The solar system appears to have a new ninth planet. Today, two scientists announced evidence that a body nearly the size of Neptune—but as yet unseen—orbits the sun every 15,000 years. During the solar system's infancy 4.5 billion years ago, they say, the giant planet was knocked out of the planet-forming region near the sun. Slowed down by gas, the planet settled into a distant elliptical orbit, where it still lurks today.

The claim is the strongest yet in the centuries-long search for a "Planet X" beyond Neptune. The quest has been plagued by far-fetched claims and even outright quackery. But the new evidence comes from a pair of respected planetary scientists, Konstantin Batygin and Mike Brown of the California Institute of Technology (Caltech) in Pasadena, who prepared for the inevitable skepticism with detailed analyses of the orbits of other distant objects and months of computer simulations. "If you say, 'We have evidence for Planet X,' almost any astronomer will say, 'This again? These guys are clearly crazy.' I would, too," Brown says. "Why is this different? This is different because this time we're right."

If you take the lessons of your middle school English teacher on faith, you probably think there's a right way and a wrong way to construct a sentence. But linguists have long acknowledged that some grammar falls into a "gray zone," a middle ground in which sentences are neither 100% right nor 100% wrong. Now, a new study shows that the linguists who map out the structure of grammar—syntacticians—rarely use this gray zone in their own studies. It also suggests a wide gap between their black-and white views and those of ordinary people.

"Grammar is not this binary thing," says Jana Häussler, a linguist at the University of Wuppertal in Germany and one of the study's authors. She adds that many of her colleagues still judge grammar using old binary models, when they should be coming up with systems that build in gradience—or the gray zone—as a possibility.

To find out just how many syntacticians use gradience, the researchers looked at 89 grammar papers published in the highly cited journal Linguistic Inquiry. Most of the authors seemed to give the gray zone its due: They used more than three categories to judge sentence grammar: "completely acceptable," "completely unacceptable," and at least one "intermediate" category. Problem was, they almost never used the intermediate categories for describing sample sentences. Instead, 94% of their sample sentences (2619 in all) made it into the "completely acceptable" or "completely unacceptable" categories, the researchers reported here this month at the Linguistic Society of America meeting.

Researchers also wanted to see how these expert conclusions tallied with the intuitions of ordinary people. In theory, syntacticians base their models on what sounds natural and right to native speakers. The judgments of regular people define the rules; syntacticians are supposed to describe and explain them. So the team took 100 "black-and-white" sentences from the studies and ran them by 65 native English speakers, recruited from the online labor-sourcing platform Amazon Mechanical Turk. Their answers didn't square with those of the linguists. On a scale of 1 to 7, participants ranked 40% of the black-and-white sentences between 3 and 5, putting them squarely in the "gray zone."

The results could affect everything from research into how the human brain processes language to building speech recognition software. By ignoring the gray zone, say the researchers, syntacticians are failing to describe how language really works.

US officials have ordered an investigation into claims China hacked a robotics research firm developing secretive military gadgets. At least one China-backed cyberspy operation has stolen data from British firm QinetiQ, a Pentagon contractor.

'The U.S.-China Economic and Security Review Commission (hereafter 'the Commission') invites submission of proposals to provide a one-time unclassified report on China's industrial and military robotics development,' the request says.

It asks for an investigation into 'what areas is China already ahead of the United States in the use or development of robotics with military applications? What U.S. or other dual-use robotics technologies have likely been acquired by China through technology transfers or cyber penetrations?'

The commission also intends to gauge the chances China's automation efforts could eclipse comparable Pentagon initiatives, including 'Offset,' a Defense Department research initiative meant to 'offset' technological advances made by adversaries, according to Defence One.

A century after observatory founder Percival Lowell speculated that a 'Planet X' lurks at the fringes of the Solar System, astronomers say that they have the best evidence yet for such a world. They call it Planet Nine.

Orbital calculations suggest that Planet Nine, if it exists, is about ten times the mass of Earth and swings an elliptical path around the Sun once every 10,000 - 20,000 years. It would never get closer than about 200 times the Earth - Sun distance, or 200 astronomical units (au). That range would put it far beyond Pluto, in the realm of icy bodies known as the Kuiper belt.

No one has seen Planet Nine, but researchers have inferred its existence from the way several other Kuiper belt objects (KBOs) move. And given the history of speculation about distant planets (see 'Solving for X'), Planet Nine may end up in the dustbin of good ideas gone wrong.

Tectonic plates may have inched across the Earth's surface to where they are now over the course of billions of years, but they left behind traces of this movement in bumps and gashes under the sea. Now, a new topographic map of the seafloor has helped researchers chronicle when the Indian-Eurasian continent formed as well as find a previously undiscovered microplate that broke off as a result of the event.

NASA's Earth Observatory released the map on Jan. 13, and it reveals the complex topography of the planet's seafloor. By analyzing these underwater peaks and ridges, researchers can decipher how and when the plates that made up the ancient supercontinent Pangaea tore apart about 200 million years ago, resulting in the birth of new ocean crust and the formation of mountain ranges.

