People may think they act independently. But we catch social behaviors faster than colds. Whether or not we vote, try a new food or wear clear plastic pants will have something to do with whether other people are doing it. Unfortunately, it’s often hard to prove exactly how contagious a particular behavior is, or which behaviors will actually spread.
A new study shows that among runners using a fitness social network, logging miles is infectious — if the runner you’re comparing yourself to is slightly worse than you. The work shows a clever new way to determine if a behavior is socially contagious. But the results also confirm something about runners: We might be a little too competitive.
Glance at any group of kids with fidget spinners or teens wearing the same brand of shoes, and it’s easy to buy into the idea of social contagions. But it’s actually not so simple to distinguish between that kind of peer influence and other outside factors. says Johan Ugander, an applied mathematician at Stanford University. It’s easy for marketers to say they want something to go viral. But it’s a lot harder to be confident that the thing that’s spreading is really a social contagion and not a common factor like location or a group of people with common interests.
For one thing, birds of a feather really do flock together. People become friends because they have things in common. You might share an important article to Facebook, and find a friend has shared the same article 20 minutes later. But is that because you influenced your friend? Or because you have the same interests and read the same kind of articles, and you just happened to see it 20 minutes before they did?
Similarly, people tend to have friends who are near them geographically. So if two neighbors gain weight, Ugander notes, it could be “because the McDonald’s opened down the street, not because I gained weight then you gained weight.”
To get around this problem of homophily, Sinan Aral, a computational social scientist at MIT, decided to look at a single behavior — running. “Running is one of the most pervasive forms of this type of exercise,” he says. “I thought it would be most generalizable.”
Runners also like to log their miles and share them with their peers. Aral was able to get data from one of several social media platforms designed for jogging buffs. Aral can’t disclose the exact app or program he used in the study (and received some funding from), but there are a few social apps out there that fit the bill, including MapMyRun, RunKeeper and Strava. Aral ended up with a vast, anonymized dataset of more than 1.1 million runners who logged more than 359 million kilometers (223 million miles) over five years. To figure out if running is contagious, there would have to be a way to make some people run and other people stay home. “The ideal study to show [a causal effect] would be to go around with a cattle prod, prodding some people to exercise more,” but leaving others alone, Aral says. “But that’s not an experiment you can run.” (Obviously.)
So Aral and colleagues used the weather as their cattle prod. Good weather beckons a runner outdoors. Rain, snow, sleet or hail will keep a runner off the street. The researchers combed through data, noting what the weather was like on a given day and how far a runner went. They then compared that runner’s logs to their friends in other cities — places far enough away that the weather would be different. With the weather serving as the prod for some to put on their running shoes or keep others at home, the scientists got a good idea of who socially infected who with the running bug.
They found that for every additional kilometer run by someone’s distant friends, the runner would add another 0.3 km (0.18 mi). Timewise, a friend spending an additional 10 minutes running will inspire an extra three minutes in someone else, Aral and his group reported April 18 in Nature Communications.
But social contagion didn’t affect everyone the same way. The runners most influenced were those who compared themselves to runners slightly worse than they were. “In the loose analogy of a race, I’m more motivated by the guy behind me than I am motivated by the person ahead of me,” Aral says.
The study also showed some gender effects. Men were most influenced by other men, but were also ready to outrace the women. In contrast, women did not tend to be influenced by men. “There have been experimental studies showing men are more competitive with one another, while women are more self-directed and motivated by internal factors,” Aral says. But that doesn’t mean that women aren’t competitive. Women were just influenced by other women.
“It’s usually very difficult to identify causal effects from correlational data, in the absence of a randomized controlled trial,” says Edoardo Airoldi, a statistician at Harvard University. The data in this study may not translate to other behaviors — even to other forms of exercise. But that isn’t the point. The beauty, Airoldi says, is in the methods. “People should know you can use the weather as an instrument to uncover patterns of human behavior that are otherwise hard to elicit,” he says.
Ugander is also a fan of the new study, but he notes that this doesn’t mean all social behaviors, or even all sports, will prove similarly contagious, especially with regard to the gender differences. “It’s not clear that that will generalize to yoga or some other sport with other gender norms,” he says.
We don’t really know what exactly drives social contagion. One theory — the complex contagion theory — posits that costly behaviors (like going for an exhausting run) require a lot of signals from a lot of people. In other words, the more people in your network are running, the more likely you are to run.
Another theory developed by Ugander’s group posits that it’s not quantity that matters, but variety, a theory called structural diversity. Your family all going running is one thing. A family member, a friend and coworker is another. “If you’re getting it from two people from different parts of your life, say sibling and coworkers, it carries more weight,” Ugander says. “But two coworkers probably got it from each other.”
A third theory suggests that embeddedness — the number of mutual connections — matters most. After all, seeing all your friends virtuously running and knowing that they are also seeing each other live the wholesome life is a lot of peer pressure.
The data from Aral’s group suggests that for running, embeddedness and structural diversity may prove the most catching. “This doesn’t mean the complex theory is wrong,” Aral notes. “We just didn’t see it for running.”
