News this Week

Science  03 May 2013:
Vol. 340, Issue 6132, pp. 530
  1. Around the World

    1 Washington, D.C.
    House Passes Helium Bill
    2 Washington, D.C., and Seoul
    Extension of Nuclear Deal Disappoints Scientists
    3 Bethesda, Maryland
    HIV Vaccine Study Meets Premature End
    4 Ontario, Canada
    Experimental Lakes Get Lifeline
    5 Brussels
    Controversial Pesticide Ban Goes Forward
    6 Priština
    Reconciliation With Serbia Opens Research Doors
    7 London
    New Libel Law for England and Wales

    Washington, D.C.

    House Passes Helium Bill

    CREDIT: © THEODORE GRAY/VISUALS UNLIMITED/CORBIS

    On 26 April, the U.S. House of Representatives passed a bill by a vote of 394 to 1 that would head off a looming helium shortage. Helium is required to run MRI machines, manufacture optical fibers and microchips, and cool samples to near absolute zero. Federal helium reserves now supply 42% of the United States' demand for helium and 35% of the global demand.

    The shortage is of the government's own making. Following a mandate by Congress, in 2003 the Bureau of Land Management (BLM) began to sell off federal helium reserves stored near Amarillo, Texas, to recoup the $1.3 billion that the government spent accumulating the helium. But by October, BLM will break even and has no further mandate to sell the remaining helium. BLM also charges a below-market price for its helium, which encourages waste and discourages the development of new sources of helium.

    The House bill would continue sales for another year and then would require at least 60% of the helium to be sold in semiannual auctions. After the reserve drops below a certain level, in about 5 years, sales would be limited to federal users. The Senate Committee on Energy and Natural Resources will hold a hearing on a similar bill on 7 May. http://scim.ag/Hebill

    Washington, D.C., and Seoul

    Extension of Nuclear Deal Disappoints Scientists

    Powered up.

    South Korea's nuclear reactors provide 40% of its electricity.

    CREDIT: YONHAP NEWS/YNA/NEWSCOM

    The announcement on 24 April that U.S. and South Korean negotiators seek to extend the conditions of a long-term agreement on nuclear power cooperation is not pleasing anyone. Under the 1974 deal, due to expire next year, the United States provides expertise and fuel to South Korea's nuclear power industry as long as the latter refrains from enriching uranium and reprocessing spent fuel. But South Korea wants to enrich uranium to supplement its growing nuclear power plant export business, and it wants reprocessing technology to handle spent fuel from its 23 reactors, which produce nearly 40% of its electricity. Such know-how, however, can be applied to producing nuclear bomb material.

    Unable to reach terms on a long-term deal, U.S. and Korean negotiators opted to extend the current agreement for 2 years. That doesn't please scientists. "Frankly, the nuclear power research community is disappointed," writes nuclear fusion specialist Gyung-Su Lee to Science in an e-mail. Lee, who led the development of South Korea's Korean Superconducting Tokamak Advanced Research reactor, noted that South Korea has adhered to the Nuclear Non-Proliferation Treaty and should be considered as trustworthy as Japan, which is developing enrichment and reprocessing technologies. http://scim.ag/USKornuc

    Bethesda, Maryland

    HIV Vaccine Study Meets Premature End

    The largest HIV vaccine study in the world came to a premature halt last week when an early analysis showed that it didn't work. The trial, launched in 2009, was taking place in 19 U.S. cities and involved giving two vaccines to 2500 men and transgender women who have sex with men.

    The vaccines, made by the U.S. National Institute of Allergy and Infectious Diseases (NIAID), consisted of HIV genes stitched into DNA and, separately, a harmless adenovirus. NIAID halted the trial 2 years before its planned end upon the recommendation of an independent data and safety monitoring board. The board found that vaccinated people became infected as readily as those given placebo shots. The vaccines also failed to help control the virus in those who became infected.

    Mitchell Warren, head of the AIDS Vaccine Advocacy Coalition in New York City, said the silver lining is that the study's early end tells the field to look elsewhere immediately. "There are other approaches that must be pursued without delay," Warren said.

    Ontario, Canada

    Experimental Lakes Get Lifeline

    Quick save.

    ELA reseachers get a reprieve.

    CREDIT: ELA

    Canada's Experimental Lakes Area (ELA) will remain open this year with money from the province of Ontario. But that funding, announced on 24 April by Ontario Premier Kathleen Wynne, may be only a temporary lifeline. The facility has conducted ecosystems research at 58 lakes since 1968. But last year, the Canadian government axed its $2 million annual appropriation, gave notice that it planned to start tearing down structures in September, and hired security guards to keep scientists off the site after 31 March.

    Wynne's announcement gives ELA a reprieve, but the provincial government has not decided how much money it will free up for operating costs, says Laurel Broten, Ontario's minister of intergovernmental affairs. Roughly $600,000 is needed to operate core ELA facilities annually, while an additional $1.4 million is needed to cover the cost of salaries for ELA staff members that carry out scientific projects or conduct the routine work of taking water samples and monitoring water flows.

    Negotiations are ongoing with the federal government and the province of Manitoba "to find the best arrangement." It's hoped that ELA can ultimately survive under the umbrella management of the International Institute for Sustainable Development. http://scim.ag/ELAOnt

    Brussels

    Controversial Pesticide Ban Goes Forward

    The European Commission is going ahead with a 2-year moratorium on three widely used pesticides that are potentially harmful to bees, although E.U. countries remain split on the issue. The decision follows reports published in January by the European Food Safety Authority (EFSA) concluding that the three neonicotinoids pose an "acute risk" to honey bees that are essential to farming and natural ecosystems.

    After two inconclusive votes by member states, the commission is allowed to drive its proposal through. Those votes occurred on 15 March, in the Standing Committee on the Food Chain and Animal Health, and in an appeals committee on 29 April. Now, the commission has decided to use its right to go ahead with the plan.

    "The Commission's role is to protect consumers. EFSA's reports have revealed a risk, so we're taking time to step back and assess the situation," says a Brussels source close to the negotiations. The 2-year restriction to pesticide use will apply to plants attractive to bees (maize, cotton, sunflower, and rapeseed) starting 1 December. It will apply across the European Union, even in the countries, including the United Kingdom, that opposed the moratorium. http://scim.ag/ECbees

    Priština

    Reconciliation With Serbia Opens Research Doors

    CREDIT: CRADEL/WIKIMEDIA COMMONS

    Three days after leaders from Serbia and Kosovo reached an E.U.-brokered agreement on 19 April, the European Commission formally proposed to let Kosovo participate in 22 E.U. programs, including the €55 billion Seventh Framework Programme (FP7) for R&D, Europe's satellite navigation program Galileo, and the European Earth-monitoring system GMES. FP7 ends this year, but the agreement is expected to also apply to its successor, Horizon 2020, which covers the next 7 years.

