Monitoring tides could predict major quakes

THE rise and fall of the tides could help us to predict major earthquakes like the magnitude 9 quake that triggered Japan's tsunami last year.

Sachiko Tanaka of the National Research Institute for Earth Science and Disaster Prevention in Tsukuba, Japan, says that as stresses build up in the Earth's crust, it becomes more susceptible to minor earthquakes triggered by tidal forces, a sign of major quakes to come. She has spent over a decade amassing evidence for her theory. According to her latest results, tidally triggered earthquakes were rife off the north-east coast of Japan for several years before 2011's massive earthquake.

"I read hundreds of earthquake prediction papers," says Ross Stein of the United States Geological Survey in Menlo Park, California. "The vast majority is dry rot. Tanaka's stands out. It could be very important."

At high tide, more water is piled up on top of geological faults, adding to the stress acting on the rocks. If the fault is already close to rupture, the effect can trigger small tremors.

Tanaka compared records of tides and submarine earthquakes from 1976 to 2011 for 100,000 square kilometres surrounding the epicentre of last year's quake. For the first 25 years of records, there was no sign of tidally triggered earthquakes, but after 2000 the number of these quakes gradually increased, reaching a peak just before last year's megaquake. Afterwards, the effect disappeared again (Geophysical Research Letters, DOI: 10.1029/2012GL051179).

Tanaka's findings show that stress was building up in the region for a decade before the main quake struck. Her earlier research had uncovered a similar effect in the run-up to three Sumatran earthquakes, including the 2004 quake that caused the Boxing Day tsunami. Tidal quakes happened more frequently in the run-up to bigger quakes, suggesting stress had built up year-on-year.

Despite decades of effort, seismologists still cannot reliably predict earthquakes. Tanaka's approach is promising, but Harold Tobin of the University of Wisconsin-Madison points out that her analysis was done after the quake happened.

Tanaka is cautious, but will now try predicting quakes. "I am planning to monitor tidal triggering in the north-eastern Japan and Sumatra subduction zones," she says.

"Just for something to have this level of promise is unique," says Sateesh

Robotic fish shoal sniffs out pollution in harbours

There is something unnatural lurking in the waters of the port of Gijon, Spain, and researchers are tracking its every move. It is not some bizarre new form of marine life, but an autonomous robotic fish designed to sense marine pollution, taking to the open waves for the first time.

"With these fish we can find exactly what is causing the pollution and put a stop to it right away," explains Luke Speller, a scientist at the British technology firm BMT and the leader of SHOAL, a European project involving universities, businesses and the port of Gijon, which have joined forces to create the fish.

Currently the port relies on divers to monitor water quality, which is a lengthy process costing €100,000 per year. The divers take water samples from hundreds of points in the port, then send them off for analysis, with the results taking weeks to return. By contrast, the SHOAL robots would continuously monitor the water, letting the port respond immediately to the causes of pollution, such as a leaking boat or industrial spillage, and work to mitigate its effects.

The SHOAL fish are one and a half metres long, comparable to the size and shape of a tuna, but their neon-yellow plastic shell means they are unlikely to be mistaken for the real thing. A range of onboard chemical sensors detect lead, copper and other pollutants, along with measuring water salinity. They are driven by a dual-hinged tail capable of making tight turns that would be impossible with a propeller-driven robot.

They are also less noisy, reducing the impact on marine life. The robots are battery powered and capable of running for 8 hours between charges. At the moment the researchers have to recover them by boat, but their plan is that the fish will return to a charging station by themselves.

Working in a group, the fish can cover a 1 kilometre-square region of water, down to a depth of 30 metres. They communicate with each other and a nearby base-station using very low-frequency sound waves, which can penetrate the water more easily than radio waves. However, this means the fish have a low data transmission rate and can only send short, predefined messages. "It's a good solution, but it requires thinking carefully about what data to transmit and how to use that data," says Kristi Morgansen, a roboticist at the University of Washington, who was not involved in the research.

Navigation relies on a related system that communicates with four "pingers" at the corners of the port, which act much like GPS satellites for the fish. If one fish senses pollution in an area it can call the others to create a detailed map of high and low concentrations around it, helping port authorities to locate the exact source of the pollutant.

Versions of the fish have been working successfully in the lab for a few years now, but trialling them in a real-life port has proved more difficult. Rough weather has often prevented the researchers from venturing out on the waves, though Speller says the fish would be fine as they can simply dive below the water. But depth has also been a problem – the waterproofing on one component is unable to withstand the pressure at 30m underwater, so it requires a last-minute replacement.

Thankfully the fish are fitted with a variety of safety features if something goes wrong, such as airbags that inflate to make the fish surface, and a GPS and cellphone chip in the fin so that a distressed fish can send its location details to Speller's phone via text message.

Having demonstrated that the fish can sense pollution and communicate underwater, the SHOAL group now plans to commercialise the design and sell it to other ports in Europe and the rest of the world. The prototypes currently cost around £20,000 each, but mass production should bring that price down.

Speller plans to do more than just track pollution, however – the fish's modular design makes it easy to swap the chemical sensors for other applications. "I like to see the fish as platform for other things that can be done in the sea, such as search and rescue, helping divers, and port security."

Morgansen says that underwater gliders have proved successful in monitoring open waters, but they cannot move within the tight spaces of a port or harbour. This means nimbler fish-inspired robots like SHOAL's may be the way forward. "I think the use of agile underwater robots for monitoring water systems will happen in most ports in the not-distant future."

