The personality of Japanese quail chicks changes depending on the kind of relationship formed between parents, a new study reports.

Casual Quail Sex Leads to More Fearful, Fatter Offspring

Hookup buddies or long-term partners? It’s a key question in 21 st -century rom-coms—and also in the world of bird romance.


 The personality of Japanese quail chicks changes depending on the kind of relationship formed between parents, according to a new study to be published in the Journal of Experimental Biology. Quail chicks born from parents who were attached to each other are more social, lighter, and less fearful.


 And this effect, found by a team of researchers at the University of Rennes, France, isn’t a question of quail parenting strategies. Instead, it’s entirely prenatal. It all depends on whether the parent quails had settled into a tight, exclusive pair bond.


 “If parents developed a pair bond, offspring are more social (although they have been reared without parents),” writes animal behaviorist Océane Le Bot, who led the study, via email. For their research, her team saved 30 male and 30 female broiler-line Japanese quail from an industrial farm.


 Half of the paired-off quail got to engage in five-minute booty calls a few times a week. The other half were put into a sort of arranged marriage with randomly chosen mates in dual-occupancy cages.


 After a few weeks, Le Bot’s matchmaking took. When separated into different cages, cohabitating quails of both sexes called out, actively searching around for their missing partners. And when reunited, these pair-bonded quails calmed down.


 By contrast, the behavior of the quail-with-benefits suggested they were more relaxed when put in separate cages. Males became louder, moved around more, or engaged in courtship behaviors—something pair bonded males don’t do. They even seemed wary, stretching their necks tall in vigilance.


 With bonds firmly in place and gendered clichés confirmed, Le Bot turned her attention to the products of these unions. To fully consider the prenatal impact of the parents’ relationship on the chicks’ nature, Le Bot raised the chicks in a big group under a heat lamp.


 In terms of average behavior, chicks from pair bonded parents were different than chicks conceived during brief hookups. When confronted with a new environment or the sudden appearance of a weird object, known to elicit surprise—a black and yellow T-shaped block—they showed less fear, as judged through calls, posture, and attempts to escape. And when placed on the path to a cage with other quail chicks they had never met, the chicks from pair bonds were more eager to join these potential new friends.


 Exactly how this happens prenatally is still unclear. Le Bot’s team checked hormonal differences between the eggs, but they haven’t yet found a smoking gun. It’s also possible that the mother’s prenatal state can subtly alter how the genetic code of the chick is expressed, a change known to affect behavior in birds and rodents.


 “This study is suggesting that actually the interactions between mom and dad are really important,” says Allison Bell, a biologist who studies animal personality at the University of Illinois. The fact that chicks inherit traces from their parents’ world raises some interesting questions the field is trying to answer, according to Bell.


 In some cases, like when mothers are extremely stressed, prenatal influences might disadvantage offspring, Bell says. “You can also think about cases where it might be adaptive…if parents can communicate something about the environment the offspring are likely to experience.”


 That kind of communication may be what’s happening with the Japanese quail, where the parent’s relationship status somehow signals the chicks. In addition to their gregariousness, the chicks from pair bonds were on average lighter than their counterparts.


 These chicks, Le Bot’s study suggests, might be prepared for two very different futures. If relationships are stable, prenatal messages tell offspring to be adventurous, open. That’s what happens in the wild, where quail almost always settle in to pair bonds. But if relationships are fleeting—as if due to predators—being a little heavier and a little more conservative might be a better survival strategy. Or, on a farm, it just might make a quail better for the broiler.


 “The question is so interesting,” Bell says, underscoring the study’s surprising finding. “There’s something about parent care bonds that might actually influence offspring development, and that’s all happening prenatally.”

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 Photo Credit:
 <a href="https://www.flickr.com/photos/sally_monster/15484751225">
 Sally Crossthwaite / Flickr (CC BY-NC-ND 2.0)
 </a>

The personality of Japanese quail chicks changes depending on the kind of relationship formed between parents, a new study reports.

