While challenging, the mission is definitely doable, said Chris Lewicki, president and chief engineer of billionaire-backed asteroid-mining firm Planetary Resources. [NASA's Asteroid-Capture Plan (Video)]
"Return of a near-Earth asteroid of this size would require today's largest launch vehicles and today's most efficient propulsion systems in order to achieve the mission," Lewicki, who served as flight director for NASA's Spirit and Opportunity Mars rovers and surface mission manager for the agency's Phoenix Mars lander, wrote in a blog post Sunday (April 7).
"Even so, capturing and transporting a small asteroid should be a fairly straightforward affair," Lewicki added. "Mission cost and complexity are likely on par with missions like the [$2.5 billion] Curiosity Mars rover."
Spurring solar system exploration
NASA's idea is similar to one proposed last year by scientists based at Caltech's Keck Institute for Space Studies in Pasadena.
The Keck study estimated that a robotic spacecraft could drag a 23-foot near-Earth asteroid (NEA) - which would likely weigh about 500 tons - into a high lunar orbit for $2.6 billion. The returns on this initial investment are potentially huge, the researchers said.
"Experience gained via human expeditions to the small returned NEA would transfer directly to follow-on international expeditions beyond the Earth-moon system: to other near-Earth asteroids, [the Mars moons] Phobos and Deimos, Mars and potentially someday to the main asteroid belt," the Keck team wrote in a feasibility study of their plan.
The mission would also help develop asteroid-mining technology, advocates say, and advance scientists' understanding of how our solar system took shape more than 4.5 billion years ago.
Asteroids "probably represent samples of the earliest matter that was made available to form our solar system and our Earth," Caltech's Paul Dimotakis, a member of the Keck study team, told SPACE.com in February.
"We learned a lot about the moon by analyzing the moon rocks that Apollo astronauts brought back," he added. [NASA's 17 Apollo Moon Missions in Pictures]
But bagging an entire asteroid and dragging it to our neck of the cosmic woods is unprecedented, and it presents several daunting challenges.
For example, the target asteroid will be spinning, which doesn't make for a smooth ride to lunar orbit. After the spacecraft captures the asteroid and brings it into a hold of sorts, the space rock will have to be de-spun, likely with thrusters, Dimotakis said.
"You might use reaction jets to take out most of it [the spin]," he said. "You would give you yourself a lot of time to do this, because there's no second chance in any of this."
Further, bringing the asteroid onboard greatly increases the spacecraft's mass, making propulsion and navigation much more difficult. And precise navigation will definitely be required to deliver the space rock to its desired orbit, Dimotakis said (though he also stressed that any asteroid chosen would pose no danger to humanity even if it somehow struck our planet).
But ion thrusters like the ones powering NASA's Dawn mission to the huge asteroid Vesta and dwarf planet Ceres should be muscular enough to make the journey, likely taking a few years to reach the asteroid and somewhat longer to come back. And the asteroid-laden probe could probably still be guided with great care, he added.
"My guess is that all of these are not insurmountable challenges, and you would be able to calibrate yourself after you snagged it and adjust your controls," Dimotakis said.
Choosing a target
Perhaps the biggest challenge of the entire mission is picking a suitable space rock to retrieve, Lewicki wrote in his blog post.
The Keck study recommends going after a carbonaceous asteroid packed full of water and other volatiles. Carbonaceous asteroids can be very dark, and it's tough to spot and characterize a 23-foot asteroid in the vast depths of space whatever its color.
So both Lewicki and Dimotakis stressed the importance of searching for potential asteroid targets sooner rather than later. Planetary Resources plans to begin launching a line of small prospecting space telescopes in 2014 or 2015, and these "Arkyd-100" craft could aid NASA's mission, Lewicki wrote.
Dimotakis, for his part, is engaged in a follow-up to the Keck study that's looking for potential targets in observations made by current telescopes.
