It’s been an eventful year, from surprising finds in space and on Earth to technological innovations and its perils to developments in biology. In fact, there were so many newsworthy science and technology advances and occurrences that we couldn’t just limit our year end’s list to the usual ten entries and instead kicked up to 11. Call it a ten-plus-one list.

10. (TIE) The Uncharted Territory of Ebola



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Ebola lingers. Health workers attempting to beat back a massive epidemic across Liberia, Guinea and Sierra Leone in west Africa continued to learn that hard lesson in 2015. The virus has killed more than 11,300 people and left an indelible mark on the global stage. But active cases are not the only concern. From studying thousands of Ebola survivors and their close contacts, clinicians are now learning that the virus remains in the body and sexual fluids much longer than they suspected and public health officials have found evidence that suggests the virus has already been sexually transmitted. The Ebola virus—or at least genetic fragments of it—can also remain in semen for some nine months, which raises questions about how long survivors need to abstain from sex or continue to use condoms.

There have also been other surprises with the virus. In at least one case the pathogen managed to reemerge and sicken a nurse in the U.K. some nine months after she was considered free from the disease (although ultimately she managed to survive this complication). Ebola researchers studying the unprecedented number of survivors are also producing a more nuanced understanding of how Ebola continues to linger in the body long after patients have officially recovered from the illness. More than half of Ebola survivors continue to suffer from symptoms including joint pain, headaches or muscle pain in the months following recovery. Many others complain of visual problems and sleeplessness. These sometimes debilitating symptoms can prevent people from returning to their jobs and lives. They can also stoke stigma and fear of Ebola survivors.

There have been other Ebola setbacks, too. Even after the World Health Organization declared Liberia disease-free last summer new cases of the Ebola developed, underscoring how quickly gains against the epidemic can be upended. In west Africa there were no new Ebola cases during the week of December 6, according to WHO. Still, the virus is likely to sicken more people.

The 2015 slowdown in the Ebola epidemic afforded opportunities to study how the outbreak grew so large in the first place. Investigations into the international Ebola response harshly criticized WHO and others for their lethargic action in 2014. But there is some good news going forward: Armed with the first promising vaccine to help combat the illness and more knowledge about how to treat those infected with the virus, the world is now better poised to respond to Ebola in the months and years ahead.—Dina Fine Maron

10. (TIE) New Discoveries about the Immune System Impacts the Brain



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Depression, autism and Alzheimer’s disease are all painfully prevalent brain disorders, but they have something else in common: they have been linked to inflammation in the brain. This essential immune response that helps us fight infections sometimes backfires—when prolonged, the action can damage tissue and negatively affect our mood and cognitive abilities. Think about the last time you had a cold: That lousy, drowsy feeling can be attributed to this effect.

Scientists are starting to understand how immune responses contribute to disorders of the brain and are beginning to test new drugs that target inflammation. Clinical trials assessing the effectiveness of anti-inflammatory drugs for depression and schizophrenia are already underway. Researchers have even tested an experimental vaccine that manipulates the immune system to lessen the fear response in rodents—a technique that could someday be used to treat and prevent post-traumatic stress disorder.

This year, scientists also discovered an unexpected line of communication between the immune system and the brain—a previously unseen network of lymphatic vessels in the meninges, the membranes surrounding the brain, that drains fluids from tissues and carries immune cells. Though abnormal immune activity had been associated with psychiatric conditions in the past, scientists believed the brain’s immune system to be separate from the body’s. This new finding suggests that malfunction in these vessels could contribute to a variety of neurological diseases with an immune component including Alzheimer’s and autism.

