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Sunday, November 22, 2009

The Brain Humanity's Other Basic Instinct: Math

by Carl Zimmer

Image: iStockphoto

Numbers make modern life possible. “In a world without numbers,” University of Rochester neuroscientist Jessica Cantlon and her colleagues recently observed in the journal Trends in Cognitive Sciences, “we would be unable to build a skyscraper, hold a national election, plan a wedding, or pay for a chicken at the market.”

The central role of numbers in our world testifies to the brain’s uncanny ability to recognize and understand them—and Cantlon is among the researchers trying to find out exactly how that skill works. Traditionally, scientists have thought that we learn to use numbers the same way we learn how to drive a car or to text with two thumbs. In this view, numbers are a kind of technology, a man-made invention to which our all-purpose brains can adapt. History provides some support. The oldest evidence of people using numbers dates back about 30,000 years: bones and antlers scored with notches that are considered by archaeologists to be tallying marks. More sophisticated uses of numbers arose only much later, coincident with the rise of other simple technologies. The Mesopotamians developed basic arithmetic about 5,000 years ago. Zero made its debut in A.D. 876. Arab scholars laid the foundations of algebra in the ninth century; calculus did not emerge in full flower until the late 1600s.

Despite the late appearance of higher mathematics, there is growing evidence that numbers are not really a recent invention—not even remotely. Cantlon and others are showing that our species seems to have an innate skill for math, a skill that may have been shared by our ancestors going back least 30 million years.

One sign that this skill truly is innate: Children enter the world with a head for numbers. Veronique Izard, a cognitive psychologist at Harvard University, demonstrated this in a recent study of newborns. She and her colleagues played cooing sounds to babies, with varying numbers of sounds in each trial. The babies were then shown a set of shapes on a computer screen, and the scientists measured how long the babies gazed at it. (The length of time a baby spends looking at an object reflects its interest.) Newborns consistently looked longer at the screen when the number of shapes matched the number of sounds they had just heard. For example, a baby who heard “tuuu, tuuu, tuuu, tuuu” would look the longest at four shapes, less at eight, and still less at twelve. Izard’s study suggests that newborns already have a basic understanding of numbers. Moreover, their concept of numbers is abstract; they can transfer it across the senses from sounds to pictures.

Mathematical intuition develops as we grow up, but probing its growth is tricky because older children draw on both their innate skills and the ones they learn. So scientists have come up with ways to force people to rely on intuition alone. Cantlon, working with Elizabeth Brannon of Duke University, ran an experiment in which adult subjects see a set of dots on a computer screen for about half a second, followed by a second set. After a pause, the participants see two sets of dots side by side. They then have a little more than a second to pick the set that is the sum of the previous two pictures.

People do fairly well on these tests, which summons up a weird feeling in them: They know they are right, but they don’t know how they got the answer. Even in toddlers who cannot yet count, these studies reveal, the brain automatically processes numbers. From infancy to old age, mathematical intuition consistently follows two rules. One is that people score better when the numbers are small than when they are large. The other is that people score better when the ratio of the bigger number to the smaller one is greater. In other words, people are more likely to correctly tell 2 from 4 than they are to tell 6 from 8, even though both pairs of numbers differ by two. As we get older, our intuition becomes more precise. Other experiments have shown that a six-month-old baby can reliably distinguish between numbers that differ by as little as a factor of two (like 4 and 8). By nine months the ratio has dropped to 1.5 (8 and 12, for example). And by adulthood the ratio is just 10 to 15 percent. The fact that the same two rules always hold true suggests that we use the same mental algorithm throughout our lives.

Brain scans using magnetic resonance imaging (MRI) and positron emission tomography (PET) are shedding some light on how our brains carry out that algorithm. Neuroscientists have found that when people do mathematical intuition problems, a strip of neurons near the top of the brain, surrounding a fold called the intraparietal sulcus, consistently becomes active. And when we confront more difficult problems—when the numbers are bigger or closer together—this region becomes more active.

Psychologists suspect that the mathematical intuition that these neurons help produce lays the foundation for all of our more sophisticated kinds of math. Justin Halberda of Johns Hopkins University and his colleagues recently carried out a telling study of mathematical intuition in a group of 14-year-olds. Some of the children demonstrated a more accurate intuition than others. Halberda then looked at the subjects’ scores on standardized school tests. Students who had a sharper mathematical intuition scored better on math tests from kindergarten onward.

