How Mars rovers have evolved in 25 years of exploring the Red Planet

Few things are harder than hurling a robot into space — and sticking the landing. On the morning of July 4, 1997, mission controllers at the Jet Propulsion Laboratory in Pasadena, Calif., were hoping to beat the odds and land a spacecraft successfully on the Red Planet.

Twenty-five years ago that little robot, a six-wheeled rover named Sojourner, made it — becoming the first in a string of rovers built and operated by NASA to explore Mars. Four more NASA rovers, each more capable and complex than the last, have surveyed the Red Planet. The one named Curiosity marked its 10th year of cruising around on August 5. Another, named Perseverance, is busy collecting rocks that future robots are supposed to retrieve and bring back to Earth. China recently got into the Mars exploring game, landing its own rover, Zhurong, last year.
Other Mars spacecraft have done amazing science from a standstill, such as the twin Viking landers in the 1970s that were the first to photograph the Martian surface up close and the InSight probe that has been listening for Marsquakes shaking the planet’s innards (SN Online: 2/24/20). But the ability to rove turns a robot into an interplanetary field geologist, able to explore the landscape and piece together clues to its history. Mobility, says Kirsten Siebach, a planetary scientist at Rice University in Houston, “makes it a journey of discovery.”
Each of the Mars rovers has gone to a different place on the planet, enabling scientists to build a broad understanding of how Mars evolved over time. The rovers revealed that Mars contained water, and other life-friendly conditions, for much of its history. That work set the stage for Perseverance’s ongoing hunt for signs of ancient life on Mars.
Each rover is also a reflection of the humans who designed and built and drove it. Perseverance carries on one of its wheels a symbol of Mars rover tracks twisted into the double helix shape of DNA. That’s “to remind us, whatever this rover is, it’s of human origin,” says Jennifer Trosper, an engineer at the Jet Propulsion Lab, or JPL, who has worked on all five NASA rovers. “It is us on Mars, and kind of our creation.”
The little microwave that could
Sojourner, that first rover, was born in an era when engineers weren’t sure if they even could get a robot to work on Mars. In the early 1990s, then-NASA Administrator Daniel Goldin was pushing the agency to do things “faster, better and cheaper” — a catchphrase that engineers would mock by saying only two of those three things were possible at the same time. NASA had no experience with inter­planetary rovers. Only the Soviet Union had operated rovers — on the moon in 1970 and 1973.

JPL began developing a Mars rover anyway. Named after the abolitionist Sojourner Truth, the basic machine was the size of a microwave oven. Engineers were limited in where they could send it; they needed a large flat region on Mars because handling a precision landing near mountains or canyons was beyond their abilities. NASA chose Ares Vallis, a broad outflow channel from an ancient flood, and the mission landed there successfully.

Sojourner spent nearly three months poking around the landscape. It was slow going. Mission controllers had to communicate with Sojourner constantly, telling it where to roll and then assessing whether it had gotten there safely. They made mistakes: One time they uploaded a sequence of computer commands that mistakenly told the rover to shut itself down. They recovered from that stumble and many others, learning to quickly fix problems and move forward.
Although Sojourner was a test mission to show that a rover could work, it managed to do some science with its one X-ray spectrometer. The little machine analyzed the chemical makeup of 15 Martian rocks and tested the friction of the Martian soil.

After surviving 11 weeks beyond its planned one-week lifetime, Sojourner ultimately grew too cold to operate. Trosper was in mission control when the rover died on September 27, 1997. “You build these things, and even if they’re well beyond their lifetime, you just can’t let go very easily, because they’re part of you,” she says.
Twin explorers
In 1998 and 1999, NASA hurled a pair of spacecraft at Mars; one was supposed to orbit the planet and another was supposed to land near one of the poles. Both failed. Stung from the disappointment, NASA decided to build a rover plus a backup for its next attempt.

Thus were born the twins Spirit and Opportunity. Each the size of a golf cart, they were a major step up from Sojourner. Each had a robotic arm, a crucial development in rover evolution that enabled the machines to do increasingly sophisticated science. The two had beefed-up cameras, three spectrometers and a tool that could grind into rocks to reveal the texture beneath the surface.

But there were a lot of bugs to work out. Spirit and Opportunity launched several weeks apart in 2003. Spirit got to Mars first, and on its 18th Martian day on the surface it froze up and started sending error messages. It took mission controllers days to sort out the problem — an overloaded flash-memory system — all while Opportunity was barreling toward Mars. Ultimately, engineers fixed the problem, and Opportunity landed safely on the opposite side of the planet from Spirit.

Both rovers lasted years beyond their expected three-month lifetimes. And both did far more Martian science than anticipated.

Spirit broke one of its wheels early on and had to drive backward, dragging the broken wheel behind it. But the rover found plenty to do near its landing site of Gusev crater, home to a classic Mars landscape of dust, rock and hills. Spirit found rocks that appeared to have been altered by water long ago and later spotted a pair of iron-rich meteorites. The rover ultimately perished in 2010, stuck in a sand-filled pit. Mission controllers tried to extract it in an effort dubbed “Free Spirit,” but salts had precipitated around the sand grains, making them particularly slippery.