DNA suggests marine reserves boost commercial fishing

If you protect fish, there will be more of them to catch. That's the reasoning conservationists have long used to persuade commercial fisheries of the benefits of marine reserves. Now they may have DNA confirmation.

Earlier research had shown that marine reserves result in larger fish that spawn more offspring, but researchers were left speculating exactly where the baby fish ended up and whether they truly help replenish other areas.

Now, with the use of new DNA profiling techniques, scientists have shown that by devoting less than a third of an area to a marine reserve network, you can double the number of juvenile fish that settle in the rest of the area. (Current Biology, DOI: 10.1016/j.cub.2012.04.008)

Garry Russ, one of the authors of the study, said he has spent the last 30 years contemplating how you can confirm exactly where fish born in marine reserves go. "To me, it's a little bit like the holy grail of marine reserves as fishery management tools," he says.

To nail the problem, Russ and colleagues at the ARC Centre for Excellence for Coral Reef Studies in Queensland, Australia caught 1620 adult coral trout and stripey snapper from a series of reserves on the Great Barrier Reef. Both species are popular with commercial and recreational fishing. They then took DNA samples from their tails, and released them alive. Later, they sampled juvenile fish from 19 locations throughout the region and checked to see if they were offspring of the fish in the reserves.

Though the reserves make up just 28 per cent of the area, the team calculated that about half of all juvenile fish were spawned by fish in the reserves – showing that the protected areas "punch above their weight in replenishing fishery stocks", as Russ puts it.

But fisheries ecologist Colin Buxton from the University of Tasmania at Sandy Bay in Tasmania, Australia isn't convinced that these results show reserves will help commercial fisheries. If the adult population isn't suffering from a shortage of juvenile fish – as he says is the case in the area studied – then introducing more young fish won't help.

Buxton adds that the only effective way to maintain sustainable fish populations is to limit the number of fish taken out of the water.

Yet Russ believes the new findings provide strong evidence that marine reserves are a useful tool in maintaining fish populations. "Doubling the number of recruits coming into a population is almost always going to affect the adult population size quite substantially," he says.

Russ and his team next plan to look at the genetic makeup of the fisheries' catches to see if they are in fact being bulked up by fish breeding in the reserves. Their future research will also require them to cast a wider net – to see just how far from the marine reserve fish spawned there will travel.

Geoengineering would turn blue skies whiter

Blue skies would fade to hazy white if geoengineers inject light-scattering aerosols into the upper atmosphere to offset global warming. Critics have already warned that this might happen, but now the effect has been quantified.

Releasing sulphate aerosols high in the atmosphere should in theory reduce global temperatures by reflecting a small percentage of the incoming sunlight away from the Earth. However, the extra particles would also scatter more of the remaining light into the atmosphere. This would reduce by 20 per cent the amount of sunlight that takes a direct route to the ground, and it would increase levels of softer, diffuse scattered light, says Ben Kravitz of the Carnegie Institution for Science in Stanford, California.

That would have knock-on effects for life – and human technology. The reduction in direct sunlight would impact the solar industry, which relies on direct sunlight to generate much of its power. But the increased indirect sunlight would boost photosynthesis beneath tree canopies. The most visible effect, though, would be above us.

The blue colour of the clear sky comes from light being scattering by molecules in the air. The scattering is much stronger for short blue wavelengths than for longer red wavelengths. Aerosol particles are much larger than molecules in the air, however, and they scatter red light more strongly, which washes out the blue light scattered by smaller molecules and makes the sky brighter and whiter.

Kravitz calculated how scattering from particles ranging from 0.1 to 0.9 micrometers in diameter would affect the spectrum of the scattered light, and how that would affect the colour of the sky. He found the sky would appear paler for all potential diameters. Particles with diameters in the middle of the range would make for much whiter skies.

The effect would be most visible in the countryside, where air pollution is generally lower, says Kravitz. "All you'd have to do to see it is to step outside."

Important uncertainties remain, including what size aerosols would be used for geoengineering and how their sizes might change over time as particles stick together. But Craig Bohren, a meteorologist and expert in atmospheric scattering at Pennsylvania State University in University Park, who was not involved in the research, says "it's difficult to argue against the claim that increasing the concentration of particles in the atmosphere will change the colour and brightness of the sky".

Ignore shocking decline of farm birds at our peril

It may or may not come as a surprise that some European bird populations are in precipitous decline, but what is more surprising and shocking is the emerging scale of the losses, and that they are occurring under our noses.

New information from the Pan-European Common Bird Monitoring Scheme shows that widespread farmland birds are declining across Europe at an alarming rate. The downward trend in an index of population of 36 specialist farmland birds for the last 30 years equates to an estimated loss of 297 million farmland birds in Europe during that period – a 50 per cent decline since 1980. That is a lot of biodiversity in anyone's money.

Just one example is the eponymous skylark, whose song is so evocative of the countryside in summer. Its numbers have fallen by nearly half – we have lost 37 million of them. While the rate of decline has slowed in recent decades, the downward trend continues and there's little room for optimism.

This is particularly the case in Eastern Europe and in those countries that joined the European Union most recently. Their traditional farming systems host some of the richest wildlife communities in Europe but they are now under severe threat.

You might assume this was all a mystery to the scientists, but it is not – the causes of the decline are well known. We probably know more about European farmland birds than most other taxa on Earth. The research is extensive and compelling, and it shows the decline of farmland wildlife has been driven primarily by changes in farming: especially a move towards intensive and specialised methods; the loss of hedgerows and marginal natural habitats; changes in crop and cropping patterns; and the increased use of fertilizers and pesticides.