Not only were the connections between the brain and immune system further solidified by studies published in 2015, but the brain’s resident immune cells also emerged as a key player in both development and disease. Though microglia were long seen solely as the primary defenders of the brain, scientists have recently recognized their critical role in eliminating unwanted synapses, the connections between neurons, during early development. Research presented at this year’s Society for Neuroscience conference in Chicago revealed how defective pruning by microglia might lead to developmental disorders like schizophrenia and autism. Scientists also provided preliminary evidence that microglial activity later in life could play a role in neurodegenerative disorders such as Huntington’s disease and blocking this activity might reduce the loss of synapses seen in such diseases. These new revelations will likely lead to better treatment options for a variety of psychiatric and neurological conditions in the years to come.—Diana Kwon

9. Drones Fly onto Regulators’ Radar



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In 2015 the U.S. Federal Aviation Administration (FAA) formally decreed that drone pilots—even hobbyists—are aviators and must accept all of the rights and responsibilities that come with that designation. In other words, if a person buys a drone weighing between 250 grams and 25 kilograms (including camera or other payload), he or she needs to register that mini-aircraft with the government.

The new FAA rules seek to balance the popularity and promise of drones with concerns about national security, radio-spectrum ranges, privacy and safety and were hardly a surprise. The guidelines came at the tail end of a year in which unlicensed drone interference with passenger aircraft nearly tripled in the U.S. And that doesn’t include a number of high-profile mishaps closer to the ground, including White House lawn landings and collisions with people the drones were set up to photograph.

The new guidelines require registration but not licensing and were announced in advance of holiday gift-giving that’s expected to add hundreds of thousands of drones to the skies. Additional unmanned air traffic will come from businesses and researchers. Already, online retailer Amazon this year further outlined its plans for using drones as delivery vehicles and is working with NASA and others on an air traffic management system. And scientists made good use of the technology to help them better understand Earth’s changing climate and wildlife ecology.

Commercial drones presently can only fly within U.S. airspace with special permission. In fact, the agency has already doled out thousands of these exemptions to farms, railroads, security services, medical facilities and others. Everyone else can expect formal commercial drone regulations by the end of next year or early 2017.—Larry Greenemeier

8. A Century of General Relativity—the Theory That Revolutionized Physics

This year marks the centennial of one of the most famous and successful scientific ideas of all time—Albert Einstein’s general theory of relativity. The theory, which turned the traditional notion of gravity and space on its head, revealed that gravity is not a pull on matter as we thought but rather a simple consequence of misshapen spacetime. This revolutionary idea deformed the landscape of physics itself, and 100 years later the threads of scientific inquiry are still following along the contours it created.

To celebrate general relativity’s anniversary Scientific American dedicated its September 2015 issue to the topic. The special package included articles on how Einstein put the idea together, what the physicist got wrong, scientists’ quest to carry on Einstein’s dream of a unified theory of physics and much more. Our Web site also published special online features such as an interactive graphic showing relativity’s impact on later research, a quiz on Einstein, the real story behind the equation E = mc2, and others.

Now is a good time to take a look back at big ideas like general relativity because physics is, once again, facing daunting challenges. The mysteries of what makes up the invisible dark matter rife throughout the universe and the mystifying dark energy that seems to be accelerating the expansion of the cosmos stand unsolved. To answer these questions science may need another breakthrough on the scale of general relativity. Clues may come from the Large Hadron Collider (LHC) outside Geneva, which recently began colliding protons together at unheard-of energies. Intriguing hints of a new particle at the LHC reported in December spurred hopes the machine may make a significant discovery in 2016. Revamped experiments aiming to detect dark matter particles directly could also turn up results very soon.—Clara Moskowitz

7. Volkswagen Sabotages “Clean” Diesel



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One of the biggest cheerleaders of so-called “clean diesel” handed the technology a major defeat in 2015. German automaker Volkswagen AG admitted to manipulating control devices in certain diesel models to pass the U.S. Environmental Protection Agency’s emissions testing. The fallout: lawsuits, recalls and the revelation that more than half a million supposedly lower-emissions vehicles sold in the U.S. and 11 million worldwide since 2008 spew up to 40 times the permitted amount of nitrogen oxides (NOx).