Opportunity, in contrast, became the Energizer Bunny of rovers, exploring constantly and refusing to die. Immediately after landing in Meridiani Planum, Opportunity had scientists abuzz.
“The images that the rover first sent back were just so different from any other images we’d seen of the Martian surface,” says Abigail Fraeman, a planetary scientist at JPL. “Instead of these really dusty volcanic plains, there was just this dark sand and this really bright bedrock. And that was just so captivating and inspiring.”

Right at its landing site, Opportunity spotted the first definitive evidence of past liquid water on Mars, a much-anticipated and huge discovery (SN: 3/27/04, p. 195). The rover went on to find evidence of liquid water at different times in the Martian past. After years of driving, the rover reached a crater called Endeavour and “stepped into a totally new world,” Fraeman says. The rocks at Endeavour were hundreds of millions of years older than others studied on Mars. They contained evidence of different types of ancient water chemistry.

Opportunity ultimately drove farther than any rover on any extraterrestrial world, breaking a Soviet rover’s lunar record. In 2015, Opportunity passed 26.2 miles (42.2 km) on its odometer; mission controllers celebrated by putting a marathon medal onto a mock-up of the rover and driving it through a finish line ribbon at JPL. Opportunity finally died in 2019 after an intense dust storm obscured the sun, cutting off solar power, a must-have for the rover to recharge its batteries (SN: 3/16/19, p. 7).

The twin rovers were a huge advance over Sojourner. But the next rover was an entirely different beast.
The SUV of rovers
By the mid-2000s, NASA had decided it needed to go big on Mars, with a megarover the size of a sports utility vehicle. The one-ton Curiosity was so heavy that its engineers had to come up with an entirely new way to land on Mars. The “sky crane” system used retro-rockets to hover above the Martian surface and slowly lower the rover to the ground.

Against all odds, in August 2012, Curiosity landed safely near Mount Sharp, a 5-kilometer-high pile of sediment within the 154-kilometer-wide Gale crater (SN: 8/25/12, p. 5). Unlike the first three Mars rovers, which were solar-powered, Curiosity runs on energy produced by the radioactive decay of plutonium. That allows the rover to travel farther and faster, and to power a suite of sophisticated science instruments, including two chemical laboratories.

Curiosity introduced a new way of exploring Mars. When the rover arrives in a new area, it looks around with its cameras, then zaps interesting rocks with its laser to identify which ones are worth a closer look. Once up close, the rover stretches out its robotic arm and does science, including drilling into rocks to see what they are made of.

When Curiosity arrived near the base of Mount Sharp, it immediately spotted rounded pebbles shaped by a once-flowing river, the first close­up look at an ancient river on Mars. Then mission controllers sent the rover rolling away from the mountain, toward an area in the crater known as Yellowknife Bay. There Curiosity discovered evidence of an ancient lake that created life-friendly conditions for potentially many thousands of years.

Curiosity then headed back toward the foothills of Mount Sharp. Along the way, the rover discovered a range of organic molecules in many different rocks, hinting at environments that had been habitable for millions to tens of millions of years. It sniffed methane gas sporadically wafting within Gale crater, a still-unexplained mystery that could result from geologic reactions, though methane on Earth can be formed by living organisms (SN: 7/7/18, p. 8). The rover measured radiation levels across the surface — helpful for future astronauts who’ll need to gauge their exposure — and observed dust devils, clouds and eclipses in the Martian atmosphere and night sky.
“We’ve encountered so many unexpectedly rich things,” says Ashwin Vasavada of JPL, the mission’s project scientist. “I’m just glad a place like this existed.”

Ten years into its mission, Curiosity still trundles on, making new discoveries as it climbs the foothills of Mount Sharp. It recently departed a clay-rich environment and is now entering one that is heavier in sulfates, a transition that may reflect a major shift in the Martian climate billions of years ago.

In the course of driving more than 28 kilometers, Curiosity has weathered major glitches, including one that shuttered its drilling system for over a year. And its wheels have been banged up more than earthbound tests had predicted. The rover will continue to roll until some unknown failure kills it or its plutonium power wanes, perhaps five years from now.

A rover and its sidekick
NASA’s first four rovers set the stage for the most capable and agile rover ever to visit Mars: Perseverance. Trosper likens the evolution of the machines to the growth of children. “We have a preschooler in Sojourner, and then … your happy-go-lucky teenagers in Spirit and Opportunity,” she says. “Curiosity is certainly a young adult that’s able to do a lot of things on her own, and Perseverance is kind of that high-powered mid­career [person] able to do pretty much anything you ask with really no questions.”

Perseverance is basically a copy of Curiosity built from its spare parts, but with one major modification: a system for drilling, collecting and storing slender cores of rock. Perseverance’s job is to collect samples of Martian rock for future missions to bring to Earth, in what would be the first robotic sample return from Mars. That would allow scientists to do sophisticated analyses of Martian rocks in their earthbound labs. “It feels, even more than previous missions, that we are doing this for the next generation,” Siebach says.