Aral himself is a runner, and admits he’s not immune to the social contagion he found. “When I have friends who are close to me in fitness in terms of their level of activity, I may be influenced,” he says. “I also feel like I’d be more influenced by someone who was slightly less of a runner than I am. If they were running more, I would think, ‘Wow, even so-and-so is out there, I need to get out there.’” This social behavior might be catching, but the vulnerable population already has a raging competition infection.
A weird new particle imitator flouts the established rules of particle physics. The discovery could help scientists simulate how particles behaved just after the Big Bang or lead to the development of new devices with unusual electromagnetic properties.
The curious new phenomenon involves a particle-like entity called a quasiparticle, formed from a jostling mosh pit of electrons that collectively act like a single particle in a solid. Found in a compound of lanthanum, aluminum and germanium, the new quasiparticle is a bit of a renegade, physicist M. Zahid Hasan of Princeton University and colleagues report June 2 in Science Advances. Known as a type-II Weyl fermion, the quasiparticle breaks a rule called Lorentz symmetry, which states that the laws of physics are the same no matter the observer’s perspective, whether moving or stationary. Lorentz symmetry is the foundation of Einstein’s special theory of relativity, which details the physics of observers zipping along near the speed of light. For a real particle, violating Lorentz symmetry would be an unallowable faux pas, but for quasiparticles, the rules are looser, so type-II Weyl fermions can behave in a way a normal particle wouldn’t.
Fermions are a class of elementary particle that includes quarks, which make up protons and neutrons, and electrons. There are three different types of fermions: Dirac, Majorana and Weyl. Dirac fermions are the garden-variety type and include electrons and quarks. Majorana fermions are their own antiparticles. Neutrinos, notoriously lightweight and elusive particles, could be either Majorana or Dirac fermions; scientists aren’t yet sure which.
Weyl fermions are a massless variety of fermion. No examples have been found in particle physics. But the quasiparticle version of Weyl fermions burst onto the scene in 2015, when scientists first discovered them in a compound made of tantalum and arsenic (SN: 8/22/15, p. 11). Soon, scientists realized that their Lorentz-violating relatives, type-II Weyl fermions, might likewise pop up in solids.
In the new study, Hasan and colleagues measured the relationship between the energy and momentum of the quasiparticles, showing that they were consistent with type-II Weyl fermions. Although previous experiments have shown hints of the unusual quasiparticles, those measurements were skin-deep, assessing particles only on the surface of the material, Hasan says. With surface measurements alone, it’s hard to confirm the type-II Weyl fermions are there, says physicist Alexey Soluyanov of ETH Zurich. But Hasan and colleagues peered inside the material. “Experimentally, this work really is a nice example,” Soluyanov says.
In solids, Weyl fermions lead to unusual behavior. Put a normal material in a magnetic field, and resistance to the flow of electricity grows, but in a solid with Weyl fermions, a magnetic field makes current flow more easily. Type-II Weyl fermions are even stranger, due to their Lorentz-violating properties. In a material with these quasiparticles, a magnetic field in one direction can increase conductivity, while in another direction it can decrease conductivity. “This type of thing can have interesting applications,” says Hasan. “In a single material, just by changing the direction of the field, now we can get different behaviors,” flipping between insulating and conducting, for example. The new material could also provide insight for particle physicists. “Of course, people have wondered what happens when you break Lorentz invariance,” says physicist Adolfo Grushin of Institut Néel in Grenoble, France. Type-II Weyl fermions could help scientists better understand theories that violate the rule. “It’s a good test-bed,” says Grushin.
For example, Hasan says, “we can test theoretical ideas in the early universe,” simulating how particles may have behaved just after the Big Bang, when Lorentz symmetry may not have been obeyed.
PORTLAND, ORE. — A great flower shape for a moth trying to get a drink in the dark turns out to be awful from the plant’s point of view.
Offering hawk moths (Manduca sexta) a range of 3-D printed flowers with different curvatures shows that a moderately curved trumpet shape lets moths sip most efficiently, Foen Peng reported June 24 at the Evolution 2017 meeting. That’s a win for a nocturnal flying insect searching for nectar. Yet drinking ease wasn’t best for the plant. During swift sips, the moths did less inadvertent bumping against the artificial flowers’ simulated sex organs than moths struggling to sip from an inconvenient shape. Less contact with real flower parts would mean less delivery and pickup of pollen.
Peng, of the University of Washington in Seattle, offered the moths three other shapes besides the gently curved trumpet. The best for the plant was a flat-topped “flower” with a right angle drop to a nectar well in the center. Previous work suggested that lack of curves made it very difficult for hawk moths hovering above a flower and extending their tonguelike proboscises to tap and probe the way to nectar in dim light.
Pollination at first glance may look like an easy mutualism evolving with the best interests of both plant and pollinator. But these experiments reveal a hidden, underlying conflict, Peng said.
Out-of-whack microbes in the vagina can raise HIV risk — and now there’s evidence that the makeup of the penis microbiome matters, too. The greater the number of anaerobic bacteria tucked under the foreskin, the more likely an uncircumcised man is to become infected with the virus, researchers report July 25 in mBio.