"We are developing software in collaboration with JPL [NASA's Jet Propulsion Laboratory] that is going to exploit the observational digital record and essentially flag things that could be of interest and might be in this class," he said. "This has never happened before."
Still, NASA should make sure that mission scientists and engineers don't just sit on their hands until an asteroid selection is made, he added.
It's important "to start developing the spacecraft before you even know where you're going," Dimotakis said. "If you do these things in parallel, then the mission timeline shrinks."
Follow Mike Wall on Twitter @michaeldwall. Follow us @Spacedotcom, Facebook or Google+. Originally published on SPACE.com.
A cyclist passes spring flowers on a day when temperatures were expected to reach lows in the 80s on Wednesday, April 10, in Philadelphia.
Books dry out on the floor of the Calvin T. Ryan Library at the University of Nebraska at Kearney, on Tuesday, April 9. The library was closed for repairs and to allow the books to dry following damage from a large spring storm.
The Zvezda Service Module array on the International Space Station reflects bright sun rays on April 3. This photograph was taken by one of the Expedition 35 crew members as part of an External Survey from International Space Station windows that was recently added to the crew's task list.
Astronaut Chris Hadfield tweeted this photo of Dublin, Ireland, from the International Space Station on April 10. He wrote, "A clear Dublin night in early Spring. pic.twitter.com/V53DJ8JIMk"
A Palestinian man rides a bicycle on the beach in Gaza City during sunset on Tuesday, April 9
Astronaut Thomas H. Marshburn tweeted this photo of sunrise over Australia from the International Space Station on April 10. He wrote, "Anatomy of Earth's atmosphere seen from sunrise over Australia pic.twitter.com/CmXKCQcZfi"
Firdous Square in Central Baghdad, Iraq, is where the statue of Saddam Hussein was pulled down by U.S. forces and Iraqis together ten years ago on April 9, 2003. The scene broadcast live worldwide became a symbol of final victory over Saddam Hussein, but for the people of Baghdad, it was only the beginning. The toppling of the statue on April 9, 2003, remains a potent symbol that has divided Iraqis ever since.
Astronaut Chris Hadfield tweeted this photo of the Mediterranean Sea from the International Space Station on April 10. He wrote, "The Mediterranean's mouth - Gibraltar, Algeciras, Ceuta. pic.twitter.com/vJPaUkqPIU"
Bubba Watson (right) watches as Scott Piercy hits a drive during a practice round for the Masters golf tournament Wednesday, April 10, in Augusta, Ga.
Astronaut Chris Hadfield tweeted this photo of Helsinki, Finland, and Tallinn, Estonia, from the International Space Station on April 10. He wrote, "Helsinki and Tallinn, two long-enduring gatekeepers to the Gulf of Finland. pic.twitter.com/w7C2kQn6WK"
California's Yosemite National Park is known for its granite cliffs, rushing waterfalls, mountain streams and giant sequoia trees. The 1,200-square-mile park is 95 percent wilderness. It has inspired photographers the world over. The great Ansel Adams once said of Yosemite, "Yosemite Valley, to me, is always a sunrise, a glitter of green and golden wonder in a vast edifice of stone and space."
Click through for photos.
Above, a view of Yosemite Valley with El Capitan, the 3,000-foot rock formation on the north side of Yosemite Valley, on the left of the image.
Half Dome is seen from Glacier Point at sunrise. Glacier Point is on the south wall of Yosemite Valley at an elevation of 7,214 feet. The point offers a superb view of Yosemite Valley, including Yosemite Falls, Half Dome, Vernal Fall, Nevada Fall, and Clouds Rest.
Stars fill the sky over Yosemite Valley near Curry Village.
Half Dome, visible on the left side of the image, is the granite dome at the eastern end of Yosemite Valley. The crest rises more than 4,737 feet above the valley floor.
Cathedral Peak is reflected in Upper Cathedral Lake.
A full moon rises over the Yosemite Valley, illuminating a fresh blanket of late December snow.
A man stands on Half Dome at sunrise.
Clouds pass over Yosemite Valley with El Capitan in the background.
