Australian fires in 2019–2020 had even more global reach than previously thought

The severe, devastating wildfires that raged across southeastern Australia in late 2019 and early 2020 packed a powerful punch that extended far beyond the country, two new studies find.

The blazes injected at least twice as much carbon dioxide into the atmosphere as was previously thought, one team’s satellite-derived estimates revealed. The fires also sent up vast clouds of smoke and ash that wafted far to the east over the Southern Ocean, fertilizing the waters with nutrients and triggering widespread blooms of microscopic marine algae called phytoplankton, another team found. Both studies were published online September 15 in Nature.

Meteorologist Ivar van der Velde of the SRON Netherlands Institute for Space Research in Leiden and colleagues first examined carbon monoxide data collected over southeastern Australia by the satellite-based instrument TROPOMI from November 2019 to January 2020, during the worst of the fires. Then, to get new estimates of the carbon dioxide emissions attributable to the fires, the team used previously determined ratios of carbon monoxide to carbon dioxide emitted by the region’s eucalyptus forests — the predominant type of forest that was scorched in the blazes — during earlier wildfires and prescribed burns.

Van der Velde’s team estimates that the fires released from 517 trillion to 867 trillion grams of carbon dioxide to the atmosphere. “The sheer magnitude of CO2 that was emitted to the atmosphere … was much larger than what we initially thought it would be,” van der Velde says. The emissions “from this single event were significantly higher than what all Australians normally emit with the combustion of fossil fuels in an entire year.”
Previous assessments of CO2 emissions from the fires, based on estimations of burned area and biomass consumed by the blazes, calculated an average of about 275 trillion grams. Using the satellite-derived carbon monoxide data, the researchers say, dramatically improves the ability to distinguish actual emissions from the fires from other background sources of the gases, giving a more accurate assessment.

That finding has worrisome implications. The fires swiftly cut a swath through southeastern Australia’s eucalyptus forests, devastating the forests to a degree that made their rapid recovery more difficult — which in turn affects how much carbon the trees can sequester, van der Velde says (SN: 3/9/21). Fires in northern and central Australia’s dry, grassy savannas are seen as more climate neutral because the grasses can regrow more quickly, he says.

And severe fire seasons are likely to become more common in southeastern Australia with ongoing climate change. Climate change has already increased the likelihood of severe fire events such as the 2019–2020 fire season by at least 30 percent (SN: 3/4/20).

The smoke and ash from the fires also packed a powerful punch. Scientists watched in awe as the fires created a “super outbreak” of towering thunderclouds from December 29 to December 31 in 2019 (SN: 12/15/20). These clouds spewed tiny aerosol particles of ash and smoke high into the stratosphere.

Aerosols from the fires also traveled eastward through the lower atmosphere, ultimately reaching the Southern Ocean where they triggered blooms of phytoplankton in its iron-starved waters. Geochemist Weiyi Tang, now at Princeton University, and colleagues analyzed aerosols from the fires and found the particles to be rich in iron, an important nutrient for the algae. By tracing the atmospheric paths of the cloud of ash and smoke across the ocean, the team was able to link the observed blooms — huge patches of chlorophyll detected by satellite — to the fires.
Researchers have long thought that fires can trigger ocean blooms, particularly in the Southern Ocean, under the right conditions, says marine biogeochemist Joan Llort, now at the Barcelona Supercomputing Center and a coauthor on the study. But this research marks the most direct observation ever made of such an event — in part because it was such a massive one, Llort says.

Large ocean blooms are “yet another process which is potentially being modified by climate change,” says biogeochemist Nicolas Cassar of Duke University, also a coauthor on the study.

One of the big questions to emerge from the study, Cassar adds, is just how much carbon these phytoplankton may have ultimately removed from the atmosphere as they bloomed. Some of the carbon that the algae draw out of the air through photosynthesis sinks with them to the seafloor as they die. But some of it is quickly respired back to the atmosphere, muting any mitigating effect that the blooms might have on the wildfire emissions. To really assess what role the algae play, he says, would require a rapid-response team aboard an ocean vessel that could measure these chemical processes as they are happening.

The sheer size of this wildfire-triggered bloom — “larger than Australia itself” — shows that “wildfires have the potential to increase marine productivity by very large amounts,” says Douglas Hamilton, a climate scientist at Cornell University who was not connected with the study.

“The impact of fires on society is not straightforward,” Hamilton adds. The same smoke that can cause severe health impacts when inhaled “is also supplying nutrients to ecosystems and helping support marine food webs.” What this study demonstrates, he adds, is that to understand how future increases in fire activity might help shape the future of marine productivity “it is crucial that we monitor the impacts closely now.”

Dog DNA reveals ancient trade network connecting the Arctic to the outside world

Ancient Arctic communities traded with the outside world as early as 7,000 years ago, DNA from the remains of Siberian dogs suggests.

