The Hindu :‘Private sector must support scientific research too'

Education and research institutions must spend more time in interacting with the industry, says Infosys chairman emeritus N. R. Narayana Murthy.

Five months after he stepped down as chairman of Infosys, N.R. Narayana Murthy speaks to Divya Gandhi about the Infosys Prize — the third edition of which was awarded on Monday — that he conceived to encourage science and social science talent. Mr. Murthy also offered his views on corporate India's role in encouraging science research, its engagement with politics and the problems that face the nation, including corruption.

It has been three years since the Infosys Science Prize was instituted. What has its impact been?

I am happy with the way the Infosys Science Prize has evolved…I must admit three years is too short a period to assess the impact. But we are very happy that we have a fine jury panel and jury chairs, and that they have selected a world class set of researchers [for the awards] every year.

There are ways of gauging the impact of such initiatives in the future: by the number of PhDs you produce and by the quality of PhDs, by the number of patents, number of papers in refereed A-Class journals, and papers presented in A-Class conferences. But of course we cannot say that this is because of a single initiative.

The Infosys Science Foundation has set out to encourage scientists with the awards but this does leave unresolved the question of science education. There is criticism, for instance, that private industry is interested in education to the extent that it addresses its own needs. What are your views?

Of all the companies I know of, Infosys probably spends the highest percentage of revenue on education and research. We have the world's largest corporate sector training centre. We also have the world's longest training programme for software engineers (29 weeks). And we have instituted the science prize in six categories, with the humanities introduced this year. I believe this company is an education friendly and research friendly one.

The Prime Minister recently said that private industry is not devoting enough resources to R&D, implying that public funding still bears the bigger burden of R&D funding. Can this change?

The Prime Minister is right. It is the responsibility of both the public governance system and the private sector to enhance the focus on research. To do that, I believe education and research institutions must spend more time in interacting with the industry in understanding their problems and in solving their problems.

What are the key problems in the software industry that science can help solve?

There are several areas where such collaborations can take place. For example, there is a lot of research that needs to be done in performance engineering, modelling of software systems, on requirements definition. There is a lot of research being done on improving collaborative, distributed software development models. These are key problems specific to Indian software companies.

At the Indian Science Congress a few weeks ago, the Prime Minister had expressed concern that India's position in the world of science has been overtaken by countries such as China. He sought an increase in spending on scientific research to two per cent of the GDP. What more do you think can be done to encourage scientific research and innovation?

I think I agree that we must enhance allocation for research from the current 0.9 per cent of GDP to perhaps 2.5 per cent of the GDP. And that contribution must come from the public governance system and the private sector, there is no doubt about that.

Having said that, [while] the need of the day is clearly money, we have to empower our research institutions and we have to provide full autonomy to institutions. We must create a platform like the National Science Foundation (an independent United State's government agency aimed at promoting science and engineering). The Indian Parliament passed a bill six years ago to constitute a similar agency, but it has not yet been created.

Do you think an anti-corruption law must include corporate corruption in its ambit?

As long as there is culpability in the corporate sector, certainly I think the corporate sector will have to answer questions. But I do not know if every transaction in the corporate sector must be vetted by some outside body. If the corporate sector is seen to have done something wrong in its interaction with the public governance system, then of course they are answerable. But this cannot be monitored by an external institution. We have a corporate governance system and shareholders. So we do have a pretty good foundation in shareholder democracy.

World's Smallest Hard Drive Built of Atoms

THE GIST

• Scientists have built a magnetic storage device made of 96 atoms.
• The advance could lead to tiny hard drives able to store 200 to 300 times more information than they can today.

enlarge

The tip of a scanning tunneling microscope precisely assembles atoms onto a surface to make the world's smallest hard drive.
Sebastian Loth/CFEL