Many animals and plants have been similarly affected. The changes themselves have been driven in large part by Europe's infamous Common Agricultural Policy (CAP), which was introduced in 1962 in a post-war climate still haunted by food shortages. No one would argue that food production and food security are not important – they are vital – but these new numbers suggest that the current balance is wrong.

You might question whether it matters that we have lost 297 million farmland birds if you're not a birdwatcher, but I'd argue that it does because it suggests a wider disregard for nature and its value. There is growing recognition that biodiversity loss can affect lives and economies directly and indirectly through the loss of a range of ecosystem services upon which we all depend. We ignore biodiversity loss at our peril.

Reversing this trend is simple: there must be a better balance between wildlife and food production and how both are valued. This isn't a choice between food and wildlife; we can have both, as plenty of farmers are demonstrating in the UK, particularly through agri-environment schemes.

However, European agricultural policy needs substantial reform so that it delivers measures to help birds and other wildlife right across the continent's farmed landscape and on a much greater scale. This means that funding for agri-environment schemes must increase significantly, and the quality and implementation of schemes must improve so they deliver wildlife's needs on the ground. For birds, this means nesting habitats and food in the summer and winter.

Policies must also support low-intensity farming systems that deliver a range of ecosystem benefits in addition to wonderful biodiversity. We know exactly what to do to start turning these devastating numbers around, but the political will is needed to make it happen. This isn't rocket science nor does it need a rocket science budget.

Quite simply, we are sleepwalking into disaster and it is time to wake up.

Profile: Richard D. Gregory is project manager of the Pan-European Common Bird Monitoring Scheme and head of species monitoring and research in the department of conservation science at the UK's Royal Society for the Protection of Birds.

Carbon dioxide levels reach a new milestone

UP, UP and away. Parts of the planet have seen levels of carbon dioxide rise above 400 parts per million for the first time. Although it's largely symbolic, the milestone is a stark reminder of humanity's powerful influence on the atmosphere.

"During the month of April, the mean was over 400 ppm for the first time, throughout the Arctic," says Pieter Tans of the US National Oceanic and Atmospheric Administration's Earth System Research Laboratory in Boulder, Colorado. CO₂ levels reach an annual peak around April as the gas is released by respiration, and then fall over the summer as plants suck it up. As a result, the 2012 average will be a little lower, at about 393 ppm.

Nevertheless, Tans says global levels will top 400 ppm in a few years.

The Arctic is not the only place seeing record levels. The Japan Meteorological Agency has reported levels above 400 ppm for both March and April at a monitoring station in Ofunato, according to local media.

Despite its psychological significance, there's nothing to suggest 400 ppm is a major threshold in the climate system, according to Tans. In fact, we don't know what a safe level of CO₂ would be.

The campaign group 350.org wants levels reduced to 350 ppm, but Tans says that is arbitrary. The safe level could be 380 ppm, or 320 ppm - we just don't know. As a result, any growth in CO₂ increases the risk of catastrophic climate change.

"We're playing a very dangerous game," Sateesh"says.

Renewable energy's growing pains

Renewable energy received record investment in 2011 and expanded massively, but it also struggled with dwindling political support and plummeting prices. The industry faces several more years of growing pains before it can properly compete with fossil fuels.

By the end of 2011, the global power capacity from renewables was more than 1360 gigawatts, and renewables supplied 20.3 per cent of global electricity, according to the REN21 Renewables 2012 Global Status Report.

Meanwhile, investment in renewables increased by 17 per cent last year to a record $257 billion – six times what it was in 2004, according to a report by the UN Environment Programme. The UNEP report, Global Trends in Renewable Energy Investment 2012, concludes there were particularly big gains for solar power, which received $147 billion – 52 per cent more than in 2010.

Yet at the same time, solar power companies suffered massive drops in share prices. Six major companies, including Solyndra and Solar Millennium, have sought bankruptcy protection.

The main reason is the steep drop in the cost of solar panels over the last three years, largely due to a switch to large-scale manufacturing. Solar power is now cheaper than diesel in countries such as India. Many governments, including the UK, also cut their financial support for solar, as tumbling prices meant consumers did not need such large subsidies to buy a panel.

It is normal for weaker firms to fall by the wayside as industries ramp up, says Michael Liebreich, chief executive of Bloomberg New Energy Finance.

"The challenge for policy-makers is to reduce support mechanisms at just the right pace," he says. Cutting subsidies too fast will stop renewables in their tracks, but maintaining them for too long will be a waste of money.

Genetically modified crops encourage beneficial bugs

Environmentalists might one day run barefooted through insect-rich fields of genetically modified crops. At least, they might if the conclusions of a two-decade study in China hold up.

Kongming Wu of the Chinese Academy of Agricultural Sciences in Beijing and colleagues looked at the impact on surrounding farms of Bt cotton, a GM crop that protects itself against bollworm larvae by making its own pesticide.

As pesticide sprays were no longer needed, beneficial predator insects such as ladybirds, spiders and lacewings could thrive and spill over onto neighbouring farms, where they ate aphids. This reduced the amount of pesticides neighbouring farmers used.

"Transgenic Bt crops with less insecticide use can promote population increases of predators in the whole agricultural landscape," says Wu.

Protesters in the UK recently threatened to disrupt a trial at Rothamsted Research in Harpenden of a GM wheat that gives off a scent repelling aphids. Rothamsted's John Pickett said the Chinese research is exciting because it shows that certain GM crops can spread beneficial insects to neighbouring farms.

