# News this Week

Science  15 Apr 2011:
Vol. 332, Issue 6027, pp. 288
1. # Around the World

1 - New Delhi
Superbug Gene Found In Tap Water
2 - Washington, D.C.
U.S. Reaches Spending Deal
3 - Fukushima, Japan
Japan Widens Evacuation Zone
4 - Nigeria
African Countries Up Investment In Agricultural R&D
5 - Harima Science Park City, Japan
World's Second X-ray Laser Declared Done

## New Delhi

### Superbug Gene Found In Tap Water

A gene that causes bacteria to become resistant to antibiotics has been found in drinking water in New Delhi. NDM-1 is commonly found in Escherichia coli but can spread to other bacteria thanks to their ability to swap DNA. The gene confers resistance to antibiotics, including potent, last-resort drugs called carbapenems.

India's warm temperatures, overcrowding, and poor sanitation are likely to blame for the gene's spread into the main water system from bacteria in people's guts, write Timothy Walsh of Cardiff University in the United Kingdom and colleagues in a paper published online last week in The Lancet Infectious Diseases. The team, which found the gene in two of 50 tap water samples and 51 of 171 samples taken from puddles and streams in the capital, say the gene could spread farther afield when tourists drink local water supplies and then return home. NDM-1 has already been found in U.K. hospitals in bacteria infecting people who had medical treatment in India and those admitted with “traveler's tummy.” The new finding raises concerns that resistant genes, so far found mainly in gut flora, are becoming widespread in natural environments, where they are highly mobile.

## Washington, D.C.

A deal between Congress and the White House to cut current government spending by $38.5 billion will also affect federal research activities. But the final agreement, due to be approved as Science went to press, is much gentler on research than earlier versions approved by the Republican-led House of Representatives. The negotiations that narrowly averted an 8 April government shutdown produced an agreement to lower discretionary spending to$1.05 trillion for the 2011 fiscal year, which ends on 30 September. The overall federal budget is three times that size, with the majority spent on so-called entitlement programs like Medicare and service on the national debt. So the next debate, over the 2012 budget and extending the $14 trillion debt ceiling, is expected to be even more contentious. For more, see page 291. ## Fukushima, Japan ### Japan Widens Evacuation Zone Japanese officials announced this week that they are expanding the evacuation zone around the stricken Fukushima Daiichi nuclear reactors after relatively high levels of radiation were found beyond the 20-kilometer evacuation zone and even the 30-kilometer zone within which people have been told to stay indoors. Japan's Nuclear Safety Commission is now recommending relocation over the next month for those living in areas where the accumulated dose over a year will reach 20 millisieverts. That's about seven times the annual dose from natural sources in the United States. The government also raised its rating of the Fukushima incident on the International Nuclear and Radiological Event Scale from five to the highest level, seven, ranking it on par with the Chernobyl disaster as a “major accident.” The contaminated areas lie northwest of the nuclear power plant, where weather patterns apparently blew a radioactive plume in the early days of the crisis. Radiation levels throughout the region have dropped over the past month as iodine-131, with a half-life of 8 days, decays. But the other main radioisotopes, cesium-134 and cesium-137, have half-lives of 2 years and 30 years, respectively. In areas not targeted for remediation, significant levels of radiation could linger for decades. http://bit.ly/evac-zone ## Nigeria ### African Countries Up Investment In Agricultural R&D Funding for public agricultural research in sub-Saharan Africa grew more than 20% to$800 million between 2001 and 2008, according to a report published last week by the International Food Policy Research Institute (IFPRI) in Washington, D.C. “African countries are starting to recognize the importance of funding agricultural research,” says Calestous Juma of Harvard University, who studies agricultural innovation in Africa.

Just six of the 32 nations surveyed dominate these gains, and Nigeria leads the pack, accounting for a third of the overall increase. But as in several other African countries, the increases—mainly for salaries and building repairs—have not yet made up for the declines of the 1990s. “What these numbers hide is that Nigeria is making up for lost ground,” says report co-author Gert-Jan Stads of IFPRI. The funding situation has worsened in 13 countries, often due to large international grants ending.