Star trails are seen over the Sierra Nevada mountains in Yosemite National Park.
The Merced River runs through Yosemite Valley.
3D Photos of snowflakes falling in mid-air. (Tim Garrett, University of Utah)
No two snowflakes are alike - but you've never seen them quite like this.
A new device can take 3D photographs of snow as it falls through the air, revealing a diverse array of shapes that mostly look completely different than the 2D representations we're used to seeing.
"Until our device, there was no good instrument for automatically photographing the shapes and sizes of snowflakes in free-fall," said Tim Garrett, an atmospheric scientist at the University of Utah, in a release from the school. "We are photographing these snowflakes completely untouched by any device, as they exist naturally in the air."
Typically, snowflakes in photographs "tend to be of a particular type that conveniently lies flat on a microscope slide, where a camera can get them perfectly in focus, and the photographer can take the time to get the light exactly right," Garrett said.
But these symmetric snowflakes are quite rare, perhaps one-in-a-thousand, he said. "Snow is almost never a single, simple crystal. Rather, a snowflake might experience 'riming,' where perhaps millions of water droplets collide with a snowflake and freeze on its surface. This makes a little ice pellet known as 'graupel.' Or snowflakes collide with other snowflakes to make something fluffier, called an aggregate. And everything is possible in between," Garrett added.
The patent-pending device, called the Multi-Angle Snowflake Camera, includes three high-speed cameras, plus two motion sensors to detect the speed of falling flakes, according to the release.
The photographs and data collected by the device will help improve computer simulations of falling snow, which could improve weather predictions, the release noted. Snowflake shape affects how weather-forecasting radar interacts with the snow, and incomplete data about the diversity of shapes can cause errors in forecasting snowfall amounts and locations.
"Snowflakes are beautiful and fascinating, and truly no two are alike," Garrett said. "This complexity almost makes them worth studying in their own right. But also, there are very serious practical reasons why we need to understand snow better."
Email Douglas Main or follow him @Douglas_Main. Follow us @OAPlanet, Facebook or Google+. Original article on LiveScience's OurAmazingPlanet.
Dark lightning is invisible to the naked eye, but in certain, extremely rare conditions could produce gamma-ray radiation in an airplane equivalent to a few chest X-rays or a full-body CT scan, the researchers said, though they emphasized that the phenomenon does not appear to be dangerous to flyers.
"It's really a brand-new thing to realize this could happen deep in our atmosphere with something as ordinary as a thunderstorm," said Joseph Dwyer, a physicist at the Florida Institute of Technology, during a webcast news conference.
The satellites currently studying this phenomenon are not designed to look at Earth; instead, the satellites probe black holes and other phenomena far away in the universe that produce gamma-rays, and happen to sense radiation from Earth that is coming from behind them.
This led scientists to say that the field of research could use a dedicated Earth-gazing satellite.
"It's an important issue, and we have to study it more," said Marco Tavani, an astrophysics researcher at the University of Rome and Italy's National Institute for Astrophysics.
Gamma-rays within the atmosphere
"Dark" lightning is a type of electrical discharge within a thunderstorm that produces what are called terrestrial gamma-ray flashes. Gamma-rays are at one extreme end of the electromagnetic spectrum of light and are higher energy than ultraviolet light or X-rays. The phenomenon of dark lightning takes place in regions of the atmosphere with strong electric fields. [Infographic: Earth's Atmosphere Top to Bottom]
The fields accelerate electrons to almost the speed of light. Then, the electrons smash into air molecules and produce gamma-rays. The gamma-rays then produce electrons and their antimatter equivalents (positrons). These particles next crash into air molecules, and produce even more gamma-rays.
When these terrestrial gamma-ray flashes were first seen in the 1990s, Dwyer explained, it was thought they came from the upper parts of the atmosphere in a region that is well away from where people are. Eight years ago, however, a research team found gamma-rays originating from well within the lower part of the atmosphere during a thunderstorm, leading to questions about how airplane flyers would be affected.