Dispelling myths

"This is another chapter of research dispelling the myth that GM crops are environmentally damaging," says Julian Little, chairman of the UK's Agricultural Biotechnology Council, which backs GM crops.

In 2010, Paul Mitchell of the University of Wisconsin-Madison found that US growers of conventional maize benefitted economically from having an adjacent Bt maize farm, because it suppressed maize-damaging pests. "This paper is part of the ongoing research documenting the environmental, economic and social benefits that Bt crops generate for more than just their users," he says.

But the Soil Association, which represents organic farmers in the UK, says earlier data from the same Bt cotton study shows that new insect pests may emerge, forcing farmers to increase crop spraying (Science, DOI: 10.1126/science.1187881).

Journal reference: Nature, DOI: 10.1038/nature11153

Kinect imaging lets surgeons keep their focus

New device lets surgeons consult medical images during an operation without having to scrub out

THE surgeon enters the operating theatre, covered in sterile blue scrubs. Machines beep and hiss. Nurses wait, tools at the ready: scalpel, forceps, bandage, Xbox... Xbox?

On Tuesday last week, a surgeon at Guy's and St Thomas' hospital in London began trials of a new device that uses an Xbox Kinect camera to sense body position. Just by waving his arms the surgeon can consult and sift through medical images, such as CT scans or real-time X-rays, while in the middle of an operation.

Maintaining a sterile environment in the operating room is paramount, but scrubbing in and out to scroll through scan images mid-operation can be time-consuming and break a surgeon's concentration or sense of flow. Depending on the type of surgery, a surgeon will stop and consult medical images anywhere from once an hour to every few minutes. To avoid leaving the table, many surgeons rely on assistants to manipulate the computer for them, a distracting and sometimes frustrating process.

"Up until now, I'd been calling out across the room to one of our technical assistants, asking them to manipulate the image, rotate one way, rotate the other, pan up, pan down, zoom in, zoom out," says Tom Carrell, a consultant vascular surgeon at Guy's and St Thomas', who led the operation on 8 May to repair an aneurism in a patient's aorta. With the Kinect, he says, "I had very intuitive control".

Carrell used the system to look at a 3D model of a section of the abdominal aorta, captured on a CT scan. This was projected on to a 2D live image-feed of the operation site, taken with a fluoroscopic X-ray camera. So Carrell could see what was happening inside the patient, as well as using the 3D model to help navigate the twists, turns and branches of the aorta. He says he consulted the system four or five times during the 90-minute operation.

Being able to check the images easily also helps surgeons maintain their concentration throughout the procedure. "You're just doing all of this stuff non-verbally and it just happens much more quickly. You're maintaining the flow of what's going on," says Carrell.

But manipulating a "touchless" medical image-viewer in a theatre filled with surgeons, nurses, machines, trays, cables and lights poses challenges of its own.

"You usually think of Kinect in a game-like scenario where you can jump around and move your hands as wide as possible, but surgeons are not allowed to reach such a large area," says Gerardo Gonzalez of Microsoft Research in Cambridge, UK, who helped develop the system in conjunction with surgeons from Guy's and St Thomas' and King's College London.

So Gonzalez and colleagues developed a set of gestures that a surgeon can perform in a constrained space, while standing at the operating table. For the most common actions - rotating the 3D model or placing a marker on the image - the team designed one-handed gestures that combine with voice commands, leaving the other hand free for operating. To position a marker, for example, the surgeon simply points at the image to activate a cursor and says, "place marker". Other functions, such as panning or zooming, require two hands.

Despite initial misgivings, Carrell is eager to continue working with the system. "I thought this was going to be a lot more awkward to start off with, but I was very pleased with the way it went today."

Free your mind

Manipulating medical images directly with gestures and voice commands doesn't just leave the surgeon free to concentrate on the task at hand, says Calvin Law, chief of surgery at Sunnybrook hospital in Toronto, Canada. It also frees up their memory. Law has completed a study of how surgeons used his Kinect-based medical-image viewer.
Surgeons usually have to look at a screen and memorise the images they need to work on. Law found that surgeons referred to images more often than normal and therefore felt fresher during surgery as they no longer had to hold everything in their own memory. His device is being developed by start-up firm GestSure, based in Seattle.

Face-reading software to judge the mood of the masses

Systems that can identify emotions in images of faces might soon collate millions of peoples' reactions to events and could even replace opinion polls

IF THE computers we stare at all day could read our faces, they would probably know us better than anyone.

That vision may not be so far off. Researchers at the Massachusetts Institute of Technology's Media Lab are developing software that can read the feelings behind facial expressions. In some cases, the computers outperform people. The software could lead to empathetic devices and is being used to evaluate and develop better adverts.

But the commercial uses are just "the low-hanging fruit", says Rana el Kaliouby, a member of the Media Lab's Affective Computing group. The software is getting so good and so easy to use that it could collate millions of peoples' reactions to an event as they sit watching it at home, potentially replacing opinion polls, influencing elections and perhaps fuelling revolutions.

"I feel like this technology can enable us to give everybody a non-verbal voice, leverage the power of the crowd," el Kaliouby says. She and her colleagues have developed a program called MindReader that can interpret expressions on the basis of a few seconds of video. The software tracks 22 points around the mouth, eyes and nose, and notes the texture, colour, shape and movement of facial features. The researchers used machine-learning techniques to train the software to tell the difference between happiness and sadness, boredom and interest, disgust and contempt. In tests to appear in the IEEE Transactions on Affective Computing, the software proved to be better than humans at telling joyful smiles from frustrated smiles. A commercial version of the system, called Affdex, is now being used to test adverts (see "Like what you see?").