What Do We Lose If We Lose Wild Axolotls?

Axolotls could revolutionize medicine, but their wild cousins are critically endangered.

Why Was 2017’s Hurricane Season So Intense?

The 2017 Atlantic hurricane season isn’t over until the end of November. But if you’ve even glanced at the headlines over the past few months, you know this year’s storms have already left an indelible mark.


 Consider the following stretch, which began in late August: First there was Harvey, which dumped three or more feet of rain over Houston, causing 75 deaths. Then Irma leveled some of the Caribbean’s Leeward Islands and slashed up through Florida, killing 14 people in the Florida Keys and some 134 overall. If that wasn’t enough, Maria later hit Dominica and Puerto Rico, which is still struggling to recover.

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<img alt="" class="richtext-image full-width" src="https://www.pbs.org/wgbh/nova/media/images/hurricane-irma-eye-still.width-990_fGPWrNi.jpg"/>
<figcaption>Hurricane Irma strengthened to a Category 5 storm with sustained winds of 185 mph.
 
 </figcaption>
</figure>

 In addition to the loss of life, the damage left in the wake of these hurricanes will probably add up to hundreds of billions of dollars. For many Americans, this summer and fall was the worst hurricane season since 2005 when Katrina and Rita tore through the Gulf of Mexico.


 At first or even second glance, this hurricane season seems like it was among the worst. But was it really? If so, why? And how does climate change fit in?

<h2>
 This year’s hurricane season really did stand out. But most of it came down to one incredible month.
</h2>

 “The season was kind of near-normal through August, and then it’s been near-normal in October,” says
 <a href="http://tropical.colostate.edu/personnel/">
 Phil Klotzbach
 </a>
 , an atmospheric scientist at the Colorado State University. “September was off the charts.”


 On Twitter and in the press, Klotzbach has spent the last few months calling attention to 2017’s hurricane superlatives. He also keeps a list of statistics,
 <a href="http://tropical.atmos.colostate.edu/Realtime">
 updated in real time
 </a>
 , of the current season as a whole.


 September was truly unique, he says. That month, not one but three unusually long-lived, strong hurricanes—Irma, Maria, and Jose—formed near the central Atlantic’s Cape Verde archipelago and moved northwards.

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<img alt="CBP responds to Hurricane Maria" class="richtext-image full-width" src="https://www.pbs.org/wgbh/nova/media/images/hurricane-maria-puerto-rico-damage.width-990_ztWUGSm.jpg"/>
<figcaption>Hurricane Maria inflicted severe damage on Puerto Rico, seen here on September 23, 2017.
 
 </figcaption>
</figure>


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 Scientists track a statistic called hurricane days, which a hurricane accrues for every day it lives. If three hurricanes coexist on the same day, they rack up three days. In this respect, September was the worst month in recorded history. It had more named storm days, more hurricane days, and more days with a Category 3 or higher hurricane than ever before.


 Hurricane watchers also track a figure called accumulated cyclone energy, which is like the total kinetic energy of every storm this season put together. In the North Atlantic, that total wind energy—now, still with a month to go—is already more than twice the average measured between 1981 and 2010.


 The 2017 season also broke a lucky streak for the continental U.S., which hadn’t been hit by a major hurricane since 2005. “Up to September of this year, a topic of popular discussion was what was going with the hurricane drought,” says
 <a href="https://environment.princeton.edu/directory/gabriel-vecchi">
 Gabriel Vecchi
 </a>
 , a geophysicist at Princeton. “There were papers being written on this.”


 But even after that remarkable September, 2017 won’t take the overall crown as the worst-ever year unless this next month is particularly unlucky. “It’s a top-ten year,” Klotzbach says, but “there’s years that have been more active.”


 While that qualifies this year’s hurricane season, it does not take away from it. This year’s storms did grow big and strong. We won’t know how exactly that happened until scientists have performed careful, quantitative analyses. But broadly speaking, two major factors are to blame.

