Ancient rock artists were drawn to echo chambers. Members of early farming communities in Europe painted images in rock-shelters where sounds bounced off walls and into the surrounding countryside, researchers say.

Rock-shelters lacking such sound effects were passed up, at least in the central Mediterranean, report archaeologist Margarita Díaz-Andreu of the University of Barcelona and colleagues in the July Journal of Archaeological Science. In landscapes with many potential rock art sites, “the few shelters chosen to be painted were those that have special acoustic properties,” Díaz-Andreu says.
Some hunter-gatherer and farming groups studied over the past couple centuries believed in spirits that dwell in rock and reveal their presence via echoes. But acoustic evidence of special echoing properties at rock art sites is rare.

Díaz-Andreu’s team studied two rock art sites in 2015 and 2016. Baume Brune is a kilometer-long cliff in southeastern France. Of 43 naturally formed cavities in the cliff, only eight contain paintings, which include treelike figures and horned animals. Rock art in the Valle d’Ividoro, on Italy’s east coast, appears in an 800-meter-long section of a gorge. Only three of its 11 natural shelters contain painted images. Researchers generally date these French and Italian paintings to between roughly 6,500 and 5,000 years ago, several thousand years after the Stone Age had ended, Díaz-Andreu says.

To investigate the acoustics of the decorated and unadorned shelters, the researchers developed a new technique for determining the direction, intensity and timing of sound waves arriving at a particular point from every direction. A special microphone connected to a digital recorder measured the acoustic properties of any echoes set off by balloons popped just outside each rock-shelter. This setup was moved to various spots outside the caves to record the acoustic reach of reflected popping sounds. Echo measurements in France were taken at distances ranging from 22 to 36 meters from cliff shelters. Due to rougher terrain in Italy, measurements there were taken at distances ranging from 77 to 300 meters.
Then, the acoustic data were transformed into 3-D, slow-motion depictions of echoes, represented by moving circles, indicating where sound reflections originated. At both sites, shelters with rock paintings displayed better echoing properties than undecorated shelters, Díaz-Andreu says. And in each location, the shelter that best reflected echoes had the highest number of paintings.
“This novel technique shows a clear correlation between audible echoes and decorated shelters,” says music archaeologist Riitta Rainio of the University of Helsinki in Finland, who did not participate in the new study.

Echoes that bounce off steep rock cliffs bordering three lakes in northern Finland also attracted ancient artists, Rainio says. She and her colleagues took acoustic measurements at Finland’s painted cliffs from 2013 to 2016. Microphones placed on boats positioned at different spots on nearby lakes measured sound waves generated, in most trials, by a starter’s pistol. These Finnish paintings date to between around 7,200 and 3,000 years ago, Rainio says.

In some cases, echoes reflect directly from cliff paintings. “That, and possible drumming figures painted on the cliffs, suggest that sound played some role in rituals at these sites,” Rainio says. Her team will report its findings in an upcoming Journal of Archaeological Method and Theory.

Creators of older Stone Age cave art also appear to have focused on sites where echoes abounded, says archaeologist Paul Pettitt of Durham University in England. For instance, many roughly 14,000- to 12,000-year-old animal drawings and engravings at France’s Niaux Cave cluster in a cathedral-like chamber where sounds echo loudly.

“The new study provides convincing evidence that echoes, which were scientifically inexplicable to prehistoric people, played a determining role in how art was created,” Pettitt says.

Big, rogue planets — ones without parent stars — are rare.

A new census of free-floating Jupiter-mass planets determined that these worlds are a tenth as common as previous estimates suggested. The results appear online July 24 in Nature.

Planets can go rogue in two ways: They can get kicked out of their parent planetary systems or form when a ball of gas and dust collapses (SN: 4/4/15, p. 22).

In the new study, Przemek Mróz of the Astronomical Observatory of the University of Warsaw and colleagues estimated the number of large, rogue planets in our galaxy using a technique called microlensing. When an object with a mass of a planet passes in front of a distant, background star, the gravity of the planet acts as a gravitational magnifying glass. It distorts and focuses the light, giving up the planet’s existence.
Mróz and colleagues looked at 2,617 microlensing events recorded between 2010 and 2015 and determined which were caused by a rogue planet. For every typical star, called main sequence stars, there are 0.25 free-floating Jupiter-mass planets, the analysis suggests.