Hard drives could one day be the size of rice grains, powering music players so small they would fit inside your ear.
Scientists at IBM and the German Center for Free-Electron Laser Science have built the world's smallest unit of magnetic storage, using just 96 atoms to create one byte of data. Conventional drives require a half a billion atoms for each byte.
The advance could lead to tiny hard drives able to store 200 to 300 times more information than they can today. Just imagine an iPod Touch that held 12.8 terabytes of music.
 5 Computer Techs to Replace Silicon Chips
"An effect that is common in nature can produce this information storage idea," said Sebastian Loth of CFEL, lead author of the research, which is being published today in the journal Science.
The natural phenomenon Loth is referring to has to do with the way electrons spin inside an atom. Modern hard drives rely on magnetic materials such as iron, where electrons all spin in the same direction perfectly aligned with each other. The drives work by reading the magnetic states of small regions on a disk and using an external field to write to them.
But these so-called ferromagnetic materials can only be shrunk down so far. If the magnetic regions get too close to each other, their magnetic fields interfere with each other and make it difficult to accurately store data.

NANOTECH REWARD

"This is a big problem if you want to pack in the magnetic density," said Loth.
But with materials that are not magnetic, known as antiferromagnetic materials, the electrons spin in opposite directions from one another and are magnetically neutral.
"Antiferromagnetic regions don't have a magnetic field so you can pack them closer," Loth said.
In fact, the scientists were able to squeeze bits into a space just one nanometer apart.
The team assembled the tiny hard drive from the atom up, using a special tool known as scanning tunneling microscope, or STM. They carefully placed atoms into rows of six atoms each. Two rows were enough to store one bit of information. Eight pairs of rows amounted to one byte of data.
Scientists Build Self-Replicating Molecule
Each pair of rows has two possible magnetic states, representing the classical 0 and 1 of binary computer data. An electric pulse from the STM tip flips the magnetic configuration from one to the other. A weaker pulse was used to read it.
"What this shows is you have all the ingredients for storing information on an antiferromagnetic grain," said Matthias Bode, an experimental physics professor at the University of Würzburg, who was not involved in the research.
It will be some time before this technology is used in a hard drive for a computer, as there are a few problems that still have to be overcome. First, this hard drive was built atom-by-atom, using an STM -- an impractical and slow method for manufacturing.
Secondly, the storage of the information -- the magnetic state -- is only stable at very cold temperatures, about 5 degrees above absolute zero. Warmer than that and the spins of the atoms get jostled.
Bode said that finding a material that works at room temperature isn't impossible. What material will work, however, remains to be seen.
Salty Hard Drives Have More Bytes
Loth noted there are lots of other materials to experiment with that are known to hold antiferromagnetic states at room temperature. "This isn’t like superconductors, where we are looking for ways to boost the critical temperature," Loth said. "We know that antiferromagnetic materials are stable."
This work is also important because it demonstrated for the scientists how few atoms they could use before the effects of quantum mechanics took over. It turns out that twelve atoms are the minimum number required. Fewer than that and quantum effects begin the mess around with the stored information.

Why Does Our Universe Have Three Dimensions?

Why does our universe look the way it does? In particular, why do we only experience three spatial dimensions in our universe, when superstring theory, for instance, claims that there are ten dimensions -- nine spatial dimensions and a tenth dimension of time?
Japanese scientists think they may have an explanation for how a three-dimensional universe emerged from the original nine dimensions of space. They describe their new supercomputer calculations simulating the birth of our universe in a forthcoming paper in Physical Review Letters.
Before we delve into the mind-bending specifics, it's helpful to have a bit of background.

