Bombing Earth-bound Asteroids a Viable Option, Experts Say

In the movies, a bomb is usually the most effective way of stopping an asteroid from wiping out life on Earth. But real scientists have had their doubts about bombing the potentially hazardous objects. (See asteroid and comet pictures.)

Now, however, some researchers are finding evidence that an explosion might not, as feared, make a bad situation worse by sending a huge cloud of harmful debris raining down on the planet.

And other scientists are suggesting that, despite previous assumptions, we wouldn't need an impossibly powerful bomb to destroy a threatening asteroid.

Considering the damage a large asteroid strike could do to humanity, bombing any so-called near-Earth objects, or NEOs, headed our way might be a viable last resort "if we have the international political will," said Robert Weaver of Los Alamos National Laboratory in New Mexico.

In such a case, "my calculations show that we have the means."

(Related: "NASA to Visit Asteroid Predicted to Hit Earth?")

Asteroid Bombing Wouldn't Require Monster Nukes

Although the exact nature of asteroids is still poorly understood, scientists think the objects fall into two broad categories: solid space rocks and loose "rubble piles" held together by gravity.

(Related: "Asteroid Probe Offers New Views of Near-Earth Object.")

It had always been assumed that explosives would be more effective at blowing apart an asteroid if inserted deep in the body's interior, Weaver said.

But in his new calculations—presented last week at a meeting of the American Astronomical Society's Division of Planetary Sciences in Pasadena, California—Weaver found that the bombing option wouldn't require any drilling to get the job done.

According to his models, a nuclear explosion equal to one megaton of TNT would blow a solid asteroid to smithereens whether the bomb was placed on the asteroid's surface or deep inside the space rock. Some countries' arsenals already include nukes of that power.

The researcher also found that destroying rubble-pile asteroids would be even easier, at least in terms of the power needed to blow them apart.

His computer programs predicted that the asteroid Itokawa—a loose pile shaped like a 1,000-foot-long (300-meter-long) potato—would be broken to bits by an explosion of just 500,000 tons of TNT. Bombs big enough to create such a blast are relatively common.

The new models are the first to incorporate sophisticated shockwave physics that have been validated with laboratory experiments, Weaver said.

Saturn's "Walnut" Moon Mystery Cracked?

Saturn's moon Iapetus looks like a walnut because it lies in a "Goldilocks zone" around the giant planet, new research suggests. The moon was once a fast-spinning blob of rock and ice, but its location was just right for locking an unusual feature in place as the spin slowed.

In general, moons that form around planets—rather than those believed to be captured objects—spin due to the motion of debris as it consolidates into a larger orbiting body.

Unlike Saturn's other spherical or ellipsoid moons, Iapetus has a unique, slightly squashed shape with an 8-mile-high (13-kilometer-high) mountain range running around much of its middle, like the cusp where the halves of a walnut shell join.

(Related: "Saturn's Largest Moon Has Ingredients for Life?")

Previous theories had suggested this odd ridge formed via plate tectonics or volcanoes. Those models tended to produce a broader "ridge zone" rather than a single narrow feature, noted co-author Mikhail Kreslavsky of the University of California, Santa Cruz.

In their new model, Kreslavsky and UCSC colleague Francis Nimmo suggest Iapetus formed in a region where the moon was far enough from the planet to retain a lot of its initial spin even after it was fully grown. However, the moon was close enough that Saturn's gravitational forces eventually slowed things down.

(Find out about a related theory that suggests Iapetus has its overall shape because it was "cryogenically preserved" when it was young.)

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Universe's Most Distant Object Spotted

Astronomers spotted a faint glimmer of infrared light from this primitive galaxy, called UDFy-38135539, using the European Southern Observatory's Very Large Telescope in Chile.

Because of the time it takes for the distant galaxy's light to reach Earth, the recently captured signal is thought to have been emitted when the universe was only 600 million years old. That means the find can help scientists better understand the so-called era of reionization, the study authors say.

For about the first billion years after the big bang, the universe was filled with an opaque fog of neutral hydrogen. As the very first stars and galaxies formed out of this fog, their radiation charged any nearby hydrogen. This ionization transformed the fog into the optically transparent interstellar medium that exists today.

