# News this Week

Science  22 Jun 2012:
Vol. 336, Issue 6088, pp. 1486
1. # Around the World

1 - Raleigh, North Carolina
Legislating Sea Level Rise
2 - London
U.K. Panel Backs Open Access
3 - Australia
Australia Creates World's Largest Network of Marine Reserves
4 - Manama
Bahrain Sentences Medics
5 - Washington, D.C.
Senate Panel Gives NIH $100 Million Boost for 2013 6 - Washington, D.C. NRC Committee Finds That Humans Are Triggering Quakes ## Raleigh, North Carolina ### Legislating Sea Level Rise By a 34-to-11 vote, on 12 June North Carolina's Senate approved a controversial bill, HB 819, which requires North Carolina's Coastal Resources Commission to base predictions of future sea level rise along the state's coast on linear rates of increase rather than allowing for accelerating events, such as the melting of polar ice sheets. The bill's supporters say that predicted acceleration would be expensive to plan for and is based on flimsy data. Climate scientist Robert Jackson of Duke University in Durham, North Carolina, who spoke before the Senate committee that approved the bill on 7 June, says the legislation would force state planners to downplay the potential impacts of global climate change. Models using linear rates of sea level increase based on past changes forecast 0.2 meters of sea level rise along the North Carolina coast by 2100, he says; in contrast, models that allow for accelerated rates forecast a 1-meter rise. The bill still needs to be approved by the North Carolina House of Representatives and signed by the governor to become law. http://scim.ag/NCsealevel ## London ### U.K. Panel Backs Open Access A U.K. government report says open-access journals should be “the main vehicle for the publication of research” but warns they will cost the country more than$80 million per year.

Most scientific papers are published by journals that charge a subscription fee. Publishers such as the Public Library of Science (PLoS) and Biomed Central have pioneered an alternate model in which authors pay a fee for publication and the paper is then freely available online.

The report, published on 19 June, suggests that journals are increasingly adopting the PLoS model. But in the interim, the report cautions, universities may end up paying author fees for some journals on top of subscription costs for others. Timothy Gowers, a mathematician at the University of Cambridge and an open-access advocate, criticizes the report for being “more concerned with the openness issue than with making a serious attempt to reduce costs.” http://scim.ag/UKopenacc

## Australia

### Australia Creates World's Largest Network of Marine Reserves

At Rio+20 this week, Australian Prime Minister Julia Gillard can hold her head high: Last week, her government unveiled the final plan for the world's largest network of marine parks. After 10 years of planning, the idea needs to pass one more 60-day comment period before coming into force at the end of the year. Protected areas will increase more than four-fold, to 3.1 million square kilometers.

“This sets a new benchmark,” says Terry Hughes, director of the Australian Research Council Center of Excellence for Coral Reef Studies at James Cook University in Townsville. Critics of the plan include the fishing lobby, which argues that parks place undue pressure on unprotected fisheries and do not increase stocks, an argument rebuffed by a recent paper in Current Biology that showed marine reserves restock fisheries up to 30 kilometers away.

The park increases the number of Australia's marine reserves from 27 to 40 and covers a wide range of habitats. Only one-third of the area will be fully excluded from fishing or gas and oil exploration, protecting habitats and species from humpback whales to green sea turtles; the other two-thirds will be managed to allow varying degrees of use.

## Manama

### Bahrain Sentences Medics

Bahrain's highest court released its final verdict on 14 June in the case of 20 medics accused of fomenting revolution in the Persian Gulf state. While most of the charges were dropped—the prosecution relied on confessions that the medics claim were extracted through torture—the defendants still face jail time ranging up to 5 years.

The verdict is a small victory for the International Human Rights Network of Academies and Scholarly Societies. The consortium of scientists, doctors, and engineers has been pressuring Bahrain's king to release the medics and clear them of all charges.