The fact that children possess a mathematical intuition long before they even start school implies that our evolutionary ancestors had it too. Indeed, recent research indicates that our forebears possessed such an intuition long before they could walk upright. Scientists have found that many primates, including rhesus monkeys, can solve some of the same mathematical problems we can. Since monkeys and humans diverged 30 million years ago, mathematical intuition presumably is at least that old.

Providing evidence of that shared heritage, Cantlon and Brannon were able to teach monkeys to do addition by intuition the same way people do. The animals’ intuition is about as good as ours, and it follows the same rules. As the ratio between numbers gets larger, the monkeys are increasingly likely to pick the right one. And when monkeys use their mathematical intuition, they rely on the same region of the brain around the intraparietal sulcus that we do.

Monkeys can even learn written numbers, a skill children develop only around age 5. In order to make the link between a 2 and a pair of objects, children use a region of the brain located underneath the temple called the dorsolateral prefrontal cortex. This region is like a blacksmith shop for forging associations between signs and concepts. Once the association has been formed, children recognize written numbers quickly, and the dorsolateral prefrontal cortex becomes quiet.

Monkeys can learn, with enough training, to pick out a 4 if they see four dots on a screen. Andreas Nieder, a physiologist at the University of Tübingen, and his colleagues have discovered that, like children, the monkeys use their dorsolateral prefrontal cortex to make those associations. They have even found individual neurons in the region that fire strongly at both the number 4 and four dots.

But does a monkey actually understand what a written 4 signifies? To find out, Nieder and his former student Ilka Diester trained monkeys for a new experiment. The monkeys learned to press a lever, after which they saw one number followed by another. If the numbers matched, the monkeys could release the lever to get a squirt of juice. If the numbers didn’t match, the monkeys had to keep the lever pressed down until a new number appeared, which was always a match.

The monkeys were able to learn to release the lever for matching numbers and to keep it down for numbers that did not match. If they had succeeded simply by matching shapes, you would expect them to sometimes confuse similar-looking numbers: They might choose 1 as a match with 4 because both are made of straight lines, for example. But Diester and Nieder found that the monkeys got confused in a different way. The monkeys were most likely to mix up numbers that were numerically close to each other: the sticklike 1 and the curvaceous 2, for example. What’s more, the monkeys took more time to release the lever if larger numbers matched than if smaller ones did—another sign that the animals were responding to quantity, not shape.

Once our ancestors linked their natural instinct for numbers with an ability to understand symbols, everything changed. Math became a language of ideas and measurements.

To neuroscientists, these studies raise a deep question. If monkeys have such solid foundations for numbers, why can’t they per­form high-level mathematics? Finding an answer may help us understand what makes humans so much better with numbers than other animals. Nieder and Cantlon have both speculated that the difference lies in our ability to understand symbols, which enables us to transform our approximate intuition of numbers into a precise understanding. When we say “2,” we mean an exact quantity, not “probably 2 but maybe 1 or 3.” We can then learn rules for handling exact numbers quickly. And then we can generalize those rules from one number to the next, thus understanding general mathematical principles. Other primates, lacking our symbolic brains, take thousands of trials to learn a new rule.

The recent studies of monkeys and infants cast a new light on the old notched bones. The earliest recorded numbers coin­cide with the first appearance of many other expressions of abstract thought, from bone flutes to carvings of zaftig female figures. Before then, humans may have thought about numbers the way monkeys (and babies) still do today. But once our ancestors began to link their natural instinct for numbers with a new ability to understand symbols, everything changed. Math became a language of ideas, of measurements, and of engineering possibilities. The rest—the skyscrapers and supermarkets and weddings—were just a matter of derivation.

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Malaria Gaining Resistance to Best Available Treatment

By Nathan Seppa, Science News

malaria

WASHINGTON — Malaria that is resistant to the best available drug is more widespread in Southeast Asia than previously reported, new research shows. The worrisome finding poses a risk that travelers could carry this strain of the malaria parasite to other parts of the globe and unwittingly spread it, scientists reported Nov. 19 at a meeting of the American Society of Tropical Medicine and Hygiene.