The EPA found that certain Audis, Porsches and VWs activated emissions controls during testing but reverted to higher emissions during normal driving. Diesel engines are more efficient than their gasoline counterparts, requiring less fuel to deliver comparable power. But diesels produce more NOx and particulates than gas engines. VW’s technology of choice to help minimize these pollutants has been its highly touted turbocharged direct injection (TDI) technology, which activates certain emissions controls.

Turns out those controls were very selective as to when they would activate a vehicle’s auxiliary emission control devices (AECDs) to adjust engine emissions. AECDs in certain vehicles included an algorithm that used steering wheel position, vehicle speed, engine-operation duration and barometric pressure to determine when the vehicle was being tested. Then it would dial back emissions to meet EPA standards. During normal driving conditions, however, the vehicle’s engine power would be ramped up by reducing the effectiveness of the emission control system.

Regulators in several countries are investigating VW’s actions and Switzerland has banned the company from selling certain diesel models. Meanwhile, VW has promised to roll out software updates and other fixes throughout 2016 that company says should provide accurate emissions readings without impairing engine output, fuel consumption or performance.

The damage to diesel may be irreparable though. A group of entrepreneurs and investors—including Tesla and SpaceX CEO Elon Musk—recently sent a letter to the California Air Resources Board arguing that VW should not be forced to fix its clean-diesel cars. Instead, the company should be required to, among other things, begin selling several zero-emissions vehicles over the next five years.—Larry Greenemeier

6. Advances in Concussion Science

The movie Concussion hits theaters this week, capping a year that has been abuzz with concussion-related news and scientific advances. The movie stars Will Smith as the doctor who discovered brain damage in former NFL players back in 2005—and just this year the NFL finally proposed a billion-dollar settlement to a lawsuit brought by players who accuse the organization of covering up the scientific findings. In the meantime scientists have been ramping up research on all fronts: prevention, diagnosis and treatment. Many of the new findings fly in the face of conventional wisdom—for instance, too much “brain rest” might prolong recovery.

On the prevention front, a call for a “heading” ban in youth soccer has been gaining momentum—but scientific findings suggest that hitting the ball with one’s head is not the main problem, it’s the player-to-player contact that occurs when they attempt to head the ball and knock noggins with each other instead. New results also point at the need to limit the number of supposedly “minor” head hits players receive even if they don’t meet the criteria for a concussion diagnosis after any single hit—the cumulative damage from a series of small blows might be just as harmful as a single serious blow.

In any case, diagnosing a concussion can be tricky—especially on the sidelines of an athletic field. Many research teams are working to develop simple verbal and memory tests that will allow coaches and parents to quickly detect whether a player might have suffered a concussion, so the athlete can be pulled out of the game before sustaining additional blows. A second concussion just after the first can lead to long-term problems involving cognition and memory and can potentially even be life-threatening. One promising technology, which utilizes the fact that many people with concussions have trouble visually tracking objects, embeds an eye tracker in goggles for sideline neurological diagnostics.

Athletes are not the only people who suffer concussions, of course. Head injury is a major problem for military personnel, and more than a million civilians per year sustain concussions in accidents, falls, fender benders or during casual physical activity. It’s difficult to determine which of these injuries will lead to long-term cognitive problems, but new research shows that a blood test may be a promising indicator. Patients can also help themselves heal with a smartphone app that offers DIY mindfulness and cognitive therapy techniques shown to improve post-concussion symptoms. Someday soon a simple cocktail of existing drugs, specifically an antibiotic and an antioxidant, could be standard in first aid kits, according to research in mice that shows the combo mitigates some of the damage from head trauma. Researchers on all fronts are hopeful that 2015’s breakthroughs will lead to fewer head injuries and better solutions for patients in the near future.—Karen Schrock Simring

5. Newly Discovered Human Species Raises Questions about Our Past



Credit: Peter Schmid and William Harcourt-Smith | Wits University

The more human fossils paleoanthropologists discover, the weirder the story of our origins gets. In September researchers led by Lee Berger of the University of the Witwatersrand in South Africa unveiled 1,500 fossil specimens representing at least 15 individuals of a human species new to science: Homo naledi. The find is one of the largest assemblages of human fossils on record. Yet despite the wealth of evidence from this latest addition to the human family, H. naledi has raised more questions about our past than it has answered.