The rover is working fast. Compared with Curiosity’s leisurely exploration of Gale crater, Perseverance has been zooming around its landing site, the 45-kilometer-wide Jezero crater, since its February 2021 arrival. It has collected 10 rock cores and is already eyeing where to put them down on the surface for future missions to pick up. “We’re going to bring samples back from a diversity of locations,” says mission project scientist Kenneth Farley of Caltech. “And so we keep to a schedule.”

Perseverance went to Jezero to study an ancient river delta, which contains layers of sediment that may harbor evidence of ancient Martian life. But the rover slightly missed its target, landing on the other side of a set of impassable sand dunes. So it spent most of its first year exploring the crater floor, which turned out to be made of igneous rocks (SN: 9/11/21, p. 32). The rocks had cooled from molten magma and were not the sedimentary rocks that many had expected.

Scientists back on Earth will be able to precisely date the age of the igneous rocks, based on the radioactive decay of chemical elements within them, providing the first direct evidence for the age of rocks from a particular place on Mars.
Once it finished exploring the crater floor in March, the rover drove quickly toward the delta. Each successive NASA rover has had greater skills in autonomous driving, able to identify hazards, steer around them and keep going without needing constant instructions from mission control.

Perseverance has a separate computer processor to run calculations for autonomous navigation, allowing it to move faster than Curiosity. (It took Curiosity two and a half years to travel 10 kilometers; Perseverance traveled that far in a little over a year.) “The rover drives pretty much every minute that we can give it,” Farley says.

In April, Perseverance set a Martian driving record, traveling nearly five kilometers in just 30 Martian days. If all goes well, it will make some trips up and down the delta, then travel to Jezero crater’s rim and out onto the ancient plains beyond.

Perseverance has a sidekick, Ingenuity, the first helicopter to visit another world. The nimble flier, only half a meter tall, succeeded beyond its designers’ wildest dreams. The helicopter made 29 flights in its first 16 months when it was only supposed to make five in one month. It has scouted paths ahead and scientific targets for the rover (SN Online: 4/19/22). Future rovers are almost certain to carry a little buddy like this.

China’s debut
While the United States has led in Mars rover exploration, it is not the only player on the scene. In May 2021, China became the second nation to successfully place a rover on Mars. Its Zhurong rover, named after a mythological fire god, has been exploring part of a large basin in the planet’s northern hemisphere known as Utopia Planitia.

The landing site lies near a geologic boundary that may be an ancient Martian shoreline. Compared with the other Mars rover locations, Zhurong’s landing site is billions of years younger, “so we are investigating a different world on Mars,” says Lu Pan, a planetary scientist at the University of Copenhagen who has collaborated with Zhurong scientists.

In many ways, Zhurong resembles Spirit and Opportunity, in size as well as mobility. It carries cameras, a laser spectrometer for studying rocks and ground-penetrating radar to probe underground soil structures (SN Online: 5/19/21).

After landing, Zhurong snapped pictures of its rock-strewn surroundings and headed south to explore a variety of geologic terrains, including mysterious cones that could be mud volcanoes and ridges that look like windblown dunes. The rover’s initial findings include that the Martian soil at Utopia Planitia is similar to some desert sands on Earth and that water had been present there perhaps as recently as 700 million years ago.

In May, mission controllers switched Zhurong into dormant mode for the Martian winter and hope it wakes up at the end of the season, in December. It has already traveled nearly two kilometers across the surface, farther than the meager 100 meters that Sojourner managed. (To be fair, Sojourner had to keep circling its lander because it relied on that lander to communicate with Earth.)
From Sojourner to Zhurong, the Mars rovers show what humankind can accomplish on another planet. Future rovers might include the European Space Agency’s ExoMars, although its 2022 launch was postponed after Russia attacked Ukraine (SN: 3/26/22, p. 6). Europe terminated all research collaborations with Russia after the invasion, including launching ExoMars on a Russian rocket.

Vasavada remembers his sense of awe at the Curiosity launch in 2011: “Standing there in Florida, watching this rocket blasting off and feeling it in your chest and knowing that there’s this incredibly fragile complex machine hurtling on the end of this rocket.… It just gave me this full impression that here we are, humans, blasting these things off into space,” he says. “We’re little tiny human beings sending these things to another planet.”

Oort cloud comets may spin themselves to death

Comets from the solar system’s deep freezer often don’t survive their first encounter with the sun. Now one scientist thinks he knows why: Solar warmth makes some of the cosmic snowballs spin so fast, they fall apart.

This suggestion could help solve a decades-old mystery about what destroys many “long-period” comets, astronomer David Jewitt reports in a study submitted August 8 to arXiv.org. Long-period comets originate in the Oort cloud, a sphere of icy objects at the solar system’s fringe (SN: 8/18/08). Those that survive their first trip around the sun tend to swing by our star only once every 200 years.
“These things are stable out there in the Oort cloud where nothing ever happens. When they come toward the sun, they heat up, all hell breaks loose, and they fall apart,” Jewitt says.

The Dutch astronomer Jan Oort first proposed the Oort cloud as a cometary reservoir in 1950. He realized that many of its comets that came near Earth were first-time visitors, not return travelers. Something was taking the comets out, but no one knew what.