The new result sharply contrasts an estimate published in 2011, which suggested that rogue Jupiters are almost twice as common as main sequence stars. About 90 percent of stars in the universe are main sequence stars, so if that estimate were accurate, there should be a lot of free-floating Jupiters.

“That result changed our conceptual framework of the universe just a little bit,” says astronomer Michael Liu of the University of Hawaii in Honolulu. It challenged long-held ideas about how planets go rogue because the known methods wouldn’t generate enough planets to account for all the wanderers.

The 2011 result was based on a relatively small sample of microlensing events, only 474. Since then, infrared telescope images haven’t detected as many free-floating planets as expected. “Over the years, serious doubts were cast over the claims of a large population of Jupiter-mass free-floaters,” Mróz says.

David Bennett, coauthor of the 2011 study, agrees that the new census failed to find evidence for a large population of Jupiter-mass rogue planets. He notes, however, that the new data do reveal four times as many Jupiter-mass failed stars called brown dwarfs than predicted in the original census. So some of the rogues that were originally classified as planets may, in fact, be failed stars. Bennett, of NASA’s Goddard Space Flight Center in Greenbelt, Md., and colleagues are working on a new analysis of potential rogues with nearly 3,000 microlensing events and plan to compare their results with those from the new census.
Liu says the latest census is much more in line with theories of how planets form. Most rogues should be Earth-mass or a little heavier. Those lighter planets get tossed out of their planetary systems much easier than behemoths like Jupiter. Still, the smaller planets are harder to detect.

The new microlensing analysis did identify several events in which stars brightened and dimmed in less than half a day. Such short events hint at the existence of Earth-mass free-floaters because smaller planets with less gravity should brighten a distant star more briefly than more massive stars. Determining whether those small planets are really rogue and counting how many there are will take better telescopes, the team notes.

A species gets only one chance to explore its solar system for the first time.

For humans, that chance began 40 years ago this month, when the twin Voyager spacecraft embarked on their “grand tour” of the solar system. A new PBS documentary airing on August 23, The Farthest: Voyager in Space, chronicles their journey to send home the first close-ups of the giant planets and to bring a message about life on Earth to the stars.
Voyagers’ launch dates took advantage of a rare planetary alignment. In 1977, the giant planets — Jupiter, Saturn, Uranus and Neptune — lined up in such a way that a spacecraft could swing past all four in less than 15 years, stealing some gravitational oomph from each world as it went.

That lucky alignment happens only once every 176 years. When NASA’s administrator went to President Richard Nixon to ask for funding for Voyager, he allegedly said: “The last time the planets were lined up like that, President Jefferson was sitting at your desk. And he blew it.”

The Voyagers almost blew it, too. The first craft (Voyager 2, confusingly) launched on August 20, 1977. It experienced so much shaking that its onboard computer — which had as much computing power as a modern car key fob — thought it was failing and put itself in safe mode.
Engineers got it back on track and fixed the problem for Voyager 1’s launch. Then that spacecraft’s rocket had a fuel leak during launch. The craft was within 3½ seconds of running out of gas before it accelerated enough to reach Jupiter.

These nail-biters are mostly told through personal, entertaining anecdotes from Voyager team members. Historical footage from press conferences and newscasts grounds the story in its era. Everyone has big ’70s computers and big ’70s hair. Cuts from shots of the scientists today to their younger selves emphasize how much time has passed. It’s strange that such a high-tech and ambitious mission seems so vintage.

Even the Voyager footage of Jupiter and Saturn coming into view for the first time has a home video quality, especially compared with the sharp, colorful images that spacecraft send back from these planets today. Watching the footage felt like watching video of my parents’ wedding: I recognize everyone, but they look so different.

But the sense of awe that the Voyager images sparked is palpable. At the time, every picture was the best planetary picture ever taken. Much of what is known about the outer solar system now — Jupiter’s moon Io has volcanoes, Europa has an ocean, Neptune has a great churning hurricane that never stops — was glimpsed for the first time with Voyager.

The Voyager spacecraft are still out there, and one may have already left the solar system (SN: 8/23/14, p. 6). Good thing because both craft carry a message in a bottle: the Golden Record.

The Golden Record was a literal record to be played on a phonograph by any aliens that might encounter the spacecraft. The package included a needle, a speaker and graphical instructions on how to play the record. A listener would hear a two-hour sampling of sounds from Earth, including babies crying, whales singing, chimps screeching, trains, thunderstorms, Beethoven, Chuck Berry, greetings in 55 languages and astronomer Carl Sagan’s son saying, “Hello from the children of planet Earth.”