<h2>
 One, the Atlantic hosted swaths of warm water this year, revving up the engine that fuels hurricanes.
</h2>

 Let’s rewind to an unlikely place. In 1824, as steam engines were transforming the world, French military engineer Nicolas Carnot figured out the math behind how they actually worked. That same math applies to hurricanes, according to MIT atmospheric scientist
 <a href="https://emanuel.mit.edu/">
 Kerry Emanuel
 </a>
 .


 What matters is the temperature difference between two reservoirs of thermal energy, called the thermal potential. In a hurricane, the contrast between the warm surface of the sea and the cool atmosphere does the work: it sucks wind gusts up the spiraling wall around the calm “eye” and then sends them curling outward.


 Carnot’s equations show that the bigger this temperature contrast is, the faster a hurricane’s winds can get at their theoretical maximum.


 This year, that difference was heightened by warmer-than-usual water. In the key month of September, the tropical Atlantic was the third warmest it has ever been, Klotzbach says. The only warmer years were the infamous 2005, which produced four separate Category 5 hurricanes, and 2010, which was also an intense hurricane year.

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 This could be because of a current called the Atlantic meridional overturning circulation. Since the 1990s, the Atlantic has been on a warm kick, fueled by the circulation of balmy tropical waters to higher latitudes. But there’s another possibility, too: At the same time that increased circulation was ramping up ocean temperatures, the Atlantic also started getting more heat from the sun than it did a few decades ago.


 This theory holds that, after World War II, American and European industries produced sulfate pollutants that floated into the atmosphere above the Atlantic. Combined with dust whipped up from arid parts of Africa, this pollution kept the ocean shaded and cool. But by the 1990s, with pollution controls in place in Europe and North America, and droughts being mitigated in North Africa, this shade was removed, and the Atlantic warmed up again. “It’s a big scientific debate, what the relative contribution of these two things is,” Vecchi says.


 Whatever the root cause, though, one fact is clear: the Atlantic was warm this year. That heat gave the engines of hurricanes their fuel. But to get powerful storms, we also need to cut their brakes.


 The other major factor behind this unusual season was that, in 2017, the wind patterns that normally quench hurricanes didn’t appear, thanks to La Niña-like conditions.

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 Since the 1990s, the Atlantic has been on a warm kick.

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 It’s hard to tell from satellite pictures, but the vortexes at the cores of hurricanes can tower ten miles high. They reach from the bottom to the top of the troposphere, the slice of atmosphere in which we live.


 This can be a major weakness, since the tops and bottoms of hurricanes are exposed to other winds unrelated to the hurricane that blow at different speeds and in different directions. This effect, called vertical wind shear, can kick the bottom out of a hurricane’s central engine, transforming it into an unsteady Jenga tower. It blocks storms from ever reaching their potential. And in 2017, vertical wind shear in the tropical Atlantic was weak.


 Blame it on conditions related to La Niña, the atmospheric phenomenon that’s the cooler counterpart to El Niño, which occurs when the Pacific Ocean warms. La Niña, though centered on the Pacific, also helps hurricanes form in the Atlantic.


 Though this year wasn’t an official La Niña, it was at least similar enough to cause a long chain of consequences, Vecchi says. The Pacific was cooler than usual, and that shifted rainfall patterns which in turn changed atmospheric currents over the Atlantic—which in turn lessened the difference between winds close to the surface and winds higher up. That gave hurricanes a more stable atmosphere in which to form, allowing them to power up and maintain that power over a longer period of time.


 On top of this, the La Niña conditions also cooled the upper atmosphere above the Atlantic, further boosting the temperature gap between the warm ocean and the cold atmosphere.


 Working together, researchers believe these factors primed the pump for an active season. But there’s another potential reason why year’s hurricane season was so intense, and that’s climate change.