(Related: "Big Bang Ripples Formed Universe's First Stars.")

"The universe at the time was quite an interesting place, as progressively more and more galaxies were formed, while the existing galaxies were merging together and growing in size and luminosity," said Michele Trenti, a postdoctoral research associate at the University of Colorado in Boulder who was not involved in the study.

"The photons emitted from these galaxies were stripping off electrons from the hydrogen atoms in the interstellar gas, creating bubbles of ionized gas surrounding these [galaxies].

"This bubble"—the one surrounding the newfound galaxy—"is proof that after about 600 million years from the big bang, stars in galaxies have almost completed the process of hydrogen reionization."

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Cosmic Spiral

In a blending of old and new, images from a camera recently removed from the Hubble Space Telescope were combined with pictures from its replacement camera to create this composite view of the spiral galaxy NGC 3982, released Tuesday.

The pictures, taken between March 2000 and August 2009, come together to reveal colorful details in the star-forming galaxy, which lies 68 million light-years away. The galaxy's dusty arms are lined with young star clusters (blue) and glowing hydrogen clouds (pink) where new stars are being born.

Moon's Silver Hints at Lunar Water Origins

It's not just poetic to call it a silvery moon: In addition to water, a NASA probe that crashed into a lunar crater last year churned up unexpected concentrations of silver and mercury, aka quicksilver, a new study says.

The metals had been found before in moon rocks brought back by Apollo astronauts, but the elements had appeared in only trace amounts. (Also see "Water Found in Apollo Moon Rocks.")

The new data, derived from the Lunar Crater Observation and Sensing Satellite (LCROSS) mission, show much higher amounts of silver and mercury in debris from the crash, which happened inside the south-pole crater known as Cabeus.

The surprising find hints at out how water may have arrived on the moon and why it become concentrated at the poles, astronomers say.

When impactors strike the lunar surface, the moon's easily vaporized metals, such as mercury and silver, tend to migrate—atom by atom—toward the cooler poles, much as water vapor in Earth's atmosphere condenses on cold surfaces.

Water and other volatile compounds brought in by asteroids and comets would similarly experience this "cold sink" effect. (See "Water Discovered on an Asteroid—A First.")

"The silver is like a tracer," said study leader Peter Schultz of Brown University in Rhode Island. "It tells us where [moon water] probably came from, and I think it's telling us that it came from comets and asteroids colliding with the moon."


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Solar System "Force Field" Shrinks Fast

As charged particles flow out from the sun, they eventually bump up against interstellar medium—the relatively empty areas between stars. These interactions "inflate" a protective bubble that shields Earth and the entire solar system from potentially harmful cosmic rays (solar system pictures).

Now IBEX has surprised astronomers by showing that this force field-like structure, the heliosphere, is an unexpectedly dynamic, unpredictable boundary.

"If we've learned anything from IBEX so far, it is that the models that we're using for interaction of the solar wind with the galaxy were just dead wrong," David McComas, principal investigator for the IBEX program, said during a NASA press conference Thursday.

Heliosphere Changes Fast

For starters, it's been assumed that the heliosphere's expansion and contraction follows the sun's roughly 11-year activity cycle, during which the flow rate of charged particles, or solar wind, fluctuates.

But when scientists compared IBEX maps of the heliosphere taken just six months apart, the researchers found that it had shrunk to a much greater extent than expected. (See "Sun's Power Hits New Low, May Endanger Earth?")

This quick shrinkage could be a concern for astronauts, said McComas, of the Southwest research Institute in San Antonio, Texas. That's because, as the heliosphere shrinks, it lets in more cosmic radiation, which can compromise the body's immune system.

(Related: "Solar System Is 'Bullet Shaped.'")

Among IBEX's other new surprises: a long, mysterious ribbon of uncharged particles found last year that has apparently lost its brightest, most energetic region since its 2009 discovery.

"What we're seeing is the knot pull apart as it spreads across a region of the ribbon," McComas said in a press statement.

"To this day the science team can't agree on exactly what causes the knot or the ribbon, but by comparing different sky maps, we find the surprising result that the region is changing over relatively short time periods. Now we have to figure out why."