“This mirrors what’s been seen in women, but it’s the first study of its kind in men,” says Deborah Anderson, a microbiologist and gynecologist at Boston University School of Medicine. The data come from heterosexual Ugandan men followed for two years as part of a larger study on circumcision. Researchers swabbed the men’s penises to collect bacteria samples at the beginning of the two-year study. Then they compared the penile bacterial composition of the 46 uncircumcised men who became infected with HIV over the course of the study with that of 136 uncircumcised men who didn’t.
The total amount of penile bacteria didn’t differ, but men with higher levels of anaerobic bacteria were more likely to have contracted HIV, researchers found. Having 10 times more Prevotella, Dialister, Finegoldia and Peptoniphilus bacteria raised the risk of contracting HIV by 54 to 63 percent after controlling for other factors that might affect risk, such as condom use habits and number of sexual partners.
The results might help explain why circumcision cuts the risk of HIV, says Thomas Hope, a cell biologist at Northwestern University Feinberg School of Medicine in Chicago: Removing the flap of foreskin takes away a moist hideout for bacteria that thrive in oxygen-starved environments. But, Hope cautions, the study only draws an association between the microbiome and HIV — not necessarily a cause and effect.
It’s not clear how certain bacteria might raise HIV risk, but the new study revealed one possible clue: Men with more anaerobic penis bacteria also had higher levels of inflammatory cytokine proteins, which call immune cells to the scene.
“Specific bacteria might cause inflammatory response that would cause the immune cells to congregate in the penis, where they’re more likely to be exposed to the virus,” says study coauthor Cindy Liu, a pathologist at George Washington University in Washington, D.C. HIV targets particular immune cells, so recruiting an immune response to the penis might have an unintended consequence — a free ferry ride for the virus into the bloodstream. Liu and colleagues hope to test that explanation more thoroughly by looking at tissue samples from circumcised foreskins, and seeing whether there’s a relationship between the penis microbiome and the kinds of immune cells found in the foreskin.
Some of these same bacteria are also linked to increased HIV risk in women, and the microbes can be swapped between partners during sex. While practicing safe sex is still the best HIV-prevention strategy, topical creams that adjust the bacterial balance on the penis might someday help lower the risk of infection, Liu says.
For flowers, too much light at night could lead to a pollination hangover by day.
Far from any urban street, researchers erected street lights in remote Swiss meadows to mimic the effects of artificial light pollution. In fields lit during the night, flowers had 62 percent fewer nocturnal visitors than flowers in dark meadows, researchers report August 2 in Nature.
For one of the most common flowers, daytime pollination didn’t make up for nightly losses, says ecologist Eva Knop of the University of Bern in Switzerland. In a detailed accounting of the pollination life of cabbage thistles (Cirsium oleraceum), Knop and colleagues found that night-lit plants produced 13 percent fewer seeds overall than counterparts in naturally dark places. Night lights could affect the entire network of plants and pollinators, the team suggests. In the test fields, nighttime pollination wasn’t just the business of a few kinds of specialized moth-loving plants. Flowers that fed a wide range of nighttime visitors also attracted a broad buzzing circus of different kinds of daytime pollinators. If the daytime insects don’t make up for nocturnal losses, a flower’s population might dwindle. And a lot of insects, both day and night, might then feel the loss of nectar and foliage, Knop says.
More than 80 percent of flower species get some help from animals in making seeds, and none evolved with light after sundown. “I hope people start to realize that it’s really something that changes the whole ecosystem,” Knop says. The new study is the first to show how artificial light affects plants’ ability to make seeds, she says. The test is also unusual because it considers all kinds of insect pollinators instead of focusing on, say, only night-flying moths. This big-picture view was so not easy to achieve. Finding possible dead-dark sites in highly developed Europe to set up LED lamps was impossible, so researchers worked in 14 dark-as-possible, remote meadows in land rising toward the Alps. But that created a problem. “If you don’t have light, you don’t have power,” Knop points out. To avoid generator growls and smells confounding their results, researchers painstakingly scouted sites where possible near water-powered energy sources and overall used “really long cables.” For the sites with natural night, researchers measured pollination by patrolling set paths and catching any insect wriggling on a flower — in complete darkness, of course. The team used night-vision goggles but still didn’t have a perfect view, she says. It’s “not that easy to catch insects without three-dimensional vision.”
Besides paying special attention to the commonly visited cabbage thistle, researchers pieced together the whole network of which pollinator species visited which plant species day or night. Analysis of this Matterhorn of data suggested that changes in the night crew could affect daytime meadows.
The idea that night light could have broad knock-on effects on daytime pollinators is still speculation at this point, says ecologist Darren Evans of Newcastle University in England, who also studies light pollution and pollination. But the risk of such spillover warrants more attention.
A boy who lived in what’s now South Africa nearly 2,000 years ago has lent a helping genome to science. Using the long-gone youngster’s genetic instruction book, scientists have estimated that humans emerged as a distinct population earlier than typically thought, between 350,000 and 260,000 years ago.