The frontline drug in question is called artemisinin, the most potent medication currently in use against malaria. Signs of malarial resistance to artemisinin have surfaced over the past several years in Cambodia (SN: 11/22/08, p. 9). The new findings confirm that resistant malaria has now cropped up beyond a spot on the border of Thailand and Cambodia where it was initially detected. Now it has appeared in Vietnam and in two spots along the Burma border with Thailand and China.

“Things are changing. There’s no doubt the signs are concerning,” said Robert Newman, director of the Global Malaria Programme at the World Health Organization in Geneva. But he added that these signals are early and need further verification.

Patients in these areas take longer on average to overcome a malaria infection when given a standard combination of artemisinin and another antimalarial. This lag results from slower clearance of the malaria parasites from the blood, said WHO’s Pascal Ringwald, a medical officer who presented the update.

Patients who remain ill for longer stretches despite treatment need extra medication to recover from malaria and are also more likely to have severe or fatal cases, Ringwald said.

Malaria is caused by a single-celled parasite that infects the blood. Symptoms include fever, headache, chills, anemia and a swollen spleen. Of the more than 350 million people who come down with malaria worldwide each year, up to 1 million die. Mosquitoes spread the parasite from person to person.

Malaria has a history of becoming resistant to drugs, and artemisinin now risks becoming the most recent addition to that list. The new reports are disheartening to doctors because artemisinin normally packs a considerable wallop. Although artemisinin is a short-acting drug that gets cleared from the body in a few hours, it makes the most of its time — driving down parasite levels dramatically.

Using artemisinin alone invites resistance. So the standard therapy teams it with one of the longer-acting drugs, which perform mop-up duty on the remaining parasites, said Christopher King, a physician and epidemiologist at Case Western Reserve University in Cleveland.

The new flashes of resistance may have arisen because combination treatment isn’t always available. And since artemisinin can be bought over the counter in many parts of Asia, people seeking relief don’t always follow the WHO guidelines of pairing artemisinin with another drug, King said.

Also, taking artemisinin for a fever that isn’t caused by malaria can allow resistant strains of the parasite to take hold, Newman said.

In the past, malaria’s resistance to other drugs has been linked to specific genetic changes in the parasite. The precise mechanism underlying resistance to artemisinin is still unsolved, King said.

Artemisinin is derived from extracts of the sweet wormwood bush. The bush’s leaves have been used as a folk remedy against fevers for roughly 2,000 years in Asia but fell out of use in the 20th century with the introduction of modern antimalarial drugs such as chloroquine.

During the Vietnam War, North Vietnamese leader Ho Chi Minh appealed to China for traditional remedies for soldiers who had malaria. Tea made from sweet wormwood leaves worked and ultimately became the basis for artemisinin drugs. It’s not clear whether parasites in Southeast Asia are the first to become resistant because they have had a long history with artemisinin, or if other factors are involved, Newman said.

Image: Malaria from Plasmodium falciparum. Flickr/Got_Jenna

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Evolution and history compulsory

classroom
Evolution should be taught early, scientists advised

Primary school children in England will have to learn about evolution and British history under a shake-up of the national curriculum.

Schools Minister Vernon Coaker says the subjects will be compulsory elements of a new primary school curriculum being introduced in 2011.

Scientists and humanists had lobbied ministers for the inclusion of evolution in the theme-based timetable.

History is already compulsory, but there were fears it would be sidelined.

Schools will not be told which parts of British history to teach.

Earlier this year, when the curriculum changes were announced, critics complained that children would learn more about the internet than history.

Ministers say they want to "reinforce" history by making it a statutory element of the new primary curriculum.

Campaign

The curriculum is set out in a new education Bill just introduced to Parliament.

It was drawn up after a review by Sir Jim Rose, which called for distinct subjects to be replaced by six new "areas of learning".

Mr Coaker said: "What and how our children learn lies at the heart of our policies to raise standards.

"We've seen that an inspiring and rigorous curriculum can transform failing schools, which is why these plans are based on the very best practice from this country's top-class teachers."

He added: "Teachers will have more freedom to use their professional judgement and creativity to make links between subjects that make sense to their pupils: from linking history to the arts, or science to PE."