Collecting emotional reactions in real time from millions of people could profoundly affect public polling. El Kaliouby, who is originally from Egypt, was in Cairo during the uprising against then-president Hosni Mubarak in 2011. She was startled that Mubarak seemed to think people liked his presidency, despite clear evidence to the contrary.

"She thought maybe Mubarak didn't think a million people was a big enough response to believe that people are upset," lab director Rosalind Picard said at the lab's spring meeting on 25 April. "There are 80 million people in Egypt, and most of them were not there. If we could allow them the opportunity to safely and anonymously opt in and give their non-verbal feedback and join that conversation, that would be very powerful."

Pollsters could even collect facial reactions on the streets, or analyse the reaction of an audience listening to a politician's speech. Picard's group recently ran an MIT-wide experiment called Mood Meter, placing cameras all over campus to gauge the general mood. To preserve privacy, the cameras didn't store any video or record faces - they just counted the number of people in the frame, and how many were smiling.

Frank Newport, editor in chief of political polling firm Gallup, headquartered in Washington DC, says such software could be useful. "There's no question that emotions and instincts have an impact in politics," he says. "We're certainly open to looking at anything along those lines." But he'd want to know how well facial responses predict actual votes.

Picard worries that the technology might have a dark side. "My fear is that some of these dictators would want to blow away the village that doesn't like them," she says. It would be important to protect the identities and IP addresses of viewers, she says.

Mind-reading robot teachers keep students focused

An automated system that detects when online pupils are distracted or snoozing and then uses tricks to keep them alert

WE ALL remember dozing off during a boring class at school. A robotic teacher that monitors students' attention levels and mimics the techniques human teachers use to hold their pupils' attention promises to end the snoozing, especially for students who have their lessons online. Tests indicate the robot can boost how much students remember from their lessons.

Intelligent tutoring systems that use virtual teachers to interact with students could play a crucial role in the expanding field of online education. The trouble with online courses is that it is usually impossible to know whether the student is concentrating and engaging with the lesson. Unlike virtual teachers, human teachers have a series of tricks for keeping their classes focused - changing the pitch or tone of their voice, for example, or gesturing to emphasise points and engage with their audience. Bilge Mutlu and Dan Szafir at the University of Wisconsin-Madison wanted to find out whether a robot could use some of the same techniques to improve how much a student retains.

"We wanted to look at how learning happens in the real world," says Mutlu. "What do human teachers do and how can we draw on that to build an educational robot that achieves something similar?"

The pair programmed a Wakamaru humanoid robot to tell students a story in a one-on-one situation and then tested them afterwards to see how much they had remembered. Engagement levels were monitored using a $200 EEG sensor to monitor the FP1 area of the brain, which manages learning and concentration. When a significant decrease in certain brain signals indicated that the student's attention level had fallen, the system sent a signal to the robot to trigger a cue. "We can't do it just at any given moment, we have to try and do it like human teachers do," says Mutlu.

The robot teacher first told a short story about the animals that make up the Chinese zodiac, in order to get a baseline EEG reading. Next, the robot told a longer 10-minute story based on a little-known Japanese folk tale called My Lord Bag of Rice, which the student was unlikely to have heard before.

During this story the robot raised its voice or used arm gestures to regain the student's attention if the EEG levels dipped. These included pointing at itself or towards the listener - or using its arms to indicate a high mountain, for example. Two other groups were tested but the robot either gave no cues, or sprinkled them randomly throughout the storytelling. Afterwards, the students were asked a few questions about the Chinese zodiac to distract them before being asked a series of questions about the folk tale.

As the team had expected, the students who were given a cue by the robot when their attention was waning were much better at recalling the story than the other two groups, answering an average of 9 out of 14 questions correctly, as compared with just 6.3 when the robot gave no cues at all. The results were presented at the Conference on Human Factors in Computing Systems in Austin, Texas, earlier this month.

The idea of recapturing students' waning attention in this way would have "significant implications for the field of education", says Andrew Ng, director of Stanford University's Artificial Intelligence Lab in California and co-founder of online classroom Coursera. It offers free courses from Stanford, Princeton University, the University of Michigan and the University of Pennsylvania, and has already attracted more than a million students since its launch last month.

"One-on-one tutoring has been repeatedly shown to give dramatic results in student learning, but the main problem with it is the cost, and that it's just difficult to scale," Ng says. "The vision of automatically measuring student engagement so as to build a more interactive teacher is very exciting."

Mars Curiosity rover to land closer to the good stuff

When NASA's Curiosity rover lands on Mars on 5 August, it will be closer to its target than previously thought.
Mission team members announced on Monday that they have shrunk the rover's landing ellipse - the area that it has a 99 per cent chance of hitting - from 25 kilometres long by 20 kilometres wide to 20 by 7.
The rover will land in a region called Gale Crater with a 5-kilometre-high mound in the centre, which astronomers are calling Mount Sharp. The most interesting rocks, which the team hope preserve a record of liquid flowing in and out of the crater, are found at the mountain's base. After the rover lands and goes through its first check-up, its most important task is to drive to the mountain as quickly as possible.
The new landing ellipse could shorten that drive by up to four months. "The earlier we get there, the more time we have for science," said project manager Pete Theisinger in a press conference.

Square Kilometre Array contest ends in a draw

My telescope is bigger than yours. That's the message South Africa is sending Australia and New Zealand after the African nation tied with the Oceanic duo to host the world's largest radio telescope.