The trick was retrieving a complete version of the ancient boy’s DNA from his skeleton to compare with DNA from people today and from Stone Age Neandertals and Denisovans. Previously documented migrations of West African farmers to East Africa around 2,000 years ago, and then to southern Africa around 1,500 years ago, reshaped Africans’ genetics — and obscured ancient ancestry patterns — more than has been known, the researchers report online September 28 in Science. The ancient boy’s DNA was not affected by those migrations. As a result, it provides the best benchmark so far for gauging when Homo sapiens originated in Africa, evolutionary geneticist Carina Schlebusch of Uppsala University in Sweden and her colleagues conclude.
In line with the new genetically derived age estimate for human origins, another team has proposed that approximately 300,000-year-old fossils found in northwestern Africa belonged to H. sapiens (SN: 7/8/17, p. 6). Some researchers suspect a skull from South Africa’s Florisbad site, dated to around 260,000 years ago, qualifies as H. sapiens. But investigators often place our species’ origins close to 200,000 years ago (SN: 2/26/05, p. 141). There is broad consensus that several fossils from that time represent H. sapiens.
Debate over the timing of human origins will continue despite the new evidence from the child, whose remains came from previous shoreline excavations near the town of Ballito Bay, says Uppsala University evolutionary geneticist and study coauthor Mattias Jakobsson. “We don’t know if early Homo sapiens fossils or the Florisbad individual were genetically related to the Ballito Bay boy,” he says.
Thus, the precise timing of humankind’s emergence, and exact patterns of divergence among later human populations, remain unclear. Researchers have yet to retrieve DNA from fossils dating between 200,000 and 300,000 years old that either securely or possibly belong to H. sapiens. However early human evolution played out, later mixing and mingling of populations had a big genetic impact. DNA evidence from more recent fossils, including those studied by Schlebusch’s group, increasingly suggests that Stone Age human groups migrated from one part of Africa to another and mated with each other along the way (SN: 10/20/12, p. 9), says Harvard Medical School evolutionary geneticist Pontus Skoglund. In the Sept. 21 Cell, he and his colleagues report that DNA from 16 Africans, whose remains date to between 8,100 and 400 years ago, reveals a shared ancestry among hunter-gatherers from East Africa to South Africa that existed before West African farmers first arrived 2,000 years ago.
That ancient set of common genes still comprises a big, varying chunk of the DNA of present-day Khoisan people in southern Africa, Skoglund’s group found. Earlier studies found that the Khoisan — consisting of related San hunter-gatherer and Khoikhoi herding groups — display more genetic diversity than any other human population.
Schlebusch’s team estimates that a genetic split between the Khoisan and other Africans occurred roughly 260,000 years ago, shortly after humankind’s origins and around the time of the Florisbad individual. Khoisan people then diverged into two genetically distinct populations around 200,000 years ago, the researchers calculate.
Ancient DNA in Schlebusch’s study came from seven individuals unearthed at six South African sites. Three hunter-gatherers, including the Ballito Bay boy, lived about 2,000 years ago. Four farmers lived between 500 and 300 years ago.
Comparisons to DNA from modern populations in Africa and elsewhere indicated that between 9 percent and 30 percent of Khoisan DNA today comes from an East African population that had already interbred with Eurasian people. Those East Africans were likely the much-traveled farmers who started out in West Africa and reached southern Africa around 1,500 years ago, the researchers propose.
MINNEAPOLIS — Birds don’t need to be drenched in crude oil to be harmed by spills and leaks.
Ingesting even small amounts of oil can interfere with the animals’ normal behavior, researchers reported November 15 at the annual meeting of the Society of Environmental Toxicology and Chemistry North America. Birds can take in these smaller doses by preening slightly greasy feathers or eating contaminated food, for example.
Big oil spills, such as the 2010 Deepwater Horizon disaster, leave a trail of dead and visibly oily birds (SN: 4/18/15, p. 22). But incidents like last week’s 5,000-barrel spill from the Keystone pipeline — and smaller spills that don’t make national headlines — can also impact wildlife, even if they don’t spur dramatic photos. To test how oil snacks might affect birds, researchers fed zebra finches small amounts of crude oil or peanut oil for two weeks, then analyzed the birds’ blood and behavior. Birds fed the crude oil were less active and spent less time preening their feathers than birds fed peanut oil, said study coauthor Christopher Goodchild, an ecotoxicologist at Oklahoma State University in Stillwater.
Oil-soaked birds will often preen excessively to try to remove the oil, sometimes at the expense of other important activities such as feeding. But in this case, the birds didn’t have any crude oil on their feathers, so the decrease in preening is probably a sign they’re not feeling well, the researchers say.
