Planetary Resources

An artist's conception shows how solar energy could be used to process material on a near-Earth asteroid.

Experts on near-Earth objects wondered whether February's meteor blast over Russia would serve as a wakeup call about asteroids — and two months later, there's ample evidence that it has. But there are two sides to that wakeup call, having to do with potential opportunities as well as potential threats.

Nothing illustrates that better than this week's developments: In Flagstaff, Ariz., researchers are discussing ways to detect, track and head off space rocks that could wreak destruction on Earth. In Pasadena, Calif., NASA's Jet Propulsion Laboratory announced that an infrared sensor for tracking asteroids and comets has passed a critical design test. And in Bellevue, Wash., the Planetary Resources space mining venture says it's partnering with the Bechtel construction company on future efforts to mine asteroids for raw materials.

"Bechtel has a history of consistently tackling the most challenging projects, beginning with the construction of the Hoover Dam more than 75 years ago," Peter Diamandis, the co-founder and co-chairman of Planetary Resources, said in a news release announcing the deal. Today, California-based Bechtel is one of the world's leaders in the engineering, procurement and construction industry. It will join Planetary Resources' billionaire-heavy list of investors — and assist the company in its long-term mission to mine near-Earth asteroids for precious metals and outer-space water.

Diamandis and his fellow co-founder, Eric Anderson, have said asteroid mining could turn into a multitrillion-dollar industry if their vision becomes reality.

"Planetary Resources' mission is ambitious, but they've assembled a world-class team to succeed," Riley Bechtel, the chairman and CEO of Bechtel, said in the news release. "Our companies share a common vision to continually innovate and push boundaries, all aimed at contributing a better quality of life."

Speaking of life, Planetary Resources' president, Chris Lewicki, is among the scores of experts attending this week's Planetary Defense Conference in Flagstaff. "It's always an extremely fun and informative conference, as it focuses entirely on asteroids ... how often do you get to consider defending the Earth from space rocks?" he wrote in a blog posting on Tuesday.

NASA's proposed mission to grab an asteroid and park it near the moon by 2021 has been one of the meeting's major topics, but the gathering also provided the latest information on the threats posed by near-Earth objects, and what to do about them:

• Experts estimate that there are 9 million near-Earth asteroids as large as the 17-meter-wide (55-foot-wide) space rock that broke apart over Russia on Feb. 15, and virtually all of them are too small to track using current observational tools. So far, detection systems have found less than 1 percent of the asteroids smaller than 100 meters (which is big enough to wipe out a city).
• Lewicki passed along word of a scientific study suggesting that even "rubble-pile" asteroids can become more cohesive over time, thanks to the forces that bind together the smallest grains in their size distrbutions.
• Several schemes for fending off dangerous asteroids were presented — including plans to deflect them with impact vehicles, divert them or blast them to smithereens with nuclear bombs, or guide them gently into non-threatening orbits using gravity tractors.

JPL's Shyam Bhaskaran described an "AutoNav" system that could guide an impactor autonomously to hit an asteroid target at speeds of up to 30,000 mph. "It's not that easy," Bhaskaran said in a news release. "Hitting an asteroid with a spacecraft traveling at hypervelocity is like shooting an arrow at a target on a speeding race car."

The conference began on Monday and runs through Friday. Check out the program, feast your eyes on the video coverage (with live streaming as well as archived clips for each session), and follow the action via Twitter with the hashtag #PDC2013.

NASA / JPL-Caltech / B612 Foundation

The artist's concepts for the NEOCam infrared telescope (left) and the Sentinel Space Telescope (right) look similar. Both are designed to scan the skies for near-Earth asteroids.

Infrared eyes
The first step in planetary defense is to find all those potentially threatening asteroids — and during the Flagstaff conference, the spotlight focused on two proposed space telescopes designed to look for space rocks. The B612 Foundation's Sentinel Space Telescope, currently scheduled for launch in 2017 or 2018, would use an infrared sensor to look for Earth-threatening asteroids from a Venus-type orbit. Ball Aerospace reportedly has 25 people working on the Sentinel project, and so far, B612 has raised $2 million of the mission's estimated $450 million cost.