Bull ants have right eye for the job

Worker bull ants have military-style night vision, while their higher status winged nest mates see best during the day, Australian researchers have discovered.

The research led by Dr Ajay Narendra from the Australian National University and colleagues is published this week in the Proceedings of the Royal Society B.

It is the first research to show that individual ants of the same species living in the same colony have huge variation in the structure of their eyes, depending on what job they do and when they do it.

A colony of bull ants contains three types or castes: sterile female workers who forage on the ground, fertile females who briefly fly then live in the dark nest as queens for up to 15 years, and winged fertile males who have a short life on the wing searching for a queen to mate with, before dying.

Biologists already puzzle over how a single colony of genetically identical ants can have such different body shapes. But now it seems even the fine structure of the eye can show dramatic variation.

The team studied four different species of bull ant (Myrmecia) living in eucalypt forests on the outskirts of Canberra.

They recorded at what time of day or night each caste member of each species was active. They then preserved the eyes of the insects and examined the fine structure under a microscope.

Pulsating Aurorae Secrets Revealed

Scientists have found the elusive trigger that sets off the most striking visual outbursts, known as pulsating aurorae or blinking lights around Earth's polar regions. (See aurorae pictures.)

Though typical auroras usually stretch more than 620 miles (a thousand kilometers), and last only minutes at a time, pulsating aurora are small glowing patches of light about a 62 miles (a hundred kilometers) wide that flash on and off every 5 to 40 seconds. This flickering gives the appearance of exploding lights in the sky.

"The driver behind auroral pulsation has been a long-standing question in the auroral physics community for more than four decades," said project leader Toshi Nishimura, a researcher at University of California, Los Angeles.

But Nishimura and colleagues discovered the driving force behind the unusual cosmic fireworks appears to be a particular type of electromagnetic wave that originates in Earth's protective, bubble-like magnetosphere.

Solar Wind Collisions Create Bursts of Light

When solar wind—a stream of charged particles released from the sun—strikes our planet's magnetic field, the wind gets funneled down into the atmosphere.

The heaviest animal in the air

At first glance it looks like a squashed ostrich, strutting proudly across the Spanish plain with its head held high. Then it takes off.

The great bustard is probably the heaviest living animal that can fly. The males normally weigh between 10 and 16 kilograms, but some can reach 21 kg. For comparison, the wandering albatross has a larger wingspan, but only the biggest reach even 16 kg.

Female great bustards are much more petite creatures, normally weighing no more than 5 kg. This is the largest size disparity of any bird species, and it can mean only one thing: females prefer chunky males. But the females aren't just picking the males for their weight. They have an eye for their necks and whiskers too.
Great bustards are a lekking species. At the start of the mating season all the males in an area gather at one site, the lek, to compete for females. The females have the chance to check out all the local males, and to choose the best to father their chicks.

The males arrive first, in January, and the females turn up in March or April. Before they do, the males compete and may even fight to establish their place in the hierarchy. The stakes are high: come the mating season, less than half the males will even attempt to copulate, and less than 10 per cent will succeed. Among males, only the most dominant pass on their genes.

Male peacocks have fantastically coloured tails, but male great bustards make do with white whiskers. Actually thin feathers, they can be 20 centimetres long and have no practical function other than to look good to females. During display sessions, the males lift them to show off their size.

During the mating season, males also develop conspicuous plumage on their necks. Instead of the usual plain grey, they acquire a two-tone pattern: white on the throat, chestnut brown towards the base. Their necks also swell up, and two stripes of bare blue skin appear down their length. As if that weren't enough, the males have bright white tails that they aim towards the sun to attract females from a distance.

How to find out if exo-Earths host life

SO CLOSE, yet so far. Gliese 581 g is the first planet discovered that is the right mass and distance from its star for the surface to be awash with liquid water and perhaps life. Chances are we'll never know for sure without an armada of space telescopes, and their future looks uncertain. But a 2014 mission could tell us whether any habitable worlds with better viewing angles have signs of life.