    If E.U. member states agree, Kosovo will move from taking part in research programs as a "third country" to becoming an "associated country." In return for paying a fee to the European Union, its representatives can take part in program management committees, and its organizations and proposals will receive the same treatment as those from E.U. member states.

    The move would give the small Balkan country fresh opportunities to shore up its minuscule research effort—but it may have to invest more to benefit from them. According to the country's own National Research Programme, published in 2010, R&D remains a "marginal undertaking" in Kosovo, with "the absence of any critical mass of research and technological development … funding for at least the last 20 years." http://scim.ag/KosovoEU

    London

    New Libel Law for England and Wales

    A defamation bill that advocates say will help protect free speech—including statements in peer-reviewed scientific publications—received the go-ahead from Parliament on 24 April. Under current English law, plaintiffs alleging spoken defamation or published libel need only show that a public statement might inflict reputational damage. Under the new law, claimants will have to present evidence of "serious financial harm."

    Reform efforts were prompted by several recent cases—including that of Simon Singh, a science writer unsuccessfully sued by the British Chiropractic Association in 2008 over a column that he wrote for The Guardian questioning the effectiveness of chiropractic treatments, and another 2008 case in which the journal Nature was dragged into a costly court battle by an Egyptian researcher who claimed his reputation was damaged by a Nature article that alleged that he had self-published many papers without peer review.

    The government still has to clarify how the law will work in practice, which will help determine the cost of future libel cases. Another area that awaits clarification is whether the new protections will extend to material published on the Internet, Singh says—which would "turn a good bill into a great bill." http://scim.ag/UKlibel

  2. Random Samples

    Obama Wishes Happy 150th to U.S. National Academy of Sciences

    CREDIT: RACHEL BRODY/NATIONAL ACADEMY OF SCIENCES

    President Barack Obama had an appreciative audience at the U.S. National Academy of Sciences (NAS) on 29 April when he delivered a speech celebrating the group's 15 decades of service as the government's technical adviser. "For 150 years, you've strived to answer big questions, solve tough problems, not for yourselves but for the benefit of the nation," he told a crowd of science luminaries.

    Obama also took a swipe at congressional efforts to impose controversial new grant-making criteria on U.S. science agencies (see p. 534). "I will keep working to make sure that our scientific research does not fall victim to political maneuvers or agendas that in some ways would impact on the integrity of the scientific process," he promised. And he drew a laugh by noting that academy members work for free. "[P]art of what's made the Academy so effective is that all the scientists elected to your elite ranks are volunteers," he said. "Which is fortunate because we have no money anyway."

    Will 'Volcanic Winter' Debate Now Cool Down?

    CREDIT: © CHARLES & JOSETTE LENARS/CORBIS

    About 75,000 years ago, Mount Toba in Indonesia blew its top in the biggest volcanic eruption of the past 2 million years. The explosion spread ash across Asia, possibly blocking sunlight and cooling the continent for up to a decade. Some researchers have suggested that ash from Toba also blew over East Africa, driving early Homo sapiens nearly to extinction. This "volcanic winter" scenario is hotly debated, however (Science, 5 March 2010, p. 1187).

    This week, in the Proceedings of the National Academy of Sciences, a team of researchers from the University of Oxford in the United Kingdom and the University of Minnesota report finding traces of ash from the Toba explosion in cores drilled into the floor of Lake Malawi, 7000 kilometers west of Toba—the farthest from the volcano yet recorded. However, these microscopic fragments of glass—sourced to the Toba explosion by their chemical composition—seem to have posed little threat to our ancestors. The composition of algae and other organic matter in sediments above and below the ash layer give no hints of dramatic temperature drops or other environmental changes at that time, the team concludes.

    ScienceLIVE

    Join us on Thursday, 9 May, at 3 p.m. EDT for a live chat on new exoplanet discoveries. How close are we to finding a mirror Earth? http://scim.ag/science-live

    Funeral Colors

    CREDIT: W. WESOLOWSKI (2)

    On 21 April 1865, 7 days after the assassination of President Abraham Lincoln, his funeral procession departed Washington, D.C., aboard a nine-car train bound for Springfield. Millions of mourners turned out to see the train pass by and pay their respects in what has been called the greatest funeral in the history of the United States.

    Despite all the eyewitness accounts, one small detail was lost to history: the precise color of the funeral car. Various accounts referred to it as "rich chocolate brown" and "claret red." The car itself was all but destroyed in a fire in 1911. Now, from the few fragments that remain, researchers from the University of Arizona say that they've solved the color mystery.

    Chemist Wayne Wesolowski had previously reconstructed a model-sized version of the railcar (top) as director of the 10-year Lincoln Train Project at Benedictine University in Chicago, Illinois. His "best guess" at the color for the model, he says, was based on the "rich chocolate brown" description. "In 1865, there was no milk chocolate—chocolate was a drink you got in coffee houses, more like Dutch chocolate. It was a rich, dark maroon color."

    Now, Wesolowski says, a group known as the Lincoln Funeral Car Project is constructing a full-scale replica of the train, which will reproduce the route of the 16th president's final journey for the upcoming 150th anniversary. To determine the right color for the car, Wesolowski and his team compared microscopic paint fragments from a surviving pencil-sized fragment of the car to national paint standards (bottom). The original color, they found, was a somber maroon—just slightly darker than Wesolowski used for his model.

  3. Newsmakers

    Tropical Medicine Researcher to Lead Wellcome Trust

    Farrar

    CREDIT: WELLCOME LIBRARY, LONDON, WELLCOME IMAGES

    Infectious diseases researcher Jeremy Farrar will take over the reins at the Wellcome Trust, the United Kingdom's most important private funder of biomedical research, on 1 October. Endowed with more than $22 billion, the Wellcome Trust spends about $1 billion annually.

    Farrar is now heading the Oxford University Clinical Research Unit in Ho Chi Minh City, Vietnam, where he has done research on drug resistance in tuberculosis and other diseases. He is "an extraordinary guy," says Nicholas White, a malaria researcher at the University of Oxford in the United Kingdom and Mahidol University in Bangkok. "He understands science and he understands people."

    In January 2004, Farrar was part of a team that diagnosed the first human case of H5N1 avian influenza in Vietnam. In recent weeks, he has collaborated in an effort to analyze travel patterns between China and the rest of the world, which may help predict how the novel H7N9 influenza virus might spread.

    Farrar succeeds Mark Walport, who had left the post in March to become the U.K. government's chief science adviser. Ted Bianco, the trust's director of technology transfer, will continue to serve as acting director until October. http://scim.ag/Farrar

  4. Mr. Borucki's Lonely Road to the Light

    1. Yudhijit Bhattacharjee

    The father of NASA's Kepler orbiting exoplanet finder had to pioneer new optical techniques and overcome decades of skepticism to get his pet project off the ground.