<h2>
 Attributing storms and seasons to climate change is tough and ongoing. But this year’s storms match the kind of hurricanes scientists expect from a warmer world.
</h2>

 A few things about this hurricane season stood out to James Kossin, an atmospheric scientist at NOAA’s Center for Weather and Climate. One was the astronomical amount of rainfall Harvey released over Houston. Another was how Irma intensified rapidly and then stayed extraordinarily strong longer than any previous storm.


 “They are consistent with the kind of changes that we expect under climate change,” Kossin says. “It’s pretty darn likely that we’re affecting these monsters.” But that’s pretty much as far as he—or the other scientists interviewed for this piece—will go at the moment.


 Right now, the National Science Foundation
 <a href="https://www.nsf.gov/pubs/2017/nsf17128/nsf17128.jsp">
 has opened up
 </a>
 a few quick grants to allow researchers to delve into the specifics of the recent storms. In the following months and years, we’ll see careful studies come out, Kossins says, which will help pinpoint the role of climate change.

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 Some are already underway. “We’ve actually done an analysis of Harvey,” says MIT’s Emanuel. According to his team’s ongoing work, hurricane-related rainstorms over Texas that should occur once in 100 years will now happen about once every 20 years, thanks to climate change. And their frequency might increase again to once every five or six years by 2100, he says.

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<img alt="South Carolina National Guard aids Southeast Texas after Hurricane Harvey" class="richtext-image full-width" src="https://www.pbs.org/wgbh/nova/media/images/hurricane-harvey-flooding-port-arthur-texas.width-990_DYA2okX.jpg"/>
<figcaption>Hurricane Harvey caused catastrophic flooding throughout southeast Texas, including Port Arthur.
 
 </figcaption>
</figure>

 In many respects, disentangling the current role of climate change in hurricanes is a tricky business. High quality hurricane data doesn’t go back many years, researchers say, making it difficult to separate climate change from the other patterns discussed above.


 But there is clear, basic science: key aspects of climate change will almost certainly lead to worse hurricanes. For every 1.8˚ F (1˚ C) the air warms, it can hold 7% more water, leading to more intense rainfall. And higher seas will lead to more dangerous storm surges, which didn’t play a big role in this year’s storms but which often contribute a sizeable share of hurricane deaths and damages.


 This year can provide an important lesson, says Vecchi, the Princeton geophysicist. “As we expect hurricanes to become more intense over the coming century, this should be something we’re concerned about.”


 “Here we are in 2017, in the United States, a very technologically advanced civilization and society, and we are very vulnerable to hurricanes,” he says. “We saw it.”


 Photo credits: CIRA/NOAA/NASA, U.S. Customs and Border Protection, NOAA, South Carolina National Guard

After a quiet start, August and September quickly became filled with violent storms. What drove the change?

Palau’s Improbably Healthy Coral Reefs

Why acidic waters haven’t killed Palau’s vibrant coral could help save many reefs from catastrophe.

Center-pivot irrigation systems near Sublette, Kansas, draw from the High Plains Aquifer.

From 310 Miles Above the Earth, Satellites Weigh Groundwater Lost to Irrigation

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 Picture a shimmering cube of water three miles high. In the past decade, that much water—nearly the volume of Nevada’s Lake Tahoe—was lost from aquifers under the American High Plains.


 That figure doesn’t come from measurements of the water level in wells. Rather, it’s drawn from orbit, in a new study that uses data from NASA’s Gravity Recovery and Climate Experiment (GRACE) spacecraft. GRACE has been weighing groundwater from on high since the late 1990s. But previous GRACE models have overlooked ways in which humans impact aquifers, says study lead author Jose Agustin Brena-Narañjo. “Which, in this case, is irrigation.”


 His team’s new technique, tested on the High Plains Aquifer, uses irrigation records to improve space-based estimates of the water left underground. It could eventually help track dwindling aquifers in places like India’s Indus Plains or the Tigris-Euphrates region.