Philip Pardey, an agricultural economist at the University of Minnesota, Twin Citites, says that rebuilding research capacity can take decades. African nations “have a very long way to go,” he says.

## Harima Science Park City, Japan

### World's Second X-ray Laser Declared Done

Scientists now have two x-ray lasers—almost. Physicists at the SPring-8 laboratory in Harima Science Park City in Japan have coaxed x-rays out of the SPring-8 Angstrom Compact Free Electron Laser, or SACLA, lab officials announced. The first x-ray free electron laser, or XFEL, turned on 2 years ago at SLAC National Accelerator Laboratory in Menlo Park, California. However, scientists in Japan have not yet demonstrated “lasing” with the new machine, says SPring-8's Tsumoru Shintake, technical director for the project. But the Japanese government wanted SACLA completed by the end of its 2010 fiscal year, which ended 31 March, so physicists put on a demonstration that it basically works, Shintake says.

## Beyond Entropy

When designing a building or a city, architects usually put things together in an orderly fashion. But in a month-long exhibition beginning 3 May at the Architectural Association School of Architecture in London, Italian architect Stefano Rabolli Pansera has challenged artists, architects, and scientists alike to embrace order's nemesis: entropy.

In the show, titled “Beyond Entropy,” eight interdisciplinary groups explore the second law of thermodynamics in the context of sound, electricity, heat, and gravitational potential energy. The works include a swinging pendulum, connected to a continuously projected image of a building being simultaneously built and destroyed; a 1-meter-high spinning “time machine”; and a pinball-like game (pictured) that invites viewers to flick Ping-Pong balls through a gap in a mirror while ruminating about potential energy. In preparation, each of the teams visited scientific institutions, including the Large Hadron Collider near Geneva, Switzerland, for inspiration.

Pansera says that his motivation for the show is to get people to think about energy not as a problem to try to solve, but “as a new way to think about space.”

4. Ecology

# Uncertain Future for Tropical Ecology

1. Craig Simons*

Three premier research outfits are scaling back ambitions—and struggling to maintain local staffs as funds grow scarce.

MADANG PROVINCE, PAPUA NEW GUINEA—Joseph Kua peers at the computer screen of a survey tripod perched precariously on a jungle hill. The 30-year-old oversees part of a team that will spend much of this year logging species in a 50-hectare plot of pristine rainforest. That may sound like the makings of a doctoral dissertation, but Kua has only a high school diploma. A native of a remote mountain village, Kua spent 2 years helping a Czech graduate student study bark beetles and then several months learning how to conduct biodiversity surveys. He's one of 18 paraecologists—locals trained to do the nuts and bolts of ecology research—employed by the New Guinea Binatang Research Center (BRC), a tropical ecology institute here on Papua New Guinea's north coast.

Western researchers point to the work of Kua and other paraecologists as an example of excellent science on a shoestring. By hiring and training locally, scientists can boost productivity and cut costs, all while supporting conservation. On the backs of paraecologists, BRC and two similar outfits in Costa Rica—the National Biodiversity Institute (INBio) and a group at Area de Conservacion Guanacaste (ACG) led by University of Pennsylvania ecologist Daniel Janzen—over the past 2 decades have discovered thousands of species and churned out hundreds of peer-reviewed articles. Although most paraecologists start with little science knowledge, some have gone on to earn advanced degrees and take key positions in national forest management and conservation.

It's “a brilliant approach that builds relevant local capacity at modest cost,” says Thomas Lovejoy, a biologist at George Mason University in Fairfax, Virginia, and a former chief biodiversity adviser to the World Bank. Thanks to paraecologists, BRC, INBio, and ACG “have had a profound impact on tropical ecology over the last 2 decades, most fundamentally through the sheer number of species identified and documented,” says Elizabeth Losos, president of the Organization for Tropical Studies, a consortium of 63 universities and institutes headquartered in Durham, North Carolina.

But paraecologists may be a vanishing breed. Money woes now bedevil all three projects and threaten the concept of local, long-term hiring for field research. INBio has shrunk its taxonomic staff from 50 in 2005 to 31 today. At ACG, Janzen and his wife, Penn biologist Winnie Hallwachs, are scrambling to avoid having to lay off 29 parataxonomists they supervise. The U.S. National Science Foundation turned down a grant application Janzen submitted last year>—leaving them without NSF money for the first time in 48 years. BRC, meanwhile, is struggling to find stopgap funding after losing the longtime support of the U.K. government's Darwin Initiative. The challenges are “lethal and nerve-wracking,” Janzen says.