    Rocket man.

    (Clockwise from lower left) Borucki as a teenaged model rocket buff in Wisconsin; at an underground ballistics range in 1962; at Kennedy Space Center with a retired Saturn V engine assembly in 1985; and today (large image).

    CREDITS: (BACKGROUND) COURTESY OF WILLIAM J. BORUCKI; (FOREGROUND) DOMINIC HART/NASA AMES RESEARCH CENTER

    At 74, many men are happy to while away their time gardening or playing poker or watching reruns of old sitcoms. William Borucki, the architect and principal investigator of NASA's exoplanet search mission, Kepler, is cut from a different cloth. On weekends, he likes to take off with his wife, Josephine, and his boyhood buddy, Gene Westerberg, to trek through Alum Rock Park, a few miles east of San Jose, in search of kempite, a rare manganese mineral found nowhere else on Earth. So far, Borucki hasn't found any, and perhaps he never will. It doesn't matter. Borucki's journey is his destination.

    If he didn't enjoy the journey so much, Borucki would have given up long before he realized his goal of launching a spacecraft to find planets outside the solar system. Kepler, which has opened the floodgates for exoplanet discoveries since its launch in 2009, would never have come about. Those who have followed Kepler from idea to reality say that the mission is a testament to Borucki's ingenuity and vision and iron will, a spirit so inured to rejection and failure that it might as well be wrapped in rhino hide.

    In the late 1980s, Borucki proposed the idea of finding exoplanets by measuring the dip in a star's brightness when an orbiting planet travels across the face of the star. For several years, he was alone in pushing the idea against a tide of scorn and hostility from many in the field who did not believe that the technique could work.

    "There was no one from NASA headquarters who would support him," says David Morrison, an astronomer at NASA Ames Research Center near Mountain View, California, who was Borucki's supervisor during the early years of the struggle. "It took a lot of courage on his part because of all the negative reactions." In the end, Morrison says, Borucki proved to be "the fighter who is knocked down and gets up, is knocked down and gets up again." For this perseverance alone, some might say, Borucki should be awarded a Ph.D. That way, he'll no longer have to correct those who refer to him as Dr. Borucki.

    An urge to explore

    Borucki is 5′6″ with kindly eyes and bushy eyebrows. One afternoon last November, he sat down for lunch with Westerberg and Josephine in the outdoor area of a restaurant, under the warm California sun. As he dug into his salad, Westerberg recalled growing up with Borucki in Delavan, Wisconsin, where Borucki's father worked at a factory that made clocks for automobiles.

    Tinkerers since childhood, Borucki and his brother built rockets when they were in high school, cutting the tips off matchsticks for fuel. Later, they and Westerberg switched to homemade gunpowder, crushing an artists' drawing set for charcoal and furtively buying the other ingredients from the town's two drugstores. "One of us could go and get the sulfur from one store, and the other could get the saltpeter from the second store," Westerberg says. "We didn't want people to connect the two."

    Building rockets was just one of many pursuits. "We built a jet engine in the basement of our house," Borucki recalls. "It worked, but it burned off part of the paint off the wall. It meant you had to clean things up pretty quickly before your folks came home." Borucki also got interested in astronomy during those years, biking to the Yerkes Observatory 15 miles away to look at the heavens. He would climb up on the garage of his house and lie on the roof to watch meteor showers. Looking up at the sky, Borucki says, he knew what he wanted to do most of all was "to go out and explore the galaxy."

    Borucki studied physics at the University of Wisconsin, Madison, earning a master's degree in 1962. Pursuing a Ph.D. didn't seem appealing. "I really don't like to just think about things," he says. "I like working on things. I like to do things. I like to see an idea put into practice."

    Like home.

    Kepler with Kepler-63c (artist's conception, inset), a "super-Earth" detected in the habitable zone of a sunlike star.

    CREDITS: NASA/AMES/JPL-CALTECH (2)

    Borucki went to work at NASA Ames and spent a decade developing heat shields for the Apollo program. In 1972, when Apollo ended, NASA fired everybody working on the program ("No good deed goes unpunished," Borucki jokes) but let them apply for other positions at the agency. He found another spot at Ames as a researcher in space sciences.

    For the next few years, Borucki studied the Earth's atmosphere and lightning on other planets in the solar system. He also attended seminars at which scientists presented ideas about ways to find planets outside the solar system. The discussions rekindled Borucki's boyhood dreams of galactic exploration.

    The seminars focused on a technique called astrometry: detecting a planet by measuring the slight wobble the planet's gravitational tug gives to its parent star. Borucki was drawn to another approach: measuring the dip in the light of a star when a planet passes in front of it. A colleague referred him to a paper that an artificial-intelligence researcher named Frank Rosenblatt had published in Icarus in 1971. The paper was the first to propose transit-based detections of planets.

    Borucki tried to contact Rosenblatt, who had spent years running computer simulations at the Cornell Aeronautical Laboratory, but learned that Rosenblatt had died in a canoeing accident shortly before the Icarus paper appeared. Borucki picked up the concept from where Rosenblatt had left it. In 1984, he and his Ames colleague Audrey Summers published a paper that laid out the potential for discovering Jupiter-sized planets with ground-based telescopes using high-precision light detectors to track the periodic dimming of stars. To discover Earth-sized planets, the authors proposed monitoring thousands of stars simultaneously from above Earth's atmosphere.

    The paper got a lukewarm reception. "People generally ignored it," Borucki says. The next year, he published another paper with a colleague predicting that the natural variability of stars would limit researchers' ability to pick out the change in brightness caused by a transit, unless more advanced photometers were developed. "That paper was ignored, too," he says.

    But Borucki pressed ahead. Using small grants of $10,000 to $15,000 from the Director's Discretionary Fund at Ames, he organized workshops to hash out how to build precise photometers. With colleagues at Ames and elsewhere, he began building prototypes that could come close to measuring the dimming of starlight with the necessary precision: a 1% dip in brightness to detect a Jupiter-sized planet around a sunlike star, a 0.01% dip to detect an Earth-sized planet.

    "Here's Bill again"

    Even as Borucki made steady progress in building high-precision photometers, he struggled to win support for his larger concept: monitoring thousands of stars across a wide field of sky to look for periodic dimming. "Here was this young guy with a crazy idea," Morrison says. "He had no history of building telescope detectors. He was just not part of the astronomy club. I think people probably didn't trust him." Morrison says that Borucki's presentations at scientific meetings drew mildly hostile reactions. "It was, 'Oh, here's Bill again. We got to listen to him for half an hour, and then we can go back to more useful things like astrometry.'"