 What Is the Large Hadron Collider Looking For?
The Big Bang theory of how the universe was born has been bolsted by some pretty compelling observational evidence, including the measurement of the cosmic microwave background and the relative abundance of elements.
But while cosmologists can gaze back in time to within a few seconds of the Big Bang, at the actual moment it came into existence, when the whole universe was just a tiny point -- well, at that point, the physics we know and love breaks down. We need a new kind of theory, one that combines relativity with quantum mechanics, to make sense of that moment.
Over the course of the 20^th century, physicists painstakingly cobbled together a reasonably efficient "standard model" of physics. The model they came up with almost works, without resorting to extra dimensions. It merges electromagnetism with the strong and weak nuclear forces (at almost impossibly high temperatures), despite the differences in their respective strengths, and provides a neat theoretical framework for the big, noisy "family" of subatomic particles.
But there is a gaping hole. The standard model doesn't include the gravitational force. That's why Jove, the physicist in Jeanette Winterson's novel, Gut Symmetries, calls the Standard Model the "Flying Tarpaulin" -- it's "big, ugly, useful, covers what you want and ignores gravity.” Superstring theory aims to plug that hole.
Pulling Strings
According to string theorists, there are the three full-sized spatial dimensions we experience every day, one dimension of time, and six extra dimensions crumpled up at the Planck scale like itty-bitty wads of paper. As tiny as these dimensions are, strings -- the most fundamental unit in nature, vibrating down at the Planck scale -- are even smaller.
ANALYSIS: Hawking: Surprise! There's No Heaven The geometric shape of those extra dimensions helps determine the resonant patterns of string vibration. Those vibrating patterns in turn determine the kind of elementary particles that are formed, and generate the physical forces we observe around us, in much the same way that vibrating fields of electricity and magnetism give rise to the entire spectrum of light, or vibrating strings can produce different musical notes on a violin.
All matter (and all forces) are composed of these vibrations -- including gravity. And one of the ways in which strings can vibrate corresponds to a particle that mediates gravity.
Voila! General relativity has now been quantized. And that means string theory could be used to explore the infinitely tiny point of our universe's birth (or, for that matter, the singularity that lies at the center of a black hole).
Shattered Symmetry
There's one more wrinkle, and that's this whole business of extra dimensions, when our world as we currently experience it has only three. Physicists have hammered out a pretty convincing hypothetical scenario for how this might have come about.
Before the Big Bang, the cosmos was a perfectly symmetrical nine-dimensional universe (or ten, if you add in the dimension of time) with all four fundamental forces unified at unimaginably high temperatures. But this universe was highly unstable and cracked in two, sending an immense shock wave reverberating through the embryonic cosmos.
The result was two separate space-times: the unfurled three-dimensional one that we inhabit, and a six-dimensional one that contracted as violently as ours expanded, shrinking into a tiny Planckian ball. As our universe expanded and cooled, the four forces split off one by one, beginning with gravity. Everything we see around us today is a mere shard of the original shattered nine-dimensional universe.
 Mysterious 'Dark Flow' May Be Tug of Other Universe
Physicists who espouse this view aren't sure why it happened, but they suspect it might be due to the incredible tension and high energy required to maintain a supersymmetric state, which could render it inherently unstable.
Imagine that you are trying to making the bed on laundry day, but the bed sheet has shrunk slightly in the wash. You manage to get it to fit around all four corners of the bed, but the sheet is stretched so tightly that it just won't stay in place.
There is too much strain on the fabric, so one corner inevitably pops loose, causing the bed sheet to curl up in that spot. Sure, you can force that corner back into place, but again, the strain will prove to be too much and another corner will pop.
Like the bed sheet, the original ten-dimensional fabric of space-time was stretched tight in a supersymmetric state. But the tension became too great, and space-time cracked in two. One part curled up into a tight little ball, while the aftershock from the cataclysmic cosmic cracking caused the other part to expand outward rapidly, a period known as inflation. This became our visible universe.
Birthing Pains
That's what the Japanese simulation shows: the universe had nine spatial dimensions at its birth, but only three of them experienced expansion. It's the first practical demonstration of how a three-dimensional universe emerges from nine-dimensional space, providing strong support in favor of the theory's validity.
What is the mechanism by which this happened? For a ten-dimensional universe, there are millions of ways for supersymmetry to break. So is there something special about three spatial dimensions that causes that configuration to be favored in our own universe? The new simulations may help shed some light on why this symmetry breaking might have unfolded the way it did.
Black Holes on a String in the Fifth Dimension
Jun Nishimura (KEK), Asato Tsuchiya (Shizuoka University), and Sang-Woo Kim (Osaka University) tackled the problem using a formulation of string theory known as the IKKT matrix model (named after the scientists who developed it in 1996, Ishibashi, Kawai, Kitazawa, and Tsuchiya). It's designed to model the complex interactions of strings.
For very complicated technical reasons, the connection between the original IKKT matrix model and the real world was, well, a bit vague, mostly because (a) it assumes weak interactions, when in fact the interactions between strings are quite strong; and (b) the variable of time in the calculations wasn't treated as "real" in a mathematical sense. These new simulations assume strong interactions, and treat time as a real variable.
So the takeaway message is that string theorists now have a useful tool for analyzing superstring theory's predictions with computer simulations, shedding light on such knotty problems as inflation, dark matter, and the accelerating expansion of the universe. And it also explains why our universe looks the way it does.
Image credits: NASA, icanhascheezburger.com, Wikimedia Commons.