Meanwhile, Bahraini doctors say that they are still in danger of political reprisals. “Patients should have access to medical care without the fear of arrest, and the doctors should be able to treat any patient without the fear of prosecution,” says Amal Habib, an ophthalmologist who has fled Bahrain and is seeking asylum abroad. http://scim.ag/Bahraindocs

## Washington, D.C.

### Senate Panel Gives NIH $100 Million Boost for 2013 The Senate Appropriations Committee last week approved a modest$100 million raise for the National Institutes of Health (NIH) in 2013. The 0.3% bump, to $30.723 billion, is better than the president's request for no increase but disappointing to the research community. The bill provides$40 million for the Cures Acceleration Network, four times its current budget (but $10 million below the president's request). It disregards the president's proposal to cut$50 million from the Institutional Development Award (IDeA) program, which boosts competition for grants in poorer states, but makes a requested $28 million trim, to$165 million, for the National Children's Study.

“We're appreciative of any increase,” says Jennifer Zeitzer, director of legislative relations for the Federation of American Societies for Experimental Biology. Still, she says, “it's going to be difficult for people in the research community.”

The bill must still be approved by the full Senate. The House appropriations panel was expected to introduce its version of the bill as soon as this week. http://scim.ag/NIHboost

## Washington, D.C.

### NRC Committee Finds That Humans Are Triggering Quakes

Fracking for natural gas and oil, formally known as hydraulic fracturing, has been responsible for only one or two earthquake-triggering episodes, a committee of the National Research Council (NRC) concluded in a report released on 15 June. But hundreds of felt quakes in 13 states have been produced by the deep injection of wastewater from fracking and other industrial activities, as well as the creation of geothermal energy sites, the enhanced recovery of oil and gas, and even the simple extraction of oil and gas. And pumping carbon dioxide captured from power plants into the ground “may have potential for inducing larger seismic events” because of the large volumes involved, the committee found.

Assessments of the risk of induced seismicity “should be undertaken before operations begin in areas with a known history of felt seismicity,” the committee wrote. Such preinjection studies have generally not been done in the past, although some new state regulations are moving in that direction. http://scim.ag/NRCfrack

2. # Random Sample

## Noted

The United States is back at the top of the supercomputing list. IBM's Sequoia, at Lawrence Livermore National Laboratory in Livermore, California, beat out Japan's Fujitsu to regain the title of the world's most powerful computing system, as ranked by the industry-standard Top500 list, released 18 June at the International Supercomputing Conference in Hamburg, Germany.

## Fewer Foxes, More Lyme Disease?

The increase in Lyme disease over the past 30 years in the United States has often been blamed on resurging populations of deer because they are a major host for adult ticks carrying the disease-causing bacteria. But a study published online this week in the Proceedings of the National Academy of Sciences puts the blame instead on the decline of red foxes, which are being displaced by coyotes. Researchers led by ecologist Taal Levi of the University of California, Santa Cruz, examined the incidence of Lyme disease in Pennsylvania, Virginia, Wisconsin, Minnesota, and New York, and found that a higher incidence of Lyme disease correlated with the scarcity of red foxes. Foxes are very effective at catching mice and other rodents that infect young ticks with Lyme-causing bacteria. “The strength of the data is impossible to ignore,” comments ecologist Richard Ostfeld of the Cary Institute of Ecosystem Studies in Millbrook, New York.

## Letter Details Einstein's Post-War Passion

A cleanup of the archives of the Jewish Telegraphic Agency in January yielded an unexpected treasure for the 95-year-old news service: hand-typed correspondence between JTA's founder, Jacob Landau, and Albert Einstein. Among the yellowing letters was a 20 January 1947 statement from Einstein on scientists' role in military research—a hot topic in the wake of World War II and the wartime use of atomic weapons.

“Non-cooperation in military matters should be a vital part of the moral code of basic scientists,” Einstein wrote, adding that keeping basic discoveries secret “would seriously harm science.”

Einstein had expressed similar antiwar views prior to writing that letter, but it does shed new light on the physicist's views “on the relationship of science and state,” says Harvard University historian Peter Galison. Einstein writes, for example, that for science, “moral law is above any obligation to the state.”