The Square Kilometre Array (SKA) will investigate the early history of the universe, dark energy, dark matter and gravity. Member countries of the SKA Organisation decided late last week that both proposed sites for the array – in South Africa and Western Australia – should help with those investigations.

The two sites will complement one another. The SKA has two lines of work: whole-sky surveys using low-frequency antennas, and more directed investigations using high-frequency antennas. South Africa will host the high-frequency dishes while the Western Australian site will host the low-frequency antennas.

The decision has been met with general satisfaction. But in a statement, Naledi Pandor, the South African minister of science and technology, expressed disappointment that her country will not host the telescope exclusively.

An independent SKA advisory committee "identified by consensus Africa as the preferred site", she said, claiming the decision to share the telescope was a compromise "in order to be inclusive".

Lion's share

The initial recommendation to favour South Africa was revealed in a report leaked to the media in March. But another committee was established soon after, tasked with evaluating the merit of a dual-site approach.

Both Pandor and Jacob Zuma, South Africa's president, emphasise that their country will host the "lion's share" of the telescope's infrastructure: more of the large radio dishes will be built in South Africa than Western Australia. Officials in Australia, meanwhile, have described the split as equitable.

In a joint statement, Pandor's Australian and New Zealand counterparts said the decision "capitalised on the strengths of each location" and would ensure the best results "scientifically and financially".

Brian Boyle, SKA director at CSIRO – Australia's national science agency – says the SKA Organisation realised over time that the telescope could be split between sites. He says the decision does not compromise any of the scientific aims.

The arrangement may incur extra initial costs, but with infrastructure already in place at both sites, there should be savings in the long run. "My view is that there can only be one winner from this split and that's the project itself," says Boyle.

The SKA will begin full science operations in 2020.

Astrophile: The outermost ocean in the solar system

Astrophile is our weekly column on curious cosmic objects, from the solar system to the far reaches of the multiverse

Object: Triton's subsurface ocean
Temperature: About -90 °C

A new day dawns on Triton. It's going to be a cold one, much like the last. And the one before that… and every day since the moon settled into its present orbit around Neptune. Even the volcanoes here spew out cold gases and liquid water rather than hot magma. But below the frigid surface, which registers a temperature of -235 °C, there's something more clement: a liquid ocean.

At first glance, Triton seems to be just another icy moon – a featureless, barren world spinning around Neptune, the outermost planet of our solar system. But Triton is different.

For one thing, it orbits Neptune backwards, moving in the opposite direction to Neptune's rotation. It's the only large moon in the solar system to do so. Satellites can't form in these "retrograde" orbits, so Triton must have begun life elsewhere before being captured by the gas giant. It looks a lot like Pluto, and probably came from the same place – the inner edge of the Kuiper Belt, close to Neptune.

The Voyager 2 spacecraft flew past Triton in 1989, sending back images of the moon's frozen surface. They revealed signs of cryovolcanism – the eruption of subsurface liquids which quickly freeze when exposed to the cold of the outer solar system. As such, Triton joins a short list of worlds in the solar system known to be geologically active.

Its surface ice is unique, too: largely composed of nitrogen, with some cantaloupe-textured terrain, and a polar cap of frozen methane.

But with a name like Triton – the messenger of the big sea in Greek mythology – this moon should really carry one more feature: is there an ocean hiding beneath its icy veneer? A new model suggests there could be. Understanding why requires a quick look at Triton's unique history.

We know that Triton was captured by Neptune. Such captured bodies start in highly elongated orbits, but as they interact with their associated planet, Triton-sized worlds are quickly dragged into more circular orbits. The process releases energy, which heats up the moon. The temperature rise would have melted not just the icy outer layers of Triton, but also its 1900-kilometre-wide core. Then it would have cooled to its current frigid state.

Earlier models had suggested an ocean exists on Triton, but they were quite simplistic. Saswata Hier-Majumder of the University of Maryland in College Park, and his student Jodi Gaeman, have now developed a more detailed model that considers both radioactive decay of core minerals and the orbital interactions that would have heated the moon.

Although heating from radioactive decay is orders of magnitude larger than heating from tidal effects, heat from the core alone could not keep the outer layer from freezing over the 4.5 billion-year life of the solar system, they say.

However, Hier-Majumder and Gaeman have found that even a small amount of heating from orbital forces makes a huge difference because it is applied to the base of the ice covering the subsurface ocean. "It puts a warm blanket on top of the cooling ocean," says Hier-Majumder. As long as the orbit is so circular that its 350,000-kilometre-radius varies by only a few kilometres, Triton should still have a substantial ocean beneath its icy surface.

That watery ocean contains a strong dose of ammonia, which keeps the liquid from freezing unless the temperature drops below about -90 °C. So, while it may be the outermost ocean in the solar system, it is not as cold as the
-180 °C hydrocarbon lakes on Saturn's moon Titan.

Journal reference: Icarus, DOI: 10.1016/j.icarus.2012.05.006

Who owns asteroids or the moon?

Plans to mine minerals on celestial bodies could violate many aspects of international space law

SHOULD asteroids rich in precious metals be regarded, in legal terms, like the fish in the sea? That is one approach the United Nations could take as it struggles to come to terms with mining plans announced by Planetary Resources, a start-up company based in Seattle.