Analysis of the DNA shows that Arctic pups thousands of years ago were interbreeding with other dogs from Europe and the Near East, even while they and their owners were living in one of the most remote places on Earth. Along with previous archaeological finds, these results suggest that Siberians long ago were connected to a vast trade network that may have extended as far as the Mediterranean and the Caspian Sea, researchers report in the Sept. 28 Proceedings of the National Academy of Sciences.

Dogs have been valuable commodities in the Arctic for the last 9,500 years and have been used for sledding, hunting, herding reindeer, clothing and food. Because the region is remote, scientists thought local dogs — and their owners — had been completely isolated from the rest of the world for much of that time, an idea supported by the fact that ancient Siberians didn’t exchange much DNA with people outside of the region, says Tatiana Feuerborn, an archaeologist at the University of Copenhagen.

But previous archaeological evidence — including the discovery of glass beads and other foreign goods entombed alongside 2,000-year-old dogs near the Yamal Peninsula in Russia — suggested that these communities were trading with other cultures beyond the Arctic.
After reading about the archaeological evidence in the news, Feuerborn wanted to see if she could use remains from the 2,000-year-old dogs and others from around Siberia to reveal whether an ancient trade network existed.

Dogs rarely wander far from their humans, meaning researchers can “use dogs to understand human movement, like migrations and even trade interactions,” says Kelsey Witt, a geneticist at Brown University in Providence, R.I., who was not involved in the study. For instance, archaeologists have used ancient dog DNA to push back the arrival date of people in the Americas (SN: 3/1/21).
In the new study, Feuerborn and colleagues analyzed DNA from the remains of 49 Siberian dogs, ranging from 11,000-year-old bone fragments to fur hoods used by Arctic explorers at the turn of the 20th century. The team found that Siberian dogs — unlike their owners — began mixing with other dog populations from the Eurasian steppes, the Near East and even Europe as far back as 7,000 years ago.

The result suggests that Siberians did bring in dogs from the outside world, Feuerborn says. This trade network could have helped transmit new ideas and technologies, such as metalworking, to the Arctic, and may have facilitated Siberian society’s transition from foraging to reindeer herding in the last 2,000 years.

“Dogs are a piece of our past,” Feuerborn says. “By looking at them, we can learn something about ourselves.”

The search for exomoons continues

David Kipping
Columbia University

After being featured in 2017, David Kipping and his colleagues formally reported in Science Advances the first detection of a potential exomoon — a moon orbiting a planet outside of the solar system. Signs of the Neptune-sized moon were spotted around a Jupiter-sized planet 8,000 light-years from Earth. Kipping has been hunting for more ever since, and has also become a hit on YouTube.

Have you found any more exomoons?
Well, I can’t really talk about that. We are close to releasing the results of a new survey of the ensemble of Jupiter-like planets discovered by the Kepler space telescope. Such planets are thought to be the best hunting ground for moons, being far from the gravitational influence of their star and large enough to support potentially massive moons. Unfortunately, the results are still not quite ready.

How have other scientists reacted?
The community is naturally skeptical. That was kind of the story of exoplanets. When researchers first discovered a hot Jupiter, no one believed it. It wasn’t until they discovered about 10 of them that people started to say that, actually, maybe these are real. I don’t know how it’s going to go with any exomoon candidate. Maybe what we’ve found is genuinely bogus, but I obviously hope not. We did our due diligence, and we’re very careful with the results.

It’s maybe not surprising that the first ones we find are going to be so large, because after all, they’re going to be the easiest to detect.… Actually, less than 1 percent of sunlike stars have hot Jupiters, but they dominated all of the first exoplanet detections just because they were so easy to find. Maybe the same thing will play out here.

In 2017, you had just launched a YouTube channel called Cool Worlds. How is that outreach going?
It’s been pretty overwhelming to us, because I’d never expected to get anywhere near the number of people watching who have watched. The last video [on what’s called the red sky paradox] got 200,000 views, and the one before it got 500,000. I mean, that’s just bonkers. I get e-mails from people, really amazing e-mails, that say how much the channel and the videos mean to them. That’s really incredible.

We have lots of people actually financially supporting us now. We give them special access to the videos and early access to the papers we’re writing. We hang out with some of them once every two months on a livestream and chat about science. It’s starting to be enough that I’m funding students through donations. I have this dream that I do research, it produces cool ideas, I talk about it on my outreach channel, people get excited about it and they support us, which enables me to do more research.

What are the greatest challenges you’ve faced since 2017?
I’m still [working to earn] tenure. It’s obviously one of the most stressful periods of your career because you don’t have that safety net yet that some young tenured colleagues enjoy. At the same time, you’re trying to raise a family and make sure you see your kids growing up. You don’t want to be a ghost at home. And so that’s been tricky, but [the pandemic] enabled me to spend a lot more time at home with the family.

— Interview by Cassie Martin

Pluto’s dark side reveals clues to its atmosphere and frost cycles

Pluto’s dark side has come into dim view, thanks to the light of the dwarf planet’s moon.