    Not having a Ph.D. didn't help, Borucki says. He recalls wincing when a Harvard University professor at Ames presented results on atmospheric chemistry: The professor shrugged off an unexpectedly low reading of stratospheric water vapor by remarking that the researcher who made the measurements didn't have a doctorate and had probably messed up. "'Thanks a lot,' " Borucki recalls saying to himself. " 'You don't know a damn thing about experimental work, and just because this person didn't have a Ph.D., you doubted his measurements?' I have never forgotten that." On another occasion, Borucki says, officials at a university where he was slated to teach for a year withdrew his invitation on learning that he wasn't Dr. Borucki.

    Morrison himself was skeptical about transit searches when he became Borucki's supervisor in 1988. A year later, he arranged for a panel of space scientists to review Borucki's idea of finding transiting planets by simultaneously observing thousands of stars with a charge-coupled device (CCD) detector. After Borucki's presentation, the panel, led by astronomer Jill Tarter, grilled him for several hours in the equivalent of a marathon dissertation defense.

    "I had an awful lot of things to defend," Borucki says. Although CCDs were becoming increasingly popular, nobody had yet shown that they could work at the level of precision that Borucki's concept demanded. The panel also wondered whether the intrinsic variability of stars—still unknown at the time—would prove too high for Borucki's proposed detectors to pick out the signature of a transiting planet. Borucki argued convincingly that the variability in stellar brightness ought to resemble that of the sun—a manageable amount of "noise" for his proposed instruments to handle. At the end of the day, the panel gave him a thumbs-up. When NASA announced a new program called Discovery to support intermediate class space missions, Borucki seized the opportunity. He persuaded a handful of colleagues at Ames, including a physicist named David Koch who was exceptionally talented at building instruments, to join him in proposing a mission concept clunkily named the Frequency of Earth-Sized Inner Planets. It was 1992—the year that astronomers detected the first exoplanets, circling a stellar cinder called a pulsar.

    Sampler.

    Kepler's discoveries include exoplanets about the size of Earth.

    CREDIT: NASA/KEPLER MISSION/WENDY STENZEL

    The proposal was rejected. Reviewers weren't convinced that light detectors then available could achieve the required precision. In 1994, Borucki and his team tried again, bolstering the proposal with new studies to show that CCDs could do the job. This time, reviewers rejected the idea as too expensive. In 1995, astronomers discovered the first exoplanet orbiting a sunlike "main sequence" star. "We felt it would help us because now we could show that there were more planets to be found," Borucki says. But the team's next submission—now named Kepler—was rejected again in 1996. The reviewers pointed out that nobody had yet monitored the brightness of thousands of stars simultaneously. "They said, 'Build an observatory and show that it can be done,'" Borucki says.

    To space at last

    One day in 1996, Borucki drove half an hour from Ames to the University of California's Lick Observatory to inspect one of its small domes. The telescope in it hadn't been used in years. The floors were rotting, the roof leaked. But Borucki was smitten. "It was beautiful," he says. "It said astronomy. It said here's a machine that you can use to build your instrument. In reality, of course, the dome didn't rotate; there was no place for a computer, and you'd freeze to death. But don't you see, I helped my dad build a house. What's so hard about building a floor?"

    Over the next several months, Borucki and his colleagues worked to overhaul the dome, often spending nights there in the company of rattlesnakes and rats. Everything had to be done on a shoestring budget. After the team had built the photometer and hooked it up to the telescope, Borucki found a way to calibrate the detectors on the cheap, using a Teflon bucket that he had bought at a hardware store. He put a bulb in the bucket and put the lid back on, using it as a diffuser to uniformly spread out the light. Hoisting the bucket on a metal pole, Borucki tipped it horizontally and pointed the lid at the telescope. It was a simple idea that worked perfectly, says Natalie Batalha, a member of the Kepler team. By the end of 1997, Borucki and his colleagues were successfully monitoring the brightness of some 6000 stars simultaneously.

    Armed with the new data, the team made a fresh bid in 1998 to get the mission greenlighted but met with another rejection. Reviewers were concerned that the detectors wouldn't be able to pick out signals of transiting Earth-sized planets amid the noise expected in orbit from vibrations experienced on a spacecraft. Borucki reacted to the rejection—the fourth one in 6 years—with his typical sequence of frustration followed by new resolve. "When I get angry, I usually rant for a while," he says. "You don't want to be around me for a couple of days. I rant for a while and then I say, 'Well, rant's done. Time to get the job done.' "

    With $500,000 from NASA Headquarters and $500,000 from NASA Ames, Borucki and his colleagues—including Koch and another physicist named Fred Witteborn—built a prototype of the instrument that they were proposing to launch into space. It was a metal box the size of a refrigerator with a small telescope inside pointed at a ball with tiny holes drilled into it. When the inside of the ball was illuminated, the holes resembled pointlike stars as would be seen by the telescope. A fine wire was strung across each hole; when a current was passed through it, it expanded slightly, blocking more light than normal to simulate the dimming of a star caused by a transit. "They [NASA reviewers] were assuming that it would take us a few years to complete this step, but we worked as fast as we could," Borucki says. In 2000, the mission was finally approved. It cost $640 million and 9 years of design, building and testing to finally launch the mission in 2009.

    In the 4 years that Kepler has been in space, monitoring the brightness of some 150,000 stars, it has discovered more than 2700 possible exoplanets. At last count, follow-up observations by ground-based telescopes had confirmed 122 as planets. Roughly half of the candidates are estimated to be twice the size of Earth or smaller; many of these could be rocky planets. The findings suggest that hordes of Earth-sized, Earth-like planets may lurk in the habitable zones of stars, waiting to be discovered.

    Borucki is convinced that astronomers will find mirror Earths in the not too distant future. And although budget constraints have made many researchers pessimistic about the prospects of flying a next-generation observatory to study such planets, Borucki is confident that such a mission will fly sooner or later. The first goal will be to study the composition of these planetary atmospheres in detail. "I don't know when such a mission will fly or if it will be a U.S. mission or a Chinese mission or a European mission," he says. "But that mission will fly. That's a certainty. You can predict some of these things. There are things that have to happen. They must happen." Like Kepler.

  5. Taking the Pulse of a Ravaged Ocean

    1. Dennis Normile

    The 11 March 2011 earthquake and tsunami wreaked havoc on fisheries and the marine environment. Researchers want to document—and aid—the recovery.

    Swamped.

    Before the Tohoku earthquake, students studied tidal zone life on this outcropping near Onagawa (left). Subsidence permanently submerged it.

    CREDIT: M. IKEDA; M. KANNO

    SHIZUGAWA BAY, JAPAN—The engine cuts to an idle as the fishing boat reaches its target coordinates. After an "OK!" from the crew chief, the deck explodes with activity. Off the starboard rail, crew members drop 10-liter plastic bottles attached to ropes and reel them in by hand to collect samples from the surface, then from 10, 20, and 30 meters down. At the port side, the crew chief casts a 3-meter-long fine mesh plankton net. After a few minutes, he gathers it in by hand and funnels the catch into small jars. To measure turbidity, he sinks a tethered white acrylic disk, the size of a dinner plate, and notes the depth at which it disappears from sight.

