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Hexbyte Glen Cove New study shows the largest comet ever observed was active at near-record distance

Hexbyte Glen Cove

The comet Bernardinelli-Bernstein (BB), represented in this artist rendition as it might look in the outer Solar System, is estimated to be about 1000 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. Credit: NOIRLab / NSF / AURA / J. da Silva / Spaceengine

A new study by University of Maryland astronomers shows that comet Bernardinelli-Bernstein (BB), the largest comet ever discovered, was active long before previously thought, meaning the ice within it is vaporizing and forming an envelope of dust and vapor known as a coma. Only one active comet has been observed farther from the sun, and it was much smaller than comet BB.

The finding will help astronomers determine what BB is made of and provide insight into conditions during the formation of our solar system. The finding was published in The Planetary Science Journal on November 29, 2021.

“These observations are pushing the distances for active comets dramatically farther than we have previously known,” said Tony Farnham, a research scientist in the UMD Department of Astronomy and the lead author of the study.

Knowing when a becomes active is key to understanding what it’s made of. Often called “dirty snowballs” or “icy dirtballs,” comets are conglomerations of dust and ice left over from the formation of the solar system. As an orbiting comet approaches its closest point to the sun, it warms, and the ices begin to vaporize. How warm it must be to start vaporizing depends on what kind of ice it contains (e.g., water, carbon dioxide, carbon monoxide or some other frozen compound).

Scientists first discovered comet BB in June 2021 using data from the Dark Energy Survey, a collaborative, international effort to survey the sky over the Southern hemisphere. The survey captured the bright nucleus of the comet but did not have high-enough resolution to reveal the envelope of dust and vapor that forms when the comet becomes active.

At 100 km across, comet BB is the largest comet ever discovered by far, and it is farther from the sun than the planet Uranus. Most comets are around 1 km or so and much closer to the sun when they are discovered. When Farnham heard about the discovery, he immediately wondered if images of comet BB had been captured by the Transient Exoplanet Survey Satellite (TESS), which observes one area of the sky for 28 days at a time. He thought TESS’s longer exposure times could provide more detail.

Farnham and his colleagues combined thousands of images of comet BB collected by TESS from 2018 through 2020. By stacking the images, Farnham was able to increase the contrast and get a clearer view of the comet. But because comets move, he had to layer the images so that comet BB was precisely aligned in each frame. 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 surrounding BB, proof that BB had a 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, which is a region much farther from the sun than comet BB where icy debris from the early solar system is plentiful. When those objects appeared crisp, with no blur, researchers were confident that the faint glow around comet BB was in fact an active coma.

The size of comet BB and its distance from the sun suggests that the vaporizing ice forming the coma is dominated by carbon monoxide. Since carbon monoxide may begin to vaporize when it is up to five times farther away from the sun than comet BB was when it was discovered, it is likely that BB was active well before it was observed.

“We make the assumption that comet BB was probably active even further out, but we just didn’t see it before this,” Farnham said. “What we don’t know yet is if there’s some cutoff point where we can start to see these things in cold storage before they become active.”

According to Farnham, the ability to observe processes like the formation of a cometary coma farther than ever before opens an exciting new door for astronomers.

“This is just the beginning,” Farnham said. “TESS is observing things that haven’t been discovered yet, and this is kind of a test case of what we will be able to find. We have the potential of doing this a lot, once a comet is seen, going back through time in the images and finding them while they are at farther distances from the sun.”



More information:
Tony L. Farnham et al, Early Activity in Comet C/2014 UN271 Bernardinelli–Bernstein as Observed by TESS, The Planetary Science Journal (2021). DOI: 10.3847/PSJ/ac323d

Citation:
New study shows the largest comet ever observed was active at near-record distance (2021, November 29)
retrieved 30 November 2021
from https://phys.org/news/2021-11-largest-comet-near-record-distance.html

This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no

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Hexbyte Glen Cove Researchers find wildfire smoke is more cooling on climate than computer models assume thumbnail

Hexbyte Glen Cove Researchers find wildfire smoke is more cooling on climate than computer models assume

Hexbyte Glen Cove

The University of Wyoming Mobile Lab measures biomass burning smoke in Wyoming from a couple of years ago. This is an example of the type of field measurement that was used to compare with computer models. Credit: Rachel Edie

A study of biomass burning aerosols led by University of Wyoming researchers revealed that smoke from wildfires has more of a cooling effect on the atmosphere than computer models assume.

