For years, San Francisco-based electrical engineer has harboured ambitious plans to build the biggest lightning generator in the world. When 快猫短视频 talked to him in 2006, he was planning to construct two giant Tesla coils that would launch electric arcs crackling across a space the size of a football stadium at an estimated cost of $8.9聽million.

Leyh鈥檚 hope of funding that project faded when the recession hit. Now he鈥檚 trying crowdsourcing to get it up and running within two years. He is for the , an equally impressive but lower-budget version costing about $350,000. 快猫短视频 asked him about his plans.

What is the Lightning Foundry?
It鈥檚 a project to create super-long electrical discharges like lightning. Two 10-storey-high Tesla coil towers will fill an area the size of a football field with lightning-like discharges hundreds of feet long. We鈥檒l possibly site it in Nevada, although that hasn鈥檛 been decided yet.

What will visitors see at demonstrations?
As the machine ramps up, it鈥檒l start sounding like a chainsaw and you鈥檒l see electrical streamers increasing in length. When they鈥檙e long enough to reach from one tower to the other, you鈥檒l have an area hundreds of feet wide filled with electrical discharges jumping around. Hopefully we鈥檒l have enough funding to get some extra props to zap 鈥� one thing I鈥檇 like to do is recreate Franklin鈥檚 kite experiment.

Will it be safe?
We鈥檒l have to test it first to make sure. If the coils trigger a runaway breakdown of the air, they could generate wild arcs 鈥� that鈥檚 something we have to know very precisely before we show it to an audience. We鈥檙e breaking new ground here so we have to approach it carefully.

What scientific question will the project answer?
Lightning can break down air up to five times more easily than normal electric arcs [between two oppositely charged rods in the lab], using tricks we don鈥檛 yet understand. However, recent theories and a few tantalising experimental results suggest that normal arcs start to gain lightning-like abilities once they grow past about 60 metres in length. If we can build a machine this large, we鈥檒l very quickly arrive at a better understanding of what鈥檚 going on.

How can you do this on a low budget?
Rather than being a purpose-built, conservatively designed facility like the original concept, the Lightning Foundry is literally designed around 鈥渙btainium鈥� 鈥� used materials, scrap and salvaged equipment like generators and transformers. So many companies have folded, and a lot of their equipment ends up in scrapyards. There鈥檚 a lot of incredible obtainium out there these days.

What will your backers get in return?
There is a range of rewards. Pledge $75 or more and you鈥檒l get two tickets to a public performance. Other reward packages include electrical discharge sculptures [an electrically zapped piece of acrylic with a branching structure showing the path of the discharge] and the chance to personally throw 8-metre arcs at any item you wish to bring along.

Charged particles called cosmic rays constantly rain in from space, creating a spray of new particles 鈥� including antiparticles 鈥� when they collide with particles in the atmosphere. Many of these become trapped inside the Van Allen radiation belts, two doughnut-shaped zones around the planet where charged particles spiral around the Earth鈥檚 magnetic field lines.

Satellites had already discovered positrons 鈥� the antimatter partners of electrons 鈥� in the radiation belts. Now a spacecraft has detected antiprotons, which are nearly 2000 times as massive.

Heavier particles take wider paths when they spiral around the planet鈥檚 magnetic lines, and weaker magnetic field lines also lead to wider spirals. So relatively heavy antiprotons travelling around the weak field lines in the outer radiation belt were expected to take loops so big they would quickly get pulled into the lower atmosphere, where they would annihilate with normal matter. The inner belt was thought to have fields strong enough to trap antiprotons, and indeed that is where they have been found.

Piergiorgio Picozza from the University of Rome Tor Vergata, Italy, and colleagues detected the antiprotons using , a cosmic-ray detector attached to a Russian Earth-observation satellite. The spacecraft flies through the Earth鈥檚 inner radiation belt over the south Atlantic.

Between July 2006 and December 2008, PAMELA detected 28 antiprotons trapped in spiralling orbits around the magnetic field lines sprouting from the Earth鈥檚 south pole (). PAMELA samples only a small part of the inner radiation belt, but antiprotons are probably trapped throughout it. 鈥淲e are talking about of billions of particles,鈥� says team member Francesco Cafagna from the University of Bari in Italy.