Funding crises at the three premier centers are the result of a perfect storm of problems. Donors have shifted funding away from taxonomy for more than a decade, leaving a huge backlog of unidentified specimens. A panel that reviewed Janzen's NSF grant application rated it as “outstanding” but expressed this concern: “Although previous work has been very successful in identifying species new to science, it is not clear from the proposal how, when or if these novel species will be described.” INBio's 2005 decision to downsize was driven partly by a backlog of unidentified specimens, says INBio Director Rodrigo Gámez. “The world does not have the number of taxonomists required to process [so many new species],” he says.

The global financial crisis intensified the problem. The Darwin Initiative was one of many donors that curtailed grants, accepting no new applications last year and driving up competition for other funds. And as projects have scaled back, some researchers worry that paraecologists are taking jobs from graduate students. One unnamed reviewer noted that Janzen's NSF grant proposal was “unusual in that no students are trained directly by [Janzen] or intellectually engaged in the project.” Janzen insists that students would have worked under his supervision at ACG. Moreover, he says, local staffers often become excellent scientists and conservation leaders and deserve opportunities to learn. “Some people in the ivory tower see [paraecologists] as incredibly useful support. Others see them as huge competition,” Janzen says.

Today's problems are a far cry from the heady early days. Janzen coined the term “paraecologist” in 1989, when he used a U.S. Agency for International Development grant to train 16 Costa Rican villagers and park service staff in collection and preservation of field specimens. “The concept,” he says, “is to take someone out of the farming community and teach them what you expect a good graduate student to be able to do in carrying out an inventory.”

Some pioneering paraecologists took jobs at INBio, which Janzen cofounded and where he continues to serve as an unofficial adviser. INBio started with the lofty vision of inventorying every species in Costa Rica and finding sustainable ways to use the country's immense biodiversity. While its leaders have since scaled back their ambitions—for example, deciding not to sample mollusks and nematodes—they have discovered two species on average each week since 1989. “Within a few years of the initiation of INBio in Costa Rica,” Losos says, “the number of insect species known to exist in the country increased more than fivefold.”

Paraecologists have enabled large-scale and long-term research at ACG and BRC as well. Janzen>'s project has cataloged more than 9000 butterfly and moth species in the 120,000-hectare ACG, a feat that could have been accomplished only with paraecologists, he says: Hiring graduate students would have required “a budget 10 times bigger.”

In Papua New Guinea, BRC is running two major initiatives. The project Kua helps lead will count every tree with a diameter of 1 centimeter or more in a 50-hectare plot; it will contribute to efforts by the Center for Tropical Forest Science, a project run by the Smithsonian Institution and Harvard University, to understand how forests change over many years. A second project is inventorying herbivorous insects on every plant in a 1-hectare plot of highland rainforest. So far, researchers have documented only a thimbleful of roughly 50,000 plant-insect interactions presumed to exist, such as a caterpillar that feeds on specific fig tree species, says BRC Director Vojtech Novotny, an ecologist who splits his time between BRC and the University of South Bohemia in the Czech Republic. “We definitely need such large studies simply because of the complexity of tropical rainforest,” he says.

Costs are also significantly lower than for studies that involve flying in researchers and equipment. At BRC, paraecologists earn roughly $300 a month plus training fees and receive room, board, and health care. Village assistants earn$4 a day and benefits—a welcome wage in a region with few job opportunities. “In most businesses and even intellectual activities, Western countries are outsourcing while tropical ecologists are still sending often overqualified postdocs or graduate students to do the type of fieldwork that could be done better and more efficiently by paraecologists,” Novotny says.

As a bonus, he says, paraecologists help doctoral students carry out dissertation research more quickly, and they promote conservation. “The forest research sites in Papua New Guinea show locals that conserving forests can bring a sustainable income,” says Chris Dahl, a 35-year-old BRC deputy director who started as a paraecologist in 1994. Local knowledge can also pay off. Five years ago, for example, villagers angered over a land dispute threatened to raze a BRC field station. Paraecologists defused the tension by presenting the villagers with a pig—a traditional peace offering.