Evolution is arguably the most important concept underlying the life sciences
Andrew Copson, British Humanist Association

The British Humanist Association (BHA) had led a campaign to have Darwin's theory of how life evolved through natural selection made a compulsory element of the new primary curriculum.

It organised a public letter signed by more than 500 from scientists and supporters.

Andrew Copson of the BHA said: "This is excellent news. Evolution is arguably the most important concept underlying the life sciences.

"Providing children with an understanding of it an early age will help lay the foundations for a surer scientific understanding later on."

He added: "Public authorities clearly need to do more to tackle the growing threat to the public's understanding of science from creationist-inspired beliefs and other pseudoscience".

Evolution is already taught in secondary schools and many primary schools, but under the curriculum changes, it will become compulsory for primary pupils, with the recommendation that they are taught the subject in their later years at school.

The new curriculum says schools must "investigate and explain how plants and animals are interdependent and are diverse and adapted to their environment by natural selection".

Professor Sir Martin Taylor, vice-president of the Royal Society, said: "We are delighted to see evolution explicitly included in the primary curriculum.

"One of the most remarkable achievements of science over the last two hundred years has been to show how humans and all other organisms on the earth arose through the process of evolution."

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Extinction of Giant Mammals Changed Landscape Dramatically

By Jeanna Bryner, Senior Writer

The last breaths of mammoths and mastodons some 13,000 years ago have garnered plenty of research and just as much debate. What killed these large beasts in a relative instant of geologic time?

A question asked less often: What happened when they disappeared?

A new study, based partly on dung fungus, provides some answers to both questions. The upshot: The landscape changed dramatically.

"As soon as herbivores drop off the landscape, we see different plant communities," said lead researcher Jacquelyn Gill of the University of Wisconsin, Madison, adding the result was an "ecosystem upheaval."

Gill and her colleagues found that once emptied of a diversity of large animals equaling or surpassing that of Africa's Serengeti, the landscape completely changed. Trees once kept in check by the mammoth gang popped up and so did wildfires sparked by the woody debris.

The results, which are detailed in the Nov. 20 issue of the journal Science, could paint a picture of what's to come if today's giant plant-eaters, such as elephants, disappear.

"We know some of these large animals are among the most threatened that we have on the landscape today and they have a lot of large habitat requirements and they eat a lot of food," Gill told LiveScience. "If these animals go extinct we can expect the landscape will respond."

Dung fungus

Gill and her colleagues analyzed sediment samples collected from Appleman Lake in Indiana as well as data from sites in New York.

They focused on a dung fungus called Sporormiella that must pass through a mammal's gut to complete its life cycle and reproduce via spores. More of such spores indicate more dung and more megafauna around to contribute to the fecal contents. Within that same sediment, the team looked at pollen and charcoal as proxies for vegetation and fires, respectively.

Sediment layers accumulate over time and can indicate when the stuff embedded in it was around. By matching up the dung spores along with vegetation and fire indicators in certain layers, the researchers figured the large herbivores were already declining before the vegetation started changing or wildfires took off.

The changes in spore abundance suggest the megafauna began to decline some time between 14,800 and 13,700 years ago. By 13,500 years ago, the decline was in full force, Gill said.

Rather than getting vaporized in an instant, the results suggest the animals gradually dwindled for about 1,000 years.

Here's how it may have gone down: The large herbivores started to decline. Without such leafy eaters to keep broad-leaved species in check, trees such as black ash and elm took over a landscape once dominated by conifers. Soon after, the accumulation of woody debris sparked an increase in wildfires, another key shaper of landscapes, the researchers say.

What killed the mammoths?

As for what drove the beasts into their graves, Gill says the findings don't put the nail in the coffin, but do rule out some ideas. To explain the extinction, scientists have put forth climate change, hunting by humans such as the Clovis people (known for using advanced spear tips), and even impact by a comet. The answer could be a combination of several factors, scientists say.

Gill says this new study is a strong one because all of the evidence comes from one place, and so the researchers aren't making comparisons across different regions whose sediments may be off in terms of timing.

If the timing is accurate, as Gill says it should be, the findings can rule out the idea of a meteor or comet killing off the creatures some 13,000 years ago.