Gliese 581 g is 20 light years from our solar system and three to four times as massive as Earth. The planet is likely to be rocky and lies squarely in the habitable zone around its star, where temperatures are just right for liquid water to exist on its surface.

To find evidence for life we would need to measure the light spectrum of the planet's atmosphere and look for the signature of water vapour, as well as possible by-products of life, such as oxygen and methane.

That would mean launching an expensive array of space telescopes to tease out the faint glow of the planet from the powerful glare of its star. NASA and the European Space Agency were hoping to launch such a mission in 2014, called the Terrestrial Planet Finder (TPF), or Darwin.

But in 2006 NASA backed away from the mission, postponing it indefinitely to free up more funds for human space exploration. Darwin/TPF was dealt another blow this August, when a key panel of US astronomers failed to recommend its construction in the next decade.

All is not lost, however, according to Paul Butler of the Carnegie Institution in Washington DC, co-discoverer of the new planet. He says the ground-based instruments that helped him discover it should soon turn up a flood of worlds in the habitable zones of their stars. "Over the next 10 years, I would be shocked if there weren't many tens of these things," he says.

About 5 to 10 per cent of these should, unlike Gliese 581 g, pass in front of their parent stars as seen from Earth, making it easier to measure their atmospheric spectra, Butler says. The James Webb Space Telescope could make such observations after it is launched in 2014, at least for the nearest stars (New Scientist, 16 May 2009, p 10). We may not have to wait too long before we see signs of a planet with life.

Eco-engineering on a giant scale

The disagreement underscores a debate that has been raging over marsh restoration for decades. Even before the spill, the marshes were disappearing at an alarming rate - the consequence of the dams, levees and canals built to provide shipping channels and protect New Orleans from flooding. Without intervention Louisiana's bayous could become open water within 50 years.

As a result, support has been growing for a suite of projects to resurrect the marshes (see map). At one end of the spectrum are those who advocate minimal intervention and letting nature take its course. At the other, the call is for yet more engineering: new, hardier breeds of grasses, seeding from the air and artificial reefs to shore up the sinking sediment.

Ultimately, the marshes are vanishing because sediment is in short supply. Wind and waves constantly erode the shoreline, and dams and levees hold back sediment flowing down the Mississippi. What's more, a network of canals dredged by the oil and gas industry carry saltwater inland, killing freshwater marshes. Add to all this rising sea levels and the largest oil spill in US history and the situation is desperate. Without its marshes, Louisiana's thriving seafood industry would crumble and the state's coast would lose its natural defences against the powerful storms that blow in from the Gulf of Mexico.

Turner advocates small-scale intervention: filling in thousands of kilometres of abandoned canals with the dredged sediment that is still piled up alongside them. He also favours helping sediment flow to the marshes. Historically, when the Mississippi's waters ran high, "crevasses" appeared in the river banks and carried sediment into the deltas. Dams and levees now prevent this, so Turner suggests punching holes in the river's embankment to spur the process. "So many marsh restoration ideas assume we can do better than nature," says Turner. "I think that's pretty arrogant."

Others say we need to think big. "Over the years, we've done all kinds of patchwork projects," says Harry Roberts, a retired sedimentary geologist at LSU. "They're not long-term solutions." Roberts has calculated that 18 to 24 billion tonnes of sediment will be needed to maintain the delta as the sea level rises in the next century (Nature Geoscience, DOI: 10.1038/NGEO553). Small crevasses can never meet that demand, he says.

For researchers like Roberts the question has become not how to restore Louisiana's lost Eden but how to create a new, improved one. As part of that, in April, a $23 million project kicked off to pipe mud more than 6 kilometres from Cote Blanche Bay to Vermilion Bay's Marsh Island Wildlife Refuge. The aim is to recreate 160 hectares of marsh.

Sun's activity flies in face of climate expectations

IF NEW satellite data can be trusted, changes in solar activity warmed the Earth when they should have cooled it.

Joanna Haigh of Imperial College London studied satellite measurements of solar radiation between 2004 and 2007, when overall solar activity was in decline. The sun puts out less energy when its activity is low, but different types of radiation vary to different degrees. Until now, this had been poorly studied.