Meanwhile, JPL is working on the components for a future space mission known as NEOCam. Like Sentinel, NEOCam would scan the skies from an outer-space vantage point, looking for the infrared glow of asteroids. The mission is getting technology development funds from NASA's Discovery Program — and on Monday, JPL said NEOCam's infrared sensor passed a design test that assessed its performance under simulated deep-space conditions. A research paper detailing the sensor's design and capabilities is to be published by the Journal of Optical Engineering.

"Infrared sensors are a powerful tool for discovering, cataloging and understanding the asteroid population," JPL researcher Amy Mainzer, a co-author of the paper, said in a news release. "When you observe a space rock with infrared, you are seeing its thermal emissions, which can better define the asteroid's size, as well as tell you something about composition."

Correction for 1:50 p.m. ET April 17: Good news, everyone! The Planetary Defense Conference runs through Friday. The bad news is that I originally wrote Wednesday instead, and that I wrote "#PDC2012" rather than #PDC2013 for the Twitter hashtag. Sorry about that!

More about asteroids:

• Asteroid miners get a boost from NASA
• NASA on asteroid threat: Pay now or pray later
• NBC News archive on asteroids

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

This story was originally published on Tue Apr 16, 2013 7:54 PM EDT

NASA says it will begin work on an ambitious mission to capture a near-Earth asteroid and bring it to a stable orbit in the Earth-moon system as part of the agency's overall $17.7 billion agenda for the coming year.

The budget request for fiscal year 2014, unveiled on Wednesday, also aims to get U.S. astronauts back to flying on U.S.-based spaceships by 2017, launch the $8.8 billion James Webb Space Telescope by 2018 and send another rover to Mars by 2020. 

The proposed budget is about $50 million less than the amount sought a year ago, but about $1 billion more than the agency's current spending plan. Billions of dollars would be set aside to continue operations on the International Space Station, keep up the work on interplanetary missions, expand the nation's network of Earth-observing satellites and upgrade aerospace technologies. However, the headline-grabber in the budget is the asteroid retrieval mission, which is budgeted for $105 million in spending during the fiscal year beginning in September.

"This mission represents an unprecedented technological feat that will lead to new scientific discoveries and technological capabilities and help protect our home planet," NASA Administrator Charles Bolden said in a statement accompanying the budget request.

Planning documents suggest that the space agency would launch a probe powered by a next-generation solar electric propulsion system sometime around 2017, to rendezvous with a 7- to 10-meter-wide (25- to 33-foot-wide) asteroid around 2019. A collapsible shroud would be wrapped around the asteroid, and then the probe would pull the space rock to a stable point in high lunar orbit or at a gravitational balance point beyond the far side of the moon.

Speaking on condition of anonymity, officials familiar with the plan told NBC News that NASA was already beginning the work to identify a candidate asteroid. The 2014 budget includes $78 million for planning the mission, and $27 million to accelerate NASA's efforts to detect and characterize potentially hazardous asteroids. NASA's chief financial officer, Elizabeth Robinson, indicated that this spending would come in addition to the $20 million that the space agency currently spends annually on asteroid detection.

The plan for the mission was formally unveiled less than two months after an asteroid streaked through the atmosphere and broke up over Russia. The breakup sparked a meteor blast that shattered windows and injured more than 1,000 people.

That asteroid was thought to have been about 17 meters (55 feet) wide. The type of asteroid targeted for the future NASA mission, in contrast, would be too small to pose a threat to Earth — even if it were to break loose somehow and plunge through the atmosphere.

Astronauts to visit
Bolden said the asteroid-grabbing mission meshed with NASA's plans to head off cosmic threats as well as to prepare for deep-space human exploration. Eventually, astronauts would be sent to study the captured asteroid and bring back samples, most likely during a beyond-the-moon test mission that's already planned for 2021.

"This asteroid initiative brings together the best of NASA's science, technology and human exploration efforts to achieve the president's goal of sending humans to an asteroid by 2025," Bolden said. "We will use existing capabilities such as the Orion crew capsule and Space Launch System rocket, and develop new technologies like solar electric propulsion and laser communications — all critical components of deep-space exploration."