鈥淚 find it very interesting to note that the Earth鈥檚 magnetic field works a little bit like the magnetic traps that we are using in the lab,鈥� says at the CERN particle physics laboratory near Geneva, Switzerland. There, researchers have been trying to trap antimatter for ever longer periods to compare its behaviour with that of normal matter.

Alessandro Bruno, another team member from Bari, says antimatter in the Earth鈥檚 radiation belts might one day be useful for fuelling spacecraft. Future rockets could be powered by the reaction between matter and antimatter, a reaction that produces energy even more efficiently than nuclear fusion in the sun鈥檚 core.

鈥淭his is the most abundant source of antiprotons near the Earth,鈥� says Bruno. 鈥淲ho knows, one day a spacecraft could launch then refuel in the inner radiation belt before travelling further.鈥�

Millions or billions of times as many antiprotons probably ring the giant planets.

It was already nicknamed 鈥淐onan the Bacterium鈥� for its ability to withstand radiation. Now it seems Deinococcus radiodurans could, in theory, survive dormant on Mars for over a million years.

at University College London and colleagues froze the bugs to -79 掳C, the average temperature at Mars鈥檚 mid-latitudes. Then they zapped them with gamma rays to simulate the dose they would receive under 30 centimetres of Martian soil over long periods of time.

The team worked out that it could take 1.2 million years under these conditions to shrink a population of the bacteria to a millionth of its original size.

Earlier studies suggested that the bacterium can endure four times as much radiation in the Martian cold as at room temperature. If a cell is frozen, radiation does less damage to it because the free radicals it creates are much less mobile. 鈥淐old is good in that respect,鈥� Dartnell says. 鈥淚t improves the chances of cells surviving radiation.鈥�

Antarctic bugs

Dartnell鈥檚 team also isolated three new strains of bacteria from the Dry Valleys of Antarctica, where winter temperatures drop to -40 潞C.

The hardiest of the bugs, a new strain of Brevundimonas, could persist for 117,000 years on Mars before its population would be reduced by a factor of a million, the team鈥檚 work suggests.

鈥淭he more we learn about Earth life, the more likely it appears that it could survive in other parts of the solar system,鈥� says Cassie Conley of NASA in Washington DC.

High vacuum

But even if terrestrial microbes could survive on Mars itself, they might not fare so well on the journey there, she cautions. To simulate spaceflight, she suggests that the experiments be repeated in a high vacuum, which can desiccate microbes. 鈥淚n space, you suck off nearly all the water molecules,鈥� Conley says. This removal of water could make it more difficult for cells to repair radiation damage.

Conley, who makes sure NASA missions minimise the risk of contaminating other worlds with microbes, says the agency鈥檚 policy on planetary protection already takes into account that some microbes are amazingly radiation resistant.

鈥淭he policy is that we won鈥檛 contaminate other planets or moons, because just one colonising event could screw up our ability to study indigenous life forever,鈥� she told 快猫短视频.

Journal reference:

Atoms called positronium inexplicably scatter off gas particles as if they were lone electrons, even though they contain an anti-electron as well. The finding hints that engineers could use the well-known scattering properties of electrons as a rule of thumb in designing future medical scanners that employ positronium. It could also help interpret puzzling astronomical observations.

鈥淜nowledge of how positronium interacts with the surrounding medium is important, whether this is human tissue or interstellar gas,鈥� says experiment leader of University College London.

Positronium atoms are like hydrogen atoms, except the proton is replaced by a positron, the positively charged antiparticle of the electron. The atoms are unstable and their two constituent particles disappear in a puff of gamma rays within a microsecond.

When a beam of electrons or positrons flies through a gas, they scatter off the gas particles at predictable rates. 快猫短视频s guessed that positronium atoms, being twice as heavy as an electron and electrically neutral, would have very different scattering rates.