One possibility was that the comets die by sublimating all of their water away as they near the heat of the sun until there’s nothing left. But that didn’t fit with observations of comets that seemed to physically break up into smaller pieces. The trouble was, those breakups are hard to watch in real time.

“The disintegrations are really hard to observe because they’re unpredictable, and they happen quickly,” Jewitt says.

He ran into that difficulty when he tried to observe Comet Leonard, a bright comet that put on a spectacular show in winter 2021–2022. Jewitt had applied for time to observe the comet with the Hubble Space Telescope in April and June 2022. But by February, the comet had already disintegrated. “That was a wake-up call,” Jewitt says.

So Jewitt turned to historical observations of long-period comets that came close to the sun since the year 2000. He selected those whose water vapor production had been indirectly measured via an instrument called SWAN on NASA’s SOHO spacecraft, to see how quickly the comets were losing mass. He also picked out comets whose movements deviating from their orbits around the sun had been measured. Those motions are a result of water vapor jets pushing the comet around, like a spraying hose flopping around a garden.

That left him with 27 comets, seven of which did not survive their closest approach to the sun.

Jewitt expected that the most active comets would disintegrate the fastest, by puffing away all their water. But he found the opposite: It turns out that the least active comets with the smallest dirty snowball cores were the most at risk of falling apart.

“Basically, being a small nucleus near the sun causes you to die,” Jewitt says. “The question is, why?”

It wasn’t that the comets were torn apart by the sun’s gravity — they didn’t get close enough for that. And simply sublimating until they went poof would have been too slow a death to match the observations. The comets are also unlikely to collide with anything else in the vastness of space and break apart that way. And a previous suggestion that pressure builds up inside the comets until they explode like a hand grenade doesn’t make sense to Jewitt. Comets’ upper few centimeters of material would absorb most of the sun’s heat, he says, so it would be difficult to heat the center of the comet enough for that to work.

The best remaining explanation, Jewitt says, is rotational breakup. As the comet nears the sun and its water heats up enough to sublimate, jets of water vapor form and make the core start to spin like a catherine wheel firework. Smaller cores are easier to push around than a larger one, so they spin more easily.

“It just spins faster and faster, until it doesn’t have enough tensile strength to hold together,” Jewitt says. “I’m pretty sure that’s what’s happening.”

That deadly spin speed is actually quite slow. Spinning at about half a meter per second could spell curtains for a kilometer-sized comet, he calculates. “You can walk faster.”

But comets are fragile. If you held a fist-sized comet in front of your face, a sneeze would destroy it, says planetary astronomer Nalin Samarasinha of the Planetary Science Institute in Tucson, who was not involved in the study.

Samarasinha thinks Jewitt’s proposal is convincing. “Even though the sample size is small, I think it is something really happening.” But other things might be destroying these comets too, he says, and Jewitt agrees.

Samarasinha is holding out for more comet observations, which could come when the Vera Rubin Observatory begins surveying the sky in 2023. Jewitt’s idea “is something which can be observationally tested in a decade or two.”

Why mosquitoes are especially good at smelling you

Some mosquitoes have a near-foolproof thirst for human blood. Previous attempts to prevent the insects from tracking people down by blocking part of mosquitoes’ ability to smell have failed. A new study hints it’s because the bloodsuckers have built-in workarounds to ensure they can always smell us.

For most animals, individual nerve cells in the olfactory system can detect just one type of odor. But Aedes aegypti mosquitoes’ nerve cells can each detect many smells, researchers report August 18 in Cell. That means if a cell were to lose the ability to detect one human odor, it still can pick up on other scents.
The study provides the most detailed map yet of a mosquito’s sense of smell and suggests that concealing human aromas from the insects could be more complicated than researchers thought.

Repellents that block mosquitoes from detecting human-associated scents could be especially tricky to make. “Maybe instead of trying to mask them from finding us, it would be better to find odorants that mosquitoes don’t like to smell,” says Anandasankar Ray, a neuroscientist at the University of California, Riverside who was not involved in the work. Such repellents may confuse or irritate the bloodsuckers and send them flying away (SN: 9/21/11; SN: 3/4/21).

Effective repellents are a key tool to prevent mosquitoes from transmitting disease-causing viruses such as dengue and Zika (SN: 7/11/22). “Mosquitoes are responsible for more human deaths than any other creature,” says Olivia Goldman, a neurobiologist at Rockefeller University in New York City. “The better we understand them, the better that we can have these interventions.”

Mosquitoes that feed on people home in on a variety of cues when hunting, including body heat and body odor. The insects smell using their antennae and small appendages close to the mouth. Using three types of sensors in olfactory nerve cells, they can detect chemicals such as carbon dioxide from exhaled breath or components of body odor (SN: 7/16/15).

In previous work, researchers thought that blocking some sensors might hide human scents from mosquitoes by disrupting the smell messages sent to the brain (SN: 12/5/13). But even those sensor-deprived mosquitoes can still smell and bite people, says neurobiologist Margo Herre also of Rockefeller University.

So Goldman, Herre and colleagues added fluorescent labels to A. aegypti nerve cells, or neurons, to learn new details about how the mosquito brain deciphers human odors. Surprisingly, rather than finding the typical single type of sensor per nerve cell, the team found that individual mosquito neurons appear more like sensory hubs.