A senior administration official told NBC News on condition of anonymity that the added cost of the asteroid mission would be around $1 billion, spread over several years. That figure doesn't include the estimated $35 billion that is being paid out to develop the SLS/Orion system for deep-space human flights.

As Bolden noted, the asteroid mission would satisfy President Barack Obama's space exploration goal for 2025, and allow NASA to turn its attention to sending astronauts to Mars and its moons in the 2030s. Last week, Bolden signaled that other potential objectives, such as sending humans back to the moon, were not on the agenda for the foreseeable future.

Nevertheless, some lawmakers want NASA to go in a different direction: A bipartisan group of House members last week reintroduced a bill calling on the space agency to develop a plan for establishing a permanent human presence on the moon.

"Last year, the National Research Council committee charged with reviewing NASA’s strategic direction found that there was no support within NASA or from our international partners for the administration’s proposed asteroid mission," Rep. Frank Wolf, R-Va., said in a statement. "However, there is broad support for NASA to lead a return to the moon. So the U.S. can either lead that effort, or another country will step up and lead that effort in our absence — which would be very unfortunate."

No guarantees
NASA's $17.7 billion spending plan accounts for less than half a percent of Obama's $3.8 trillion request to Congress for fiscal 2014. The entire budget is likely to come under close scrutiny in the Republican-controlled House as well as the Democratic-controlled Senate, and there's no guarantee that the final version will look anything like the White House's proposal. In fact, last year's budget request ended up going nowhere. Instead, the federal government is currently operating under a budget sequestration plan that cut back on previous spending levels.

"This was a meat-ax approach that I think nobody initially intended to have take effect," White House science adviser John Holdren said Wednesday during a budget briefing.

Holdren said the total amount of money budgeted for research and development in 2014 would come to $142.8 billion, which represents a "small decline" in inflation-adjusted dollars compared with 2012 spending levels.

"Although this is not the budget that we would want if financial times were better, it reflects an extraordinary effort by this administration to preserve a key investment in research, development, innovation and STEM [science, technology, engineering and math] education that our country's future requires," Holdren said.

Update for 9:15 p.m. ET April 10: NASA's asteroid retrieval mission could complement commercial efforts to identify and exploit bigger near-Earth objects, said Chris Lewicki, president of the Planetary Resources asteroid-mining venture. He said he's already been involved in an "ongoing discussion" about how such a mission could benefit the public as well as private enterprise.

"Maybe this is a model for a COTS-like program where there are operations put in place for private industry to help develop a marketplace," Lewicki told NBC News.

But Lewicki said the mission will not be easy. "It represents something new that will require NASA and the contractors that help them do it to really stretch their capabilities," he said.

For example, Lewicki said it would be "very challenging" to identify and track deep-space objects in the size range that NASA is targeting — that is, 7 to 10 meters wide. Such objects usually can't be spotted unless they make a close approach to Earth.

"With what's been proposed in the budget, NASA is putting more money on the table to accelerate and leverage more observation activities," Lewicki said. "The question is, is that enough? And is it going to be soon enough?"

More reaction:

• Planetary Resources: Asteroid plan offers 'bold new thinking'
• Deep Space Industries calls for partnerships (via Moon and Back)
• University of Arizona experts welcome asteroid plan
• Rep. Lamar Smith, R-Texas: Plan comes 'seemingly out of the blue'
• Coalition for Space Exploration backs budget proposal

More about asteroids:

• Asteroid miners are getting a boost from NASA
• How asteroid mission could lead to Mars
• Cosmic Log archive on asteroids

Correction: I originally wrote that the full budget proposal was seeking $3.8 billion, but it's actually $3.8 trillion. Unfortunately, it's not the first time one of those wayward "illions" has slipped through the net. Thank goodness I have sharp-eyed commenters to set me straight.

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

This story was originally published on Wed Apr 10, 2013 2:54 PM EDT

DigitalSpace

An Orion exploration vehicle approaches a near-Earth asteroid in this artist's conception. Such a mission would be carried out in 2021 under the White House's new plan for NASA exploration beyond Earth orbit.

NASA's accelerated vision for exploration calls for moving a near-Earth asteroid even nearer to Earth, sending out astronauts to bring back samples within a decade, and then shifting the focus to Mars, a senior Obama administration official told NBC News on Saturday.