These days BRC itself could use an offering. Staff now “absolutely have to raise new grants” this year, Novotny says. “If we don't, we'll become dormant here.” Janzen faces similar problems. When NSF turned down his grant application last summer, he scrambled to raise $500,000 from private sources, enough to pay staff salaries through this coming July, and began building what he hopes will become a$10 million endowment. He also reapplied to NSF with a slimmed-down proposal. Even if he gets the grant, he says, he must raise at least $400,000 a year from other sources to maintain his budget. At INBio, until 2005 a pair of 7-year grants had covered most of the inventory program's$900,000 annual budget. Today, almost its entire \$471,000 budget is self-funded, largely by ventures that include a biodiversity theme park, a publishing house, a bioprospecting unit, and an environmental consultancy. INBio built those businesses as Costa Rica grew richer in the 1990s and foreign governments cut aid to projects, including INBio.

Here in Papua New Guinea, BRC is hunkering down for a hard year. Whereas visiting scientists can pack up and go home when grant money dries up, Novotny must meet payroll for the station's staff—including its indispensable paraecologists. “We really can't afford to have a gap in funding, even for a single year,” he says. New growth is out of the question, he adds. “Now our best-case scenario is to stabilize the place.”

• * Craig Simons is a writer in Beijing.

5. Retrotransposons

# Do Jumping Genes Spawn Diversity?

1. Gretchen Vogel

The data are clear. Transposable elements move in developing brain cells. But the question remains: Does the brain tolerate them or take advantage of them?

In theory, the behavior of inbred mice reared and housed under seemingly identical conditions should be as similar as their perfectly matched genes. But, to the frustration of researchers, the rodents don't act like exact copies of each other. “You control for everything you can, and in behavioral tests, the variance is enormous,” says Fred Gage, a neuroscientist at the Salk Institute for Biological Studies in San Diego, California. Even within a single litter, he says, “one mouse will be unusually smart, another below average.”

Of the possible explanations for such differences, Gage and his colleagues have found evidence for a particularly unexpected one: jumping genes in the brain. Formally known as transposable elements, they are small bits of genetic material that can move around the genome. They have generally been seen as troublemakers; when they jump, they can land in places that cause mutations or otherwise skew the expression of important genes. But Gage and his former postdoc Alysson Muotri, now at the University of California, San Diego, argue that such changes might have a positive side, helping to generate diversity in brain cells. Such diversity might be important in brain development, they think, providing the raw material for building a flexible organ able to react to new environments and situations. And because a transposable element creates a slightly different genome each time it moves, it could explain why genetically “identical” mice aren't identical after all.

It's far from a proven idea, but it has started to gain attention among geneticists who study jumping genes. The team's discoveries have prompted some scientists to expand their ideas about the role of these mobile bits of DNA, which they have frequently dismissed as “junk” that got in the way of sequencing an organism's genome and identifying its genes.

The data from brain cells “overturned a dogma” that transposable elements primarily jump in germ cells and tumor cells, says John Moran, a geneticist at the University of Michigan Medical School in Ann Arbor, who is a co-author of several of Gage and Muotri's papers. “They opened people's eyes to say, ‘Wait, might there be other places where these elements can jump?’ And where people have started to look, they have started to find them,” he says. That includes, surprisingly, very early embryos, which means that tissues other than the brain might also be affected by jumping genes. Still unclear is what effect the movements of transposable elements are having on the brain, let alone elsewhere in an animal's body, Moran and others caution. “What is the functional consequence? At this point, it remains speculative,” says Pierre Vanderhaeghen, a developmental biologist at the University of Brussels.

## Copy-and-paste parasites

Gage and Muotri's work focuses on a transposable element called L1 that can copy itself and paste the new version elsewhere in the genome. Such copy-and-paste jumping genes are called retrotransposons because their replication machinery is similar to that of retroviruses, such as HIV. They are considered genetic parasites because they use an organism's genome to proliferate. Over time, they have been quite successful: Scientists estimate that the human genome includes more than 500,000 copies of L1. Most have mutations in key stretches of their DNA sequence and can't replicate. But roughly 100 copies are active, able to spawn new L1s that jump to new chromosomal locations.