The Farthest weaves the story of exploration with the story of the making of the record. The record’s producers and champions recount how they pulled the whole thing together in just six weeks. What to leave in — a map to Earth, in case the aliens want to visit — and what to leave out — full frontal nudity — was fiercely debated.

At times, refrains of “Wow!” and “It was a first” feel repetitive. Some of the stock footage and spacecraft animations are a little cheesy. But The Farthest is a tender tribute, tinged with nostalgia and existential awe. For those like me, who weren’t alive or aware when the first pictures of Jupiter came back, The Farthest offers a sense of what we missed.

As luck (or exceptionally precise astronomical modeling) would have it, my new, small Oregon town happens to lie in the upcoming eclipse’s path of totality. For nearly two glorious minutes on August 21, we will look up and see the unworldly sight of the moon completely blocking the sun.

To put it mildly, Oregon is going bonkers. Local radio is warning of gas shortages and apocalyptic traffic. Schools and businesses are closing. Emergency services are ramping up for the expected onslaught. Every local store has a pile of eclipse glasses near the register, yours for a very reasonable $2. (Oregonians don’t price gouge.)

I bought glasses (the good kind) for my family and put them in a high drawer. But as a parent to a 2-year-old, I realize that my eclipse prep can’t stop there. I’ve seen what the girl does to regular sunglasses, so I’ve got a few ideas to preschooler-proof these eclipse glasses for her.

Except for during the brief window of totality (when the sun’s surface is completely blacked-out), you shouldn’t look directly at the sun during an eclipse without wearing proper, eclipse-specific eyewear. The powerful light can cause extensive, sometimes permanent eye damage, a condition called solar retinopathy.

As you may imagine, it might be hard to impress this risk on children. Take the cases of these three Australian kids. After watching the 2012 partial eclipse of the sun through binoculars, a 10-year-old boy hurt his eyes. Examinations three months after the injury revealed persistent damage. Another boy, this one 8 years old, stared at the same partial eclipse directly. His eyes showed signs of harm five months later. And an 11-year-old girl who peeked at the 2012 transit of Venus with only her right eye also suffered persistent eye damage.

Those cautionary examples, described in 2015 in the Journal of the American Association for Pediatric Ophthalmology and Strabismus, made me want to duct tape my children’s eclipse glasses to their heads, mummy-style.

In lieu of that, I’m opting for super thick and stretchy fabric bands that I’ll staple and tape to the arms of the glasses. I’m also experimenting with a headband to limit movement on the top of the head, and perhaps even a paper plate taped around the front of the glasses to block incidental light. You could even take a note from 1963 schoolchildren, who put big boxes over their heads to see a projection of an eclipse.
I was happy to see that my DIY ideas aren’t totally off: Amid its wealth of eclipse information, the American Astronomical Society recommends modifying eclipse glasses with elastic or tape around the back so they sit firmly on small faces.

Of course, if you have a little Houdini who regularly squirms out of constricting clothes, you may consider any tweaking to be too risky. A simple pinhole projector, which doesn’t require looking anywhere near the sun, might be better.

Clearly, eye protection is something to take seriously. But don’t let that worry keep you and your children from seeing this once-in-a-lifetime celestial event. It’s the type of natural phenomenon that people — especially really young ones — can grab onto and understand. After all, kids love shadows, and this is going to be one heck of a shadow.

To halt the misuse of opioids, it may help to slash the number of pills prescribed, a new study suggests.

Five months after the implementation of new opioid prescription guidelines at a University of Michigan hospital, roughly 7,000 fewer pills went home with patients — a drop that might reduce the risk of accessible pills leading to substance abuse. But the opioid reduction didn’t leave patients who had undergone a routine surgery with more pain, the team reports online December 6 in JAMA Surgery.
“The decline in opioid volume after the intervention was dramatic,” says physician Mark Bicket of Johns Hopkins University School of Medicine, who was not involved in the study.

Around 50 percent of people who misuse opioids get the drugs from a friend or relative for free, while 22 percent obtain them from a doctor, according to the U.S. Department of Health and Human Services. Michael Englesbe, a surgeon at the University of Michigan in Ann Arbor, says that part of doing a better job of managing patients’ pain “will be preventing chronic opioid use after surgical care and making sure fewer pills get into the community.”