    Prior to 11 March 2011, this bay on Japan's Pacific coast, east of Sendai, was famous for wakame seaweed and oysters cultured on ropes and racks suspended from buoys. The massive tsunami unleashed by a magnitude-9.0 earthquake that day swept all that away, as well as most of the fishing boats and onshore facilities.

    Buoys once again dot the bay, indicating a return of aquaculture. But it is by no means back to business as usual. Last year, the normally deep-green wakame was yellowish, and nobody wanted to buy it. Solving the mystery of the pallid seaweed is one of several challenges facing the scientists. Abalone and sea urchin, once plentiful in shallow waters, have disappeared. And fin fish are scarce. Fishing is bringing in just 20% to 30% of predisaster revenues in a region whose economy depends on the bounty of the sea.

    This cruise on a crisp March morning is part of an unprecedented effort to understand how the Tohoku tsunami affected marine ecology and to monitor its recovery. Some 300 researchers from more than a dozen institutions will spend the next decade documenting everything from changes in water quality, pollution, and the strength of currents to shifts in biodiversity and the population genetics of marine life. One big challenge is teasing out how intensive coastal development and wetland reclamation may have exacerbated the marine disaster, and how onshore rebuilding may degrade the marine environment. Working with local fishing cooperatives, researchers intend to help develop sustainable fisheries plans and revitalize the region's aquaculture.

    Beneath the surface

    Smashed buildings, wrecked cars, and washed-out roads and railways, not to mention a horrific loss of life: The devastation visited on coastal communities by the earthquake and tsunami, which topped 3-story buildings in hard-hit locations, was obvious. The disaster's effects on marine ecosystems are also severe, but they are harder to discern. Tectonic shifts reshaped the coastline, submerging wetlands and altering currents. Turbulence destroyed kelp forests and washed away shellfish beds and fish breeding grounds.

    Tsunamis are a regular phenomenon, and coastal environments recover over time. But the March 2011 disaster was unique. According to Akihiro Kijima, a marine population geneticist at Tohoku University in Sendai, the amount of humanmade debris flushed out to sea by the Tohoku tsunami vastly exceeded that of the December 2004 Indian Ocean tsunami. The Tohoku coast was far more developed than coastlines hit in 2004, with the narrow shore thick with buildings and industrial facilities. Besides sweeping out bits and pieces of houses, smashed boats, and cars, fuel oil and chemicals leaked from storage tanks and factories. And, in a first, the tsunami resulted in massive radiological contamination of the ocean (see sidebar, p. 547).

    Launched in January 2012, the 10-year Tohoku Ecosystem-Associated Marine Sciences (TEAMS) project is still establishing observing sites and gathering baseline data. In some locations, researchers have been monitoring water quality and marine life for years; in others they will have to estimate and extrapolate to predisaster conditions.

    But scientists are already making preliminary observations. One is the likely reason for the yellowed wakame. Kijima, one of the project leaders, blames coastal subsidence, which appears to have altered currents. Fresh ocean water no longer sweeps into the inner reaches of Shizugawa Bay, and turbid water is not being flushed out, so near-shore marine life forms are starved of nutrients, he says.

    Netting results.

    Plankton abundance is a key benchmark of ocean health.

    CREDIT: D. NORMILE/SCIENCE

    At least one group was off the blocks before TEAMS started. Just 3 months after the disaster, Tohoku University's Masakazu Aoki, who studies benthic organisms, began monthly monitoring of 26 sites in three bays. His group noted that turbulence from the tsunami washed away algae, such as kelp, or stripped off its fronds. And many areas of the rocky bottom were smothered by mud. Abalone, sea urchins, and other organisms that feed on the algae largely disappeared, except for some mature individuals that somehow hung on.

    By last fall, things were looking up. Aoki's team observed new kelp growth, although kelp in water deeper than 4 meters was faring poorly because of persistent turbidity. Juvenile sea urchins were also reappearing. Curiously, abalones were still missing, and it is not clear why, Aoki says.

    He and his group found that the harm from the earthquake and tsunami extends to areas that escaped the brunt of the waves. The west side of Oshika Peninsula, which juts southward into the Pacific from a bend in Honshu Island, was sheltered from the tsunami, which struck from the east. But the coast in this area sank as much as 90 centimeters during the quake. Deeper patches of kelp were starved of sunlight and died. Although spared the turbulence of a direct hit, the west side of the peninsula was inundated with tsunami-dredged mud, which "had a profound effect on the rocky shore communities," Aoki says. There, as in waters battered by the tsunami, kelp, sea urchins, and abalones suffered greatly.

    Changes to marine ecosystems may not be easily reversed. As part of TEAMS, Japanese researchers at a 23 March symposium in Sendai compared notes with scientists who studied the 2004 Indian Ocean tsunami. Zulfigar Yasin, a marine ecologist at Universiti Sains Malaysia, in Penang, reported that post-tsunami mud was a factor there, too. Total biomass recovered, Yasin says, but "there was a long-term change in the composition of fauna." Fish species that tolerate cloudy water moved in and are still there. Turbidity is expected to be a chronic problem in Tohoku, as dirt washes into rivers and bays during coastal reconstruction.

    On Shizugawa Bay, mud is also on the minds of the sampling crew. Finished with the water column, they use a scooplike Smith-McIntyre bottom grab sampler to retrieve buckets of mud. From one grab, they carefully extract samples to preserve the order of sediment layers. From the next bucket, the crew chief notes the color and odor; he reassuringly reports that there is no oily or chemical scent. The team sieves the contents of several buckets for bottom-dwelling worms and crustaceans, and puts these in jugs. In 90 minutes, they have collected more than 70 samples of all sorts. Back in the lab, these will be analyzed for salinity, dissolved oxygen, chlorophyll, metallic and chemical contaminants, and the density and variety of organisms, among other things.

    The captain revs the engine and points the boat toward a spot near the mouth of the bay. Findings from this cruise and others will not only aid in the region's recovery, Kijima says. Data will be archived, he says, "so it will be useful for the next marine disaster anywhere in the world."

  6. The Pacific Swallows Fukushima's Fallout

    1. Dennis Normile

    The Tohoku disaster had one unprecedented impact: an enormous amount of radiation was deposited in the ocean.

    Hot water.

    Elevated radioactivity persists in the sea and sediments near the Fukushima Daiichi Nuclear Power Plant, but in puzzling patterns.