The letters also illuminate Einstein's ties to Landau, who founded the news service to cover the Jewish diaspora in 1917. Einstein's long-standing friendship with the pressman—who named his son Albert E. Landau—helped shape the scientist's views on the Holocaust, Israel, and other topics. To raise funds for a new Web site, JTA auctioned the letters at Sotheby's last week, where they fetched $34,375. ## By the Numbers 287 million tonnes The collective weight of the world's adult human population, according to a BMC Public Health study. Fifteen million tonnes of that is due to overweight people.$100 billion Amount U.S. research universities need in new federal support over the next decade to remain the best in the world, according to a report released 14 June by the National Academies.

£20,000 Cash prize offered with the newly announced Wellcome Trust Screenwriting Prize, intended to help develop films inspired by medicine and biology.

## ScienceLive

Join us Thursday, 28 June, at 3 p.m. EDT for a live chat on whether we're training too many graduate students. http://scim.ag/science-live

3. # Newsmakers

At his synthetic neurobiology lab at the Massachusetts Institute of Technology, Edward Boyden is exploring the circuitry of the brain. On 19 June, Boyden received the inaugural A. F. Harvey Engineering Research Prize of £300,000 ($470,000), awarded by the Institute of Engineering and Technology, an international professional society, for his work in the development of optogenetics, a powerful technique that enables precise control of neuronal activity with laser light. Q:What are the latest developments in your lab? A:In collaboration with mechanical engineers at [the Georgia Institute of Technology], we've built robots that automate recordings from inside nerve cells, which can be scaled up to record from hundreds or thousands of cells. We're also developing the ability to characterize neural network computations by simultaneously controlling and reading out brain activity. Q:What's the future of optogenetics? A:I'm interested in devices that can record from, and deliver information to, multiple points in the brain, with a computer that processes the information and determines exactly what needs to be restored [to correct a brain disorder]. Devices that interface with entire neural circuits at single-cell resolution would allow understanding of how the cells work together … and how they go awry in diseases. Q:What are the biggest challenges? A:The most obvious challenge is how to deliver genes encoding light-sensitive proteins to specific cells in the human brain. Gene therapy trials are promising, but we need to understand its consequences fully. Another question is [whether] these genes (obtained from microbes) will elicit immune responses when introduced into the human body. ## ‘Protein Detective’ Wins Körber Prize Matthias Mann, 52, a physicist and bioinformatician at the Max Planck Institute of Biochemistry in Martinsreid, Germany, has won the 2012 Körber European Science Prize for his groundbreaking work on the proteome, the entire complement of proteins in a living organism. The prize comes with an award of €750,000. As a Ph.D. student at Yale University, Mann worked with analytical chemist John Fenn, who received the Nobel Prize in chemistry in 2002 for his work on developing electrospray ionization, which makes it possible to measure proteins using mass spectroscopy methods, once the province primarily of chemists and physicists. Mann refined the technique so that all the proteins in a cell could be analyzed at once; in 2010, he and his team were the first to successfully sequence the complete proteome of a living organism. “Matthias is a splendid choice for this high award,” says geneticist Gilbert Omenn, of the University of Michigan, Ann Arbor. “He is a remarkable innovator … and he and his laboratory have made numerous important biological applications.” 4. Mars Exploration # Hang On! Curiosity Is Plunging Onto Mars 1. Richard A. Kerr The performance this August of a brand-new system for landing on Mars means life or death for NASA's next rover mission, but future Mars exploration hangs on a perfect touchdown as well. NASA's video depicting the next Mars rover's descent toward the martian surface makes some planetary scientists nervous (http://scim.ag/rovervideo). NASA has$2.5 billion riding on the success of Curiosity's scary-new “sky-crane” landing system designed by engineers at NASA's Jet Propulsion Laboratory (JPL). If Curiosity crashes as it dangles by cables from its flying platform festooned with blazing rockets, some scientists will see a decade or more of their careers crash with it.