Scientists retrieved the remains from a difficult-to-access chamber within a cave system called Rising Star, located outside Johannesburg. The fossils exhibit a novel mix of traits characteristic of our predecessors the australopithecines, and those associated with our genus, Homo. The H. naledi hip joint, for instance, resembles that of the famous australopithecine skeleton known as Lucy; the foot, in contrast, looks like a modern human’s. The H. naledi assemblage includes nearly every bone in the body—many more than have been recovered for most other extinct Homo species. The dearth of comparable fossil material from other species and the fact that the age of the H. naledi fossils has yet to be determined have left many experts puzzled over where our new relative fits in the family tree.

Even more mystifying is what the bones may reveal about H. naledi’s behavior. When researchers find fossils of human ancestors, they typically spot animal bones in the vicinity, too. But no animal remains accompanied the H. naledi fossils, apart from a smattering of small bird and rodent bones. That absence of medium- to large-size animals is among the evidence that suggests the cave chamber was inaccessible to such creatures, and that H. naledi took pains to dispose of its dead there. Such behavior was thought to be exclusive to the large-brained anatomically modern humans (and possibly Neandertals). Yet H. naledi’s brain was the size of an orange.

Critics have challenged both the claim that the remains represent a new species and the suggestion that they were deliberately disposed of as part of a mortuary ritual. Resolution may come from efforts that are currently underway to date the site and further analyze the bones.—Kate Wong

4. Record Climate Change



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Climate change was one of the year’s hottest stories, literally and politically. By early December, meteorologists had determined that the average global temperature in 2015 was already destined to be the highest on record, by a significant margin. The ongoing heat may have helped to produce the strongest El Niño the planet has experienced. Water temperature in the central Pacific was the highest ever measured in association with the atmospheric-ocean circulation pattern, which alters weather across North American in particular as well as other parts of the world. Although strong El Niño conditions can sometimes amplify precipitation in California—much needed for the state’s ongoing drought—new research showed that the phenomenon does not necessarily enhance snowpack in the Sierra Nevada mountains, which the state relies on to recharge groundwater each spring.

A warm Pacific Ocean also provided energy for the most powerful hurricane seen anywhere on earth. On October 23, as Hurricane Patricia approached Mexico’s west coast, its peak winds topped 200 mph. That surpassed “super typhoon” Haiyan, which struck the Philippines in 2013 with 195 mph winds.

Such dramatic events may have emboldened representatives from 196 countries to push for ambitious goals on carbon emissions when they met in Paris for climate negotiations this month. On December 12, after 20 prior meetings since 1992, the nations at COP21 agreed to reduce emissions of carbon dioxide enough to limit global warming to “well below 2 degrees Celsius,” and they set a more ambitious objective to try to keep the temperature rise to 1.5 degrees C.

Shortly before COP21, President Barack Obama on November 11 denied TransCanada’s application to build the Keystone XL pipeline, effectively ending any realistic chance for Canada to export to the U.S. large volumes of oil derived from tar sands, considered the dirtiest fossil fuel. Obama said the State Department had determined that the oil pipeline “would not serve the national interest of the United States.”

A few months earlier, on August 3, the president released the Clean Power Plan. It requires states to meet specific targets, set by the EPA, for reducing carbon emission from power plants inside their boundaries. The Republican-led Congress, against the move, vowed to derail it in 2016.