The map, which is bright blue and red like a heat map, was compiled by an international team of researchers using a gravity model of the ocean, which is in turn based on altimetry data from the CryoSat-2 and Jason-1 satellites.

Altimetry measures the height of the sea surface from space by timing how long it takes a radar signal to reflect off the ocean and return to the satellite. The subtle highs and lows of the ocean surface mimic both seafloor topography and Earth's gravity field, according to NASA.

Working with mice, researchers at Johns Hopkins have contributed significant new evidence to support the idea that high doses of cocaine kill brain cells by triggering overactive autophagy, a process in which cells literally digest their own insides. Their results, moreover, bring with them a possible antidote, an experimental compound dubbed CGP3466B.

A summary of the study, which also found signs of autophagy in the brain cells of mice whose mothers received cocaine while pregnant, will be published online the week of Jan. 18 in the Proceedings of the National Academy of Sciences.

"We performed 'autopsies' to find out how cells die from high doses of cocaine," says Solomon Snyder, M.D., professor of neuroscience at the Johns Hopkins University School of Medicine. "That information gave us immediate insight into how we might use a known compound to interfere with that process and prevent the damage."

After discovering in 1990 that brain cells use the gas nitric oxide to communicate, Snyder and his research team have spent decades studying its impact. In 2013, the team found that nitric oxide is involved in cocaine-induced cell death through its interactions with GAPDH, an enzyme, but didn't learn how precisely the cells were dying.

A newly discovered mechanism in the brain may explain how we can recall nearly all of what happened on a recent afternoon, or make a thorough plan for how to spend tomorrow, in a fraction of the time that it takes to actually live out the experience.

The findings could advance research into schizophrenia, autism spectrum disorders, Alzheimer's disease, and other disorders where real experiences and ones that exist only in the mind can become distorted.

The mechanism compresses information needed for memory retrieval, imagination, or planning and encodes it on a brain wave frequency that's separate from the one used for recording real-time experiences.

Brain cells share different kinds of information with one another using a variety of different brain waves, analogous to the way radio stations broadcast on different frequencies. Researchers found that one of these frequencies allows us to play back memories, or envision future activities, in fast forward.

Their shapes are so different that they look like five different species.

But genetic studies have shown single species of nematode worm, newly discovered inside figs, can develop into five distinct forms. It is a striking example of physical divergence without genetic divergence.

"We were shocked," says team member Erik Ragsdale of the University of Indiana. "It is remarkable and unusual."

Young Pristionchus nematodes hitch a ride to new figs on the wasps that fertilise the figs. If you look inside the fig soon after the wasps arrive, only a small form of the nematode can be found. It has a simple tube-like mouth for feeding on microbes.

You may think your home is your castle, protected from animal invaders by cleaning products, sealed windows, doors, and walls. But scientists who have conducted the world's first survey of arthropods—creepy crawlies like insects, spiders, mites, and centipedes—in U.S. homes, report otherwise.

They randomly sampled the arthropod community in 50 homes in Raleigh, North Carolina, in 2012. The houses ranged in age from 7 to 94 years old, and from 840 to 4833 square feet. Armed with forceps, aspirators, and butterfly nets, the scientists hand-collected specimens—living and dead—from each room. They searched under and behind furniture, along baseboards, ceilings, on shelves, and in closets, amassing a collection of more than 10,000 specimens.

They gathered at least 579 morphospecies—animal types that are difficult to precisely identify—from 304 families. Flies were the most abundant, followed by spiders, beetles, ants, and book lice, whereas fleas and the American cockroach were relatively rare, the scientists report in today's issue of PeerJ.

Some of these, such as the book lice, have a long evolutionary history of living with humans. But the vast majority of specimens were inadvertent visitors, such as gall midges, leafhoppers, and ground beetles (like the false bombardier beetle, pictured above), who had wandered in and were likely looking for the exit.

Roughly half of Americans use marijuana at some point in their lives, and many start as teenagers. Although some studies suggest the drug could harm the maturing adolescent brain, the true risk is controversial. Now, in the first study of its kind, scientists have analyzed long-term marijuana use in teens, comparing IQ changes in twin siblings who either used or abstained from marijuana for 10 years. After taking environmental factors into account, the scientists found no measurable link between marijuana use and lower IQ.

"This is a very well-conducted study ... and a welcome addition to the literature," says Valerie Curran, a psychopharmacologist at the University College London. She and her colleagues reached "broadly the same conclusions" in a separate, nontwin study of more than 2000 British teenagers, published earlier this month in the Journal of Psychopharmacology, she says. But, warning that the study has important limitations, George Patton, a psychiatric epidemiologist at the University of Melbourne in Australia, adds that it in no way proves that marijuana—particularly heavy, or chronic use—is safe for teenagers.

Most studies that linked marijuana to cognitive deficits, such as memory loss and low IQ, looked at a single "snapshot" in time, says statistician Nicholas Jackson of the University of Southern California in Los Angeles, lead author of the new work. That makes it impossible to tell which came first: drug use or poor cognitive performance. "It's a classic chicken-egg scenario," he says.