Most of the time, cells keep these elements under wraps, tagging the L1 DNA with methyl groups, which prevent its genes from being expressed and making the enzymes that perform the copying and pasting. But from time to time, as a cell removes methylation to allow the expression of important genes, the L1s escape their shackles and new copies start jumping again. “They're like the velociraptors in Jurassic Park,” Moran says. “They keep banging on the fence, looking for a way to get through. Sometimes they succeed.”

Because they are parasites that need to commandeer their host's machinery, what better place to jump than into the cells that will give rise to sperm and eggs? Any new working copy of L1 in a gamete will then be passed on to every cell in the resulting offspring. The fact that nearly 45% of the human genome is made up of jumping genes and their remnants demonstrates that heritable jumps have happened quite often in evolution.

Many scientists had assumed that somatic cells—those that don't give rise to sperm or eggs—would keep their transposable elements under stricter control to prevent the potential damage the jumps can cause. For many years, tumor cells were the only adult cells that seemed to have actively jumping elements.

But researchers hadn't really been looking elsewhere for jumping genes. In fact, because there are so many inactive copies of L1 cluttering the genome, many experiments are designed to filter out their DNA. But in 2002, researchers in Gage's lab spotted something surprising as they were searching for signals that play a role in the development of brain cells. They were searching for genes that were overexpressed in rat neural progenitor cells, which give rise to neurons and other brain cells, and unexpectedly found L1 RNA expressed at high levels.

When Muotri joined the lab, Gage asked him to follow up on the observation. To find out whether the L1 elements were really jumping in developing brain cells, the scientists used a genetically engineered copy that incorporates the gene for green fluorescent protein (GFP). When this modified L1 is active in a cell, the cell glows green. In 2005, the scientists reported in Nature that when they inserted the transgenic L1 into cultured rat neural stem cells, many of the differentiating cells turned green, indicating that the L1 was making new copies of itself. They also found that cells in which L1 jumped were more likely to become neurons and that one of the newly created L1s inserted next to a gene important to neuronal differentiation, increasing its expression (Science, 17 June 2005, p. 1729).

Muotri's research background was in cancer, in which L1s were thought to cause trouble in cells, so he was initially taken aback by the suggestion that such elements might be useful. “If they were really being mobilized in neural stem cells, they could cause cancer or do other damage,” he says. “But we soon realized that might not be the whole story.”

Because their research suggests that L1 activity happens in normal neural stem cells, the researchers wondered whether jumping DNA plays a regular role in brain development. The mammalian brain produces far more neurons than it needs, and during development—even into childhood in humans—it ultimately prunes many of its cells and connections. Gage, Muotri, and their colleagues hypothesize that L1's effects on neuronal genes during development provide a range of neurons with subtly different properties on which a kind of natural selection then acts. “In evolution, there are two players: generation of diversity and then selection,” Gage says. The L1 activity “provides enough [neuronal] diversity so that you can optimize your response to the variety of environments you might encounter throughout life.”

## Jumping all over

Since their initial findings, the researchers have strengthened their case, extending their work from rodent to human cells. In August 2009, Gage, Moran, and their colleagues reported in Nature that L1 elements also jump in lab-grown human neural stem cells. Again they found that the new copies of L1 sometimes landed near genes that are expressed in neurons, suggesting that such jumps could alter important functions of the brain cells. They also documented significantly more copies of L1 in the genomes of brain cells from an adult human than in the liver or heart cells from the same individual. Using an extremely sensitive PCR technique, they estimated that brain cells had about 80 additional copies of L1 compared with other tissues. Furthermore, within the brain, the scientists found even higher numbers of L1s in the hippocampus, an area in which neurons continue to form throughout life. So in theory, L1s could influence both adult neurogenesis and initial brain development.