In the next few months water temperatures in the Pacific Ocean near the equator will cool, as is usual each spring, thus weakening the El Niño weather pattern for the moment. But by then the presidential race will be in full swing, and the political climate debate will continue to be hot.—Mark Fischetti

3. Massive Data Breach Highlights Widespread Cybersecurity Shortcomings



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The theft of millions of data records from the U.S. Office of Personnel Management’s computer systems is a cautionary tale

Much of what you need to know about the state of cybersecurity in 2015 can be gleaned from the U.S. Office of Personnel Management’s (OPM) massive data breach, which the agency revealed in June. The theft of more than 21.5 million records, which took place over several months beginning in March 2014 (or possibly earlier), raised the specter that China had declared cyber war on the U.S. Lawmakers quickly seized on the incident to justify flawed cybersecurity legislation, including the Cybersecurity Information Sharing Act (CISA). Subsequent investigations into OPM’s cybersecurity measures revealed the kind of lax policies and practices—endemic throughout both the public and private sectors—that enabled high-profile data thefts to become commonplace.

Health care provider Anthem and dating Web site Ashley Madison joined OPM on the list of biggest data security failures for 2015. As is often the case, these organizations had been warned about poor security practices prior to the data breaches but failed to address those concerns. OPM’s inspector general had likewise issued a report in November 2014 detailing the agency’s cybersecurity deficiencies. Given the cost, complexity and commitment required to improve cybersecurity in large organizations—not to mention the sheer number of attacks launched at any given time—it’s unlikely the situation will improve in 2016.

The Chinese government denied that the OPM attack had been state-sponsored and later announced it had arrested a group of hackers in connection with the hack. Given how difficult it is to prove the source of a cyber attack, both U.S. and Chinese officials have more recently begun calling the incident a crime rather than an act of war. In September U.S. and Chinese presidents Barack Obama and Xi Jinping tried to further smooth over tensions by promising to cooperate during cyber-crime investigations and announcing that neither the U.S. nor the Chinese government would steal intellectual property, trade secrets or other confidential information online. Representatives from the two countries met in December to begin working out the details of this pact.

Congress, meanwhile, cited the stolen OPM records as one more reason to pass a law such as CISA that would encourage companies to share cyber-threat information with the government. CISA supporters insisted that this sharing—including data about attack victims—would help both government and industry better prepare for the next attack. Opponents rightly debunked this notion, pointing out that among other things CISA does not force companies to improve their cybersecurity defenses and would create new vulnerabilities if victims’ personal information is turned over to the government, whose own computer systems were pilfered with alarming regularity throughout 2015. Pres. Obama ultimately approved CISA on December 19 as part of a $1.1 trillion federal budget bill.—Larry Greenemeier

2. The CRISPR Revolution Gains Momentum



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And yet, researchers captivated by the latest gene-editing technology paused in 2015 to address simmering ethical issues

When the idea for a faster, simpler way to edit genes first burst on the scientific landscape in 2012, researchers around the globe were eager to check it out for themselves. Within two years, many of them had abandoned their older, more cumbersome techniques for the so-called CRISPR–Cas9 approach, which allows editing multiple genes at once. Not since the 1980s, when a new method known as PCR was developed for greatly amplifying small amounts of DNA, has a new technology taken over research labs so quickly.

The CRISPR revolution happened so fast, however, that certain ethical issues started being widely addressed only this year. Earlier this month Scientific American associate editor Dina Maron attended an international summit held in Washington, D.C., to debate whether or how quickly researchers should try editing human genes using the CRISPR–Cas9 system. "Although most scientists at the meeting appear enthusiastic about conducting gene-editing work to cure diseases in individual patients," Maron wrote, "they remain more wary of making changes to eggs, sperm or embryos that would have lasting repercussions in future generations."

By the end of the three-day summit, however, the scientists decided that such germ-line editing could proceed as long as it was confined to the lab and "the modified cells [were] not . . . used to establish a pregnancy."