 GRACE doesn’t take pictures from space to map groundwater. Instead, it feels along the contours of Earth’s dimpled gravity like a hand reading Braille. It works like this: the two GRACE spacecraft fly over Earth one behind the other. If the first satellite flies above a continent, for example, it’s accelerated away from the trailing satellite—gravity is subtly stronger over the continents, which are heavier than the oceans. By measuring tiny changes between the GRACE satellites as they pass one after the other over an area, scientists map bumps in the planet’s mass. It’s even possible to tease apart the weight added by underground water. Yet existing GRACE studies of aquifers have elided the very factor that places so many aquifers at risk: watering crops.


 The challenge is to subtract the weight of wet soil from the total water mass known from GRACE, leaving behind just the water in the aquifer. Soil moisture is usually estimated from complex models of climate and geology. But Brena-Narañjo and his collaborators argue that records of irrigation can better predict soil moisture, at least in heavily irrigated areas. With many well measurements to check against, the High Plains Aquifer offers a perfect test case.

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 The High Plains aquifer sprawls across eight U.S. states, from Wyoming to Texas. Since the 1950s, the aquifer has been pumped relentlessly, in part to water crops, and has fallen over 14 feet, on average. Rising concerns about water use have made the High Plains system among the planet’s most studied.


 In the north, the High Plains system is in decent health, according to Orrin Feril, who manages Big Bend, the fifth of five Groundwater Management Districts in Kansas. “Our water table recovers nicely” after drought, he writes in an email. Down in Texas, though, the situation is dire.


 “Bottom line is we’re pumping six times as much out of the aquifer as we think is coming back in,” says Robert Mace, deputy executive administrator at the Texas Water Development Board. “If you run your checking account that way, every month you’re going to see less in the bank,” says Mace. “That’s what we’re seeing.”


 Compared to the usual GRACE method, Brena-Narañjo found, the combo of gravity data and irrigation records is a closer match to actual measurements from High Plains wells. The harsh drought between 2010 and 2013, unseen by the traditional GRACE analysis, came across clear. Brena-Narañjo’s technique also suggests that the water lost from the High Plains Aquifer in the last decade alone is between a fourth and a third of the total amount lost since the 1950s.

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 An expert source who reviewed the research raised questions in an email, pointing out that Brena-Narañjo’s team “tuned” their model “using the same data (observed groundwater) that they used for evaluation.” Anthony Kendall, a co-author on the study, admits this weakness, which he hopes further work will address. “The fact that all the wiggles match really well provides you with some degree of confidence, even though you’d like more,” he says.


 For his part, Mace told me this work dispels some doubts he’s had about past GRACE groundwater studies. “The trends they show on [water] storage changes look reasonable,” he says.


 Texas’ slice of the High Plains Aquifer, benighted as it is by drought, is already pinpricked with enough wells to make space-based measurements unnecessary. Which is why, after this first test, Brena-Narañjo hopes to apply his model elsewhere, in places like South Africa, India, and the Middle East where GRACE can fill in gaps of data on the ground. “When you go to any region of the world where you have irrigation fields,” he says, “it’s very likely you’re going to have these problems.”


 Image credit: NASA

The twin GRACE satellites read dimples in Earth&#x27;s gravity like fingers reading Braille, including those caused by overdrawn aquifers.

New Ant Species Thrives by Hacking Another Species's Culture

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 The aggressive Brazilian ant
 
 Crematogaster ampla
 
 has a free rider problem. Imposter ants copy its body language. They infiltrate its territory, follow its scent trails, and mooch from its food sources. But for now these infiltrators must avoid touching their hosts, because something about them just doesn’t smell right.


 The imposter is the mirror turtle ant
 
 Cephalotes specularis
 
 , as described in a new study by Scott Powell, an ant biologist at George Washington University. The way
 
 Ce. specularis
 
 “mirrors”
 
 Cr. ampla
 
 on jaunts through
 
 Cr. ampla
 
 ‘s heavily guarded territory is a never-before-seen stage in the evolution of social parasitism, or when one organism hacks the culture of another.