Black Holes May Turboboost Super-Civilizations

Because our galaxy is teeming with planets it should be home to countless extraterrestrial civilizations. That is unless, through some perverse twist in nature, intelligent life is an evolutionary dead-end.
But let's be optimistic and assume that some fraction of far-flung worlds rise to the status of a hosting a super-civilization.

This was described in 1964 by Russian astronomer Nikolai Kardashev who hypothesized that a so-called Type III civilization would control the entire energy output of a galaxy. (We don't even reach Type I status because we have failed to harness nuclear fusion or build a constellation of solar power satellites.)
But why should a super-civilization be so energy voracious? And how in the heavens do they tap the energy of an entire galaxy?
First, a far-advanced society would need a lot of energy to support a rapidly growing wave of colonization, ambitious astroengineering projects, and burgeoning populations. Green technology can only go so far.
Secondly, super-smart extraterrestrials have far more than the total stellar energy output of the entire Milky Way at their fingertips. They could tap into the mother of all storage batteries: the supermassive black hole in the core of our galaxy. This gravitational engine is vastly more efficient at converting matter to energy than stellar nuclear fusion.
ANALYSIS: Super-Civilizations Might Live Off Black Holes
A huge amount of radiation is generated by the million degree accretion disk of trapped gas whirling around the 4 billion solar mass black hole at our galaxy’s heart.

Makoto Inoue of the Institute of Astronomy and Astrophysics in Taipei, and Hiromitsu Yokoo of Chiba University are proposing that advanced civilizations might pool their resources to construct a ring of "power stations" at the galaxy's core. They would orbit the central black hole just beyond its solar system-sized accretion disk.
Some fraction of the radiation seething from the disk would be reflected and focused onto the power plants. Each power plant would transmit collected energy as a collimated microwave beam from a 100-mile diameter antenna.
ANALYSIS: Astronomers Aim To Take First Picture of Black Hole
Or, aliens might use molecular interstellar clouds to fashion an efficient transmission system, by means of a maser. A maser (an acronym for Microwave Amplification by Stimulated Emission of Radiation), creates an intense coherent beam of radiation when atoms or molecules in a gas, liquid or solid medium, force an incoming mix of wavelengths to work in phase, or, at the same wavelength. This would amplify radiation from the accretion disk and make a sharp collimated beam.
Nature has already fashioned mega-masers in clouds near galactic black holes, and therefore radiation pumping by artificial means may not be so difficult to set up, say the authors.
A consortium of super-civilizations might pool resources to build a chain of power stations encircling the black hole. It would be the heart of a robust and fault-tolerant energy grid connecting numerous worlds like a fantasy scene out of the film "Tron."
However, I think it is more likely that a federation of expanding space colonies, spawned from a single mother civilization, would work together to maintain their viability. This wouldn't run into the thorny question of how two or more independent but similarly co-evolved species manage to contact each other and work out a practical energy infrastructure.
But could we detect evidence of such a mega-engineering project?

Probably not say the authors, because the energy would be highly beamed and therefore only be visible if you were along the line-of-sight.
Chances for detection increase slightly if many power plants use a very large antenna or use a multi-beam system.
ANALYSIS: Our Galaxy's Black Hole Has the 'Munchies'
Curiously, the mechanism behind natural mega-masers is not fully understood. For example, it's mysterious that all the maser components in front of the black hole are all aligned almost on the same orbit.
The mirror system designed to reflect and transmit the energy could be detected as a shadow against the bright accretion disk. But it would be tough trying to explain these transits as anything other than natural bodies drifting through space.
These beams would be so powerful that they could be detected in neighboring galaxies that are tilted edge-on to our view.
So if the Milky Way is lacking a Galactic Empire, maybe a super-civilization commands another nearby island universe.
Image credit: Philip Armitage/Kees Dullemond, Makoto Inoue/Hiromitsu Yokoo, NASA

Hawking radiation glimpsed in artificial black hole

You might expect black holes to be, well, black, but several decades ago Stephen Hawking calculated that they should emit light. Now, for the first time, physicists claim that they have observed this weird glow in the lab.