Genetic analyses confirmed that some of the olfactory nerve cells had more than one type of sensor. Some cells produced electrical signals in response to several mosquito-attracting chemicals found in humans such as octenol and triethyl amine — a sign the neurons could detect more than one type of odor molecule. A separate study published in April in eLife found similar results in fruit flies, which suggests such a system may be common among insects.

It’s unclear why having redundant ways of detecting people’s odors might be useful to mosquitoes. “Different people can smell very different from one another,” says study coauthor Meg Younger, a neurobiologist at Boston University. “Maybe this is a setup to find a human regardless of what variety of human body odor that human is emitting.”

Common, cheap ingredients can break down some ‘forever chemicals’

There’s a new way to rip apart harmful “forever chemicals,” scientists say.

Perfluoroalkyl and polyfluoroalkyl substances, also known as PFAS, are found in nonstick pans, water-repellent fabrics and food packaging and they are pervasive throughout the environment. They’re nicknamed forever chemicals for their ability to stick around and not break down. In part, that’s because PFAS have a super strong bond between their carbon and fluorine atoms (SN: 6/4/19). Now, using a bit of heat and two relatively common compounds, researchers have degraded one major type of forever chemical in the lab, the team reports in the Aug. 19 Science. The work could help pave the way for a process for breaking down certain forever chemicals commercially, for instance by treating wastewater.
“The fundamental knowledge of how the materials degrade is the single most important thing coming out of this study,” organic chemist William Dichtel said in an August 16 news conference.

While some scientists have found relatively simple ways of breaking down select PFAS, most degradation methods require harsh, energy-intensive processes using intense pressure — in some cases over 22 megapascals — or extremely high temperatures — sometimes upwards of 1000⁰ Celsius — to break the chemical bonds (SN: 6/3/22).

Dichtel, of Northwestern University in Evanston, Ill., and his team experimented with two substances found in nearly every chemistry lab cabinet: sodium hydroxide, also known as lye, and a solvent called dimethyl sulfoxide, or DMSO. The team worked specifically with a group of forever chemicals called PFCAs, which contain carboxylic acid and constitute a large percentage of all PFAS. Some of these kinds of forever chemicals are found in water-resistant clothes.

When the team combined PFCAs with the lye and DMSO at 120⁰ C and with no extra pressure needed, the carboxylic acid fell off the chemical and became carbon dioxide in a process called decarboxylation. What happened next was unexpected, Dichtel said. Loss of the acid led to a process causing “the entire molecule to fall apart in a cascade of complex reactions.” This cascade involved steps that degraded the rest of the chemical into fluoride ions and smaller carbon-containing products, leaving behind virtually no harmful by-products. .

“It’s a neat method, it’s different from other ones that have been tried,” says Chris Sales, an environmental engineer at Drexel University in Philadelphia who was not involved in the study. “The biggest question is, how could this be adapted and scaled up?” Northwestern has filed a provisional patent on behalf of the researchers.

Understanding this mechanism is just one step in undoing forever chemicals, Dichtel’s team said. And more research is needed: There are other classes of PFAS that require their own solutions. This process wouldn’t work to tackle PFAS out in the environment, because it requires a concentrated amount of the chemicals. But it could one day be used in wastewater treatment plants, where the pollutants could be filtered out of the water, concentrated and then broken down.

Asteroid impacts might have created some of Mars’ sand

Sand on Earth is continuously being created by the slow erosion of rocks. But on Mars, violent asteroid impacts may play an important role in making new sand.

As much as a quarter of Martian sand is composed of spherical bits of glass forged in the intense heat of impacts, a new study shows. Since windblown sand sculpts the Martian landscape, this discovery reveals how asteroid impacts contribute to shaping Mars, even long after the collisions occur, Purdue University planetary scientist Briony Horgan and colleagues suggest. The team will present their results August 18 at the 85th Annual Meeting of the Meteoritical Society in Glasgow, Scotland.
Using data collected by spacecraft orbiting Mars, Horgan and collaborators looked at different wavelengths of visible and infrared light reflected from the planet’s surface to determine the minerals present in Martian sand. The team found signatures of glass all over the planet, particularly at higher latitudes.

One explanation for all that glass is volcanic eruptions, which are known to produce glass when magma mixes with water. But the most glass-rich swath of Mars — the planet’s northern plains — is conspicuously bereft of volcanoes, the researchers note. That rules out volcanic eruptions as the culprit in that location and instead suggests that far more cataclysmic events — asteroid impacts — might be involved.

That’s a plausible argument, says Steven Goderis, a geochemist at the Vrije Universiteit Brussel in Belgium who was not involved in the research. “Often Mars is seen as a volcanic planet. But there’s also a very strong impact component, and this is often overlooked.”