In just under two years, Planetary Resources says it will launch the first of a series of space telescopes into low-Earth orbit in a bid to spot nearby asteroids of a size and mineral composition potentially worth mining. When a strong candidate is found, it plans to dispatch a robotic probe to assess the asteroid's precious metal content, with platinum a priority. If that is found, yet-to-be developed robots will be dispatched to mine it. If it is small enough, the asteroid could be brought into an Earth orbit first, to make the process easier.

Planetary Resources's plans seem well advanced and others are not far behind. And it's not just asteroids in these firms' sights. Moon Express, a start-up based in Las Vegas, is planning to prospect the moon for platinum and other metals deposited on its surface by meteorites.

It all sounds mind-bogglingly expensive and complicated, and it is. But those planning the operations have more earthly concerns to deal with, too. Mining asteroids or the moon appears to violate many of the tenets of international space law.

The most important of these is the UN's Outer Space Treaty of 1967, which in rather pompous language states that "the exploration and use of outer space shall be carried out for the benefit of all countries and shall be the province of all mankind".

It also specifically prohibits states from making territorial claims in space. "States cannot claim rights over an asteroid," says Joanne Wheeler, a lawyer at London legal practice CMS Cameron McKenna and a UK government adviser on the UN's Committee on the Peaceful Uses of Outer Space. "The Outer Space Treaty says the moon and celestial bodies such as asteroids are not subject to national appropriation. Whether that means no one owns the asteroids, or we all do under some common heritage, what's clear here is there is no state sovereignty over them."

What applies to sovereign states probably also applies to private companies. "It is not possible for Planetary Resources to say it owns all of an asteroid even if they are the first there," says Wheeler.

If the ownership of an asteroid is in question, who, then, has legal title to the ores extracted from it and sold back on Earth? Again, it is not clear, though Wheeler points out that there is already a legitimate market for space rocks in the form of meteorites. This probably puts Planetary Resources in the clear.

Eric Anderson, co-founder of Planetary Resources, doesn't see a problem: "Our analysis shows we have an unequivocal right to mine asteroids. Nothing in the Outer Space Treaty prevents that." He doesn't agree that asteroids, especially those in the 50 to 500-metre size range, are "celestial bodies". Meteorites are fallen asteroids, he says, and they are not regarded as celestial bodies.

Some even see the treaty as irrelevant to asteroid mining. "The Outer Space Treaty is a paper tiger with no teeth," says Michael Gold, a lawyer specialising in commercial spaceflight in Washington DC. "It's unenforceable and any state can pull out of it with a year's notice. I expect mining capability will trump the law in any situation."

Whichever interpretation you prefer, it is clear that there is no international regime explicitly governing asteroid mining. "Planetary Resources are in a rather grey zone," says Wheeler. "This is no legal certainty over whether they can do it or not."

She suggests that a future regime could be based on the law of the sea. "The fish in the high seas are not owned by anyone. You can 'mine' the high seas by taking fish out of them and you can sell them," she says. "Similarly, asteroids might not be owned by anyone but you might be able to mine the resources and then sell them on."

Mining the moon is also fraught with legal uncertainties. In principle it is governed by an international treaty informally called the Moon Agreement, which seeks to manage our satellite's natural resources. But the treaty is largely worthless because it has not been ratified by any of the spacefaring nations.

"The Moon Agreement recognises that mining of the moon is about to become feasible," says Wheeler. "But the US, China and Russia are not signatories, so it lacks teeth." The UN is encouraging members to sign, but the concern is that a fait accompli by a mining company could render the treaty moot.

Finally, what if space mining operations go wrong? If miners cause an asteroid that they have nudged nearer to Earth to plummet into the planet, who would be liable? This is covered by another UN treaty, the Space Liability Convention, which makes the nation that launches a spacecraft liable for damages. "This concept worked back when it was a clear-cut case of governments launching objects, but with many entrepreneurs now launching spacecraft it's getting much more difficult to apportion blame," says Wheeler. As a result, the US and Japan are investigating new liability mechanisms, she says.

The chances of Planetary Resources causing impacts are minimal, says Timothy Spahr, director of the asteroid-hunting Minor Planet Center at Harvard University. Orbital mechanics are well understood, he says, making asteroid trajectory calculations simple. "Hitting the Earth is a damn hard thing to do."

Like many astronomers, Spahr has an asteroid named after him. How would he feel about 2975 Spahr being captured and mined? "That's a tough question," he says. "You'd have to ask a lawyer."

Saturn moon spouts plasma unlike any seen before

A NEW form of matter surrounds Saturn - a plasma put there by Enceladus, the planet's tiny moon.

"It's a type of charged particle that has never been observed before," says Tom Hill of Rice University in Houston, Texas.

Shortly after it arrived at the Saturn system in 2004, the Cassini spacecraft discovered that the small icy moon Enceladus was spouting a watery geyser. The plume contained water vapour, as well as micrometre-sized dust grains.

Yet in 2009, Cassini saw something else in the plume: nanometre-sized grains that each carried an electric charge. That meant the plume was a powerful source of plasma, a form of matter in which positively and negatively charged particles move around separately. It seems that Enceladus provides most of the plasma in the magnetic bubble, or magnetosphere, surrounding Saturn.

But it was unclear how the particles got their charges. Now, after three fly-bys during which Cassini's plasma detectors could investigate the nanograins, Hill and colleagues think they have an answer.

The sun's ultraviolet light strips electrons from the gas and other material in the plume, creating a cloud of free electrons. As the uncharged nanograins leave Enceladus and move through this charged cloud, they pick up about one electron each to create a plasma.

But that means that the structure of the plasma is backwards, says Hill. Most plasmas contain positive ions, which carry mass, and negative free electrons, which carry almost no mass. Here, most of the mass is in the form of negatively charged grains (Journal of Geophysical Research, DOI: 10.1029/2011JA017218).