But there's even more riding on Curiosity's safe touchdown at 10:31 p.m. PDT this 5 August (5:31 UTC on 6 August). Not only will NASA have to slow the most massive load ever delivered to another planet's surface from hypervelocity bullet speeds to a dead stop, all in the usual “7 minutes of terror.” But NASA is also attempting to deliver Curiosity to the surface of Mars more precisely than any mission before, within a 20-kilometer-long ellipse some 240 million kilometers from Earth. Both feats are essential to NASA's long-term goals at Mars: returning samples of martian rock and sending humans to the Red Planet.

“I'm very confident in our system,” says Steven Sell of JPL, a lead engineer on the seven-person team responsible for Curiosity's atmospheric “entry, descent, and landing,” or EDL. “We know [EDL] inside and out. I feel very confident we have done everything we can do to make it as reliable as possible.” Still, he adds, “I'll be as nervous as anyone on landing day.”

## Designing 7 minutes of terror

Six times before, NASA has managed to land spacecraft safely on Mars, starting with the two Viking landers in 1976. This time, NASA planners wanted a bigger and better—and, therefore, heavier—rover to advance the search for life. Curiosity, clamped inside its entry vehicle like the innards of a clam, weighs in at 3.3 tons—three times larger than any previous entry vehicle. Still, as in past missions, the job of safely braking the rover from 21,240 kilometers per hour falls to the drag of the wispy martian atmosphere. Starting at Mach 20, the bulletlike heat shield bears the brunt of the slowing (see figures, upper left panel). Then a lone parachute deploys at Mach 2 (upper right). To handle the greater mass, engineers had to enlarge and beef up both the heat shield and the parachute. They expect these scaled-up “heritage” designs to get Curiosity through the fireball entry stage, the parachute phase of descent, and thus 98% of speed reduction.

The next stage, though, presented a problem. Some earlier missions delivered immobile landers. In their final, powered descent stage, touchdowns like those of the Vikings had depended on easing the lander down on retrorockets to land on its own legs, as in 1950s sci-fi movies. The three mobile rovers have instead bounced onto Mars inside the NASA equivalent of beach balls. But landing the much bigger Curiosity on a legged, powered platform would be trickier, Sell says. The bigger lander would be less stable on uncertain slopes, and the whole system would be more sensitive to the critical timing of engine shutdown. And a beach ball just wasn't going to work. “The airbag system was as big as it could be made,” he says. “It had played out.”

So engineers brainstormed. “On Earth, how do we deliver big things?” Sell asks rhetorically. “On construction sites, they use cranes or helicopters. Thus, the rover-on-a-rope was born.” Curiosity, its six wheels deployed, will be lowered 7.5 meters below its rocket-powered descent stage on three cables in the “sky crane” phase of descent (lower left panel). Once the rover eases onto the surface (lower right), the control system will sense the drop in tension on the cables and the descent stage will fly out of harm's way.

Less innovative was the engineers' solution to the problem of shrinking the rover's landing zone from an ellipse 100 kilometers long to one just 20 kilometers long. Planners wanted to be able to land their bigger, better rover near the most interesting geology, whether or not there was a broad swath of forgiving terrain there. So Curiosity engineers borrowed the concept of “guided entry” from the system used for returning Apollo astronauts to Earth.

All previous Mars landers had entered the atmosphere like bullets; they could hit their targets no more accurately than they were aimed. Throw in the vagaries of entry vehicle performance and martian winds, and they arrived a good deal less accurately than that. The limited targeting accuracy of the previous generation of rovers kept them out of Gale crater, whose central mound boasts a Grand Canyon–like exposure of early Mars history.

With guided entry, Curiosity's 3.3-ton bullet becomes more like a guided missile. Tilted slightly up so it can “surf” the martian atmosphere, the entry vehicle will sense departures from its intended entry track. Then it will fire side thrusters to get back on track. The promised accuracy of guided entry let the Curiosity team, with community guidance, target the flat Gale crater floor within driving distance of the mound (Science, 29 July 2011, p. 508).