“The study addresses the impact of wildfires on , and we extensively used the NCAR-Wyoming supercomputer (Cheyenne),” says Shane Murphy, a UW associate professor of atmospheric science. “Also, the paper used observations from UW and other teams around the world to compare to the results. The main conclusion of the work is that wildfire smoke is more cooling than assume.”

Murphy was a contributing author of a paper, titled “Biomass Burning Aerosols in Most Climate Models Are Too Absorbing,” that was published Jan. 12 (today) in Nature Communications, an open-access journal that publishes high-quality research from all areas of the natural sciences. Papers published by the journal represent important advances of significance to specialists within each field.

Hunter Brown, who graduated from UW in fall 2020 with a Ph.D. in atmospheric science, was the paper’s lead author. Other contributors to the paper included researchers from Texas A&M University; North Carolina A&T State University; the University of Georgia; the Finnish Meteorological Institute; the Center for International Climate and Environmental Science, and Norwegian Meteorological Institute, both in Oslo, Norway; the University of Reading in the United Kingdom; North-West University in South Africa; the University of Science and Technology of China in Hefei, China; and Pacific Northwest National Laboratory in Richland, Wash.

The composition, size and mixing state of biomass burning aerosols determine the optical properties of smoke plumes in the atmosphere which, in turn, are a major factor in dictating how these aerosols perturb the energy balance in the atmosphere.

“We found that many of the most advanced simulate biomass burning aerosols or smoke that is darker, or more light absorbing, than what we see in observations,” says Brown, of Juneau, Alaska. “This has implications for the climate predictions made by these models.”

The National Science Foundation/National Center for Atmospheric Research (NSF/NCAR) C-130 aircraft measures biomass burning smoke during the WE-CAN (Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption and Nitrogen) field campaign in 2018. Credit: Shane Murphy

Observations and models used in the study covered a wide temporal range. Africa, South America and Southeastern Asia, in addition to boreal fire regions, were chosen because these are the largest contributors to biomass burning smoke emissions in the world, Brown says.

The National Center for Atmospheric Research (NCAR)-Wyoming Supercomputing Center (NWSC) in Cheyenne was used for all of the data processing and the model sensitivity simulations, Brown says. Some of the other model data used for comparison in this study were generated elsewhere.

“When we compare global observations of wildfire smoke to simulated wildfire smoke from a collection of climate models, the vast majority of the models have smoke that is more light absorbing than the observations,” Brown explains. “This means that more energy from the sun is going toward warming the atmosphere in these models, as opposed to what we see in these field campaigns and laboratory studies, which report less absorbing smoke that has more of a by scattering light away from the Earth and back to space.”

How absorbing these aerosols are in the atmosphere depends on the type of fuel that is burning, as well as the climate of the fire region. Generally, hot, dry grassland fires in Africa and Australia tend to have much darker smoke, which is more absorbing, while cooler, wetter boreal forest fires in North America and Northern Asia tend to have much brighter smoke, which is less absorbing.

After researchers made aerosol improvements to the model, African wildfire smoke still tended to be more absorbing than observations. This might be explained by simplifications in how aerosols evolve over time in the model, or it may be due to a lack of observations from this part of the world biasing the results toward the boreal fire regime, Brown explains.

“We were able to trace the disagreement between the model and observations to how the models represented the individual smoke particles, or aerosols, in the model,” Brown says. “This came down to how the model characterized their makeup, their size and the mixtures of different types of biomass burning aerosol. When we changed these variables in one of the models, we saw considerable improvement in the simulated smoke.”

This comparison of computer models and global observations is valuable for model development groups and may help reduce uncertainty in biomass burning climate impacts in models, Brown says.



More information:
Hunter Brown et al, Biomass burning aerosols in most climate models are too absorbing, Nature Communications (2021). DOI: 10.1038/s41467-020-20482-9

Citation:
Researchers find wildfire smoke is more cooling on climate than computer models assume (2021, January 12)
retrieved 13 January 2021
from https://phys.org/news/2021-01-wildfire-cooling-climate-assume.html

This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no
part may be reproduced without the written permission. The content is provided for information purposes only.