Englesbe and colleagues looked at 170 people who had a minimally invasive surgery to remove their gallbladders at the University of Michigan hospital from 2015 to 2016. All had received a prescription for opioids. Of those patients, 100 completed a survey detailing how much of the prescription they took, whether they also used a common painkiller such as ibuprofen or acetaminophen, and how they rated their pain during the first week after surgery.

The 170 individuals typically received a prescription equivalent to 40 to 60 tablets, each containing 5 milligrams of hydrocodone. Seven of the 170 patients requested an opioid prescription refill. The 100 patients who completed the survey used very little of their prescriptions, usually somewhere from one to 12 pills. And their average pain score on a scale of zero (no pain) to 10 (the worst pain imaginable) was five.
Based on this information, guidelines for opioid prescriptions following the same type of surgery were implemented at the hospital in November of 2016. The researchers recommended prescriptions of 15 opioid pills, plus the use of common painkillers.

In the five months after the guidelines went into effect, 200 patients had the gallbladder surgery. Five of those patients asked for an opioid prescription refill. Eighty-six of the patients filled out the survey and reported that they used even less of their prescriptions — from zero to nine pills — than the pre-guidelines survey group. These patients also noted the same average pain score as the previously surveyed group and similar common painkiller use.

The study demonstrates “a relatively simple intervention at the institutional level with promising results,” Bicket says. “Patients receive opioid prescriptions within a health care system, so it makes sense to focus on getting our systems to work better in reducing the unnecessary supply of opioids after surgery.”

Along with this gallbladder procedure, Englesbe and colleagues have developed opioid prescribing recommendations for other routine surgeries, such as appendix removal and hernia repair, for the state of Michigan.

There have been hints for years that playing football might come at a cost. But a study this year dealt one of the hardest hits yet to the sport, detailing the extensive damage in football players’ brains, and not just those who played professionally.

In a large collection of former NFL players’ postmortem brains, nearly every sample showed signs of chronic traumatic encephalopathy, or CTE, a disorder diagnosed after death that’s associated with memory loss, emotional outbursts, depression and dementia. Damaging clumps of the protein tau were present in 110 of 111 brains, researchers reported in JAMA (SN: 8/19/17, p. 15).
Those startling numbers captured the attention of both the football-loving public and some previously skeptical researchers, says study coauthor Jesse Mez, a behavioral neurologist at Boston University. “This paper did a lot to bring them around.” And that increased awareness and acceptance has already pushed the research further. “The number of brain donors who have donated since the JAMA paper came out has been astronomical,” Mez says.
As the largest and most comprehensive CTE dataset yet, the results described in JAMA are a necessary step on the path to finding ways to treat or prevent CTE, and not just for professional athletes.
Former college and high school football players’ brains were also examined, though in small numbers. Three of 14 high school players and 48 of 53 college players had signs of CTE. Many of the brains were donated by relatives who suspected something was amiss. That skewed sample makes it difficult to draw broad conclusions. Still, the study raised troublesome questions about the safety of youth sports.

Those questions haven’t been answered, though other research this year provided clues. A study of concussed hockey players ages 11 to 14 suggested that young brains may need more time than is usually allotted to heal after a hard knock. Players had troublesome changes in white matter tracts — nerve cell bundles that carry messages across the brain — three months after injury, despite normal thinking and memory abilities, researchers reported in November in Neurology.

To fully understand CTE, scientists need a way to identify and follow the disease as it progresses. A comprehensive study is now under way to look for CTE markers in live people, and has already hit on one clue.

Compared with postmortem brain tissue taken from healthy people and those with Alzheimer’s, tissue from people who had CTE had higher levels of an inflammation protein called CCL11, Mez and other researchers reported in September in PLOS ONE. In people with CTE, the more years that a person played football, the more CCL11. CCL11 levels, or other factors circulating in cerebrospinal fluid or blood, might one day let scientists monitor the brain health of athletes and others exposed to head trauma.

The battle of the sexes, at least among certain ocean mammals, may come down to well-placed skin folds, suggests research by Patricia Brennan, an evolutionary biologist at Mount Holyoke College in South Hadley, Mass., and colleagues.