Exactly how the oil affects the birds’ activity levels isn’t clear. Researchers suspected that oil might deprive birds of oxygen by affecting hemoglobin, which carries oxygen in the blood. Blood tests didn’t turn up any evidence of damaged hemoglobin proteins but did find some evidence that oil-sipping birds might be anemic, Goodchild said. At the higher of two crude oil doses, birds’ blood contained less hemoglobin per red blood cell, a sign of anemia. The findings, while preliminary, add to a growing pile of evidence that estimates of the number of animals impacted by oil spills might be too low. For instance, even a light sheen of oil on sandpipers’ wings makes it harder to fly, costing birds more energy, a different group of researchers reported earlier this year. That could affect everything from birds’ daily movements to long-distance migration.
PHILADELPHIA — If you want to beat them, join them. Some breast cancer tumors may follow that strategy to spread through the body.
Breast cancer tumors can fuse with blood vessel cells, allowing clumps of cancer cells to break away from the main tumor and ride the bloodstream to other locations in the body, suggests preliminary research. Cell biologist Vanesa Silvestri of Johns Hopkins University School of Medicine presented the early work December 4 at the American Society for Cell Biology/European Molecular Biology Organization meeting.
Previous research has shown that cancer cells traveling in clusters have a better chance of spreading than loners do (SN: 1/10/15, p. 9). But how clusters of cells get into the bloodstream in the first place has been a mystery, in part because scientists couldn’t easily see inside tumors to find out.
So Silvestri and colleagues devised a see-through synthetic version of a blood vessel. The vessel ran through a transparent gel studded with tiny breast cancer tumors. A camera attached to a microscope allowed the researchers to record the tumors invading the artificial blood vessel. Sometimes the tumors pinched the blood vessel, eventually sealing it off. But in at least one case, a small tumor merged with the cells lining the faux blood vessel. Then tiny clumps of cancer cells broke away from the tumor and floated away in the fluid flowing through the capillary. More work is needed to confirm that the same process happens in the body, Silvestri said.
T he Okarian rover was in trouble. The yellow Humvee was making slow progress across a frigid, otherworldly landscape when planetary scientist Pascal Lee felt the rover tilt backward. Out the windshield, Lee, director of NASA’s Haughton Mars Project, saw only sky. The rear treads had broken through a crack in the sea ice and were sinking into the cold water.
True, there are signs of water on Mars, but not that much. Lee and his crew were driving the Okarian (named for the yellow Martians in Edgar Rice Burroughs’ novel The Warlord of Mars) across the Canadian Arctic to a research station in Haughton Crater that served in this dress rehearsal as a future Mars post. On a 496-kilometer road trip along the Northwest Passage, crew members pretended they were explorers on a long haul across the Red Planet to test what to expect if and when humans go to Mars.
What they learned in that April 2009 ride may become relevant sooner rather than later. NASA has declared its intention to send humans to Mars in the 2030s (SN Online: 5/24/16). The private sector plans to get there even earlier: In September, Elon Musk announced his aim to launch the first crewed SpaceX mission to Mars as soon as 2024.
“That’s not a typo,” Musk said in Australia at an International Astronautical Congress meeting. “Although it is aspirational.”
Musk’s six-year timeline has some astrobiologists in a panic. If humans arrive too soon, these researchers fear, any chance of finding evidence of life — past or present — on Mars may be ruined.
“It’s really urgent,” says astrobiologist Alberto Fairén of the Center for Astrobiology in Madrid and Cornell University. Humans take whole communities of microorganisms with them everywhere, spreading those bugs indiscriminately.
Planetary geologist Matthew Golombek of NASA’s Jet Propulsion Laboratory in Pasadena, Calif., agrees, adding, “If you want to know if life exists there now, you kind of have to approach that question before you send people.”
A long-simmering debate over how rigorously to protect other planets from Earth life, and how best to protect life on Earth from other planets, is coming to a boil. The prospect of humans arriving on Mars has triggered a flurry of meetings and a spike in research into what “planetary protection” really means.
One of the big questions is whether Mars has regions that might be suitable for life and so deserve special protection. Another is how big a threat Earth microbes might be to potential Martian life (recent studies hint less of a threat than expected). Still, the specter of human biomes mucking up the Red Planet before a life-hunting mission can even launch has raised bitter divisions within the Mars research community. Mind the gaps Before any robotic Mars mission launches, the spacecraft are scrubbed, scoured and sometimes scorched to remove Earth microbes. That’s so if scientists discover a sign of life on Mars, they’ll know the life did not just hitchhike from Cape Canaveral. The effort is also intended to prevent the introduction of harmful Earth life that could kill off any Martians, similar to how invasive species edge native organisms out of Earth’s habitats.
“If we send Earth organisms to a place where they can grow and thrive, then we might come back and find nothing but Earth organisms, even though there were Mars organisms there before,” says astrobiologist John Rummel of the SETI Institute in Mountain View, Calif. “That’s bad for science; it’s bad for the Martians. We’d be real sad about that.”
To avoid that scenario, spacefaring organizations have historically agreed to keep spacecraft clean. Governments and private companies alike abide by Article IX of the 1967 Outer Space Treaty, which calls for planetary exploration to avoid contaminating both the visited environment and Earth. In the simplest terms: Don’t litter, and wipe your feet before coming back into the house.