 “This is literally the discovery of a species and a new parasitic syndrome at the same time,” said ant ecologist Michael Kaspari of the University of Oklahoma, who was unaffiliated with the work. “It’s the best kind of discovery science.”


 Even in the world of ant parasitism—a world of
 <a href="http://www.nature.com/scitable/knowledge/library/social-parasitism-in-ants-13256421">
 slavery and Manchurian-candidate queens
 </a>
 —
 
 Ce. specularis
 
 is weird. Powell first noticed the species out of the corner of his eye, in the midst of a swarm of
 
 Cr. ampla
 
 on a baited tree
 
 .
 

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 “Something I’d just seen wasn’t quite right,” he said. “There were these two or three ants that were almost identical to the host ant, but just sort of dodging around in amongst the chaos.” Powell and his Brazilian colleagues were intrigued. What kind of intruder was this?


 The Brazilian
 
 cerrado
 
 , where both ants live, is wooded savannah. As many as 20 ant species can coexist on a single tree. Yet Powell’s team didn’t find any other ant species at nearly 200 of the host
 
 Cr. ampla’s
 
 feeding sites, likely because of the zeal with which
 
 Cr. ampla
 
 chases—and then dismembers—foreigners. No other ants, that is, except the turtle ant
 
 Ce. specularis
 
 .


 While most other turtle ants adopt squat, defensive stances,
 
 Ce. specularis
 
 protects itself through mimicry. Unlike even their own soldiers, foraging
 
 Ce. specularis
 
 worker ants are dark and shiny, and they walk with their rear ends raised up in the air—all to dupe the host
 
 Cr. ampla.
 
 They even copy the same walking speed and stilt-like posture.


 This lets mirror turtle ants “pass” in hostile territory, granting them access to the same food their hosts find. Although mirror turtle ants live separately from their hosts, their nests are exclusively found in
 
 Cr. ampla
 
 ’s domain, suggesting deep dependence. Lab work shows that
 
 Ce. specularis
 
 ants are drawn to the pheromones marking
 
 Cr. ampla
 
 scavenging trails even more than the signals left by their own species.


 That tension, between free living and dependence, is what makes
 
 Ce. specularis
 
 so interesting. Evolution treats successful species like
 
 Cr. ampla
 
 as obstacles in a landscape, forcing other creatures to find ways to go around—or through. Parasitism is a fascinating option, Kaspari said.

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 “Parasites were the first neurobiologists,” he said. “Natural selection has provided ample opportunity for one organism to mess with another organism, to exploit it by understanding how it perceives the world.”


 Although the mirror turtle ant has appearances down, it still hasn’t fooled its host’s finely tuned sense of smell. When traffic is congested along
 
 Cr. ampla
 
 trails,
 
 Ce. specularis
 
 skirts the edges, shuffling out of the way to avoid contact. If jostled together, Powell’s team observed, the host ants do a “double-take.” But before
 
 Cr. ampla
 
 can take up arms, the intruders have already fled.


 The endgame, for many parasites, is seamless integration and dependence. But
 
 Ce. specularis
 
 isn’t there – at least not yet. Regardless of whether the mirror turtle ant is heading down that road, its current semi-independent lifestyle makes it easier to study than parasites who cohabitate with their hosts.


 “You’re offered a lot of opportunities to understand some of the costs and benefits of that evolutionary transition from free-living to parasite,” Powell said. With “a deeply entrenched parasite, you can never tease those things apart.”


 Finding such a unique relationship takes careful attention and knack for details, Kaspari notes. Dedication doesn’t hurt, either. Building off earlier studies, he said, Powell attracted his ants with a high-sodium bait the paper refers to as “vertebrate urine.”


 “His team fills up bottles every morning,” Kaspari said. “They really give 110%.”


 Photo credit: Scott Powell

The mirror turtle ant lives among the aggressive Crematogaster ampla thanks to some clever social engineering.