In some species, enhanced male-female genital fit has evolved over time in ways that make mating easier. This is an example of what scientists call congruent evolution. In other species, genital anatomy reflects a battle, as shape and form change over time to give one sex an edge in control of fertilization. Fittingly, this is called antagonistic evolution.
Brennan’s recent collaboration, examining genitalia of porpoises, dolphins and seals, required extra creativity. In previous studies, her team used saline to inflate preserved penises from birds, snakes, sharks and bats. But the tough, fibroelastic penises of the cetaceans would not inflate with saline alone. So her collaborator, Diane Kelly, a penis biomechanics expert at the University of Massachusetts Amherst, suggested pressurizing the saline with a beer keg.

“We looked at each other and said, ‘This could be the best or worst idea we’ve ever had,’ ” Brennan laughs. But it worked. The scientists then created vaginal endocasts with dental silicone and made 3-D mathematical models to examine male-female fit. The team, led by marine mammalogist Dara Orbach of Dalhousie University in Halifax, Canada, described the work in the Oct. 11 Proceedings of the Royal Society B.

Story continues below image
The results show both antagonistic and congruent coevolution. In the model vaginas of short-beaked common dolphins ( Delphinus delphis) and harbor seals ( Phoca vitulina ), penises encountered no physical barriers to penetration.
But in harbor porpoises (Phocoena phocoena) and bottlenosed dolphins (Tursiops truncatus), the scientists found vaginal folds that may help females physically exert choice over sperm. By subtly changing body position during sex, females may use those folds to decrease penetration depth, reducing the likelihood of fertilization by unwanted males, Brennan says.
Brennan’s work has, understandably, made a splash over the years, attracting media coverage and, in 2013, criticism. Conservative news websites and internet trolls attacked her research, calling it “wasteful government spending.” Surprised by the reaction, Brennan responded publicly with an essay in Slate , arguing that basic science moves society forward and is a valid and valuable use of public funds. The experience convinced her that scientists must defend basic science.
Our ability to innovate is undermined without curiosity-driven science, she says. Brennan has developed an outreach program on basic science and plans to keep expanding knowledge of vertebrate genitalia. “In every species we have looked,” she says, “we have found something weird that nobody else knew.” Reason enough to keep discovering.

NASA’s next mission will go where some spacecraft have gone before. The two finalists in the agency’s selection process will return to either Saturn’s moon Titan or comet 67P/Churyumov-Gerasimenko, NASA announced in a press teleconference on December 20.

The Dragonfly mission would launch a drone-like craft to Saturn’s largest moon in 2025 that would land in 2034. NASA’s Cassini-Huygens mission showed that Titan has lakes and rivers of liquid ethane and methane, and may have chemistry that is conducive to life.
“We can test how far prebiotic chemistry has progressed in an environment that we know has the ingredients for life,” said lead investigator Elizabeth Turtle of the Johns Hopkins Applied Physics Laboratory in Laurel, Md.

The other finalist, the Comet Astrobiology Exploration Sample Return (CAESAR) mission, would launch a spacecraft before the end of 2025 to collect a 100-gram sample from the surface of comet 67P, which was mapped by ESA’s Rosetta spacecraft, and return it to Earth in 2038.

Story continues after image
Rosetta’s mapping work “dramatically improves the chances of success for a very difficult activity, which is grabbing a piece of a comet,” said lead investigator Steven Squyres of Cornell University.
Each project will receive funding to further develop the mission concepts. In July 2019, NASA will announce which mission will fly.

Two other missions, one to search for signs of life in the plumes of Saturn’s moon Enceladus and one to land on Venus, will receive funding to tackle specific technology questions to prepare the missions for future competitions.

A new robotic arm made of DNA moves 100,000 times faster than previous DNA machinery.

The DNA nanobot is shaped like a gearshift, with an extendible arm that ranges from 25 to more than 400 nanometers long that’s attached to a 55-by-55-nanometer platform. Researchers remotely control this DNA device, described in the Jan. 19 Science, with electric fields that tug on charged molecules in its arm. Those electric fields help the nanomachine’s arm move much more quickly than previous DNA robots, which relied on chemical interactions between DNA molecules to move (SN: 9/11/10, p. 18).

Friedrich Simmel, a biophysicist at the Technical University of Munich, and his colleagues could swivel their DNA robotic arm 360 degrees in a matter of milliseconds. To lock the arm down in particular positions, the team built latches made of short, single-stranded DNA into the platform.