The official said the mission would "accomplish the president's challenge of sending humans to visit an asteroid by 2025 in a more cost-effective and potentially quicker time frame than under other scenarios." The official spoke on condition of anonymity because there was no authorization to discuss the plan publicly.

The source said more than $100 million would be sought for the mission and other asteroid-related activities in its budget request for the coming fiscal year, which is due to be sent to Congress on Wednesday. That confirms comments made on Friday by Sen. Bill Nelson, D-Fla., a one-time spaceflier who is now chairman of the Senate Commerce Subcommittee on Science and Space. It also confirms a report about the mission that appeared last month in Aviation Week.

The asteroid retrieval mission is based on a scenario set out last year by a study group at the Keck Institute for Space Studies. NASA's revised scenario would launch a robotic probe toward a 500-ton, 7- to 10-meter-wide (25- to 33-foot-wide) asteroid in 2017 or so. The probe would capture the space rock in a bag in 2019, and then pull it to a stable orbit in the vicinity of the moon, using a next-generation solar electric propulsion system. That would reduce the travel time for asteroid-bound astronauts from a matter of months to just a few days.

The Keck study estimated the total mission cost at $2.6 billion — but the administration official said the price tag could be reduced to $1 billion, or roughly $100 million a year, if the mission took advantage of an already-planned test flight for NASA's heavy-lift Space Launch System rocket and Orion crew exploration vehicle. That flight would send astronauts around the moon and back in 2021.

"This mission would combine the best of NASA's asteroid identification, technology development, and human exploration efforts to capture and redirect a small asteroid to just beyond the moon to set up a human mission using existing resources and equipment, including the heavy-lift rocket and deep-space capsule that have been under development for several years," the official said in an email.

The 2014 budget would set aside $78 million for planning the asteroid retrieval mission, plus $27 million to accelerate NASA's efforts to detect and characterize potentially hazardous asteroids. The federal government currently spends $20 million annually on asteroid detection.

Meteor sparked action
The official said the plan had been under discussion for months, but coalesced after February's meteor blast over Russia. The meteor's breakup injured more than 1,000 people and sparked a worldwide sensation. It also sparked a series of congressional hearings about threats from space, during which Republicans as well as Democrats hinted that they would support more funding to counter asteroid threats.

"This plan would help us prove we're smarter than the dinosaurs," said the official, referring to the asteroid that wiped out the dinosaurs and many other species 65 million years ago. An asteroid in the 7- to 10-meter range would be about half as wide as the one that broke up over Russia. That's far too small to pose any threat to Earth, even if the space rock was coming directly at our planet. But the captured asteroid could provide valuable insights for dealing with bigger ones in the future. 

Initial preparations for the mission won't have to wait for a deal to end budget sequestration, or approval of the budget for the 2014 fiscal year. NASA would begin immediately to identify the asteroid for retrieval, and take advantage of existing efforts funded by the agency's science, technology and human exploration directorates. The most expensive element of the plan, the multibillion-dollar Orion/SLS launch system, is already being funded under the terms of an agreement with Congress.

Discussions with NASA's international and commercial partners will continue in the months and years ahead, the official said. The retrieved asteroid could conceivably become a target for other scientific missions or asteroid-mining operations. In the process, governments might have to address issues surrounding the ownership and exploitation of space resources.

"We're trying to force the question," the official said. "We're trying to push the envelope on this new frontier."

Questions raised
Some observers have already raised questions about the plan, based on the advance reports. Scott Pace, the director of George Washington University's Space Policy Institute, told The Associated Press that it was a bad idea on scientific as well as diplomatic grounds. It would be better for the United States to join forces with other countries to conduct a comprehensive survey of all potentially dangerous asteroids, Pace said.

Rick Tumlinson, chairman of an asteroid-mining venture called Deep Space Industries, said he was concerned that NASA's asteroid mission might interfere with private-sector efforts — and he called on NASA to rely on private enterprise wherever possible. The administration official assured NBC News that cooperation with commercial ventures as well as other groups such as the B612 Foundation was part of the plan.