Haigh's measurements showed that visible radiation increased between 2004 and 2007, when it was expected to decrease, and ultraviolet radiation dropped four times as much as predicted.

Haigh then plugged her data into an atmospheric model to calculate how the patterns affected energy filtering through the atmosphere. Previous studies have shown that Earth is normally cooler during solar minima.Yet the model suggested that more solar energy reached the planet's surface during the period, warming it by about 0.05 °C (Nature, DOI: 10.1038/nature09426).

The effect is slight, but it could call into question our understanding of the sun's subtle effects on climate. Or could it? Stefan Brönnimann of the University of Bern in Switzerland says Haigh's study shows the importance of looking at radiation changes in detail but cautions that the results could be a one-off. He points out that the sun's most recent cycle is known to have been atypical

Grey wolf hunt creates bitter row in US

THE iconic grey wolf of the wild, wild west is the subject of a bitter row in the US. Idaho and Montana both established hunting seasons in 2009, after the US Fish and Wildlife Service decided the states' wolf populations were no longer endangered. But in August a federal judge ruled the decision illegal, halting the 2010 hunts.

Both states are now appealing that ruling. Officials argue that hunting has little effect on populations because many wolves die anyway of starvation or disease, and females can compensate by producing more young. These assumptions are wrong, says Scott Creel of Montana State University in Bozeman.

He analysed the findings of previous studies of 21 North American wolf populations, and found that hunting increased overall death rates and also reduced population growth rates (PLoS ONE, DOI: 10.1371/journal.pone.0012918).

A combination of sport hunting and state-sponsored culls killed 63 per cent of the Montana population last year. Creel calculates that humans should only take 22 per cent for the population to remain stable.

Vague carbon emission checks put deal in balance

CHINA is this week playing host to the last stage of preparatory climate talks before delegates gather at the annual United Nations climate change summit, in Cancún, Mexico, in December. They will attempt once again to reach a deal on limiting emissions of carbon dioxide and other greenhouse gases.

But any deal may fail because those emissions cannot yet be measured with sufficient accuracy. This has been a significant sticking point in talks. The world badly needs an independent carbon police to check the figures and catch the carbon frauds. Can science deliver?

Even the easiest emission to assess - CO2 from burning fossil fuels in developed nations - may only be known to within 10 per cent, according to Gregg Marland of the Oak Ridge National Laboratory in Tennessee. And a report by energy consultant Irving Mintzer for WWF, published in June, found that China does not record CO2 emissions from its small coal-burning factories and long-standing fires in mines, which may result in under-reporting by as much as 20 per cent.

The uncertainties for other greenhouse gases are even greater. Globally, declared nitrogen dioxide emissions are less than half those known to reach the atmosphere.

Verifying national emissions requires both "bottom-up" independent oversight of the inventories, and better "top-down" monitoring of the atmosphere, says Matthias Jonas of the International Institute for Applied Systems Analysis in Laxenberg, Austria.

The first step will be to add to the global network of some 150 stations measuring CO2 and other gases in the atmosphere, run by the World Meteorological Organization. This logs gas levels at places distant from major pollution sources, but what is now needed is the exact opposite - stations sniffing the air close to major sources. Such a network is being discussed by the WMO.

As well as this, there should be more research aircraft doing spot checks. This summer, the US National Oceanic and Atmospheric Administration flew aircraft downwind of refineries and power stations in California. Their preliminary results suggest that methane emissions from Los Angeles are a third higher than expected.

Also needed are more flights to remote regions. Last year, a research flight by the US National Center for Atmospheric Research discovered methane leaking out of the Arctic Ocean. The race is on to find out if the source is new gas fields off Alaska or melting permafrost.

A new climate treaty will also need carbon sniffers in tropical forests, especially in countries that sign up to a part of the deal called REDD (Reduced Emissions from Deforestation and Forest Degradation). REDD would offer cash to countries that conserve their forests so they can soak up atmospheric CO2. This means knowing how much carbon is actually being absorbed by the forests. In August, a study of Peruvian forests by Greg Asner of Stanford University, California, found existing estimates of carbon stored and released could be out by as much as 50 per cent.