The Parker Solar Probe is the first spacecraft to visit the sun’s atmosphere

For the first time, a spacecraft has made contact with the sun. During a recent flyby, NASA’s Parker Solar Probe entered the sun’s atmosphere.

“We have finally arrived,” Nicola Fox, director of NASA’s Heliophysics Science Division in Washington, D.C., said December 14 in a news briefing at the fall meeting of the American Geophysical Union. “Humanity has touched the sun.”

Parker left interplanetary space and crossed into solar territory on April 28, 2021, during one of its close encounters with the sun. While there, the probe took the first measurements of exactly where this boundary, called the Alfvén critical surface, lies. It was about 13 million kilometers above the sun’s surface, physicists reported at the meeting, held online and in New Orleans, and in Physical Review Letters on December 14.

“We knew the Alfvén critical surface had to exist,” solar physicist Justin Kasper of the University of Michigan in Ann Arbor said at the news briefing. “We just didn’t know where it was.”
Finding this crucial layer was one of Parker’s main goals when it launched in 2018 (SN: 7/5/18). The Alfvén critical surface is important because it marks where packets of plasma can separate from the sun and become part of the solar wind, the speedy stream of charged particles that constantly emanates from the sun (SN: 8/18/17). The solar wind and other, more dramatic forms of space weather can wreak havoc on Earth’s satellites and even on life (SN: 2/26/21). Scientists want to pinpoint exactly how the wind gets started to better understand how it can impact Earth.

The Alfvén critical surface also may hold the key to one of the biggest solar mysteries: why the sun’s corona, its wispy outer atmosphere, is so much hotter than the sun’s surface (SN: 8/20/17). With most heat sources, temperatures drop as you move farther away. But the sun’s corona sizzles at more than a million degrees Celsius, while the surface is only a few thousand degrees.

In 1942, physicist Hannes Alfvén proposed a solution to the mystery: A type of magnetic wave might carry energy from the solar surface and heat up the corona. It took until 2009 to directly observe such waves, in the lower corona, but they didn’t carry enough energy there to explain all the heat (SN: 3/19/09). Solar physicists have suspected that what happens as those waves climb higher and meet the Alfvén critical surface might play a role in heating the corona. But until now, scientists didn’t know where this frontier began.

With the boundary identified, “we’ll now be able to witness directly how coronal heating happens,” Kasper said.

As Parker crossed the invisible boundary, its instruments recorded a marked increase in the strength of the local magnetic field and a drop in the density of charged material. Out in the solar wind, waves of charged particles gush away from the sun. But below the Alfvén critical surface, some of those waves bend back toward the surface of the sun.
Surprisingly, Parker’s measurements showed that the Alfvén critical surface is wrinkly. “That was one of the big outstanding questions,” says solar physicist Craig DeForest of the Southwest Research Institute in Boulder, Colo., who is a member of the Parker probe team but was not part of this measurement.

“There was some debate in the community about whether the Alfvén surface would exist as a surface at all,” he says. Decades ago, scientists imagined the boundary as a smooth sphere surrounding the sun like a snow globe. More recently, some thought it would be so ragged that it wouldn’t be apparent when the spacecraft crossed it.

Neither of those images turned out to be correct. The surface is smooth enough that the moment of crossing was noticeable, Kasper said. But during the spacecraft’s close approach to the sun in April, it crossed in and out of the boundary three times. The first dip lasted about five hours, the last only half an hour.

“The surface clearly has some structure and warp to it,” Kasper said.

That structure could influence everything from the way solar eruptions leave the sun to the way the solar wind interacts with itself farther out from the sun, DeForest says. “That has consequences that we don’t know yet, but are likely to be profound,” he says. “This is very exciting. It’s terra incognita.”

Parker is still orbiting the sun and planning to make several more close approaches over the next few years, eventually getting within 6 million kilometers of the solar surface. That should bring Parker into the solar corona again and again, solar physicist Nour Raouafi of the Johns Hopkins Applied Physics Laboratory in Laurel, Md., said in the news briefing. The spacecraft may have made another journey past the Alfvén critical surface in August and will have another opportunity in January.

“The expectation is that as we fly closer and closer to the sun, we’ll keep crossing this boundary,” Raouafi said. But the boundary might not be in the same place every time. As the sun’s activity changes, the level of the Alfvén critical surface is expected to rise and fall as if the corona is breathing in and out, he said.

That’s another thing that scientists hope to observe for the first time.

Huge numbers of fish-eating jaguars prowl Brazil’s wetlands

In a tract of central Brazilian wetlands, jaguars spend their days wading through chest-deep waters searching for fish. When not hunting, the big cats playfully grapple with each other back on land. Their life is unlike any other known jaguar population’s existence in the world.