The official noted that the mission would provide a relatively low-cost route to satisfying President Barack Obama's goal of sending astronauts to a near-Earth asteroid by 2025. The lessons learned during the mission could be applied to future missions aimed at diverting other asteroids — perhaps to head off a potential threat, or conduct further scientific study, or exploit the potentially valuable resources that asteroids contain.

After the asteroid mission, NASA would turn its attention to a farther-out destination: Mars. The Obama administration has called for astronauts to travel to the Red Planet and its moons by the mid-2030s, and that would be the next major target for space exploration. The administration official told NBC News that other concepts, such as sending astronauts back to the moon or creating a deep-space platform beyond the far side of the moon, are not on the agenda for the foreseeable future. 

More about asteroids:

• Asteroid miners get boost from NASA
• Senator says asteroid mission is in the works
• Cosmic Log archive on asteroids

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

Planetary Resources

An artist's concept shows Planetary Resources' Arkyd Interceptor spacecraft closing in on an asteroid.

Commercial ventures are planning to send out profit-hunting missions to asteroids by the year 2020 — but in the shorter term, they're bringing in money by developing technologies that may show up on NASA spacecraft before they're put to use commercially.

For example, NASA said this week that it would award up to $125,000 to Arkyd Astronautics for a software system that would allow spacecraft to maneuver autonomously in close proximity with near-Earth asteroids — or the International Space Station. "Companies like SpaceX and others providing commercial resupply services to the ISS, as well as vehicles like HTV and ATV, could benefit from the proposed software," Arkyd said in its proposal.

So who's behind Arkyd Astronautics? Arkyd is actually an old code name for the Planetary Resources asteroid-mining company.

Planetary Resources' ultimate goal is to identify promising near-Earth asteroids, and then process the water and the precious metals they contain. The metals could be used in space or transported back to Earth, while the water could be turned into breathable air and rocket fuel for deep-space missions. If the reality matches the vision, asteroid mining could become a multitrillion-dollar industry. "It's just waiting to be had," said the company's co-founder and co-chairman, Eric Anderson.

The software system that won NASA's backing, known as COARSE, could be used on the spacecraft that Planetary Resources will send to asteroids. But it could conceivably be used before that on NASA's OSIRIS-REx mission, which is due for launch to a near-Earth asteroid in 2016. The same dual-use principle applies to a $124.960 NASA grant that Planetary Resources won last year for work on a laser-based communication system for small satellites.

Planetary Resources has said it is also receiving funding from the Pentagon's Defense Advanced Research Projects Agency. "With reference to DARPA, the company cannot comment on any specific project work at this time," company president Chris Lewicki told NBC News in an emailed statement. "When appropriate, more details will be released."

By themselves, technology development contracts from NASA and DARPA won't get Planetary Resources to the company's near-Earth nirvana. But the income stream serves as a supplement to the money put into the venture by billionaire investors such as Google's Larry Page and Eric Schmidt.

More funding ahead
There could be more government funding ahead: Last month, Aviation Week reported that NASA was planning to ask for $100 million as a down payment on a multibillion-dollar mission to corral a 23-foot-wide (7-meter-wide) asteroid and bring it to the vicinity of the moon for study. Also last month, lawmakers hinted that they'd support increased funding for asteroid research, particularly in light of February's meteor blast over Russia.

That beefed-up government spending could be seen as competition for commercial asteroid ventures — but it's more likely to turn into an opportunity.

"Let's create a cooperative situation from the very beginning, where different companies get a chance to participate and use some of that taxpayer money to catalyze the beginning of an industrial economy in space," said Rick Tumlinson, chairman of Deep Space Industries.

Like Planetary Resources, Deep Space Industries is trying to get into the asteroid-mining business — and looking for closer-to-home opportunities in the meantime. Tumlinson said his company is in the midst of discussions with NASA officials about potential deals. He doesn't mind the fact that he's competing with Planetary Resources for the business.

"One company is an anomaly. Two companies is an industry," Tumlinson said.

Selling technology
Both companies want to capitalize on technologies long before they hit the asteroid jackpot: Deep Space Industries touts 3-D printers that can turn ground-up metal into high-strength parts, even in zero gravity. Planetary Resources, meanwhile, plans to sell its Arkyd space telescopes for Earth observation or space exploration.