## Testing, testing, testing

“That's a lot of parts that have to work together,” as one scientist observed after watching the EDL video. So with 30 or 40 other engineers, the Curiosity EDL team “analyzed, peer-reviewed, and tested the hell out of” the EDL system, as Curiosity project manager Peter Theisinger of JPL put it during a press teleconference last week. The problem is that “you cannot test as you fly,” he noted. “It is impossible to replicate the EDL conditions of Mars.”

Instead, engineers first tested each EDL component as realistically as they could. They checked the strength of a full-size, 21-meter-diameter Curiosity parachute in the world's largest wind tunnel, tested a scaled-down version for aerodynamic stability in another wind tunnel at realistic supersonic speeds, and investigated aerodynamic regimes inaccessible in wind tunnels in computer simulations. Then they tweaked their design and tested again.

Entry-to-touchdown testing came in a computer simulation of “the entire spacecraft built in a computer,” Sell says. That let them “fly EDL over and over and over again. We do that with thousands of variables and run the system millions of times.” Such testing makes the EDL system “as robust as possible to variations at Mars,” he says, from a gust of wind to an underperforming retro-rocket. “We're still doing it,” Sell says, and “we'll keep doing it until landing day.”

“We're confident we've done everything we know how to do,” Theisinger said. “You do the best testing you can on Earth, but it's not the same. That's where the trepidation is. It's really the unknown unknowns we'll be worried about on the 5th.” That's what stung engineers in 1999 during Mars Polar Lander's Viking-style EDL. Investigators suspect that the onboard control system mistook the jolt of the lander's legs snapping into place for touchdown and cut the retrorockets while the lander was still 40 meters off the ground, ending the mission. Phoenix later landed using the same EDL system (with a software fix), but unknown unknowns are likely still in any EDL. As Sell puts it, “good or bad, August 5th we're on Mars.”

5. Planetary Science

# Could a Whiff of Methane Revive The Exploration of Mars?

1. Richard A. Kerr

The controversy over claimed detections of martian methane—a possible product of life on Mars—could be settled come August once the Curiosity rover arrives at the Red Planet.

How many cows are there on Mars? That depends on which planetary scientist you're asking. Some would say there have been thousands of head of cattle, judging by how much methane three independent groups reported detecting in the atmosphere of Mars in 2003. Earthly cows belch the digestive gas all day long, so a bovine equivalent for Mars is a convenient, if playful, way to quantify martian methane. Whether the reported methane is from microbes eking out a living beneath the surface or from deep stirrings of the geologically moribund planet, no one can say. Either would excite scientists, but only martian biology could rejuvenate a troubled NASA Mars program.

Despite the playful units, planetary researchers are quite serious about their methane on Mars. “I'm shocked by these results,” said planetary scientist Michael Mumma of NASA's Goddard Space Flight Center in Greenbelt, Maryland, when he first announced his team's methane detection at a meeting in 2004, but “our results are certain.” The researchers reported that they had detected a few tens of parts per billion (ppb) by volume of martian methane. They found it by reading the squiggly lines of infrared spectra recorded by ground-based telescopes. Two other independent groups backed up Mumma with their own reported spectroscopic detections.

But some planetary scientists now see no credible signs that there ever was any methane on Mars. Last October, planetary scientist Kevin Zahnle of NASA's Ames Research Center at Moffett Field in California called his invited seminar on the subject “Lack of Evidence for Animal Husbandry on Mars.” Zahnle has never done spectroscopy of any sort. But he and more spectroscopically inclined colleagues have scrutinized Mumma's results, noting that the reported parts-per-billion detection relied on instruments looking through the 2000-times-more-abundant methane of Earth's atmosphere. Correcting for that earthly methane “is just really, really hard,” Zahnle says. “I don't think they can possibly do it.”