When an asteroid moving at several kilometers per second slams into a rocky planet like Mars, the energy of the event melts nearby rocks and launches them skywards. That molten shrapnel fragments and produces sand grain–sized pieces that are roughly spherical. Those bits of glass — called impact spherules — eventually rain back onto the planet (SN: 3/31/21).
Over the last 3 billion years, asteroid impacts could have plausibly blanketed the surface of Mars in a layer of impact spherules roughly half a meter thick, Horgan and her colleagues calculate. All that material added to the sand on Mars that formed through normal erosion. “Impacts helped supply sand to the surface continuously over time,” Horgan says.

Scientists might have the opportunity to analyze Martian impact spherules in the future. NASA’s Perseverance rover is currently storing samples of Martian sand and rocks for eventual return to Earth (SN: 9/10/21). That’s exciting, Horgan says. “The record of all this is in the sand.”

Spiraling footballs wobble at one of two specific frequencies

In American football, some passes are caught and some are dropped — but all wobble as they fly.

Spiraling pigskins tend to visibly wobble at either a slow or fast frequency, depending on how the ball is thrown, researchers report online June 23 in the ASME Open Journal of Engineering. That wobble, and to a lesser extent Earth’s rotation and the ball’s spin, cause passes to stray sideways — so don’t completely blame the quarterback this upcoming season.
“The fact that [a football] wobbles and the fact that it doesn’t go straight — those are the two big effects that you see in a pass,” says mechanical engineer John Dzielski of the Stevens Institute of Technology in Hoboken, N.J.

Using physics equations from ballistics studies and data from wind tunnel experiments with footballs, Dzielski and software engineer Mark Blackburn, also of the Stevens Institute, ran computer simulations of a spiraling football pass.

They found that a pigskin flying at around 27 meters per second with around 600 rotations per minute would visibly wobble either one or five times per second. Wobbling occurs as the ball’s spinning momentum interacts with a twisting force that acts to turn the football’s nose away from the direction of flight. The faster wobble dominates when extra energy is applied during throws by twisting of the wrist or lateral motion of the arm.

That wobbling generates lift that pushes the ball sideways, potentially changing the landing point by several meters, the team reports. Earth’s rotation also could cause a pass to drift several centimeters. And the Magnus effect — whereby a spinning projectile becomes sandwiched by low- and high-pressure zones of air, bending its trajectory — had double that impact.

Dzielski and Blackburn are now interested in refining their simulations by developing an instrument to gather data from footballs in flight.

Two new books show how sexism still pervades astronomy

Becoming an astronomer might seem straightforward. An awe of the night sky sparks a child to someday study astronomy in school, eventually leading to a graduate degree and a job in the field. But as two new books make clear, few women find the road so simple.

In A Portrait of the Scientist as a Young Woman, Lindy Elkins-Tanton, a geologist turned planetary scientist, recounts her struggles with depression and anxiety as a child and with the sexism she faced early in her career. In one example, she and colleagues (all men but one) were collecting rock samples in Siberia, searching for evidence of a connection between volcanic eruptions and past extinction events. Taking her time to set her chisel at just the right spot to break the rock, Elkins-Tanton could “practically smell the silent impatience from the men nearby,” she writes. “Yes, they could have done it faster, and with fewer blows. But why should that be the important metric? Why is it not more important to let each person do the tasks they want and need to do, at their own pace?”

Her male colleagues’ implicit and explicit bias against women in science, she writes, fanned her own self-doubt. To demand the same respect as male scientists, she learned she had to insist, gently, to carry her own baggage and take her own samples, her way and on her time. The lessons she learned in Siberia and in the lab, she writes, helped her develop a compassionate and just leadership style as the director of Arizona State University’s School of Earth and Space Exploration and as the head of NASA’s upcoming Psyche mission. That mission will send a spacecraft to probe a metal-rich asteroid to better understand Earth’s iron-rich core.

Every scientist’s experience is unique, but elements of Elkins-Tanton’s story, particularly the sexism in science, find voice throughout The Sky Is for Everyone: Women Astronomers in Their Own Words. Edited by astronomer Virginia Trimble and author David Weintraub, this anthology of 37 short autobiographies covers more than six decades of astronomy and shows the varied paths of female astronomers and the roadblocks that can slow or sideline their success.
Astrophysicist France Córdova, for instance, opens her story with an evocative description of the time she spent in the summer of 1968 in a pueblo near Oaxaca City, Mexico, working on a cultural anthropology project. She had planned to study anthropology in graduate school, but after watching a TV show on dead stars, she realized she “had a deeper wanderlust inside,” she writes, “to connect with something wider, deeper than I could imagine — the stars and the Universe that held them.”

As a child, Córdova hadn’t known anyone who believed women could be scientists. Her parents thought finding a husband should be her college goal. Instead, she chose to pursue a graduate degree in astrophysics. She launched a career in X-ray astronomy and then pivoted again to policy and leadership, assuming the role of NASA’s chief scientist and later head of the National Science Foundation — positions where, she writes, she could advocate more effectively for women in science.