Such quick, efficient DNA nanobots could someday help move tiny cargo, such as molecules or nanoparticles, in a nanofactory that manufactures new types of materials.

Though they be but little, they are fierce.

Airborne particles smaller than 50 nanometers across can intensify storms, particularly over relatively pristine regions such as the Amazon rainforest or the oceans, new research suggests. In a simulation, a plume of these tiny particles increased a storm’s intensity by as much as 50 percent.

Called ultrafine aerosols, the particles are found in everything from auto emissions to wildfire smoke to printer toner. These aerosols were thought to be too small to affect cloud formation. But the new work suggests they can play a role in the water cycle of the Amazon Basin — which, in turn, has a profound effect on the planet’s hydrologic cycle, researchers report in the Jan. 26 Science.
“I have studied aerosol interactions with storms for a decade,” says Jiwen Fan, an atmospheric scientist at the Pacific Northwest National Laboratory in Richland, Wash., who led the new study. “This is the first time I’ve seen such a huge impact” from these minute aerosols.

Larger aerosol particles greater than 100 nanometers, such as soot or black carbon, are known to help seed clouds. Water vapor in the atmosphere condenses onto these particles, called cloud condensation nuclei, and forms tiny droplets. But water vapor doesn’t condense easily around the tinier particles. For that to be possible, the air must contain even more water vapor than is usually required to form clouds, reaching a very high state of supersaturation.

Such a state is rare — larger aerosols are usually also present to form water droplets, removing that extra water from the atmosphere, Fan says. But in humid places with relatively low background air pollution levels, such as over the Amazon, supersaturation is common, she says.
From 2014 to 2015, Brazilian and U.S. research agencies collaborated on a field experiment to collect data on weather and pollution conditions in the Amazon Basin. As part of the experiment, several observation sites tracked plumes of air pollution traveling from the city of Manaus out across the rainforest. During the warm, wet season, there is little difference day to day in most meteorological conditions over the rainforest, such as temperature, humidity and wind direction, Fan says. So a passing pollution plume represents a distinct, detectable perturbation to the system.

Story continues after image
The international team examined vertical wind motion, or updrafts, and aerosol concentration data from one of these stations from March to May 2014. When a large plume of aerosols with an abundance of ultrafine particles passed by an observation station, the researchers observed a corresponding, more powerful vertical wind motion and heavier rain. Such updrafts intensify storms, helping to drive stronger circulation.

Next, the researchers conducted simulations of an actual storm that occurred on March 17, 2014, matching its temperature, wind and water vapor conditions, as well as a low level of background aerosols in the atmosphere. Then, the team introduced several pollution scenarios to interact with the storm, including no plume and a typical plume from the Manaus metropolis. The results suggested that the ultrafine aerosol particles, in particular, were not only acting as cloud condensation nuclei over the Amazon Basin, but also that the water droplets the aerosols created significantly strengthened the gathering storm.

If the conditions are right, the sheer abundance of the ultrafine particles in such a plume would rapidly create a very large number of cloud droplets. The formation of those droplets would also suddenly release a lot of latent heat — released from a substance as it changes from a vapor to a liquid — into the atmosphere. The heat would rise, creating updrafts and quickly strengthening the storm.

Aside from the Amazon, Fan notes that such pristine, humid conditions can also exist over large swaths of the oceans. One recent study in Geophysical Research Letters that she points to found a link between well-traveled shipping lanes, which would contain abundant exhaust including ultrafine aerosols, and an increase in lightning strikes. “This mechanism may have been at play there,” she says.

Atmospheric scientist Joel Thornton of the University of Washington in Seattle, who led the study on the shipping exhaust, says it’s possible that ultrafine particles play a role in that scenario. “What this paper does is raise the stakes in needing to develop a deeper, more accurate understanding of the sources and fates of atmospheric ultrafine particles,” Thornton says.

Meteorologist Johannes Quaas of the University of Leipzig in Germany, who was not involved in either study, agrees. “It’s a very interesting hypothesis.”

But the observations described in the new study don’t definitively demonstrate that ultrafine aerosols alone drive updrafts, Quaas adds. The weather conditions may appear highly consistent from day to day, but such systems are still highly chaotic. Everything from wind to temperature to how the land surface interacts with incoming solar radiation may be variable, he notes. “In reality, it’s not just the aerosols that change.”