"Their experiment is the very first observation of Hawking radiation," says Ulf Leonhardt of the University of St Andrew's, UK. He was not involved in the work but led a team that created an "analogue" black hole using laser pulsesin 2008 (Science, DOI: 10.1126/science.1153625). "Hawking radiation is not a mere theoretical dream, but something real," he says.

Others are not yet convinced of the team's evidence, or argue that Hawking radiation cannot come from anything other than a real black hole. If further experiments confirm that the new measurements, made at Insubria University in Como, Italy, are a form of Hawking radiation, however, it could open a new window into some of the most exotic objects in the universe. The finding also suggests that the bizarre physics once thought unique to black holes is much more widespread.

A black hole is an incredibly dense concentration of mass with an extreme gravitational field around it. Black holes earned their moniker because inside a certain radius, known as the event horizon, nothing escapes – not even light.

Uncertainty principle

Or so it seemed. Then in 1974 Hawking showed that, according to quantum theory, black holes should emit radiation after all. This is a consequence of the uncertainty principle, which says we can never be sure that an apparent vacuum is truly empty and, instead, that virtual particles are constantly appearing in pairs. These couples, made of a particle and its antimatter counterpart, rapidly annihilate and vanish again, so normally go unnoticed.

However, if a pair of photons pops up right at the event horizon, they may find themselves on different sides, with one flying free outside and the other trapped forever within. This prevents them from merging and vanishing, so the outside photon is effectively emitted by the black hole (see diagram, above right).

Hawking predicted black holes should give off a steady stream of such radiation – and many scientists assume he is right. The problem is that no one has ever actually seen it.

Escape velocity

In recent years, physicists have been toying with laboratory experiments that imitate the physics of an event horizon. This marks the point where escape from a black hole is impossible because the velocity required exceeds the speed of light, the cosmic speed limit.

Analogue black holes have a similar point that cannot be crossed because the speed required is too great. Unlike in a real black hole however, this "horizon" is not created by intense gravity, since we do not know how to synthesise a black hole, but by some other mechanism – utilising sound or light waves, for example. However, no one had seen photons resembling Hawking radiation emerging from these analogues, until now.

To create their lab-scale event horizon, Daniele Faccio of Heriot-Watt University in Edinburgh, UK, Francesco Belgiorno of the University of Milan, Italy, and their colleagues focused ultrashort pulses of infrared laser light at a wavelength of 1055 nanometres into a piece of glass. The extremely high intensity of these pulses – trillions of times that of sunlight – temporarily skews the properties of the glass. In particular, it boosts the glass's refractive index, the extent to which the glass slows down light travelling through it.

The result is a moving point of very high refractive index, equivalent to a physical hill, which acts as a horizon. Photons entering the glass behind this "hill", including ones that are part of a virtual pair, slow as they climb the hill and are unable to pass through it. Relative to the slow-moving pulse, they have come to a stop and remain behind the pulse until it has passed through the glass's length.

Mysterious photons

To see if this lab-made event horizon was producing any Hawking radiation, the researchers placed a light detector next to the glass, perpendicular to the laser beam to avoid being swamped by its light. Some of the photons they detected were due to the infrared laser interacting with defects in the glass: this generates light at known wavelengths, for example between 600 and 700 nanometres.

But mysterious, "extra" photons also showed up at wavelengths of between 850 and 900 nanometres in some runs, and around 300 nanometres in others, depending on the exact amount of energy that the laser pulse was carrying. Because this relationship between the wavelength observed and pulse energy fits nicely with theoretical calculations based on separating pairs of virtual photons, Faccio's team concludes that the extra photons must be Hawking radiation (Physical Review Letters, in press).