The same week, in Nature Neuroscience, Muotri, Gage, and colleagues reported another link between L1 and the brain. They showed that a molecule called Wnt can trigger the expression of a transcription factor called NeuroD1, which can help induce the development of neurons in the adult brain. The same Wnt-mediated pathway, they found, also triggers expression of L1. A month later, the researchers reported online in Hippocampus that exercise, known to prompt the growth of new neurons, also triggered increased expression of L1 in the brains of mice. “They have clearly established the idea that L1 retrotransposition seems to be triggered by neurogenesis,” Vanderhaeghen says.

The story took a new twist last November when the team reported in Nature that the gene underlying Rett syndrome is connected to L1. Rett syndrome affects children who carry a mutation in a gene called MeCP2, causing developmental problems, including some symptoms that resemble autism. The gene is involved in methylation, and work in other labs had shown that MeCP2 cooperates with a gene already known to silence L1. Maria Carol Marchetto, a postdoc in Gage's lab (and Muotri's wife), wondered how the MeCP2 mutation would affect L1's behavior in brain cells. To find out, the researchers inserted the GFP-engineered L1 into the genome of mice carrying an MeCP2 mutation and found that the rodent brains were full of green cells—indicating that the L1 was jumping much more often than in normal mouse brains.

Researchers outside Gage's lab are impressed but perplexed. “The work itself is such a high order of technical proficiency. It's really a tour de force,” says Anthony Furano, who studies L1 at the U.S. National Institute of Diabetes and Digestive and Kidney Diseases in Bethesda, Maryland. “Now the question is, what does it mean? Is this having an important effect on the phenotype of neuronal cells?”

Other researchers are starting to take a closer look at L1 elements in different developmental stages. In 2007, Moran and his colleagues found that L1 is active in human embryonic stem cells, suggesting that they might also be jumping in early embryos. Last year, Haig Kazazian Jr., a geneticist until recently at the University of Pennsylvania and now at Johns Hopkins University in Baltimore, Maryland, and his colleagues reported in Genes and Development that L1 elements are indeed active in the earliest embryos of mice, before the embryo implants in the uterus. When an L1 replicates in one of the few cells of an early embryo, that new copy will propagate into a subset of the body's final tissues, making them genetically distinct from the rest of the animal. Given how often this may happen in the early embryo, there may be much more genomic variation within individuals than most researchers had assumed. “We were really surprised,” Kazazian says, to find more L1 jumps in early embryos than even in sperm or egg cells. “It made us think that maybe [Gage] is on to something.”

6. Lunar And Planetary Science Conference

# Asteroid Model Shows Early Life Suffered a Billion-Year Battering

1. Richard A. Kerr

Geologists and planetary scientists at the Lunar and Planetary Science Conference reported evidence of a prolonged pummeling by huge asteroids several billion years ago that would have dwarfed the one that killed off the dinosaurs.

Life was hard on early Earth, but geologists and now planetary scientists are reporting evidence of even more biotic stress several billion years ago: a prolonged pummeling by huge asteroids that would have dwarfed the one that killed off the dinosaurs.

Geologists were the first to suspect that the Archean eon—the time from 3.8 billion years ago to 2.5 billion years ago—suffered far more big hits than anyone had thought. In the past decade, routine fieldwork began turning up odd, centimeters-thick rock layers that turned out to contain impact debris: droplets of molten rock that crystallized and fell to form a layer of distinctive little balls, or spherules. The dinosaur-killer impact 65 million years ago was the only impact of the past half-billion years big enough to create a widespread spherule layer.

During the Archean, however, big, spherule-bed-generating impacts were far more frequent than that, geologists have reported at prior meetings here. Taken together, the known impact beds suggest that there was a large impact every 40 million years on average in the Archean, not every 500 million years, as has lately been the case.

At this meeting, planetary dynamicist William Bottke of the Southwest Research Institute in Boulder, Colorado, and colleagues offered an explanation for the severe, lengthy pummeling. A raised impact rate at any time means the smaller bodies of the solar system must have been shaken up gravitationally. For example, to explain the brief burst of impacts 3.9 billion years ago, called the late heavy bombardment, a group of planetary dynamicists has proposed that an inward drift of the giant planets Jupiter and Saturn could have gravitationally shaken up the asteroid belt between Mars and Jupiter and scattered asteroids toward Earth and its moon (Science, 17 July 2009, p. 262). But the resulting shower of impacters would have lasted only 100 million years or so, not the billion years geologists have found, so it can't explain the prolonged Archean shower.