No doubt they had determined that a complete moratorium on human embryo research was impractical. Earlier this spring Chinese scientists reported that they had used CRISPR technology to make changes in the DNA of human embryos. The researchers deliberately worked on embryos that were so genetically flawed that they could not have been carried to term. Although they were able to make changes in the gene that they had targeted, a number of uncontrolled changes took place in other genes as well, underscoring their conclusion that CRISPR–Cas9 technology is not yet safe enough to be tried in the clinic.—Christine Gorman

1. Year of the Dwarf Planets and New Views of Mars



Credit: NASA/JPL-Caltech/Univ. of Arizona

There was plenty of space news in 2015, including reports about vanishing quasars, mysterious gamma rays from the center of the Milky Way and tantalizing hints of a mysterious object orbiting a distant star that might be an alien superstructure (but probably isn’t). The most exciting discoveries of the year, however, took place closer to home, where the New Horizons and Dawn space probes found astonishing surprises during the first-ever close encounters with the dwarf planets Pluto and Ceres, respectively; the Rosetta mission ran rings around a comet; and the evidence for water on Mars—not just on the Red Planet billions of years ago, but flowing on its surface right now—grew stronger than ever.

Pluto flyby

Even at half a million kilometers out from its July 14 flyby, early images from the New Horizons probe proved that project lead Alan Stern was right when he began lobbying for a Pluto mission back in the early 1990’s. The dwarf planet, demoted from the ranks of full-fledged planets shortly after New Horizons launched in 2006, showed evidence of remarkably active geology, including flowing glaciers of frozen nitrogen, huge, wrinkled ridges of water ice and perhaps ice volcanoes as well.

Charon, Pluto’s largest moon, sports a fractured surface, including a crack four times the length of the Grand Canyon, and evidence of its own cryovolcanoes. All of this is based on images and other readings taken as the craft sped by the Pluto–Charon system at some 52,300 kilometers per hour. It all happened last summer, but those high-resolution images and data will take a total of 16 months to upload to Earth—which means plenty of surprises, and a much fuller understanding of Pluto’s structure and history, are still to come.

Dawn orbits Ceres

The original discoveries of Ceres and Pluto—the former in 1801, the latter in 1930—turned out to be harbingers of a new understanding of the solar system. Ceres would turn out to be just the first and biggest of hundreds of thousands of asteroids discovered, mostly sitting between Jupiter and Saturn. Pluto was simply the easiest of potentially millions of icy bodies of the Kuiper Belt, out beyond Neptune, to spot.

Now, the Dawn mission, which reached Ceres last March after an interim stop at the smaller asteroid Vesta in 2011, has confirmed another similarity. Not only are Pluto and Ceres charter members of the dwarf planet club, formed in 2006 (a demotion for Pluto, a promotion for Ceres), they’re also closer in composition, with icy Pluto containing more rock and rocky Ceres more ice, than planetary scientists once believed. Comets (Pluto’s smaller cousins) and asteroids evidently aren’t entirely different sorts of objects either; instead, they lie at opposite ends of a compositional spectrum.

Density estimates had hinted at Ceres’ H2O-rich composition before, but the discovery of mysterious bright spots on its surface confirmed it. The spots themselves aren’t made of ice, as astronomers first thought they might be. They do seem to mark spots where ice or slush has erupted from below, however, leaving white, ammonia-rich mineral deposits behind when the ice sublimed into space. Not only that: Dawn has detected haze over some of the white spots, suggesting that eruptions aren’t just a thing of the dim past.

Mars

Astronomers have known since images from the first spacecraft to orbit Mars, Mariner 9, in the early 1970’s suggested that water once flowed freely across Mars’s surface—a discovery that has been confirmed over and over by a succession of orbiters and rovers including, most recently, the Mars Science Laboratory, aka Curiosity.

Ancient water is one thing (albeit a big thing, because it might point to a primordial Mars that could have been hospitable to life). But water flowing over the Martian surface today is something else entirely—and although the Mars Reconnaissance Orbiter didn’t see water itself, it did see dark streaks that appear to form in summer on steep slopes, then disappear in winter. The streaks have been spotted before but the orbiter has now shown that they contain water-soluble minerals—making it clear that ice on or near the surface is melting, flowing downhill, then refreezing. No one is suggesting that life of any sort currently exists on the Red Planet, if it ever did. But the presence of water means that no one can rule it out, either.—Michael Lemonick