But this guiding principle doesn’t tell engineers how to avoid contamination. So the international Committee on Space Research (called COSPAR) has debated and refined the details of a planetary protection policy that meets the treaty’s requirement ever since. The most recent version dates from 2015 and has a page of guidelines for human missions.
In the last few years, the international space community has started to add a quantitative component to the rules for humans — specifying how thoroughly to clean spacecraft before launch, for instance, or how many microbes are allowed to escape from human quarters.
“It was clear to everybody that we need more refined technical requirements, not just guidelines,” says Gerhard Kminek, planetary protection officer for the European Space Agency and chair of COSPAR’s planetary protection panel, which sets the standards. And right now, he says, “we don’t know enough to do a good job.”
In March 2015, more than 100 astronomers, biologists and engineers met at NASA’s Ames Research Center in Moffett Field, Calif., and listed 25 “knowledge gaps” that need more research before quantitative rules can be written.
The gaps cover three categories: monitoring astronauts’ microbes, minimizing contamination and understanding how matter naturally travels around Mars. Rather than prevent contamination — probably impossible — the goal is to assess the risks and decide what risks are acceptable. COSPAR prioritized the gaps in October 2016 and will meet again in Houston in February to decide what specific experiments should be done. Stick the landing The steps required for any future Mars mission will depend on the landing spot. COSPAR currently says that robotic missions are allowed to visit “special regions” on Mars, defined as places where terrestrial organisms are likely to replicate, only if robots are cleaned before launch to 0.03 bacterial spores per square meter of spacecraft. In contrast, a robot going to a nonspecial region is allowed to bring 300 spores per square meter. These “spores,” or endospores, are dormant bacterial cells that can survive environmental stresses that would normally kill the organism.
To date, any special regions are hypothetical, because none have been conclusively identified on Mars. But if a spacecraft finds that its location unexpectedly meets the special criteria, its mission might have to change on the spot.
The Viking landers, which in 1976 brought the first and only experiments to look for living creatures on Mars, were baked in an oven for hours before launch to clean the craft to special region standards.
“If you’re as clean as Viking, you can go anywhere on Mars,” says NASA planetary protection officer Catharine Conley. But no mission since, from the Pathfinder mission in the 1990s to the current Curiosity rover to the upcoming Mars 2020 and ExoMars rovers, has been cleared to access potentially special regions. That’s partly because of cost. A 2006 study by engineer Sarah Gavit of the Jet Propulsion Lab found that sterilizing a rover like Spirit or Opportunity (both launched in 2003) to Viking levels would cost up to 14 percent more than sterilizing it to a lower level. NASA has also backed away from looking for life after Viking’s search for Martian microbes came back inconclusive. The agency shifted focus to seeking signs of past habitability.
Although no place on Mars currently meets the special region criteria, some areas have conditions close enough to be treated with caution. In 2015, geologist Colin Dundas of the U.S. Geological Survey in Flagstaff, Ariz., and colleagues discovered what looked like streaks of salty water that appeared and disappeared in Gale Crater, where Curiosity is roving. Although those streaks were not declared special regions, the Curiosity team steered the rover clear of the area. But evidence of flowing water on Mars bit the dust. In November, Dundas and colleagues reported in Nature Geoscience that the streaks are more likely to be tiny avalanches of sand. The reversal highlights how difficult it is to tell if a region on Mars is special or not.
However, on January 12 in Science, Dundas and colleagues reported finding eight slopes where layers of water ice were exposed at shallow depths (SN Online: 1/11/18). Those very steep spots would not be good landing sites for humans or rovers, but they suggest that nearby regions might have accessible ice within a meter or two of the surface.
If warm and wet conditions exist, that’s exactly where humans would want to go. Golombek has helped choose every Mars landing site since Pathfinder and has advised SpaceX on where to land its Red Dragon spacecraft, originally planned to bring the first crewed SpaceX mission to Mars. (Since then, SpaceX has announced it will use its BFR spacecraft instead, which might require shifts in landing sites.) The best landing sites for humans have access to water and are as close to the equator as possible, Golombek says. Low latitudes mean warmth, more solar power and a chance to use the planet’s rotation to help launch a rocket back to Earth.
That narrows the options. NASA’s first workshop on human landing sites, held in Houston in October 2015, identified more than 40 “exploration zones” within 50 degrees latitude of the equator, where astronauts could do science and potentially access raw materials for building and life support, including water.
Golombek helped SpaceX whittle its list to a handful of sites, including Arcadia Planitia and Deuteronilus Mensae, which show signs of having pure water ice buried beneath a thin layer of soil.
What makes these regions appealing for humans also makes them more likely to be good places for microbes to grow, putting a crimp in hopes for boots on the ground. But there are ways around the apparent barriers, Conley says. In particular, humans could land a safe distance from special regions and send clean robots to do the dirty work.
That suggestion raises a big question: How far is far enough? To figure out a safe distance, scientists need to know how well Earth microbes would survive on Mars in the first place, and how far those organisms would spread from a human habitat. The most desirable places on Mars for human visits offer access to water in some form and are near the equator (for increased solar power and to get a boost when launching a return rocket). Rovers and landers have found evidence of a watery Martian past. Planners of future robotic and human missions have potential landing spots in mind. Map excludes polar regions.