    CREDIT: MASNARI GENKO/YOMIURI SHIMBUN/ASSOCIATED PRESS

    The Tohoku disaster had one unprecedented impact: an enormous amount of radiation was deposited in the ocean. The good news is that any long-term effects are likely to be trivial. And, thanks to strict testing of seafood, the radiation should not harm human health. But there are lingering conundrums.

    Flooding from the tsunami overwhelmed the Fukushima Daiichi Nuclear Power Plant, triggering hydrogen explosions on 12 and 14 March 2011; prevailing winds blew most of the vented radiation out to sea. A second calamity occurred from 2 to 6 April that year, when an estimated 520 cubic meters of highly contaminated cooling water leaked into the ocean. Together, the two events deposited an estimated 3.5 to 27 petabecquerels into the Pacific—a small fraction of the radiation released during the Chernobyl accident.

    Measured radioactivity levels in seawater fell rapidly, thanks to dilution and radioactive decay. At many monitoring points, radiation levels have returned to background levels, says Masashi Kusakabe, a chemical oceanographer at the Marine Ecology Research Institute in Tokyo, which has monitored the ocean near Fukushima for almost 30 years.

    One puzzle is a small harbor formed by a breakwater in front of the Fukushima plant. Once the cooling water leak was plugged, radiation levels there declined. But they remain elevated above those of the nearby ocean, suggesting that "there is some radioactivity coming from somewhere," says Jota Kanda, a biogeochemical oceanographer at Tokyo University of Marine Science and Technology. Tokyo Electric Power Co., the plant operator, has maintained that there is no evidence of continuing leaks from the power plant to the sea.

    There are other anomalies among the 30 seawater locations monitored by the Marine Ecology Research Institute. Two radiation hot spots are close to the mouth of the Naka River, 125 kilometers south of the power plant; another one is 70 kilometers north of the plant, near the outlet of the Abukuma River. Kusakabe says it is possible the two rivers are carrying fallout-laden sediment into the ocean. But there is another location with a persistently high level of radioactivity 75 kilometers south of the plant that is not near any major river, and points closer to the power plant are less contaminated. "We don't have an explanation for this," he says.

    Contamination in marine sediment near Fukushima is even more troubling. The seafloor is a mosaic of muddy, sandy, and rocky patches, and currents move sediment to and fro, Kusakabe says. From the surface, he says, it is difficult to ensure that grab samplers hit the same spot for comparisons over time. Despite these challenges, the team has measured levels as high as 300 becquerels per kilogram of radioactivity in sediment, far higher than the 1 becquerel per kilogram measured prior to the accident. And some plankton and fish samples have also turned up with unexpectedly high levels of contamination.

    None of this threatens human health, Kusakabe says. Radioactivity levels in seawater are below the limit set in Japan for drinking water: 100 becquerels per liter. And marine products from Tohoku are tested before going to market, with anything over 100 becquerels per kilogram rejected. Fishing is still prohibited off Fukushima, and it's unlikely to resume until the riddle of the contaminated sediment is solved.

  7. A Gallery of Planet Hunters

    1. Yudhijit Bhattacharjee,
    2. Daniel Clery

    Science presents an overview of planet-hunting techniques and representative efforts for the nearly 900 confirmed exoplanets and the hundreds of fresh candidates that are turning up every month.

    In 1992, astronomers announced that a whirling neutron star called a millisecond pulsar harbored the first known planets outside our solar system: extrasolar planets, or exoplanets. Two decades on, exoplanets are practically an astronomical commodity. Nearly 900 of them have been confirmed, and hundreds of fresh candidates are turning up every month. Some resemble the familiar orbs circling our sun, but others are truly alien: hot Jupiters, mini-Neptunes, super-Earths.

    To help readers navigate the bewildering variety of new worlds and their discoverers, Science presents this guide for the perplexed: an overview of planet-hunting techniques and representative efforts, followed by an informal glossary of popular exo-objects.

    Radial Velocity

    Radial velocity measurement is the mother of exoplanet search techniques. Michel Mayor and Didier Queloz of the Observatory of Geneva in Switzerland used it in 1995 to make the first confirmed detection of an exoplanet around a sunlike star, and it's still going strong.

    As a planet orbits a star, its gravity causes the star to move around their common center of gravity, usually inside the star. If we view such a system edge-on, the star would appear to be wobbling from side to side. Current telescopes can't detect such tiny movements, but they can spot a wobble back and forth along the line of sight because such changes in radial velocity raise and lower the frequency of the star's light.

    HARPS and HIRES (Ongoing)

    CREDIT: ESO/F. KAMPHUES

    To spot exoplanets this way, astronomers don't need a huge telescope or one in space—just an extremely sensitive spectrometer and lots of time. It can require between 500 and 1000 separate observations of a star to detect the signature of a planet circling around it. Today's best instruments can detect radial velocities down to about 1 meter/second. Jupiter makes our sun move at 12 m/s, but small planets cause much smaller movements—Earth shifts the sun by less than 0.1 m/s.

    HARPS and HIRES (Ongoing)

    Many groups around the world have hitched spectrometers to their telescopes and started looking for wobbling stars, but two groups have dominated the discovery of new exoplanets with several hundred detections each. The first is the Geneva Observatory team with an instrument called High Accuracy Radial velocity Planet Searcher (HARPS) fitted to the European Southern Observatory's (ESO's) 3.6-meter telescope at La Silla in Chile. The second team, led by Geoff Marcy of the University of California, Berkeley, uses the High Resolution Echelle Spectrometer (HIRES) on the Keck I telescope at Mauna Kea, Hawaii.

    Automated Planet Finder (Imminent)

    CREDIT: © LAURIE HATCH/WWW.LAURIEHATCH.COM

    Since the Kepler space mission began detecting new candidate exoplanets by the thousands using the transit technique (see p. 567), radial velocity teams have changed focus from discovering new planets to confirming Kepler detections and measuring their mass. Kepler observations can measure a planet's size but not its mass, which is key to separating gas giants from rocky planets. Radial velocity fills that gap, and so the teams are trying to shift up a gear.

    Automated Planet Finder (Under Construction)

    Because radial velocity measurement is so slow, both teams are aiming to develop new instruments and telescopes dedicated to planet searching. The HIRES team has built the Automated Planet Finder, a 2.4-meter telescope and spectrometer on Mount Hamilton near San Jose, California. Its spectrometer is about as sensitive as that of HIRES, and starting this month it will spend all night, every night looking for planets—taking 25 spectra per night.

    HARPS and ESPRESSO (Installed; planned)

    HARPS and ESPRESSO (Installed; Planned)

    CREDIT: TNG/A. HARUTYUNYAN

    Meanwhile, the HARPS team and collaborators have made another version of their spectrometer for the northern hemisphere. HARPS-N is fixed to Italy's 3.6-meter Galileo National Telescope in the Canary Islands, which can observe the same patch of sky that Kepler does. The researchers are also designing a next-generation spectrometer called ESPRESSO, which will operate from 2016 at ESO's Very Large Telescope at Cerro Paranal in Chile. VLT is an array of four 8.2-meter scopes; ESPRESSO will be portable enough to attach to whichever has available observing time.