The right head count of martian livestock could have multibillion-dollar implications for the exploration of Mars. NASA's Mars science program took a severe hit in President Barack Obama's 2013 budget request this past February (Science, 24 February, p. 900). But once before, in the 1990s, hints of ancient martian life—that time in a meteorite from Mars—helped resuscitate NASA's Mars program. So within weeks after its arrival this August, NASA's rover Curiosity could again fan the flames of life on Mars if it detects uncontestable martian methane.

## Methane, methane everywhere?

Martian methane burst on the scene in March 2004 at a press conference in Paris (Science, 26 March 2004, p. 1953), and was soon followed by two more independent claims in a meeting and its press conference. All three research groups reported at least 10 ppb of methane in the atmosphere of Mars in 2003. That's just 10 cubic centimeters of methane dispersed in the thousand cubic meters of a 10-meter cube of thin martian air. The three claimed detections—all since published in leading peer-reviewed journals—are still often cited as reinforcing one another, implying some measure of consensus. But they have not fared equally well among experts.

All three reported detections rely on recognizing methane's signature in the sun's infrared radiation reflected from the surface of Mars. As solar radiation passes through the martian atmosphere, methane molecules—carbon atoms studded with four hydrogen atoms—absorb infrared energy at specific wavelengths. A spectrometer's optics break the reflected radiation into a rainbowlike spectrum in which scientists can recognize the narrow “lines” of absorption unique to methane.

First to announce the detection of methane was Vittorio Formisano of the Institute of Physics and Interplanetary Space in Rome and the orbiting Mars Express spectrometer team. After the announcement at that Paris press conference, Formisano told Science that he and his team “have seen methane on Mars. A very little amount, but the result is clear.” The group's paper appeared in the 3 December 2004 issue of Science (p. 1758), but its reported detection of 10 ppb averaged across Mars has fared the worst of the three claims.

Sushil Atreya, an atmospheric chemist at the University of Michigan, Ann Arbor, and second author on the Mars Express paper in Science, says the Mars Express result was not a true “detection.” The spectrometer's ability to separate methane's absorption lines from interfering lines, its spectral resolution, was not up to snuff, he says, adding, “I would put more stock in ground-based” results.

The two ground-based claims of martian methane in fact look somewhat better. At times working with colleagues, planetary astronomer Vladimir Krasnopolsky of the Catholic University of America in Washington, D.C., has used spectrometers mounted on large telescopes to search for methane. In three papers in Icarus, the first in 2004, Krasnopolsky reported methane detections.

But Mumma, who has published with Krasnopolsky and supervised him at Goddard, has his doubts. Krasnopolsky's first two reported detections suffered from technical problems in processing the data, Mumma says. In a third paper, in the January 2012 issue of Icarus, Krasnopolsky reports detecting 10 ppb of methane over the Valles Marineris canyon region of Mars in 2006. Mumma calls the result “interesting,” although his own group's observations a few weeks before and after Krasnopolsky's found no detectable methane over Valles Marineris.

## The Cadillac of data reductions

By all accounts, Mumma's observations have fared the best. For one thing, Mumma is highly regarded in the planetary observing community. He has measured 10 different volatile compounds, including methane, spewing from 30 active comets. Mumma and his group are also seen as having most thoroughly accounted for the bugaboo of ground-based observers: Earth's own methane. An absorption line from Earth's methane should be 2000 times as strong as a line from 20 ppb of methane on Mars would be. (After all, Earth has actual belching cows.)

Mumma first reported detection of martian methane at the annual meeting of the Division for Planetary Science (DPS) in November 2004. In his talk, Mumma reported finding 86 ppb of methane using one absorption line and 66 ppb using another line. That rough agreement from two independent absorption lines remains the backbone of the Goddard group's defense of their numbers. “The methane is secure,” he said. At a press briefing later the same day, however, he mentioned a methane concentration of 250 ppb. Over the next year or two, Mumma continued to report readings as high as 700 ppb, Atreya recalls. But none of the numbers appeared in DPS abstracts because Mumma considered them still preliminary.

