Study: The giant comet Bernardinelli-Bernstein is among the most distant active comets in the solar system

According to a new analysis of data from NASA’s Transient Exoplanet Survey Satellite (TESS).

Co-added images of comet Bernardinelli-Bernstein (C/2014 UN271) from 2018 and 2020, showing a coma with asymmetry towards the sun; Combined images of several Kuiper Belt objects and asteroids show examples of moving objects of similar brightness that are known not to have a coma. Image credit: Farnham et al., doi: 10.3847/PSJ/ac323d.

Comet Bernardinelli-Bernstein was first observed by the Dark Energy Survey (DES) at a heliocentric distance of 29.3 AU in 2014, with additional sightings through 2018.

But it was only discovered in 2021 when a targeted search for trans-Neptunian objects on DES data was carried out.

At 100 km (62 miles) in diameter, Comet Bernardinelli-Bernstein is by far the largest comet ever discovered, and it is farther from the Sun than the planet Uranus.

“Our new observations push the distances for active comets considerably further than we previously knew,” said Dr. Tony Farnham, astronomer in the Department of Astronomy at the University of Maryland.

In the new research, Dr Farnham and his colleagues combined thousands of images of Comet Bernardinelli-Bernstein collected by TESS from 2018 to 2020.

By stacking the images, they were able to increase the contrast and get a clearer view of the comet.

They spotted the hazy glow of dust surrounding the comet, evidence that it was in a coma and was active.

The size of the comet and its distance from the Sun suggest that the vaporizing ice forming the coma is dominated by carbon monoxide.

Since carbon monoxide can begin to vaporize when it is up to five times farther from the Sun than Comet Bernardinelli-Bernstein was when it was discovered, it’s likely the comet was active long before that. to be observed.

“We assume Comet Bernardinelli-Bernstein was probably active even farther out, but we just hadn’t seen it before,” Dr Farnham said.

“What we don’t know yet is if there is an end point where we can start seeing these things in cold storage before they become active.”

“The ability to observe processes like cometary coma formation further than ever before opens an exciting new door for astronomers.”

“This is just the beginning. TESS is looking at things that haven’t been discovered yet, and this is kind of a test case of what we can find. We have the potential to do a lot of that once we get there. a comet is seen, going back in time in the images and finding them while they are at farther distances from the Sun.

The findings were published in the Journal of Planetary Science.


Tony L. Farnham et al. 2021. Early activity in comet C/2014 UN271 Bernardinelli-Bernstein observed by TESS. Planet. Science. J 2.236; doi:10.3847/PSJ/ac323d

Arline J. Mercier