Bottke and colleagues now think they have an explanation. Last year at the meeting, they proposed that as Jupiter and Saturn moved inward, they also scattered asteroids out of a now-missing inner band of the asteroid belt. In the researchers' computer simulations, many of those asteroids scattered into sharply tilted orbits just inside the asteroid belt. The asteroids still lingering in this outlier group are called the Hungaria asteroids.

This year, Bottke and colleagues report that the Hungaria asteroids could have been the source of all those Archean impacts. That's possible because once scattered into the realm of the Hungarias, a body is particularly slow to leave it and possibly hit Earth. This dynamical “stickiness” could have prolonged the bombardment of the inner solar system through the Archean and even a ways into the Proterozoic of 0.5 billion to 2.5 billion years ago.

The group's model gave a good match to what scientists see: the number of current Hungaria asteroids, the number of huge impact basins on the moon, the number of dinosaur-killer-size impacts on the early moon, and the number of impact-generated spherule beds on the Archean Earth. “I'm always a little leery of results from one or a few simulations,” says Renu Malhotra of the University of Arizona in Tucson, herself a dynamical modeler, “but it seems plausible. I don't see any obvious problems.”

The larger Archean impacts would have been disastrous—boiling off the upper ocean, for example—but how the later Archean pounding affected the single-celled life in the oceans then remains to be seen. Bottke sees some eerie coincidences, however; for example, both the end of huge impacts and the first appearance of atmospheric oxygen occurred 2.5 billion years ago. “Do connections exist?” he asks in his meeting abstract. “The game is afoot!

7. Lunar And Planetary Science Conference

# Prime Science Achieved at Asteroid

1. Richard A. Kerr

At the Lunar and Planetary Science Conference, Japanese researchers announced that detailed analyses of the sample the Hayabusa spacecraft returned from asteroid Itokawa have confirmed that the most common type of meteorite falls to Earth from a class of asteroids long cloaked by a mysterious discoloration.

A crippled Hayabusa spacecraft barely made it back to Earth last June, and it returned only a wisp of a sample from Itokawa, the asteroid it visited in 2005. But at the meeting, Japanese researchers announced that the little spacecraft that could has scored a solid scientific success. Detailed analyses of the sample—the first ever returned from an asteroid—have confirmed the oft-contentious claim that the most common type of meteorite falls to Earth from a class of asteroids long cloaked by a mysterious discoloration.

The first chore for Hayabusa analysts was to get their sample out. The spacecraft's malfunctioning sampling mechanism did collect asteroidal rock particles, just mostly smaller than 10 micrometers. A specially designed extraction tool was a bust. A Teflon spatula worked much better. In the end, turning the canister upside down and rapping it 20 times with a screwdriver did the trick. All told, there were about 1500 particles from Itokawa smaller than 100 micrometers.

Next, researchers across Japan applied an alphabet soup of microanalytical techniques—XRD, XRF, UMT, FIB, TEM, SEM, EPMA, and SIMS—to 52 particles. Their directly determined chemical, mineralogical, and isotopic compositions, it was hoped, would finally settle a decades-long debate (Science, 14 July 2006, p. 158). Judging solely from spectral colors, researchers had found that S-type asteroids—the most common in the inner asteroid belt—appeared to have a composition different from the most common type of meteorite found on Earth, the ordinary chondrites.

Closer remotely observed spectral signatures eventually led most researchers to conclude that exposure to the rigors of space had “weathered” the surfaces of ordinary chondrite asteroids until they no longer spectroscopically resembled chondritic meteorites. By 2001, astronomer Richard Binzel of the Massachusetts Institute of Technology and his colleagues concluded from telescopic observations that Itokawa was indeed chondritic—a member of the compositionally distinct LL subclass of ordinary chondrite meteorites.

Hayabusa analyses presented at the meeting now clearly show that Itokawa is a space-weathered ordinary chondrite, and an LL ordinary chondrite at that. That brings an “irrefutable closure to the long-standing ‘S asteroid conundrum,’” says asteroid specialist Clark Chapman of the Southwest Research Institute in Boulder, Colorado. “This is a stunning validation of the power of remote-sensing mineralogical analysis of asteroids.” Next up, analyzing more Hayabusa particles to pin down what sort of space weathering muddled the field for so long.