New findings reveal a degree of flexibility in diet and lifestyle previously unseen among jaguars. The discovery may provide key context on the cats’ role in food webs, helping scientists better understand the effect of environmental changes on the species, researchers report October 6 in Ecology.

Jaguars (Panthera onca), which are usually territorial loners that hunt on land, live in a wide array of habitats, ranging from North American deserts to grasslands and tropical rainforests in Central and South America. The cats are also found in the Pantanal, an immense tropical wetland — the largest of its kind in the world — that sprawls over parts of Brazil, Bolivia and Paraguay.

Ecologists Manoel dos Santos-Filho of the Universidade do Estado de Mato Grosso in Cáceres, Brazil, and Carlos Peres of the University of East Anglia in Norwich, England, knew of rumors of large numbers of jaguars sighted near Brazil’s Taiamã Ecological Station. That large ecological reserve is located in the remote, northern reaches of the Pantanal.
After relaying these anecdotes to Taal Levi, a wildlife ecologist at Oregon State University in Corvallis, the researchers started a project to better understand the jaguars’ biology and population status in the protected area.

Taiamã is seasonally flooded, with no roads or trails, so the team had to access the reserve by boat, setting up motion-activated cameras along waterways to gather data on jaguar numbers. The area’s abundance of jaguars, however, was obvious immediately.

“You set your foot out of the boat, and there’s a jaguar footprint there already,” says Charlotte Eriksson, a wildlife scientist also at Oregon State University. “There are scratches on trees. There are jaguar scats. There’s just an unbelievable presence of this apex predator wherever you go, which is something I’ve never experienced anywhere before.”

The team deployed 59 cameras, which operated from 2014 to 2018, and collected more than 1,500 videos of jaguars. The researchers also captured 13 jaguars and fitted them with GPS or radio-tracking collars to gain insight into the animals’ population density, movements and social interactions.

Based on their data, Eriksson and colleagues estimate that the Taiamã Ecological Station hosts the highest density of jaguars ever recorded: 12.4 animals per 100 square kilometers, nearly triple some of the next highest estimates elsewhere. Jaguars were also the most common mammal spotted on the cameras.

Video footage showed jaguars carrying off large fish. When the team analyzed 138 scat samples, the researchers found 46 percent had fish remains in them and 55 percent contained aquatic reptiles, such as caiman or turtles. Just 11 percent contained mammal remains.
Jaguars are well-documented in taking on challenging prey, including underwater fare (SN: 7/15/16). Eriksson and her team think that the Taiamã felines have not only the most fish-dependent diet among jaguars, but also among all big cats. There are tigers in Bangladesh that live in flooded mangrove forests and sometimes eat fish, but those cats still primarily eat land-based food, the researchers say.

The cameras and tracking collars also showed that the Taiamã jaguars were spending a lot of time near each other, sometimes traveling, fishing and playing together. This is all exceptionally odd behavior for jaguars, at least based on what scientists know about the cats elsewhere in the world.

In terms of social behavior, “what we knew of jaguars from before this study is basically that they are solitary, and they meet up to mate. And that’s about it,” Eriksson says, noting anecdotes of the cats sharing prey carcasses as rare counterexamples.
The profusion of aquatic prey in the flooded preserve — protected from human encroachment — may be responsible for the jaguars’ superlative density and their rich social lives. It’s possible there’s so much food available, Eriksson says, that there is “no real need to fight over it.”

Another idea is that aquatic prey concentrated along the river margins are accessible in only certain areas, Levi says. This may encourage jaguar territories to dissolve, since obtaining access to multiple fishing spots requires getting along with other jaguars. Other animals behave in similar ways. Brown bears, for example, congregate in great numbers to feed at salmon spawning grounds, despite the bears’ typically solitary nature, Levi says.

The abundance of jaguars and their social behavior is not surprising, given the available food resources, says Todd Fuller, a conservation biologist at the University of Massachusetts Amherst. Still, he finds the new information exciting.

Fuller, who was not involved with the research, says the study helps bring researchers’ understanding of jaguars’ ecology and conservation closer to what’s known about most other large cat species, and “that is a very good thing.”

Jaguars in the Pantanal face many threats and are declining within Brazil, Eriksson says, suffering from drought, fire and agricultural expansion. Evaluating how jaguars might respond to such changes is paramount. In 2020, half of the study area burned, so Eriksson is currently assessing the impact of the fires on the jaguars and their periodically submerged home.

She also wants to investigate how the Taiamã jaguars’ taste for fish is affecting how often the animals eat land-living prey and what strategies the cats use to catch fish.