And since the plant community didn't change until after the big guys began to decline, that's a mark against climate change. (A warming climate was considered the cause of a revamping of vegetation, and thus animal habitat.)

"At this site, we can say that habitat loss didn't cause the decline, because the major habitat shift happens after the collapse [of the megafauna]," Gill said. "And habitat change is a big line of argument in the climate camp. If climate change is causing these extinctions, you'll have to evoke another process than habitat loss."

Hunting, at least that by the Clovis people, can also be ruled out at the site.

"It seems as though the animals were already in decline by the time [Clovis] people adopted this tool kit," Gill said, referring to the advanced spear tips thought to be more efficient at taking down large prey than hunting instruments used by humans prior to the Clovis.

The new study was funded by the Wisconsin Alumni Research Foundation, the UW-Madison Center for Climatic Research in the Nelson Institute for Environmental Studies, and the National Science Foundation.

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Bangladesh arsenic poisoning mystery solved

Arsenic-bangladeshx-large A team from the Massachusetts Institute of Technology may have solved one of the great environmental disaster riddles of the last 30 years -- where did the arsenic that has poisoned between two and 25 million people in Bangladesh come from?

In a paper from this week’s edition of the journal Nature Geoscience, engineers from MIT, Harvard and the Bangladesh University of Engineering and Technology in Dhaka, Bangladesh offer a new potential source -- tens of thousands of human-dug ponds.

The ponds were dug over the past 50 years to provide dirt so home could be sited on high ground and so flood barriers could be built.

Using chemical tracers, the researchers show that when organic carbon settles at the bottom of these ponds, it seeps underground where microbes consume it. This creates a chain of biochemical events that causes naturally occurring arsenic to dissolve out of the sediment and into the ground water.

Tragically, international health agencies in the 1970s began a successful push to get villagers to dig shallow tube wells for water, to stop the spread of cholera and other water-borne bacterial diseases that came from drinking pond and river water. Upwards of 40% of those wells are now contaminated with arsenic.

Beginning in the late 1970s the country was struck with severe, widespread arsenic poisoning. The immediate symptoms are violent stomach pains, vomiting, diarrhea, convulsions and cramps. Over the longer term, serious skin diseases can result.

Scientists at MIT and Harvard also estimate that the in the end the exposure will result in 125,000 cases of skin cancer, and 3,000 deaths from internal cancers.

The researchers found that when rice fields are irrigated with this arsenic-laden water, the rice filtered arsenic out of the water system. So one solution is to dig wells for drinking water below the level of the ponds. Another would be to put shallow wells under rice fields which naturally filter the arsenic.

They estimate that by replacing 31% of the wells in the country with deeper wells the health effects of the arsenic could be reduced by 70%.

By Elizabeth Weise
Photo: Installing a pore-water sampler into the soil of a rice field. (Sarah Jane White, Nature)

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Water mission returns first data

By Jonathan Amos
Science reporter, BBC News

First uncalibrated data from Smos (Esa)
Smos builds up its map data in strips as it sweeps around the Earth

Europe's latest Earth observation satellite has returned its first data.

Smos was launched earlier this month on a quest to help scientists understand better how water is cycled around the Earth.

The spacecraft will make the first global maps of the amount of moisture held in soils and of the quantity of salts dissolved in the oceans.

The data will have wide uses but should improve weather forecasts and warnings of extreme events, such as floods.

"Smos is performing like a dream," said Dr Yann Kerr, a lead investigator on the mission from the Centre for the Study of the Biosphere from Space (Cesbio), Toulouse, France.

"Everything went as clockwork and exactly as expected or better up to now. We did not expect to have images so soon," he told BBC News.

The European Space Agency's (Esa) Soil Moisture and Ocean Salinity (Smos) satellite was launched on 2 November.

Smos artist's impression (Esa)
The mission will run for three years in the first instance

After its initial check-out in orbit, its sole instrument - an interferometric radiometer called Miras - was sent live on Tuesday this week.

The first publicly released image on this page has not been properly calibrated by researchers but they say it proves the instrument is in good shape.

Miras is some eight metres across; it has the look of helicopter rotor blades.