After almost 4 years of increasingly thorough processing of the raw data, including accounting for terrestrial methane, Mumma and colleagues published their 2003 observations in the 20 February 2009 issue of Science (p. 1041). The group reported much lower final values for the 2003 methane detections—20 to 45 ppb—along with a detection of 5 ppb from 2006. Methane was concentrated in the vicinity of Syrtis Major and Nili Fossae near the equator and varied in abundance from season to season and year to year.

To Mumma's group, that evanescent, plume-like behavior of methane suggested that shortly before the 2003 observations—and perhaps at other times—the planet had been spewing a couple of tons of methane an hour from the ground. The methane might have been microbial, trapped kilometers beneath the frozen crust and released occasionally through crustal cracks. Or it could have been geological, escaping from volcanic or geothermal vents. No one can say what the source would have been, and no one has reported detecting any methane since 2006.

Key to determining whether the martian methane plumes were real is the procedure for removing the spectral signal of Earth's methane. Ground-based observers avoid most of the interference by observing Mars when it is moving toward or away from Earth. That's when the Doppler effect shifts a given martian methane absorption line away from the same line created by terrestrial absorption, making the two lines distinguishable.

Mumma thinks that he and his co-authors—most of whom are at Goddard—have reliably accounted for any remaining methane interference using a sophisticated model of Earth's atmosphere. The 20-person spectroscopy group he directs at Goddard is “a powerhouse in the world community,” he says. That view is widely shared. “Mumma has given [his data] about as good a look as can be,” says atmospheric chemist Paul Wennberg of the California Institute of Technology (Caltech) in Pasadena.

## Not so fast

Zahnle wasn't having any of it. With 30 years of experience modeling the atmospheric chemistry of the planets, he “just couldn't imagine anyone taking [methane on Mars] seriously,” he says. “Methane doesn't behave like this. It was such an obvious joke. I was upset that the community wasn't taking an interest” in critically evaluating detection claims. Instead, methane claims were propelling a proposed orbital mission to Mars, NASA's Trace Gas Observer, on its way to launching in 2016.

So Zahnle looked at methane on Mars the best way he knew how: from a chemical perspective. He concluded that the proposed scenario—repeated injections of methane into the atmosphere, followed by the methane's rapid destruction—would wreak havoc on the composition of the martian atmosphere.

As Zahnle lays out in an April 2011 Icarus paper, destroying that much methane that quickly would consume the atmosphere's meager endowment of oxygen in 7000 years. That might not happen if exotic processes had been overlooked—say, chemical oxidizing agents generated on the dust of self-electrifying dust devils.

But that doesn't seem to be the case, Zahnle says. The standard model of how solar energy creates and destroys chemical compounds already neatly explains the trace gas composition of the martian atmosphere without invoking any such hidden methane-busters. And nonphotochemical means of removing methane, such as adsorbing it onto soil, don't work either if theory, lab experimentation, and the trace gas composition of Mars are any indication, he says. Even microbes feeding on the methane probably couldn't cause the proposed disappearing plumes, Zahnle says. That's because the martian atmosphere abounds in carbon monoxide—a molecule that microorganisms with anything like earthly metabolisms would finish off before starting to consume methane.

Zahnle concludes that there is no support for claims that martian methane plumes were popping up repeatedly almost a decade ago. However, he can't exclude the possibility that a single plume appeared in 2003. “If it's one time in 100 years, it's not a problem,” he says. That relieves atmospheric chemists' great unease with the idea of methane coming and going on Mars. “The photochemical argument Kevin made seems to be pretty solid,” Atreya says.

## About that spectroscopy

Next, Zahnle looked for possible problems in Mumma's spectroscopic methane detection. As an atmospheric chemist, he needed lots of help. So he brought in Richard Freedman of Ames, an astrophysicist and stellar spectroscopist, and David Catling of the University of Washington, Seattle, “somebody who knows something about Mars.”