“We think we know a lot about these charismatic, large predators,” she says, “but there are still things to learn.”

Ancient human visitors complicate the Falkland Islands wolf’s origin story

The enigmatic, now-extinct Falkland Islands wolf had human visitors on the remote archipelago up to 1,070 years ago. The find suggests that Indigenous people could have originally brought the foxlike creatures, also known as the warrah, to the islands.

Scientists have debated how the islands’ only land mammal journeyed to the region: by a long-ago land bridge or with people. But little evidence of a human presence before Europeans arrived in 1690 had been found. Now, traces of ancient fires and hunting show that Indigenous people arrived on the Falkland Islands centuries prior to Europeans, researchers report October 27 in Science Advances. The Yaghan people — historically fire-wielding seafarers who kept foxes as companions — may have been the visitors.

Abrupt spikes in charcoal levels in sediments offer “telltale signs of human arrival” from 1,070 to 620 years ago on New Island, says Kit Hamley, a paleoecologist and archaeologist at the University of Maine in Orono. Those spikes mirror later traces of Europeans’ fires around 250 years ago.

And massive piles of sea lion and penguin bones imply hunting by humans from 745 to 600 years ago, Hamley says. Before being hunted to extinction by Europeans in 1875, the Falkland Islands wolf (Dusicyon australis) also consumed marine predators such as sea lions and penguins, nitrogen levels in two warrah bones and one tooth show.
The researchers newly dated that tooth and found it to be from 3,860 years ago. That vastly predates the fire-and-bone-pile evidence, leaving a gap “between when the warrah arrives, and when we can definitively say people were there,” Hamley says.

But Indigenous people’s presence up to 1,070 years ago raises new questions about whether the warrah hitchhiked there with earlier human visitors, Hamley says.

Next, Hamley and colleagues plan to partner with the few remaining Yaghan communities in Tierra del Fuego in Argentina to piece together “parts of the story that have been lost or taken away.”

How our SN 10 scientists have responded to tumultuous times

ach year since 2015, Science News has featured the work of outstanding early- and mid-career scientists in our SN 10: Scientists to Watch list. They’re nominated by Nobel laureates and members of the National Academy of Sciences, and are recognized because of their curiosity, passion, determination and, of course, their discoveries.

But we decided that 2021 begs for something different. The coronavirus pandemic continues to rage worldwide, with its burdens falling hardest on those least able to bear them — inequities already on our minds due to Black Lives Matter, #MeToo and other social movements. At the same time, we’re learning that the window to reverse some of climate change’s most devastating effects is closing fast. With all the upheaval, we wondered: How do these extraordinary times change a scientist’s work?

Here, we catch up with 10 noteworthy Scientists to Watch alumni. Emily Fischer, who studies wildfire smoke, has faced the threat of fires firsthand, cognitive neuroscientist Jessica Cantlon is fighting sexual harassment in the sciences and economist Parag Pathak is taking his efforts to make institutions more equitable from schools to hospitals. Other scientists reveal how their work has gained new urgency and meaning for them. The interviews that follow have been edited for length and clarity.

Astronomers have found the Milky Way’s first known ‘feather’

The Milky Way has a “feather” in its cap.

A long, thin filament of cold, dense gas extends jauntily from the galactic center, connecting two of the galaxy’s spiral arms, astronomers report November 11 in the Astrophysical Journal Letters. This is the first time that such a structure, which looks like the barb of a feather fanning off the central quill, has been spotted in the Milky Way.

The team that discovered our galaxy’s feather named it the Gangotri wave, after the glacier that is the source of India’s longest river, the Ganges. In Hindi and other Indian languages, the Milky Way is called Akasha Ganga, “the river Ganga in the sky,” says astrophysicist Veena V.S. of the University of Cologne in Germany.

She and colleagues found the Gangotri wave by looking for clouds of cold carbon monoxide gas, which is dense and easy to trace, in data from the APEX telescope in San Pedro de Atacama, Chile. The structure stretches 6,000 to 13,000 light-years from the Norma arm of the Milky Way to a minor arm near the galactic center called the 3-kiloparsec arm. So far, all other known gas tendrils in the Milky Way align with the spiral arms (SN: 12/30/15).

The Gangotri wave has another unusual feature: waviness. The filament appears to wobble up and down like a sine wave over the course of thousands of light-years. Astronomers aren’t sure what could cause that, Veena says.

Other galaxies have gaseous plumage, but when it comes to the Milky Way, “it’s very, very difficult” to map the galaxy’s structure from the inside out, she says. She hopes to find more galactic feathers and other bits of our galaxy’s structure. “One by one, we’ll be able to map the Milky Way.”