Hover over or tap the map points to explore. A no-grow zone Initial results suggest that Mars does a good job of sterilizing itself. “I’ve been trying to grow Earth bacteria in Mars conditions for 15 years, and it’s actually really hard to do,” says astrobiologist Andrew Schuerger of the University of Florida in Gainesville. “I think that risk is much lower than the scientific community might think.”
In 2013 in Astrobiology, Schuerger and colleagues published a list of more than a dozen factors that microbes on Mars would have to overcome, including a lot of ultraviolet radiation from the sun; extreme dryness, low pressure and freezing temperatures; and high levels of salts, oxidants and heavy metals in Martian soils. Schuerger has tried to grow hundreds of species of bacteria and fungi in the cold, low-pressure and low-oxygen conditions found on Mars. Some species came from natural soils in the dry Arctic and other desert environments, and others were recovered from clean rooms where spacecraft were assembled.
Of all those attempts, he has had success with 31 bacteria and no fungi. Seeing how difficult it is to coax these hardy microbes to thrive gives him confidence to say: “The surface conditions on Mars are so harsh that it’s very unlikely that terrestrial bacteria and fungi will be able to establish a niche.”
There’s one factor Schuerger does worry about, though: salts, which can lower the freezing temperature of water. In a 2017 paper in Icarus, Schuerger and colleagues tested the survival of Bacillus subtilis, a well-studied bacterium found in human gastrointestinal tracts, in simulated Martian soils with various levels of saltiness.
B. subtilis can form a tough spore when stressed, which could keep it safe in extreme environments. Schuerger showed that dormant B. subtilis spores were mostly unaffected for up to 28 days in six different soils. But another bacterium that does not form spores was killed off. That finding suggests that spore-forming microbes — including ones that humans carry with them — could survive in soils moistened by briny waters.
The Okarian’s trek across the Arctic offers a ray of hope: Spores might not make it very far from human habitats. At three stops during the journey across the Arctic, Pascal Lee, of the SETI Institute, collected samples from the pristine snow ahead and dirtier snow behind the vehicle, as well as from the rover’s interior. Later, Lee sent the samples to Schuerger’s lab.
The researchers asked, if humans drive over a microbe-free pristine environment, would they contaminate it? “The answer was no,” Schuerger says.
And that was in an Earth environment with only one or two of Schuerger’s biocidal factors (low temperatures and slightly higher UV radiation than elsewhere on Earth) and with a rover crawling with human-associated microbes. The Okarian hosted 69 distinct bacteria and 16 fungi, Schuerger and Lee reported in 2015 in Astrobiology.
But when crew members ventured outside the rover, they barely left a mark. The duo found one fungus and one bacterium on both the rover and two snow sites, one downwind and one ahead of the direction of travel. Other than that, nothing, even though crew members made no effort to contain their microbes — they breathed and ate openly.
“We didn’t see dispersal when conditions were much more conducive to dispersal” than they will be on Mars, Schuerger says. The International Space Station may be an even better place to study what happens when inhabited space vessels leak microbes. Michelle Rucker, an engineer at NASA’s Johnson Space Center in Houston, and her colleagues are testing a tool for astronauts to swab the outside of their spacesuits and the space station, and collect whatever microbes are already there.
“At this point, no one has defined what the allowable levels of human contamination are,” Rucker says. “We don’t know if we’d meet them, but more importantly, we’ve never checked our human systems to see where we’re at.”
Rucker and colleagues have had astronauts test the swab kit as part of their training on Earth. The researchers plan to present the first results from those tests in March in Big Sky, Mont., at the IEEE Aerospace Conference. If the team gets the tool flight-certified to test it on the ISS, the results could fill a knowledge gap about how much spaceships carrying humans will leak and vent microbes.
A Russian experiment on the ISS may be giving the first clues. In November 2017, Russian cosmonauts told TASS news service that they had found living bacteria on the outside of the ISS. Some of those microbes, swabbed near vents during spacewalks, were not found on the spacecraft’s exterior when it launched.
Blowing in the wind These results are important, says Conley, but they don’t give enough information alone to write quantitative contamination rules.
That’s partly because of another knowledge gap: how dust and wind move around on Mars. If Martian dust storms carry microbes far enough, the invaders could contaminate potential special regions even if humans land a safe distance away.
To find out, COSPAR’s Kminek suggests sending a fleet of Mars landers to act as meteorological stations at several fixed locations. The landers could measure atmospheric conditions and dust properties over a long time. Such landers would be relatively inexpensive to build, he says, and could launch in advance of humans.
But these weather stations would have to get in line. There’s a launch window between Earth and Mars every two years, and the next few are already booked. Weather stations would have to be stationary, so they couldn’t be added to rover missions like ExoMars or Mars 2020.