It measures changes in the wetness of the land and in the salinity of seawater by observing variations in the natural microwave emission coming up off the surface of the planet.

It does this through 69 antennas positioned on a central structure and along the lengths of its three arms.

Generally speaking, the "colder" (blue) the "temperature brightness" of the microwave signal, the saltier the water and the wetter the soil; but a lot of processing will be needed before any real values can be attached to the measurements coming down from Smos.

"Moreover, there seem to be radio frequency interferences (RFIs) over China, western Russia and parts of Europe (the reddish stripes)," explained Dr Kerr.

"We will have to tune the reconstruction algorithm before we can reduce or address these."

Scientists were well aware before launch that RFIs might be a problem. Smos is operating in the so-called L-band (21cm) which is supposed to be protected, but pre-flight testing established known interference hotspots, such as airports.

The 315m-euro ($465m; £280m) Smos programme, although led by Esa, has with significant input from French and Spanish interests. The satellite is expected to operate for at least three years.

Soil moisture and ocean salinity explainer (BBC)
The amount of water retained in soils varies between about 5% and 50%
This will cover most conditions from 'bone dry' to 'mud bath'
Smos sees the entire range with an accuracy of 4% at the 50km scale
Natural salinity in water covers the range from near zero to 30%
Drinking water might be one extreme; salt lakes would be the other extreme
Smos is seeking sea waters which are typically in the 3-3.5% range
This needs high accuracy (0.01-0.02%). Maps are at the 200km scale

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Water found in lunar impact probably came from comets

Volatiles, including hydrocarbons known to be present in comets, have been detected in lunar material kicked up by NASA's LCROSS mission (Image: T.A.Rector/I.P.Dell'Antonio

by Dana Mackenzie, Houston

The mystery of where the moon's water came from may soon be solved. Evidence from NASA's LCROSS mission suggests much of it was delivered by comets rather than forming on the surface through an interaction with the solar wind.

In October, the mission crashed two impactors – a spent rocket stage and a few minutes later, the LCROSS spacecraft itself – into a crater near the moon's south pole. The spacecraft snapped images and took spectra of lunar debris kicked up by the rocket's impact and found that it contained the unmistakable signs of water.

Previous missions have also found hints of lunar water but its source has not been clear. One idea is that it forms when hydrogen atoms from the solar wind latch onto oxygen atoms in the lunar soil, creating hydroxyl and water.

But now, the evidence is mounting in favour of an alternative explanation – comet impacts. The data was discussed this week at the Lunar Exploration Analysis Group meeting, a gathering of 160 lunar scientists in Houston, Texas.

'Dirty iceballs'

The first line of evidence comes from compounds that vaporise readily, called volatiles. LCROSS found spectral signs of volatiles containing carbon and hydrogen – likely methane and ethanol – as well as others such as ammonia and carbon dioxide. "It appears that we impacted into a very volatile-rich area," LCROSS principal scientist Tony Colaprete told the conference.

These compounds should have been mostly lost to space billions of years ago, when the moon coalesced from the debris of an impact between the Earth and a Mars-sized object. Water formed through an interaction with the solar wind would therefore be relatively pure – and free of volatiles.

But comets, which are thought to have been responsible for many of the moon's impact scars, are "dirty iceballs" known to contain volatiles such as methane. "If you can nail down the source of the water [on the moon], that could tell us a lot about the cometary history of the moon for the last couple of billion years," says Larry Taylor of the University of Tennessee.

High concentrations

The second line of evidence pointing to comets comes from the amount of water detected. The solar wind is expected to form water in minute amounts, amounting to concentrations of no more than 1 per cent in the lunar soil.

LCROSS team members are still analysing the data, but calculations suggest the concentration of water is higher than that. "The data are consistent with a total hydrogen content in the range of several per cent," says Colaprete.

Beyond their link to comets, volatiles generated excitement at the meeting because of their value as a resource for human spaceflight. While water is important for survival on the moon, it is the water's hydrogen that can be used as rocket propellant.

The possibility of finding compounds like ethanol and methane, which can be used as fuel directly, makes the economic case for returning astronauts to the moon even sweeter. "LCROSS has given us our ticket back to the moon," says Noah Petro of NASA's Goddard Space Flight Center in Greenbelt, Maryland.

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