Not everyone is ready to agree. Adam Helfer at the University of Missouri in Columbia says the term Hawking radiation is best reserved for actual black holes with gravitational fields. "There is a parallel between them to a certain extent, [but] the laboratory experiments, interesting as they are, do not really bear on the very deep problems which are special to black holes." These revolve around how to fully marry gravity and quantum mechanics when describing these objects.

Quantum entanglement

In future, Ted Jacobson at the University of Maryland in College Park suggests testing for a key characteristic of Hawking radiation – whether the pairs of photons separated by the horizon are quantum entangled. Faccio says that using an optical fibre, as Leonhardt and colleagues did in 2008, rather than a glass block, might allow photon pairs separated by a laser horizon to be analysed for entanglement.

Meanwhile, Hawking radiation is also popping up in other, less direct black hole imitators. A team led by Silke Weinfurtner at the University of British Columbia in Vancouver, Canada, announced in August that they had observed a water-wave version of Hawking radiation in an experiment involving waves slowed to a halt to form a horizon (arxiv.org/abs/1008.1911).

Hawking radiation is turning out to be "a general phenomenon that occurs whenever you have a horizon of any sort", says Matt Visser of Victoria University of Wellington, New Zealand, who was not involved in either of the experiments.

He is not the only one intrigued by the indication that the sequence of events leading to Hawking radiation arises in analogue horizons, as well as real black holes. "The line of reasoning is more generic than it might at first seem, giving more faith that it may also be right for black holes," says Bill Unruh, who collaborated with Weinfurtner on the water-wave experiment and is known for the "Unruh effect", a predicted phenomenon that is similar to Hawking radiation but occurs outside a black hole.

"All the pieces of the puzzle seem to have suddenly fallen together at the same time," says Faccio. "This is all very exciting."

This story was updated to reflect the fact that the research was led by Daniele Faccio of Heriot-Watt University in Edinburgh, UK, and that the measurements were carried out at Insubria University in Como, Italy.

Thinnest silicon-chip wires refuse to go quantum

Not everything is weird at the nanoscale. Wires so small you'd expect them to obey the strange laws of quantum mechanics have instead displayed the same electrical properties as ordinary electrical interconnects.

The finding bodes well for conventional computers, because these tiny, conductive wires could make chips smaller. It could be bad news, though, for the super-fast quantum computers that are hoped to come next.

So far, conventional computers have followed Moore's law: the density of transistors that a conventional integrated-circuit chip can hold doubles approximately every two years, yielding ever-better performance out of ever-smaller devices.

However, it's getting harder to build smaller interconnects to wire up the devices on the silicon chip. As the width of metal wires drops to few tens of nanometres, their resistivity soars because electrons start interacting with nearby surfaces, dissipating more heat and lowering efficiency.

Phosphorous infusion

Also, as wires get down to nanometre scales, quantum behaviour usually dominates. For instance, the entire wire can exist in a superposition of statesbecause of a property called quantum coherence. The wave behaviour of electrons in the wire might then cause them to interfere with each other, disrupting the electrical properties you would expect to see at larger scales.

Now, Michelle Simmons of the University of New South Wales in Sydney, Australia, and colleagues have etched channels in a silicon chip just 1.5 nanometres wide that behave just like larger wires.

The trick was to infuse them with phosphorus atoms, which provide electrons that can move freely and conduct electricity, turning each channel into a wire. Because the entire wire, except for its ends, was enclosed in the silicon, it was isolated from other surfaces that could disrupt its conductivity.

Coolly classical

The team found that these wires conducted electricity nearly as well as state-of-the-art copper interconnects used in modern microprocessors – despite being much thinner. Moreover, when they built wires of different lengths, the wires followed Ohm's law, in which the resistance of a wire increases with length – a property of non-quantum, or "classical" conductors.

The lack of quantum behaviour surprises David Ferry of Arizona State University in Tempe – especially because the experiments were carried out at a mere 4.2 kelvin. "Usually when you go to [such] low temperatures, you expect quantum mechanics to dominate the world. Here they have Ohm's law, suggesting that it's just like classical behaviour at room temperature," he says.