"If you wanted to send a camera to Mars or Venus, you could do it yourself," Planetary Resources' Anderson said.

Anderson provided an update on Planetary Resources' plans this week during a Hacker News Seattle meet-up. Here are some of the high points:

• The first prototype telescope is now scheduled to launch within about 22 months, most likely as a secondary payload on a rocket yet to be determined. That's roughly a year later than the initial projections, but Anderson told NBC News that the time frame was dependent on launch opportunities.
• Eventually, swarms of six to 12 probes would be sent out to near-Earth asteroids. Anderson said the first such deep-space reconnaissance mission could be launched in five to seven years.
• One of the asteroids on Anderson's "top 20 list" of prospects is an object cataloged as 2011 UW158, which is about a kilometer (half a mile) wide. The travel time for a space probe would be a little more than half a year, and if 2011 UW158 could be successfully mined, the value of the raw materials could range from $300 billion to $5.4 trillion, Anderson said. "That is a nice piece of rock," he said.
• Platinum-group metals, or PGMs, are among the most valuable (and most talked about) resources that asteroids could yield. The price of platinum is currently just a bit less than the price of gold — about $1,520 per ounce. Anderson said a single 500-meter-wide (quarter-mile-wide) asteroid could contain more platinum than has been mined during the history of humanity. Planetary Resources is looking at a process that would turn the extracted platinum into 220-pound, 7-foot-wide "wiffleballs" of foamed metal that could be sent down through the atmosphere without breaking up. The balls would hit the ground at a velocity of about 60 mph.

Is all this doable? Does it sound like pie (or platinum) in the sky? Either way, feel free to share your view in the comment section below.

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

Congress got the word from NASA on Tuesday about its options for dealing with the threats posed by asteroids and comets: Lawmakers can either provide adequate funding for detecting and characterizing near-Earth objects, and diverting them if necessary — or they can pray.

Threats from space are generally the stuff of science-fiction movies such as "Armageddon" and "Deep Impact," but members of the House Science Committee took a hard look at the realities during Tuesday's hearing, which came in response to the Feb. 15 meteor explosion over Russia as well as a close encounter that same day with a much bigger asteroid known as 2012 DA14.

The lawmakers didn't always like what they heard. The committee's chairman, Rep. Lamar Smith, R-Texas, told the panelists more than once that the progress report they delivered was "not reassuring." But representatives from both parties were receptive to the idea of putting more resources into the effort to counter cosmic threats.

White House science adviser John Holdren noted that the funding devoted annually to cataloging potentially threatening asteroids has risen from $5 million to more than $20 million over the past couple of years. But even at that level, NASA Administrator Charles Bolden estimated that it would take until 2030 to catalog 90 percent of the near-Earth objects between 140 meters and 1 kilometer in width, as mandated by Congress.  

"Maybe we can help you out with the budget. Don't know," Smith replied. He said "we need to find ways to prioritize NASA's projects."

Holdren said the single most useful project would be to put an infrared-sensing telescope in a Venus-like orbit, like the Sentinel Space Telescope being developed by the nonprofit B612 Foundation. The telescope could look for asteroids that currently can't be spotted from the ground because they spend much of their time within Earth's orbit, where they're lost in the sun's glare. The 55-foot-wide (17-meter-wide) rock that blew up without warning over Chelyabinsk in Russia last month was just such an asteroid.

"It came from a direction where our [existing] telescopes could not look," Holdren said. "We cannot look in the sun." 

Don Davis

Artwork by Don Davis shows a meteor streaking across the skies over the Russian city of Chelyabinsk. More of Davis' work is available at his website, DonaldEDavis.com.

Holdren estimated the cost of an asteroid-hunting space telescope at $500 million to $750 million, and said it could reduce the congressionally mandated survey time to six to eight years. Following through on the Obama administration's plan to send astronauts to a near-Earth asteroid by 2025 would cost about $2 billion a year, Holdren said.

The automatic spending cuts known as sequestration will affect NASA's asteroid-hunting effort as well as the plans for human exploration, Bolden warned.

"The president has a plan. But that plan is incremental," Bolden said, referring to the Obama administration's budget proposal. "And if we want to save the planet, because I think that’s what we’re talking about, then we have to get together ... and decide how we’re going to execute that plan."

