‘Megacomet’ Bernardinelli-Bernstein – an enormous iceball that’s 1,000 times more massive than a typical comet – is among the most distant ice balls with an active stream of dust and gas around it, a new study claims.
Satellite images have been analysed by astronomers to identify the comet as C/2014 UN271, also called this year.
Active comets like Bernardinelli-Bernstein (BB) develop a thin envelope of vaporized ice and dust surrounding it, known as a coma, as they approach the Sun.
BB’s vaporized ice is not water, but carbon monoxide, the researchers found, which is known on Earth for its ability to fatally poison humans.
Comet Bernardinelli-Bernstein (BB), represented in this artist rendition as it might look in the outer Solar System, is estimated to be about 1,000 times more massive than a typical comet. The largest comet discovered in modern times, it is among the most distant comets to be discovered with a coma, which means ice within the comet is vaporizing and forming an envelope of dust and vapor around the comet’s core
BB was named after its finders and is 62 miles wide (100 km). This is more than 10x the size of a typical comet. Most comets measure no more than half of a mile (1 km) in diameter.
Although it’s often referred to as the most massive comet in history, some people have pointed out Comet Sarabat which measures more than 513,000 miles and was spotted at close range of 1729 is much larger.
BB’s mass is thought to be at least 1,000 times higher than that of typical comets.
BB is over 1.8 billion miles (2.9 billion km) distant from Earth. But, it’s slowly moving closer to the center of the Solar System.
Since March 2014 it has been in the orbit orbit of Neptune. It will be inside Uranus’ orbit by December 2022.
In January 2031, it will make its closest approach to Earth – around 930 million miles away from our planet. It doesn’t present a risk to humans, however.
There has only been one active comet that was seen farther away from the sun. This comet was significantly smaller than comet BB.
The new study was conducted by researchers at the University of Maryland (UM), who say BB is among the most distant comets to be discovered with a coma.
The researchers didn’t actually determine the size in the new study, but quote the size as at least 100 km, as given by Bernardinelli et al., in their discovery announcement earlier this year.
Tony Farnham from the UMD Department of Astronomy, said that the observations were pushing the distances of active comests far further than what we had previously realized.
Comets are often called “dirty snowballs” or “icy dirtballs”. They consist of conglomerations made up of dust and water left over from formation of our solar system.
When an orbiting Comet is close to its nearest point to the Sun it heats up and the ices begin vaporizing, forming a Coma.
How far from the Sun the ice starts to vaporize depends on what kind of ice it is – either water, carbon dioxide, carbon monoxide or some other frozen compound.
In June 2021, scientists discovered comet BB using data from Dark Energy Survey. It is an international project to study the skies over the Southern Hemisphere.
Images of comet Bernardinelli-Bernsteinomet from 2018 and 2020, showing coma with a ‘sunward asymmetry’
While the spacecraft captured the bright nucleus and the dust that formed when it became active, the resolution was not high enough to see the rest of the atmosphere.
Farnham was shocked to learn of the discovery and immediately sought out information about whether images of BB were captured by NASA’s Transient Exoplanet Survey Satellite, (TESS). This satellite observes one region of the sky every 28 days.
Farnham, along with colleagues, combined thousands of photos of comet BB from TESS in 2018 to 2020.
Farnham was able increase contrast by stacking images to get a clearer look at the comet. He had to stack the images in order for comet BB to be perfectly aligned within each frame, since comets are mobile.
The researchers studied images from the Transient Exoplanet Survey Satellite, a NASA mission to spend two years discovering transiting exoplanets (artist’s impression)
That technique removed the errant specks from individual shots while amplifying the image of the comet, which allowed researchers to see the hazy glow of dust surrounding BB – proof that BB had a coma and was active.
To ensure the coma wasn’t just a blur caused by the stacking of images, the team repeated this technique with images of inactive objects from the Kuiper Belt, the doughnut-shaped ring of icy objects that extends just beyond the orbit of Neptune.
Researchers were certain that comet BB’s faint glow was actually an active coma when the objects looked sharp and clear.
Comet BB is large and far from the Sun, suggesting that carbon monoxide dominates the vaporizing ice forming a coma.
Carbon monoxide could begin to vaporize if it’s five times farther from the Sun that comet BB when discovered. This suggests that BB may have been active long before this observation.
Kuiper Belt is a region where there is a lot of icy material from the early solar systems. It is farther away from the Sun that comet BB.
The researchers believe BB was active as much as 23 astronomical units (AU) from the Sun – or more than 2 billion miles.
Farnham explained that while we assume comet BB may have been active further out than this, it was not visible to us before.
“What we do not know is whether there will be a cutoff at which we are able to start seeing these items in cold storage, before they turn active.”
Farnham says that astronomers have exciting opportunities to see processes such as the formation of a cometary-coma from a greater distance than ever before.
Farnham explained that this is just the start. “TESS observes things yet to be discovered, so this test case is just a preview of what we’ll find.”
The study has been published in The Planetary Science Journal.