He reckons the large number of phosphorus atoms in the wire provided a very high density of electrons (10²¹ per cubic centimetre) and that their mutual scattering destroyed any quantum coherence, leading to classical behaviour.

That bodes well for doing the experiment at higher temperatures. "If they behave classically at low temperature, then they are also likely to behave classically at room temperature," says Simmons.

Coherent problem?

Indeed, Simmons says that the new wires are great news for those hoping for ever-tinier computing devices. "It shows that you can maintain low resistivity and make very thin conducting wires, which is obviously essential for down-scaling devices towards the atomic scale," she says.

The implications for quantum computing are less clear. Simmons's team had already shown that individual phosphorus atoms can exist in a superposition of spin states, making up the quantum bits, or qubits, needed for quantum computation. She thinks that the nanowires could be used to interconnect qubits and help build quantum circuits.

Ferry thinks otherwise. "This lack of quantum coherence is good for Moore's law, but it's bad for quantum computing, because you need quantum coherence for quantum computing. This may make it less likely to occur."

Journal reference: Science, DOI: 10.1126/science.1214319

Hundreds of tiny moons may be orbiting Earth

THE moon may look lonely, but it is far from alone. Small asteroids too dim to detect seem to stray into Earth's orbit quite frequently and stay for short periods of time. We may even be able to bring one of these moonlets back to Earth for study.

Researchers have long suspected that wandering asteroids might occasionally get snagged by Earth's gravity and become temporary moons, and a few years ago one of these was spotted. Called 2006 RH120, it is a few metres across and wandered into orbit around Earth in July 2006 before drifting off again a year later.

Some initially thought it might be a discarded rocket stage. But Paul Chodas of NASA's Jet Propulsion Laboratory in Pasadena, California, analysed its motion and showed that it was too heavy to be a rocket stage, making the asteroid explanation more likely. But it wasn't clear how common such captured asteroids might be. Now, new calculations suggest many other temporary moons are orbiting Earth, but are too small and dim to be easily spotted by surveys of the sky.

Mikael Granvik of the University of Helsinki in Finland and colleagues ran computer simulations of the abundance of asteroids of various sizes in Earth's neighbourhood and the likelihood of their capture in a close encounter.

To be captured, an object must start out in an orbit nearly identical to Earth's. That means it is travelling at roughly the same speed as our planet, making it easy for it to get snagged by Earth's gravity, helped by gravitational tugs from the sun and moon. Similar perturbations eventually shake them loose.

The team found that, on average, one asteroid about 1 metre across is in Earth's orbit at any given time, and 1000 or so smaller space rocks down to 10 centimetres across should be in orbit too (Icarus, DOI: 10.1016/j.icarus.2011.12.003). "There's a lot more of these than people may have been thinking," Granvik says.

They orbit at distances between five and 10 times as far from Earth as the moon. Most stay in orbit less than a year, although some stay much longer. One object in the team's simulations stayed in orbit for almost 900 years.

Given the huge numbers of small space rocks out there, it makes sense that Earth captures some of them from time to time, says Richard Binzel of the Massachusetts Institute of Technology, who was not involved in the study. "It would be a little more surprising if they weren't there at all," he says.

It is possible that some have been seen in the past by asteroid surveys, but not followed up because they were assumed to be artificial satellites or bits ofspace junk, Granvik says. Future surveys by the Pan-Starrs telescope and the planned Large Synoptic Survey Telescope might be able to spot the small, dim objects more easily.

If we could find one, we might be able to grab it and bring the whole rock back to a lab on Earth, says Granvik. This would give us a better picture of what pristine asteroids are like as opposed to the roasted, shattered meteorites we sometimes find on Earth, he says. Since asteroids are leftover building blocks from the early solar system, studying them could provide insights into how the planets formed.

NASA, the European Space Agency and the Japanese space agency JAXAare each planning missions to return samples from the asteroid belt, but these little moons would be far easier to get to, says Granvik. "The price of the mission would actually be pretty small."