When NASA’s New Horizons spacecraft flew past Pluto in 2015, almost all the images of the dwarf planet’s unexpectedly complex surface were of the side illuminated by the sun (SN: 7/15/15). Darkness shrouded the dwarf planet’s other hemisphere. Some of it, like the area near the south pole, hadn’t seen the sun for decades.

Now, mission scientists have finally released a grainy view of the dwarf planet’s dark side. The researchers describe the process to take the photo and what it tells them about how Pluto’s nitrogen cycle affects its atmosphere October 20 in the Planetary Science Journal.

Before New Horizons passed by Pluto, the team suspected the dwarf planet’s largest moon, Charon, might reflect enough light to illuminate the distant world’s surface. So the researchers had the spacecraft turn back toward the sun to take a parting peek at Pluto.
At first, the images just showed a ring of sunlight filtering through Pluto’s hazy atmosphere (SN: 7/24/15). “It’s very hard to see anything in that glare,” says planetary scientist John Spencer of the Southwest Research Institute in Boulder, Colo. “It’s like trying to read a street sign when you’re driving toward the setting sun and you have a dirty windshield.”

Spencer and colleagues took a few steps to make it possible to pull details of Pluto’s dark side out of the glare. First, the team had the spacecraft take 360 short snapshots of the backlit dwarf planet. Each was about 0.4 seconds long, to avoid overexposing the images. The team also took snapshots of the sun without Pluto in the frame so that the sun could be subtracted out after the fact.

Tod Lauer of the National Optical Astronomy Observatory in Tucson, Ariz., tried to process the images when he got the data in 2016. At the time, the rest of the data from New Horizons was still fresh and took up most of his attention, so he didn’t have the time to tackle such a tricky project.

But “it was something that just sat there and ate away at me,” Lauer says. He tried again in 2019. Because the spacecraft was moving as it took the images, each image was a little bit smeared or blurred. Lauer wrote a computer code to remove that blur from each individual frame. Then he added the reflected Charon light in each of those hundreds of images together to produce a single image.
“When Tod did that painstaking analysis, we finally saw something emerging in the dark there … giving us a little bit of a glimpse of what the dark pole of Pluto looks like,” Spencer says.

That the team got anything at all is impressive, says planetary scientist Carly Howett, also of the Southwest Research Institute and who is on the New Horizons team but was not involved in this work. “This dataset is really, really hard to work with,” she says. “Kudos to this team. I wouldn’t have wanted to do this.”

The image, Howett says, can help scientists understand how Pluto’s frigid nitrogen atmosphere varies with its decades-long seasons. Pluto’s atmosphere is controlled by how much nitrogen is in a gas phase in the air and how much is frozen on the surface. The more nitrogen ice that evaporates, the thicker the atmosphere becomes. If too much nitrogen freezes to the ground, the atmosphere could collapse altogether.
When New Horizons was there, Pluto’s south pole looked darker than the north pole. That suggests there was not a lot of fresh nitrogen frost freezing out of the atmosphere there, even though it was nearing winter. “The previous summer ended decades ago, but Pluto cools off pretty slowly,” Spencer says. “Maybe it’s still so warm [that] the frost can’t condense there, and that keeps the atmosphere from collapsing.”

There was a bright spot in the middle of the image, which could be a fresh ice deposit. That’s also not surprising, Howett says. The ices may still be moving from the north pole to the south pole as Pluto moves deeper into its wintertime.

“We’ve thought this for a long time. It makes sense,” she says. “But it’s nice to see it happening.”

Neutron star collisions probably make more gold than other cosmic smashups

The cosmic origins of elements heavier than iron are mysterious. One elemental birthplace came to light in 2017 when two neutron-rich dead stars collided and spewed out gold, platinum and other hefty elements (SN: 10/16/17). A few years later, a smashup of another neutron star and a black hole left scientists wondering which type of cosmic clash was the more prolific element foundry (SN: 6/29/21).

Now, they have an answer. Collisions of two neutron stars probably take the cake, scientists report October 25 in Astrophysical Journal Letters.

To create heavy elements after either type of collision, neutron star material must be flung into space, where a series of nuclear reactions called the r-process can transform the material (SN: 4/22/16).

How much material escapes into space, if any, depends on various factors. For example, in collisions of a neutron star and black hole, the black hole has to be relatively small, or “there’s no hope at all,” says astrophysicist Hsin-Yu Chen of MIT. “It’s going to swallow the neutron star right away,” without ejecting anything.

Questions remain about both types of collisions, spotted via the ripples in spacetime that they kick up. So Chen and colleagues considered a range of possibilities for the properties of neutron stars and black holes, such as the distributions of their masses and how fast they spin. The team then calculated the mass ejected by each type of collision under those varied conditions. In most scenarios, the neutron star–black hole mergers made a smaller quantity of heavy elements than the neutron star duos — in one case only about a hundredth the amount.

Still, the ultimate element factory ranking remains up in the air. The scientists compared just these two types of collisions, not other possible sources of heavy elements such as exploding stars (SN: 7/7/21).