Tavani said Earth-gazing satellites should feed into an early warning system that weather forecasters and airline officials would have access to, just as a precaution.
The concern is how gamma-rays can produce neutrons, which would increase the background level of these particles that humans are exposed to when flying.
Gamma-rays of large enough energy, Tavani explained, "excite" the nuclei in oxygen or nitrogen in the atmosphere, as well as the aluminum that makes up planes. The nuclei then decay, which can lead to brief periods where the number of neutrons in the vicinity increases.
"Neutrons are pretty nasty," Tavani said. (Neutron radiation is a harmful side effect of nuclear reactions, for example.)
He added, however, that flyers are already exposed to 300 times more neutrons per second in the air than they are on the ground. The aviation industry is aware of this normal background, but the bursts of neutrons produced in thunderstorms are not as well understood, Tavani said.
New detector coming
Gamma-rays on Earth are currently being studied by Italy's AGILE satellite, which is designed to hunt X-rays and gamma-rays in the universe, and NASA's Fermi Gamma-ray Space Telescope. A modest Earth-gazing detector is on the way to orbit soon, however.
The Atmosphere-Space Interactions Monitor (ASIM) instrument is expected to launch to the International Space Station aboard a robotic HTV cargo ship in 2013 or 2014.
The European instrument, which includes a suite of cameras and a gamma-ray detector, will study "extreme thunderstorms" as well as the Earth's clouds, atmosphere and water cycle.
Follow Elizabeth Howell @howellspace, or OurAmazingPlanet on Twitter @OAPlanet. We're also on Facebookand Google+.Original article at LiveScience's OurAmazingPlanet.
The European Space Agency opened a new space weather center last week in Brussels to keep tabs sun storms that could interfere with satellites in orbit and power grids on Earth.
Formally inaugurated on April 3, the Space Weather Coordination Centre (SSCC) will gather information on space weather and solar storms, as well as disturbances in the Earth's geomagnetic environment and ionosphere. Experts at the center will issue alerts and provide support for satellite operators, government agencies and research institutes whose work might be affected by space weather, according to a statement from ESA.
The SSCC, housed in the Royal Observatory of Belgium, is part of ESA's Space Situational Awareness (SSA) program, which keeps track of hazards like space junk and potentially dangerous asteroids that pose a threat to Earth and its systems in orbit.
"With the SSCC inauguration, our SSA Programme is taking concrete steps to develop a European capability to operationally monitor space weather, enhance international cooperation and establish the effective distribution of information, warnings and alerts to users in economically vital sectors," astronaut Thomas Reiter, ESA's head of human spaceflight and operations, said in a statement.
"The SSCC will help to get the right information to the right people at the right time," Reiter added.
In the United States, the Space Weather Prediction Center, a division of the National Oceanic and Atmospheric Administration (NOAA), is the official source of space weather alerts, watches and warnings.
Follow SPACE.com on Twitter @Spacedotcom. We're also on Facebook and Google+. Original article on SPACE.com.
A flag flutters over what remains of the sanctuary of the Botkinburg Foursquare Church in Botkinburg, Ark., Thursday, April 11, after a severe storm struck the building late Wednesday.
Astronaut Chris Hadfield tweeted this photo of New Zealand's South Island from the International Space Station on April 11. He wrote, "Sometimes Mother Nature uses a protractor, like here in New Zealand's South Island. pic.twitter.com/u7xwmn4qpx"
An Afghan boy walks through a poppy field in Khogyani district of Jalalabad east of Kabul, Afghanistan, Thursday, April 11. When foreign troops arrived in Afghanistan in 2001, one of their goals was to stem drug production. Instead, they have concentrated on fighting insurgents, and have often been accused of turning a blind eye to the poppy fields.
Astronaut Chris Hadfield tweeted this photo of Italy from the International Space Station on April 10. He wrote, "Tonight's Finale: Italy, heel and toe. pic.twitter.com/8thZhMaKvR"
North Koreans dance together beneath a mosaic painting of the late leader Kim Il Sung during a mass folk dancing gathering in Pyongyang Thursday, April 11.
