research was published in Planetary Science.

Source: Science Alert

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