    Transits

    MEarth (Ongoing)

    CREDIT: JONATHAN IRWIN

    The idea is simple enough: monitoring a star for the dips in its brightness caused by a planet passing in front of it. In practice, however, such transit-based detection is like trying to tell when a seagull flies across the beam from a lighthouse.

    That's why it took astronomers years to convert the idea into a workable technique capable of finding not just gigantic planets, which block more than 1% of their star's light, but also planets the size of Earth. Their efforts have paid rich dividends, enabling the discovery of more than 231 exoplanets to date.

    MEarth (Ongoing)

    On a mountaintop in Arizona, eight remote-controlled robotic telescopes search the skies every night for transits around M dwarfs. The most common stars in our galaxy, M dwarfs are much smaller than the sun, so the dip in their brightness due to a transiting planet should be larger than the dimming of a sun-sized star. In 2009, MEarth discovered its first super-Earth, a planet orbiting a red dwarf 40 light-years from us.

    TESS (Planned)

    TESS (Planned)

    CREDIT: CHESTER BEALS/MASSACHUSETTS INSTITUTE OF TECHNOLOGY

    The Transiting Exoplanet Survey Satellite (TESS)—recently chosen by NASA for possible launch in 2017—will aim to survey the brightest stars in the sun's neighborhood using an array of widefield cameras in search of exoplanets ranging from gas giants to extraterrestrial Earths in habitable zones. Some of those planets, researchers hope, will be candidates for follow-up studies of their atmospheres by the James Webb Space Telescope, scheduled for launch in 2018.

    Kepler (Ongoing)

    Kepler (Ongoing)

    CREDIT: NASA/KEPLER MISSION

    Launched in 2009, NASA's Kepler spacecraft has entered an extended phase, having completed its planned 3.5 years of observing. The mission has surveyed 150,000 stars and found more than 2740 planet candidates, 115 of which astronomers have confirmed to be planets by follow-up observations using ground-based telescopes. Several of the candidates are Earth-sized or smaller; in February, astronomers confirmed one of them to be a planet approximately the size of our moon. Data from Kepler are helping researchers get a better handle on how abundant different kinds of planets are.

    CHEOPS (Under Construction)

    CHEOPS (Under Construction)

    CREDIT: SWISS SPACE CENTER/CHEOPS TEAM

    If all goes as planned, by 2017 European astronomers will launch a spacecraft to look at transits of nearby bright stars already known to harbor planets. Characterizing Exoplanets Satellite (CHEOPS)—chosen for development by the European Space Agency in 2012—is designed to reveal in detail the nature of those planets. High-precision measurements by the satellite should help astronomers nail down planet sizes. Combined with radial velocity observations from the ground, which provide the mass of these planets, the observations will help figure out how dense they are.

    Microlensing

    If you point a telescope at a star in the center of the galaxy and stare long enough, sooner or later a second star will pass in front of it. (Yes, it could take millions of years.) Depending on its mass and position, the foreground star can exert enough gravity to bend the light from the background star, acting as a lens. Such "microlensing" makes the background star appear brighter than usual.

    A planet orbiting the foreground star can make brightening or dimming contributions of its own. Such deviations from what would otherwise be a smooth microlensing event can be picked up by planet hunters to reveal the existence of the planet. With precise observations of this signal, astronomers can determine the mass of the planet and its distance from the parent star.

    Using microlensing, astronomers can detect planets much less massive than Earth, which other methods would miss. The drawback is that it's a one-shot deal: Microlensing events, lasting days to weeks, are so rare that researchers are unlikely to get a second chance to study a particular foreground star. That's why ongoing microlensing-based searches involve networks of robotic telescopes that can watch big swaths of the sky to spot as many events as possible. The technique has yielded the discovery of 17 exoplanets to date.

    The Optical Gravitation Lensing Experiment (Ongoing)

    The Optical Gravitation Lensing Experiment (Ongoing)

    CREDIT: K. ULACZYK

    In the mid-1990s, a group of Polish astronomers led the construction of a 1.3-meter telescope at the Las Campanas Observatory in Chile. The Optical Gravitational Lensing Experiment's main goal has been to search for dark matter using microlensing, but since the early 2000s, the telescope has also proved its utility as a planet-hunting tool. Its capabilities have greatly improved since first light. In 2009, the telescope was mounted with a new, 32-chip mosaic camera, a far cry from the single-chip instrument used in its early years.

    MOA (Ongoing)

    MOA (Ongoing)

    CREDIT: MOA

    A 1.8-meter telescope at Mount John University Observatory in New Zealand has been surveying the sky for microlensing events since 2006, driven by a collaboration among astronomers in Japan, New Zealand, and the United States. Microlensing Observations in Astrophysics (MOA) has the biggest field of view of any telescope involved in microlensing surveys: an area of 2.2 square degrees of sky. Observations using MOA have led to the discovery of rogue planets: planetary bodies that appear to be gravitationally unbound from any stars.

    Astrometry

    Like the radial velocity technique, astrometry seeks to detect the slight wobble in a star's position caused by the gravity of an orbiting planet. Astrometry does it by plotting the star's position in the sky with extreme accuracy, through many observations repeated over time. Astronomers have been claiming the detection of "unseen companions" to stars using astrometry since 1855, but none have stood up to scrutiny. To date, there have been no confirmed exoplanet detections using the technique.

    Gaia (Coming Soon)

    Gaia (Coming Soon)

    CREDIT: ESA

    Astronomers hope that things will change later this year when the European Space Agency launches Gaia, an orbiting observatory that will accurately map the positions and motions of a billion stars in our galaxy, 1% of its population. Gaia's goals include detecting tens of thousands of exoplanetary systems. Researchers hope that Gaia will tell them more about the distribution of exoplanets around the galaxy: Are there more near the center or in the spiral arms? Are planets more common in areas rich in heavy elements?

    Direct Imaging

    The Holy Grail of exoplanet searching is direct imaging. If you can gather light from the planet itself, you can get a spectrum and find out the planet's temperature and what it's made of, compare its composition with those of its star and sister planets, and look for signs of life.

    The problem is that a planet is very close to a star that is a million or more times brighter—a firefly in the glare of a searchlight. Spotting one is not impossible. A handful of planets have been observed by both ground-based telescopes and Hubble. These, however, have tended to be "low-hanging fruit": large planets with wide orbits around dim stars.

    Direct imaging is all about contrast: picking out the faintest thing that can be discerned next to the star. Current systems can detect planets about a millionth as bright as their star. To do that, a telescope needs two things: a coronagraph and wavefront control. A coronagraph is simply an opaque patch that blocks the light of the star so that the dim planet can be seen. Starlight diffracted around its edge can still swamp the planet's light, so sophisticated optics are employed to ensure that this edge light is directed out of the way.