Astronaut Chris Hadfield tweeted this photo of Antwerp, Belgium, from the International Space Station on April 10. He wrote, "Antwerp, Belgium with the Scheldt river like lightning sparking up the city. pic.twitter.com/T0Cw3d4YNG"
NASA's newest Landsat satellite captured this image of the central California coast, including the city of Lompoc, on March 22. The image was released by the Earth Observatory on April 11.
Ksenia Monko and Kirill Khaliavin of Russia perform during the Ice Dance Short Dance of the ISU World Team Trophy in Figure Skating in Tokyo, Thursday, April 11.
Astronaut Chris Hadfield tweeted this photo of Invercargill, New Zealand, from the International Space Station on April 11. He wrote, "Invercargill in Autumn in the deep south of New Zealand. pic.twitter.com/apfdHTWxcE"
Edward Gonzales from Herndon, Va., whose family is from El Salvador, shields himself from the sun with a U.S. flag as he participates in a rally for immigration reform on Capitol Hill in Washington, Wednesday, April 10.
Here's a picture we received from the Tornado in Prairie Point - Noxubee County. #WCBI #mxwx twitter.com/WCBIWEATHER/st...
- WCBIWEATHER (@WCBIWEATHER) April 11, 2013
WBCIWEATHER uploaded this photo of a funnel cloud in Mississippi on April 11 and wrote, "Here's a picture we received from the Tornado in Prairie Point - Noxubee County. #WCBI #mxwx pic.twitter.com/8vtH3x1b2x"
Two men work to remove a truck that was overturned when a severe storm struck Botkinburg, Ark., Thursday, April 11.
Kristin Little, manager of the Ferguson Optical shop in Hazelwood, talks on the phone as she describes the damage caused to her shop by a storm on Wednesday, April 10, in St. Louis, Mo.
Larry Gammill (left) and Tim Parks survey damage at Botkinburg Foursquare Church in Botkinburg, Ark., Thursday, April 11, after a tornado struck the building late Wednesday.
The street light at Howdershell Road and Lynn Haven Lane lies damaged following high winds from a strong storm in Hazelwood, Mo., late Wednesday evening, April 10.
A car lays on it's side in Hazelwood, Mo., after a storm blew through the area on Wednesday, April 10.
A fallen tree lies on a home on Lynn Haven Lane in Hazelwood, Mo., during a storm that caused extensive damage to homes and businesses on Wednesday, April 10.
Twitter user Maddie143x0x0 uploaded this photo and wrote, "Praying that my dad gets home safely. #tornado pic.twitter.com/jktf2f5KnU"
Twitter user tracesofjuniper uploaded this photo and wrote, "Look at this damage (via Brian Emfinger) near Clinton, Arkansas. #ARwx http://tvnweather.com/live #tornado pic.twitter.com/UVmmCtsPC3"
A fallen tree rests on the roof of Susan Strebeck's home in Hazelwood, Mo., after a storm blew through the area causing extensive damage on Wednesday, April 10.
Andy Banker uploaded this photo to Twitter and wrote, "Hazelwood in total darkness, truck under tree #tornado #fox2news @fox2now pic.twitter.com/tc1oh885VV"
Rory Schmalzried uploaded this photo to Twitter and wrote, "#Tornado or straight line winds? This farm shop shot took direct hit. #COWX had it all in last 24-hrs. @247Weather pic.twitter.com/iJkClizVVK"
Andy Banker uploaded this photo to Twitter and wrote, "God help hazelwood #tornado @gfox2now pic.twitter.com/HaQamIRDvN"
BarouskiDave uploaded this photo to Twitter and wrote, "Damage from #Mississippi #tornado via @skeen31 (location unknown) #mswx "What's left of my clients shop and house." pic.twitter.com/Hxuw7ZujZx"