The trio found several possible problems with both the space- and ground-based spectroscopy, as they reported in the Icarus paper. But the focus of their criticism became the two absorption lines at the core of Mumma and colleagues' reported detections. Mumma, they note, is relying on only two methane lines and can see only one of them on any given observing night.

More worrisome, they say, is their suspicion that the same Doppler shift that conveniently brings Mars methane lines into view, by moving them away from Earth's methane lines, also moves a Mars line to where a minor Earth methane line can impersonate the Mars line. The Mumma group has never seen methane when Mars is moving away from Earth; it is only seen when Mars is moving toward Earth, and the lines are shifted toward the blue end of the spectrum. Zahnle and colleagues suggest that in such a blue shift, the line of methane that contains the heavy carbon-13 isotope comes into coincidence with the martian line of normal methane. The heavy-carbon methane line is about 25 times as strong as the line of martian methane at 20 ppb would be. So the Earth line, the group contends, could appear to signify abundant methane on Mars.

“I'm no spectroscopist, but it's going to be challenging to correct for that,” Zahnle says. “The point is not to slam Mike Mumma. This is just really, really hard; it's ridiculously difficult.”

Mumma disagrees. “I respect Kevin as a colleague,” he says, but “there are so many errors” in the Zahnle et al. paper, some of which “were egregious.” He points to three sorts of consistent behavior in the spectroscopic data that support martian methane. One involves the nonappearance of the terrestrial carbon-13 methane line when, as he sees it, Zahnle's reasoning would have it there. “We've got carbon-13 methane modeled correctly,” Mumma says.

All this debate, which has not gotten much of a public airing, has left the larger planetary community a bit adrift. With 50 years working in the Mars community, geologist Michael Carr of the U.S. Geological Survey in Menlo Park, California, finds methane on Mars “such an iffy thing.” John Mustard of Brown University does spectroscopy of the martian surface from orbiters. “It looks really problematic for Mumma's [detections],” he says. All the variability “just doesn't make sense. I'm thinking it's not there.”

David Crisp of NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, does atmospheric spectroscopy. “My intuition is there's methane there,” he says, “but it's not clear [Mumma] is seeing time and spatial variations.” Interfering atmospheric dust is just too variable on Mars, he says. “If anything, I would trust the detection of methane more than the [reported] absolute amount,” says Mark Allen of Caltech, who was the principal investigator of the now-canceled Trace Gas Orbiter mission. Mumma “is really doing differences of [two] large numbers to get a small number,” Allen says, always a tricky bit of arithmetic.

## Last chance?

Confirming such contentious claims will require getting up close and personal with Mars. The Trace Gas Orbiter was going to carry a capable spectrometer that “could detect three cows on Mars,” Allen says. But NASA killed the mission when it restarted its Mars program in the wake of the Obama Administration's lowered budget request. Next up is NASA's Curiosity rover, arriving at Mars on 6 August. It carries a different sort of spectrometer, the Tunable Laser Spectrometer (TLS). It has two lasers whose beams bounce back and forth 81 times through a sample cell filled with martian atmosphere. The lasers scan across infrared wavelengths in which methane has not one or two but three absorption lines that form a distinctive fingerprint for methane. “It's a very simple, direct, and unambiguous measurement,” says TLS developer Christopher Webster of JPL.

TLS will also be extremely sensitive. Its first quick measurement, scheduled for the first few weeks of the mission, should be able to detect as little as 1 ppb of methane. Mumma calculated that the 2003 release of methane would have amounted to 6 ppb once it spread around the planet. Although Mumma sees his observations as suggesting that methane on Mars has a lifetime of a few years, atmospheric chemists still think martian methane would last several centuries. If they are right, almost all of 6-ppb methane should still be there. And even if it is destroyed faster, when TLS takes a longer look at atmospheric samples, it will be able to detect 50 to 100 parts per trillion of methane, according to Webster. If methane really is long-lived on Mars, Zahnle says, Curiosity “is going to crush this.”