The idea of enlisting other countries as well as amateur astronomers to "crowdsource" the hunt for threatening asteroids struck a responsive chord with lawmakers. But Rep. Dana Rohrabacher, R-Calif., reminded Bolden that China couldn't be on the list of partners due to a congressional ban.

Congressional teach-in
The hearing served as a teach-in for some of the panel members. At one point, Rep. Randy Weber, R-Texas, asked whether the $8.8 billion James Webb Space Telescope could be retrofitted to look for asteroids. "No, sir," Bolden replied. At another point, Gen. William Shelton, head of the Air Force Space Command, had to explain to lawmakers that the space-based surveillance system used for monitoring missile launches on Earth could not watch out for rocks coming in from deep space.

Holdren and Bolden provided a status report on the asteroid search, reporting that about 95 percent of the near-Earth objects larger than a kilometer are being tracked. However, only about 10 percent of the 13,000 to 20,000 asteroids bigger than 140 meters have been detected. If an asteroid of that size were to strike land, it "could devastate the better part of a continent," Holdren said.

Looking on the bright side, Holdren added that such asteroids are thought to hit Earth only every 20,000 years or so.

Bolden said less than 1 percent of the space rocks in the 30- to 100-meter range have been found. Such asteroids may not be continent-killers, but they are bigger and more potentially destructive than last month's Chelyabinsk meteor.

Lawmakers repeatedly asked how much advance warning would be required to deflect a threatening asteroid, and were repeatedly told that it would take years. Shelton said that if time was limited, "probably nuclear energy is what we're talking about." But even a nuclear-armed mission to blast an asteroid, Bruce Willis-style, would require lots of lead time. Rep. Bill Posey, R-Fla., asked Bolden about the strategy for dealing with an Earth-threatening asteroid that was discovered with three weeks' warning.

"If it's coming in three weeks ... pray," Bolden said. "The reason I can't do anything in the next three weeks is because for decades we have put it off."

More about threats from space:

• 'Marsageddon' comet adds to concerns
• The global plan to deal with asteroids
• Cosmic Log archive on asteroids

Ali Weinberg is an associate producer with NBC News in Washington.

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

Chris Smith / NASA file

An artist's conception shows a comet streaking through Martian skies.

It sounds like an "Armageddon" sequel, set on Mars instead of Earth: A supermassive doomsday comet is heading toward the planet in 2014, and there's nothing anyone can do about it. Not even Bruce Willis.

The comet presents a good-news, bad-news situation for the Red Planet, and for us earthlings as well. NASA says Comet 2013 A1, also known as Comet Siding Spring, is almost certain to miss Mars on Oct. 19, 2014. However, there's still a chance — a less than a 1-in-600 chance — that Mars could be hit, due to the remaining uncertainty about the comet's path. That uncertainty is likely to be cleared up over the next few months, eventually resulting in an all-clear.

Even if the comet did hit, there'd be no negative effect on Earth. However, the "Marsageddon" scenario is already adding to the concern that was generated by last month's Russian meteor blast and a near-miss by a larger asteroid.

The case of Comet Siding Spring led Henry Vanderbilt, founder of the Space Access Society, to ask a scary what-if question. "If it was coming straight at us (no more or less likely than it coming straight at Mars), and given our existing space capabilities, could we do anything about it other than prepare to die?" he wrote in a posting to the Moon and Back blog. "The short answer is: Maybe."

The comet's size is the most worrisome part of the story. Based on its observed brightness, astronomers estimate that the iceball could be anywhere from 9 to 30 miles (15 to 50 kilometers) in diameter. In comparison, the asteroid that's been blamed for killing off the dinosaurs 65 million years ago is thought to have been 6 miles (10 kilometers) in diameter.

A direct hit on Mars' backside wouldn't tear the planet apart, but it would produce an explosion that Bad Astronomy's Phil Plait estimates at somewhere around a billion megatons of TNT. That would create a huge crater, blast tons of debris into space and perhaps set off a flood reminiscent of the one that washed over Marte Vallis millions of years ago.

On Earth, the impact would be a civilization-killer.