8. Lunar And Planetary Science Conference

# Snapshots From the Meeting

1. Richard A. Kerr

Snapshots from the Lunar and Planetary Science Conference include briny flows and new crater-forming meteorite hits on Mars.

## Briny flows on Mars?

No one has proved that the water on Mars gets warm enough to flow, but Alfred McEwen of the University of Arizona in Tucson said at the meeting that he has pictures of “the most viable targets for actual liquid on Mars today.” Taken by the camera on board Mars Reconnaissance Orbiter, for which McEwen is the principal investigator, the pictures seem to show multitudes of rivulets that have dampened and darkened the soil and may even have cut shallow, meterwide channels as they streamed from rock outcrops down steep slopes. McEwen and colleagues found that their “transient slope lineae” form where and when the ground would be warm enough for liquid water or brine and fade away after summer warmth. Even if water were involved, it may be too salty for life, McEwen noted, but these lineae certainly bear watching.

## Craterin' time on Mars.

The slow, steady drizzle of meteorites onto a planet, like sand falling in an hourglass, is the only clock Mars scientists have to keep track of geologic time. So the surprising report that Mars suffers 100 new crater-forming meteorite hits a year garnered some attention. Planetary scientist Ingrid Daubar of the University of Arizona in Tucson and her colleagues used two cameras on board the Mars Reconnaissance Orbiter to identify 201 fresh impact sites formed in recent years. That's surprisingly close to an estimate other researchers had made by extrapolating from counts of much larger, ancient craters to small, modern ones—not a guaranteed sort of calculation. The finding lends tentative support to crater-counting dating of geologically recent events on Mars, from the cycling of ice ages to the cutting of gullies by ever-elusive liquid water.

9. Lunar And Planetary Science Conference

# A Badly Battered Vesta Awaits Dawn's Arrival

1. Richard A. Kerr

A group of impact modelers argued at the Lunar and Planetary Science Conference that the object that crashed into asteroid Vesta—the asteroid belt's second-most-massive body—and reshaped its geology was eight times as massive as previously thought.

Planetary scientists are waiting eagerly for July, when the Dawn spacecraft is due to arrive at asteroid Vesta. If greater complexity makes for greater scientific interest, they're in for a bonanza. The asteroid belt's second-most-massive body has had quite a complicated life. It melted early on to form an iron core and rocky mantle and crust, spewed volcanic outpourings, and then suffered a massive impact.

Now, to spice things up even more, a group of impact modelers is arguing that the object that crashed into Vesta and reshaped its geology was eight times as massive as previously thought. “Vesta really gets messed up by this impact,” impact specialist H. Jay Melosh of Purdue University in West Lafayette, Indiana, said at the meeting.

When the Hubble Space Telescope gave astronomers their first fuzzy glimpse of Vesta in 1997, they saw an impact crater 460 kilometers in diameter—nearly as wide as the asteroid itself—centered at its south pole. Researchers estimated that another asteroid about 40 kilometers in diameter had plowed into Vesta at 20,000 kilometers per hour.

Impact modelers Boris Ivanov of the Institute for Dynamics of Geospheres in Moscow, Melosh, and Elisabetta Pierazzo of the Planetary Science Institute in Tucson, Arizona, set out to put a firm number on the size of the Vesta impactor. They ran a computer simulation of the collision using impactors of different sizes until the final model Vesta matched the squashed shape seen in Hubble images. The best fit required an 80-kilometer impactor—twice the size previously assumed, with eight times the mass and thus eight times the impact energy.

Geologists should get an eyeful on Dawn's arrival. “I would be astonished if we didn't see some mantle exposed” in the crater, Melosh says. Mantle rock from as deep as a few tens of kilometers down may be visible in the crater's center where rock rises into a peak. Crust, on the other hand, would have been thrown across the rest of Vesta all the way to the antipode, possibly in shapes that might be mistaken for more conventional geologic forms such as crustal folds. Interesting indeed.