"That changes the basic behaviour of the plasma," says Hill - although we will have to wait until Cassini next flies by the plume in more than a year to see in what way.

Small, cheap black-hole hunter could be new NASA model

You don't have to be big to hunt black holes. NASA's telescope NuSTAR, which was due to take off from an island in the South Pacific on 13 June, is small enough to fit beneath the belly of an aircraft, even including its launch rocket. Once in orbit, it will unfold to the length of a school bus.

The Nuclear Spectroscopic Telescope Array will be the first telescope to bring high-energy X-rays into focus, letting astronomers map and study the extreme physics around black holes and the explosions of massive stars. Its images of these objects will be 10 times crisper and 100 times more sensitive than those of previous telescopes.

To make such sharp images, the telescope needs to focus X-rays with energies of up to 100 kiloelectronvolts – 10 times as energetic as those sought by previous X-ray telescopes – onto a small area. Visible light telescopes can manage this with a focusing lens relatively close to the eyepiece. But because the X-rays are so energetic, NuSTAR's camera needs to be 10 metres away from the focusing lens.

Ingenious model

NuSTAR is on a tight budget: the whole mission should cost only $170 million. As the team could not afford to launch a 10-metre-long telescope, NuSTAR got scrunched up.

"It's no ordinary-looking telescope," says NuSTAR's principal investigator, Fiona Harrison of the California Institute of Technology in Pasadena. Its "lens" is made up of 133 nested shells of fingernail-thin glass. At launch, the cameras will sit right next to the lenses. A week after it settles into orbit, NuSTAR will push the lenses away from the camera on a thin scaffold.

Harrison, who conceived of NuSTAR in the 1990s, thinks the cheap, ingenious scope could be a new model for budget-bedevilled NASA. "It shows you can make huge advances with a relatively small mission," she says.

Titan's tropical lake hints at hydrocarbon wells

THE Caribbean it ain't, but the "tropical" regions of Saturn's moon Titan seem to harbour lakes of liquid methane. The pools are surprisingly long-lasting, suggesting that they may be replenished by underground wells of hydrocarbons.

The Cassini spacecraft confirmed the presence of liquid-hydrocarbon lakes in Titan's polar regions in 2004, but it was unclear whether similar pools could survive in the moon's marginally warmer lower latitudes - its "tropics" - without evaporating.

Caitlin Griffith and colleagues at the University of Arizona in Tucson analysed the sunlight reflected from Titan's tropical regions, recorded by Cassini. They found a highly reflective oval-shaped black feature, 2400 square kilometres in size. They say the combination of shape and colour is consistent with a liquid methane lake (Nature, DOI: 10.1038/nature11165). If it is a lake, it is long-lived, persisting since at least 2004, through both rainy and dry seasons. This means it's unlikely to be a big rain puddle and could be fed by hydrocarbon wells, say the researchers.

Jonathan Lunine, a planetary scientist at Cornell University in Ithaca, New York, says such lakes might be good habitats for simple life, but that Titan's larger polar lakes are better candidates.

Black holes could act as cosmic Rosetta Stones

A QUANTUM makeover means black holes can be described in the two disparate languages of physics - gravity and quantum mechanics. As well as paving the way for a much-sought-after theory of quantum gravity, the idea helps solve some mysteries surrounding these bizarre objects.

Black holes are full of puzzles. Theory says they should evaporate and give off heat at a constant temperature, though no one knows why. For some reason, they also get hotter as they shrink.

Einstein's theory of general relativity, the most popular theory of gravity, is the usual way of describing black holes, which can weigh as much as billions of suns. Georgi Dvali of CERN near Geneva, Switzerland, and Cesar Gomez of the Autonomous University of Madrid, Spain, decided to try the language of quantum mechanics, usually reserved for very small objects.

The first step in building this "quantum portrait", says Dvali, was to define black holes in terms of particles. "In quantum field theory, the building blocks are particles," he said at the Harvard-Smithsonian conference on theoretical astrophysics on 16 May, where he presented the idea.

The pair picked gravitons, the hypothetical massless particles that are thought to carry the force of gravity, just as photons carry the electromagnetic force. Dvali and Gomez reasoned that since a black hole is the densest object known, the gravitons must be packed in as tightly as possible.

Quantum mechanics already has a word for such a system: a Bose-Einstein condensate. In this state particles are so cold and densely packed that they behave as a single quantum object, making quantum effects visible on a macroscopic scale. Considering black holes as an overpacked bucket of gravitons allowed the pair to solve several mysteries, including why black holes radiate energy and get hotter as they evaporate (arxiv.org/abs/1112.3359).

Due to quantum fluctuations, every so often a graviton will get enough energy to leap out of the bucket. An observer outside the black hole will see a temperature rise corresponding to that graviton's energy. With fewer gravitons in the bucket, those remaining cling to each other more tightly, so the next graviton to escape will need more energy.

The quantum portrait could be combined with existing gravitational pictures of black holes, allowing physicists to translate between the two like a Rosetta stone. That might lead to a theory of quantum gravity.

"In this picture, we write down gravitational properties of gravitons in the quantum mechanical language," Dvali says. "We are building a quantum version of Einstein's theory."

Not everyone is convinced. "In my view, black holes are something more subtle than just condensates of gravitons," says Gerard 't Hooft of Utrecht University in the Netherlands. But Dvali thinks the idea is elegant enough to be taken seriously.

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