    Wavefront control employs a range of techniques to improve the dynamic range of the image by correcting for optical faults in the telescope. In ground-based instruments, it is essential to include extreme adaptive optics: computer-controlled deformable mirrors that move in real time to correct for atmospheric distortion.

    WFIRST (Under Consideration)

    WFIRST (Under Consideration)

    CREDIT: WFIRST TEAM/NASA GODDARD SPACE FLIGHT CENTER

    Atmospheric disturbance limits what ground-based telescopes can do, so to observe Earth-like planets will require instruments in space. Both NASA and the European Space Agency have designed dedicated planet-imaging spacecraft—Terrestrial Planet Finder and Darwin—with mirrors several times the size of the Hubble Space Telescope's. But both projects have been shelved as too costly.

    Hoping to get something more modest into orbit, exoplanet researchers have suggested adding a coronagraph to the proposed Wide-Field Infrared Survey Telescope (WFIRST), which was designed to look for exoplanets by gravitational microlensing (see p. 568) and to probe dark energy. WFIRST was supposed to have a 1.5-meter mirror, but that plan is being reconsidered since the U.S. National Reconnaissance Office gave NASA two 2.4-meter telescopes built for spy satellites (Science, 15 February, p. 748). NASA asked for proposals for using the two scopes; ideas include turning one into WFIRST and building a dedicated exoplanet imager. NASA will continue to study the proposals this year.

    Gemini and SPHERE (Coming Soon)

    Gemini and SPHERE (Coming Soon)

    CREDIT: ESO/B. TAFRESHI/TWANIGHT.ORG

    Several projects around the world are attempting to image exoplanets. Later this year, two purpose-built instruments will begin to bring direct imaging into the mainstream by improving contrast to about 1 in 107. The Gemini Planet Imager is a second-generation coronagraph with adaptive optics that will be attached to the 8-meter Gemini South telescope at Cerro Pachón in Chile. SPHERE is a system being installed at the European Southern Observatory's Very Large Telescope (pictured) at Cerro Paranal in Chile that incorporates adaptive optics and three different coronagraphs. Both instruments will seek to image giant planets around nearby stars. They'll target young star systems because recently formed planets will still be hot and so will emit their own infrared light. Observed in the infrared, planets appear brighter and stars dimmer than at visible wavelengths.

  8. And a Glossary of Their Quarry

    1. Lizzie Wade

    Science presents an overview of planet-hunting techniques and representative efforts for the nearly 900 confirmed exoplanets and the hundreds of fresh candidates that are turning up every month.

    CREDIT: NASA/APOLLO 17 CREW; NASA/JPL; NASA/JPL/UNIVERSITY OF ARIZONA

    Hot Jupiter

    Mini-Neptune

    CREDIT: NASA/TIM PYLE

    Gas giants more than 50 times the mass of Earth orbiting too close to their stars to be habitable. Make up 42% of confirmed planets. Example: 51 Pegasi b.

    Puffy Planet

    Similar to a hot Jupiter in mass and proximity to a star, but much less dense and thus larger. Synonym: Inflated hot Jupiter. Example: HAT-P-1.

    Hot Neptune

    Planets between 10 and 50 Earth masses orbiting close to their stars. Example: Gliese 436 b.

    Super-Earth

    A planet with about two to 10 times the mass of Earth. Can be hard to distinguish from a mini-Neptune. Example: Kepler-62 e and f.

    Earth-mass planet

    A planet about the mass of Earth, but not necessarily within its star's habitable zone. Example: Planet orbiting Alpha Centauri Bb.

    Exo-Earth

    Pulsar planet

    CREDIT: NASA/JPL-CALTECH/R. HURT/SSC

    A rocky planet with one to 10 times the mass of Earth, orbiting in the habitable zone of its star. Possible example: expected any time. Synonyms: Twin Earth, Goldilocks planet, Earth 2.0, Earth analog, Earth-like planet.

    Mini-Neptune

    A planet that is less massive than Neptune but shares its characteristic thick atmosphere of hydrogen and helium. Current detection techniques can have trouble telling them from super-Earths. Example: Kepler-11 b-f.

    Pulsar

    Exomoon

    CREDIT: ESA/NASA/L. CALÇADA/ESO FOR STSCL

    An exoplanet orbiting a pulsar, a spinning neutron star left behind after a supernova; probably debris from the explosion, trapped by the neutron star's strong gravity. Only a handful are known. Not habitable. Examples: PSR 1257+12 b, c, and d, the first exoplanets ever discovered back in 1992.

    Exomoon

    A moon orbiting an exoplanet. Some exomoons of gas giants may have molten interiors thanks to tidal heating, which could keep them warm even outside their stars' habitable zones and make them easy to spot from afar. But so far, no exomoons have been observed. Possible example: Fomalhaut b.

    Brown dwarf

    Brown dwarf

    CREDIT: NASA/JPL

    Sometimes called a failed star, a brown dwarf forms when a cloud of gas collapses but is not massive enough to ignite the fusion reactions that fuel fully formed stars. Brown dwarfs can be 13 to 75 times the mass of Jupiter. Less massive bodies are rogue planets; more massive ones can sustain fusion and are thus stars. Some brown dwarfs have their own planets. Example: 2M1207.

    Rogue

    A planet that does not orbit a star. Astronomers don't know whether these wandering planets were ejected from star systems or formed by themselves in interstellar space. Rogue planets can be up to 13 times the mass of Jupiter; more-massive bodies are classified as brown dwarfs. Without stars to keep them warm, they are always frigid. Synonyms: orphan planet, homeless planet, nomad planet, free-floating planet, sub-brown dwarf. Example: CFBDSIR 2149-0403.

    Circumbinary planet

    Circumbinary planet

    CREDIT: NASA/JPL-CALTECH

    A planet that orbits a binary star system and thus has two suns instead of one. Examples: Kepler-16 b, Tatooine.

    Eccentric planet

    With orbits the shape of stretched-out ellipses, these planets can swoop through drastically different temperature zones in the course of a year. Example: HD 80606 b.

    Waterworld

    A super-Earth covered in water—in the form of ice, oceans, or a water-vapor atmosphere, depending on the planet's proximity to the star. Example: Gliese 1214b.

    Core planet

    Core planet

    CREDIT: NASA/ESA/D. AGUILAR/HARVARD-SMITHSONIAN CENTER FOR ASTROPHYSICS

    The rocky core left behind after the gas of a hot Jupiter evaporates as a result of orbiting so close to its star. Synonym: chthonian planet, evaporated remnant core. Example: COROT-7b (suspected); HD 209458 b is in the process of evaporating.

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