Dara Norman, in contrast, never questioned that she’d become an astronomer; by age 10 she was certain. She earned a Ph.D. in 1999 after studying bias in the measurements of distant galaxies that can distort our understanding of the universe. To her, the similarities between biases in scientific data and biases in the culture of science were blatant. “I am amazed that as scientists we understand the idea of bias in our data and methods…. We work tirelessly to identify such biases … and eliminate that bias,” she writes. “However, when confronted with bias in our profession … many of us continue to deny the existence of the issue.”
Norman realized the traditional path of an astronomer wasn’t for her. The joy of doing research was overshadowed by the negative experiences she endured “as a Black American woman just trying to be a scientist.” Like Córdova, she now works to improve the culture of science, at the National Optical-Infrared Astronomy Research Lab in Tucson.

That culture is changing, slowly. Before 1990, fewer than 40 women held full-time positions in astronomy or astrophysics at North American universities. Now, the number is high enough that it’s not as easy to track how many women successfully pursue a career in the field, Trimble and Weintraub note. Although those numbers point to progress, both books remind readers that blatant and subtle acts of sexism are still present and that careers in science can still be precarious for women. And yet women persist, perhaps, as Elkins-Tanton writes, driven by the “realization that we are only a tiny part of a vast unexplored universe.” If true, it’s a pillar of resilience to aspire to.

Protons contain intrinsic charm quarks, a new study suggests

Protons may be intrinsically charming.

The subatomic particles are a mash-up of three lighter particles called quarks: two of the type known as up quarks and one down quark. But physicists have speculated for decades that protons may also host more massive quarks, called “intrinsic” charm quarks. A new analysis supports that idea, physicists report in the Aug. 18 Nature.

Charm quarks are much heavier than up or down quarks. So heavy that, mind-bendingly, “you can have a component of the proton which is heavier than the proton itself,” says theoretical physicist Juan Rojo of Vrije Universiteit Amsterdam.
Rojo and colleagues combined a variety of experimental results and theoretical calculations in hopes of unveiling the proton’s hypothetical charm. Measuring this feature is key to fully understanding one of the most important particles in the universe, Rojo says.

Physicists know that the more deeply you probe a proton, the more complicated it appears. When observed at very high energies, as in collisions at particle accelerators like the Large Hadron Collider, or LHC, near Geneva, protons contain a motley crew of transient quarks and their antimatter counterparts, antiquarks (SN: 4/18/17). Such “extrinsic” quarks are created when gluons, particles that help “glue” the quarks together inside protons, split into quark-antiquark pairs.

Extrinsic quarks aren’t fundamental to the identity of the proton. They’re simply a result of how gluons behave at high energies. But charm quarks might exist inside protons even at low energies, in a more persistent, deep-seated form.

In quantum physics, particles don’t take on a definite state until they’re measured — they are instead described by probabilities. If protons contain intrinsic charm, there’d be a small probability to find within a proton not only two up quarks and a down quark, but also a charm quark and antiquark. Since protons aren’t well-defined collections of individual particles, a proton’s mass isn’t a simple sum of its parts (SN: 11/26/18). The small probability means that the full mass of the charm quark and antiquark isn’t added to the proton’s heft, explaining how the proton may contain particles heavier than itself.

Using thousands of measurements from experiments at the LHC and other particle accelerators, combined with theoretical calculations, the team found evidence for intrinsic charm in the proton at a statistical level called 3 sigma. The intrinsic charm quarks carry about 0.6 percent of a proton’s momentum, the researchers report.

But 5 sigma is typically required for a conclusive result. “The data and analysis are not yet sufficient … to get from ‘evidence for’ to ‘discovery of’ intrinsic charm,” says Ramona Vogt, a theoretical physicist at Lawrence Livermore National Laboratory in California who wrote a perspective piece on the study for Nature.

What’s more, defining what is meant by “intrinsic charm” isn’t straightforward, muddling the comparison of the new finding with earlier results from different groups. “Previous studies have found different limits on intrinsic charm partly because they have used different definitions and schemes,” says theoretical physicist Wally Melnitchouk of Jefferson Lab in Newport News, Va.

Notably, the new analysis incorporates results from the LHCb collaboration, which reported measurements potentially consistent with intrinsic charm in the proton in the Feb. 25 Physical Review Letters. Including that data in the analysis is “what’s really new,” says theoretical physicist C.-P. Yuan of Michigan State University in East Lansing. But Yuan has reservations about the type of calculation used to interpret the data. “It’s not done at what we today call the state-of-art analysis.”

Scientists need to pin down the proton’s intrinsic charm content to better understand results at the LHC and other facilities that smash protons together and observe what comes out. Researchers have to be able to gauge the ins and outs of the objects they’re colliding.

Data from future accelerators such as the planned Electron-Ion Collider could help, says theoretical physicist Tim Hobbs of Fermilab in Batavia, Ill. For now, the proton remains mysterious. “The problem is still with us; it remains very challenging.”

The first known monkeypox infection in a pet dog hints at spillover risk

The first recorded case of person passing monkeypox to a dog could be harbinger of other animals catching the sometimes disfiguring and deadly virus. If that happens, monkeypox could establish animal reservoirs outside of Africa for the first time.

Two men in France appear to have spread monkeypox to their Italian greyhound, researchers report August 10 in the Lancet. The men reported letting the dog sleep in bed with them.