Competing effects

To test this, Laricchia鈥檚 team fired positronium atoms at 1100 to 4400 kilometres per second into various gases, including hydrogen, krypton and water vapour. Curiously, the scattering rates for positronium were almost identical to that of a plain electron, as though the positron鈥檚 influence was somehow 鈥渃loaked鈥�.

, a theorist at Queen鈥檚 University Belfast who studies matter-antimatter interactions, says the result will be tough to explain mathematically because the scattering process is so complex.

鈥淲hen positronium hits an atom, the electrons in the atom don鈥檛 know what to do 鈥� do they stick with the nucleus, or try to chase after the positron?鈥� he asks. 鈥淭here鈥檚 a lot of competition going on and theoretically it鈥檚 difficult to model that accurately.鈥�

Limiting damage

Laricchia speculates that the electron might play a dominant role in each positronium scattering by getting closer to a gas particle, on average, than the positron does.

Whatever the reason for the strange results, they could have important consequences for medical PET (positron emission tomography) scanning. PET scanners pick up gamma rays emitted by positronium formed when a radioactive tracer that emits positrons is injected into the body.

Knowing the positronium scattering rates should clarify how the particles deposit energy along their tracks as they collide with molecules in tissue. 鈥淭hat鈥檚 required to limit damage to healthy tissue,鈥� Laricchia told 快猫短视频. It would also help refine estimates of how far positronium travels, allowing tumour volumes to be measured more accurately.

Positronium also forms in space. Understanding its interaction with interstellar gas clouds could prove crucial for determining the positions of some mysterious positron sources in the Milky Way.

Journal reference:

A new study suggests that cost-effective galactic radio transmissions would be at higher frequencies than SETI projects traditionally monitor, and ET鈥檚 attempts to make contact would be only few and far between.

鈥淚f ET was building cost-effective beacons, would our searches have detected them? The answer turns out to be no,鈥� says , president of the company in Lafayette, California.

Cosmic water hole

Aliens wishing to communicate would probably broadcast at frequencies between 1 and 10 gigahertz, where there is less astronomical background noise than in other wavebands. Most SETI projects tune in to the 鈥渃osmic water hole鈥� waveband between 1.42 and 1.72 gigahertz. The reasoning goes that alien astronomers might expect earthly scientists to be looking there anyway as this is the frequency of radiation emitted by interstellar hydrogen and hydroxyl clouds.

But this fails to consider the cost to aliens. 鈥淪ocieties are always constrained by their resources,鈥� Benford points out. 鈥淲hy did cathedrals take centuries to build? Partly because they had only so many artisans, but also their capital was limited.鈥�

Benford鈥檚 analysis of the economics of extraterrestrial beacons with his brother at the University of California, Irvine, and son at NASA鈥檚 Goddard Space Flight Center in Maryland suggests that aliens would choose to transmit at nearer to 10 gigahertz, as this makes it easier and cheaper to create a powerful beam.

Little and often

Short pulses rather than a continuous signal would also enable frugal aliens to use small and cheap transmitters. Small transmitters can beam out powerful radiation using high voltages 鈥� but only if they broadcast brief pulses that don鈥檛 give the electric fields time to discharge.

Benford concludes that frugal aliens would swing a pulsed microwave beam across the disc of the Milky Way, where most of our galaxy鈥檚 stars reside. 鈥淭hey wouldn鈥檛 want to target individual stars: there are far too many of them,鈥� he says. 鈥淚nstead, they鈥檇 build a powerful beacon, then swing that beacon around and repeat it.鈥�

He calculates that aliens could use a dish antenna 0.9 kilometres wide to sweep a beam across the Milky Way鈥檚 disc once a year, broadcasting a single 35-second blast of microsecond pulses to all the stars within 1080 light years.

If aliens did follow that strategy, their signals would not repeat for many months. 鈥淎stronomers have seen some unexplained signals that lasted for tens of seconds then were never seen again,鈥� says Benford. 鈥淪ome of those could have been extraterrestrial beacons but there wasn鈥檛 enough observing time to wait for any repeats.鈥� He urges astronomers to look through their archives for any signals that might fit the bill.

Journal references: Astrobiology, DOI: and