That means it’s possible that SpaceX or another company will try to send humans to Mars before the reconnaissance missions necessary to write rules for planetary protection are even built. If COSPAR is the tortoise in this race, SpaceX is the hare, along with a few other private companies. Only SpaceX has a stated timeline. Other contenders, including Washington-based Blue Origin, founded by Amazon executive Jeff Bezos, and United Launch Alliance, based in Colorado, are developing rockets that some analysts say could be part of a mission to the moon or Mars.
Now or never Those looming launches prompted Fairén and colleagues to make a controversial proposal. In an article in the October 2017 Astrobiology, provocatively titled “Searching for life on Mars before it is too late,” the team suggested sending existing or planned rovers, even those not at the height of cleanliness, to look directly for signs of Martian life.
Given the harsh Martian conditions, rovers are unlikely to contaminate regions that might turn out to be special on a closer look, the group argues. The invasive species argument is misleading, they say: Don’t compare a microbe transfer to taking Asian parrots to the Amazon rainforest, where they could thrive and edge out local parrots. It would be closer to taking them to Antarctica to freeze to death.
Even if Earth microbes did replicate on Mars, the researchers wrote, technology is advanced enough that scientists would be able to distinguish hitchhikers from Earth from true Mars life (SN: 4/30/16, p. 28).
In a sharp rebuttal, published in the same issue of Astrobiology, Rummel and Conley disagreed. “Why would you want to go there with a dirty spacecraft?” says Rummel, who was NASA’s planetary protection officer before Conley. “To spend a billion dollars to go find life from Florida on Mars is both irresponsible and completely scientifically indefensible.”
There’s also concern for the health and safety of future astronauts. Conley says she mentioned the idea that scientists shouldn’t worry about getting sick if they encounter Earth organisms on Mars to a November meeting of epidemiologists who study the risks of Earth-based pandemics.
“The room burst out laughing,” she says. “This is a room full of medical doctors who deal with Ebola. The idea that we know about Earth organisms, and therefore they can’t hurt us, was literally laughable to them.”
Fairén has already drafted a response for a future issue of Astrobiology: “We acknowledge [that Rummel and Conley’s points] are informed and literate. Unfortunately, they are also unconvincing.”
The issue might come to a head in July in Pasadena, Calif., at the next meeting of COSPAR’s Scientific Assembly. Fairén and colleagues plan to push for more relaxed cleanliness rules.
That’s not likely to happen anytime soon. But with no concrete rules in place for humans, would a human mission even be allowed off the ground, whether NASA or SpaceX was at the helm? Currently, private U.S. companies must apply to the Federal Aviation Administration for a launch license, and for travel to another planet, that agency would probably ask NASA to weigh in.
It’s hard to know if anyone will actually be ready to send humans to Mars in the next decade. “You’d have to actually believe them to be scared,” says Rummel. “There are many unanswered questions about what Elon Musk wants to do. But I think we can calm down about people showing up on Mars unannounced.”
But SpaceX has defied expectations before and may give slow and steady a kick in the pants.
Movies and other media are full of mixed messages about the risks and rewards of building machines with minds of their own. For every manipulative automaton like Ex Machina’s Ava (SN: 5/16/15, p. 26), there’s a helpful Star Wars droid. And while some tech titans such as Elon Musk warn of the threats artificial intelligence presents, others, including Mark Zuckerberg, dismiss the doomsayers.
AI researcher Toby Walsh’s Machines That Think is for anyone who has heard the hype and is seeking a critical assessment of what the technology can do — and what it might do in the future. Walsh’s conversational style is welcoming to nonexperts while his endnotes point readers to opportunities for deeper dives into specific aspects of AI. Walsh begins with a history of AI, from Aristotle’s foundation of formal logic to modern facial-recognition systems. Excerpts from computer-composed poetry and tales of computers trouncing humans at strategy games (SN: 11/11/17, p. 13) are a testament to how far AI has come. But Walsh also highlights weaknesses, such as machine-learning algorithms’ reliance on so much data to master a single task.
This 30,000-foot view of AI research packs a lot of history, as well as philosophical and technical explanation. Walsh personalizes the account with stories of his own programming experiences, anecdotes about AI in daily life — like his daughter’s use of Siri — and his absolute, unapologetic love of puns.
Later in the book, Walsh speculates about technical hurdles that may curb further AI development and legal limits that society may want to impose. He also explores the societal impact that increasingly intelligent computers may have. For instance, Walsh evaluates how likely various jobs are to be outsourced to AI. Some occupations, like journalist, will almost certainly be automated, he argues. Others, like oral surgeon, are probably safe. For future job security, Walsh recommends pursuing careers that require programming acumen, emotional intelligence or creativity.
AI also has the potential to revolutionize warfare. “Like Moore’s law, we are likely to see exponential growth in the capabilities of autonomous weapons,” Walsh writes. “I have named this ‘Schwarzenegger’s law’ to remind us of where it will end.” Walsh isn’t resigned to a Terminator-like future, though. If governments ban killer robots and arms developers use automation to enhance defensive equipment, he believes military AI could actually save many lives.
In fact, Walsh argues, all aspects of AI’s future impacts are in our hands. “Artificial intelligence can lead us down many different paths, some good and some bad,” he writes. “Society must choose which path to take.”