Massive Meteor-Induced Climate Swings May Have Made Mars’s Valleys

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 The proof is in the dirt: There’s little doubt that water carved ancient Mars. Between 3.5 and 4 billion years ago, it ran down into valleys, forming branching rivulets that spacecraft above the Red Planet now study from orbit.
 

 But simulations of the early Martian atmosphere don’t match the observed erosion features, a new study argues. Since it’s too cold and too low-pressure for liquid water to last on the modern Martian surface, the planet’s climate must have been different than it is today. Exactly what that early climate was like—and how exactly the water erosion happened—remains a mystery.
 

 Scientists are narrowing the possibilities, though. The shape of the erosion features allowed study author Philip von Paris of the German Aerospace Center to estimate the amount of rain it would take to form them. The answer: a lot. “Many of the valleys would need tropical rainforest values of precipitation to make them,” von Paris says.
 
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<img alt="mars valleys" class="richtext-image full-width" src="https://www.pbs.org/wgbh/nova/media/images/mars-valleys.width-990_lUQ28Sh.jpg"/>
<figcaption>The Mars Reconnaissance Orbiter took this image of gully channels in a crater in the southern highlands of Mars.
 
 </figcaption>
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 That’s a problem, because the ancient Martian atmosphere, according to his and other simulations, was freezing cold and dry. It couldn’t produce anywhere near enough rain—at least not as a global average. “The discrepancy was huge,” von Paris says. That suggests rain might not be the culprit at all.
 

 “We tried to tried to reconcile geomorphology and climate simulations under the assumption of a continuously wet early Mars,” von Paris says of the comparison. His study is the first to quantify the two approaches together. “It doesn’t work, so that means the assumption is probably not true.”
 

 The idea that early Mars may have been warm and wet, Earthlike even, dates back to the early 1970s. Scientists working on the Mariner 9 probe, including the young Carl Sagan seen in a NASA educational video, were stunned to see what looked like dried streambeds on some of the oldest exposed Martian terrain.
 
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 Carl Sagan describes the findings of the Mariner 9 program of the 1970s.
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 It’s difficult to test, because the ancient Martian climate isn’t something planetary scientists can observe. “It’s 3.8 billion years ago, so we didn’t have rovers then,” von Paris says. Instead, scientists have to use different approaches—climate modeling, hydrology, mineralogy—to try to understand what Mars was like from multiple angles at once.
 

 Modern-day atmospheric modelers like von Paris and Robin Wordsworth, a planetary scientist at Harvard, have trouble in their simulations making ancient Mars warm enough for liquid water. “The current most accurate models in existence suggest that episodic, not long-term warming is the reason for early Mars’ surface erosion,” Wordsworth writes in an email.
 

 That’s because 4 billion years ago, the Sun wasn’t as bright as it is today. And even a likely atmosphere with lots of carbon dioxide can’t conjure up enough global warming to let water linger on the planet’s surface.
 

 The simulations lead Wordsworth, von Paris, and other climate modelers to argue that rains and rivers didn’t form the valley networks. Instead, rare events like meteorite impacts and volcanoes may have melted fallen snow on the highlands, which could then run into valleys and carve out the observed channels.
 

 The climate modeling camp’s conclusions are far from universal, says Nicolas Mangold, a member of the Curiosity rover’s ChemCam team at the University of Nantes, France. Minerals on the Martian surface suggest water once flowed freely. “At least part of the minerals are due to weathering” from water, he writes in an email. Curiosity has also found clays that appear to have formed in a lake.
 

 “None of these observations can be explained by a cold freezing early Mars or we should still observe the same processes in the present or recent times,” Mangold writes. “My point of view is that observations will remain, whereas models will change.”
 

 It’s possible that both hypotheses are correct. After all, plenty could have happened on Mars four billion years. “One thing I’m fairly convinced of is that it’s probably insufficient to talk of any single, steady early climate,” Wordsworth writes.
 
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 Image credit: NASA JPL

Joshua Sokol

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