Monkeypox can spread through skin-to-skin contact, such as the intimate contact that happens during sex. Even more casual contact such as dancing in close confines can spread the virus, an Aug. 15 study in Emerging Infectious Diseases suggests. So can contact with objects an infected person has used, including bedding and clothing. Infectious monkeypox viruses linger more often on such soft, porous materials than on hard surfaces, researchers report August 11 in Emerging Infectious Diseases. Some 60 percent of soft goods and 5 percent of hard surfaces tested still carried viable virus for at least 15 days, the team found.
In the case of the dog, the animal developed pustules about 12 days after its owners reported symptoms. Viral DNA from one of the men matched that from the dog, suggesting that the human had given monkeypox to an animal.

Usually monkeypox goes the other way, from animals — especially rodents in some parts of Africa — to people in “spillover,” or zoonotic, infections. “This is a classic case of reverse zoonoses,” or spillback, in which a viral disease hops from humans back into animals, says Grant McFadden, a pox virologist at Arizona State University in Tempe.

Such spillback events are fairly common with other viruses; people are known to have given COVID-19 to dogs, cats and zoo animals, for instance (SN: 3/5/20; SN: 3/31/20). Some pox viruses, including cowpox, can infect a wide range of species, while others like smallpox and a rabbit pox virus called myxoma virus can infect only one or a few species.

How widely monkeypox can spread among nonrodent animal species isn’t known. Researchers have documented that the virus can infect 51 species, including apes and monkeys, and other animals including anteaters, porcupines and opossums.

Right now, monkeypox is endemic in some parts of Africa. But some scientists worry that the global outbreak, which has infected more than 36,000 people so far, creates more chances for the virus to jump from humans to animals. If that happens, the virus could become established in animal populations around the world, setting up new reservoirs that could cause repeated infections in humans and animals.

Preliminary research suggests that monkeypox may be able to infect two to four times more species than previously thought, researchers from the University of Liverpool in England report August 15 in a preprint on bioRxiv.org. The team used machine learning trained to consider the genetic makeup of the virus, the number of species of animals in a genus known to be infected by pox viruses, diet composition of potential hosts, where the animals live and other factors that could contribute to a species becoming a new host for monkeypox, says virologist Marcus Blagrove.

About 80 percent of the potential new hosts for monkeypox are rodents or primates, the researchers predict. But domestic animals like dogs and cats were also predicted to be susceptible to infection. The researchers didn’t know about the case of the dog in France when they made the prediction, Blagrove says, so the report of the canine infection “was a quite nice validation that the method works.”

Red foxes and brown rats are two potential monkeypox hosts that the researchers say are particularly worrisome. Foxes (Vulpes vulpes) scavenge from garbage, which could bring them in contact with monkeypox-contaminated items. Brown rats (Rattus norvegicus) are already known hosts for cowpox. They are common in sewers in Europe and could get infected through feces containing monkeypox. Though the study emphasized the risk in Europe, where more than half the monkeypox cases in people in the current outbreak have been reported, the findings could be applicable more widely. Brown rats are found on every continent except Antarctica. Red foxes roam much of the Northern Hemisphere, including North and Central America, Europe, Northern Africa and parts of Asia.
The study also names three European rodents that could become reservoir species. The herb field mouse (Apodemus uralensis), yellow-necked field mouse (Apodemus flavicollis) and Alpine marmot (Marmota marmota) all have pockets of big populations that could be ideal for passing the virus around.

“These are examples of wild animals that might be a reservoir. We can’t say for certain, but they might be susceptible,” Blagrove says. Those species along with foxes and brown rats should be regularly surveyed for monkeypox to prevent new reservoirs from being established, he says.

But just because an animal can get infected with monkeypox doesn’t mean they can pass it on. “There is a difference between accidental hosts and a reservoir,” says Giliane de Souza Trindade, a pox virologist at the Federal University of Minas Gerais in Brazil. Accidental hosts are often dead ends for the virus. A true reservoir species must be able to pass the virus from animal to animal, and then sometimes to humans they encounter.
If dogs can easily get monkeypox, they may be able to pass it to humans, other dogs or other animals through feces or saliva, Trindade says. Domestic animals that live with people who get monkeypox should be isolated from sick people and from other animals outside the home, she says.

Trindade and her colleagues are preparing to study pets of people who have monkeypox to see whether the virus passes easily to cats and dogs, she says. But she is more worried about live animal markets. “Animals are in cages very close together and people are passing by all the time.” Such settings are ripe for transmitting viruses between species. The COVID-19 pandemic probably got its start at a live animal market in Wuhan, China, researchers reported July 26 in Science.

McFadden stresses that the dog’s case is still an isolated report. “We don’t know is this a rare thing or have we just not paid attention to it?” For now, he says, efforts should be focused on containing the outbreak among humans. While people with monkeypox should take care not to pass the virus to their pets, this case shouldn’t cause undue worry, he says. “We’re not at the panic button stage just yet.”

Scientists are also still learning how monkeypox spreads among people. Some people may have monkeypox, but not develop symptoms, researchers report August 16 in the Annals of Internal Medicine. It’s not known whether asymptomatic people can transmit the virus to others, but if they can, vaccinating close contacts of symptomatic people may not be enough to contain the outbreak, the researchers warn.