Giant comet active at a greater distance from the Sun than we thought

Comets are made up of dust and ice formed in the early days of the solar system. When a comet passes close to the sun, its ice begins to vaporize and form an envelope known as a coma, making it an active comet. However, the distance from the sun at which a comet becomes active largely depends on the type of ice it contains: water, carbon dioxide or carbon monoxide, for example.

A new study conducted by University astronomers of Maryland shows that Comet Bernardinelli-Bernstein (BB) became active much further from the Sun than expected. But at those distances the temperatures are too cold for the water ice to turn into steam. Thus, the findings may help determine what exactly the comet is made of and provide new insight into the conditions of the early solar system, according to a university statement.

Early estimates suggest that comet BB may have a diameter up to 100 kilometers, among the largest comets discovered to date. The object was first identified by scientists when it was beyond the planet Uranus.



Compared to this, most comets are less than 1 km wide and they are discovered much closer to the sun. In fact, the scientists only spotted one other active comet this far from the Sun, and it was much smaller than comet BB, according to the statement.

Using data from the Dark Energy Survey, an international effort to study the sky over the southern hemisphere, astronomers first discovered the bright core of comet BB in June 2021. However, at the time, the observations did not have a high enough resolution to show the comet's coma.

Instead, the recent study used images taken by NASA's Transient Exoplanet Survey Satellite (TESS), launched in 2018 that spends most of its time searching for planets orbiting nearby stars. But to conduct that work, the telescope captures longer exposures and, in turn, a more detailed view of the sky that can be used for a variety of objects.

Researchers combined thousands of TESS images taken between 2018 and 2020 to get a clearer view of the comet and the hazy glow of the dust surrounding it. By layering the images so that the comet was aligned in each frame, the researchers revealed the comet's coma, showing that it was active at a considerable distance from the sun.