How do you stop something like that? Scientists have proposed a variety of deflection techniques for smaller objects, when the collision threat can be detected years or even decades in advance. Those techniques range from space-based gravity tractors, to paintball shooters, to laser blasters, to laser bees, to solar sails, to "Armageddon"-style nuclear bombs. Just this week, Iowa State University's Asteroid Deflection Research Center proposed a $500 million mission to test a nuclear-armed asteroid interceptor.

"It's not a laughing matter," center director Bong Wie said in a news release.

There would definitely be no one laughing if a 20-mile-wide comet were coming at us with less than two years of advance warning. In that scenario, the only realistic option would be hydrogen bombs, and lots of them. Vanderbilt estimates it would take about 250 megatons' worth of energy to divert an object like Comet Siding Spring. At 1 to 5 megatons per bomb, that would mean 50 to 250 bombs from the nuclear powers' stockpile. 

"Whether we can effectively apply that energy to successfully divert the comet, we just don’t know," Vanderbilt wrote. "The problem has been studied a fair amount, and the answers vary. Nobody’s actually tested it. We would, under the circumstances, have little choice but to try."

For the time being, Comet Siding Spring is shaping up as a huge near-miss: NASA's Jet Propulsion Laboratory's latest estimate has it missing Mars by about 31,000 miles (50,000 kilometers) — and at that distance, not even the debris flying off the comet is expected to affect the Red Planet or the probes flying around it. It helps that the comet's tail will be pointing away from the planet, as explained in this blog posting by the Planetary Society's Emily Lakdawalla.

The comet would make an impressive sight if you were watching it from Mars (magnitude zero or brighter), and NASA's rovers will likely be doing just that. But it isn't expected to reach naked-eye brightness for earthly observers. Chances are that Comet Siding Spring will make its biggest impact as another reminder that we have to address the perils posed by cosmic threats sooner or later.

Considering what's happened over the past month, how many more reminders do we need?

More about cosmic threats:

• What's worse, asteroids or comets?
• Experts: Don't blame comet for culture's doom
• Cosmic Log archive on asteroids

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

Don Davis

Artwork by Don Davis shows a meteor streaking over Chelyabinsk. More of Davis' art is on his website.

Now that they've worked out the orbital path of the meteor that blew up over Russia last month, scientists are saying that the asteroid behind the blast crossed Earth's orbit regularly for thousands of years. Two weeks ago, it looked as if the 1.1 million residents of the city of Chelyabinsk had been hit by a cosmic stroke of bad luck — but now they're talking about turning the most powerful asteroid impact in more than a century into a tourist attraction.

The Feb. 15 aerial explosion and the shock wave it set off caused an estimated $33 million in property damage, much of it in the form of shattered windows and weakened walls. It also injured about 1,200 people, with most of them hurt by the flying glass from those windows. Authorities started the cleanup work almost immediately, while researchers rushed to figure out the scale of the explosion.

Based on the readings from infrasound sensors stationed all over the world to monitor nuclear-weapons tests, NASA said the energy release was equivalent to 500 kilotons of TNT, or roughly 30 times the energy released by the atomic bomb dropped on Hiroshima at the end of World War II. That translated into an object about 17 meters (55 feet wide), weighing 10,000 tons. The space agency said it was the biggest cosmic impact recognized since the 1908 Tunguska asteroid blast that leveled millions of trees in Siberia.

Less than a week after the blast, Colombian astronomers worked out a rough orbital path for the Chelyabinsk asteroid, based on an analysis of the videos captured by dashboard cameras and traffic cams in the area. On Friday, NASA produced a more definitive orbital track, based not only on the videos but also on the readings from the federal government's space sensors. The report took advantage of a recently signed agreement with the Air Force Space Command for the public release of previously hush-hush data.

Sizing up a superbolide
Friday's assessment is the first entry in a new NASA database for fireballs and bolide reports, which classifies the Chelyabinsk meteor as a "superbolide."

The latest readings confirm the conclusion that the object's orbit ranged from the main asteroid belt, beyond the orbit of Mars, to well within Earth's orbit. They also show that the Chelyabinsk asteroid's approach couldn't have been detected by ground-based optical telescopes because the space rock was hidden in the sun's glare.

P. Chodas et al. / NASA / JPL-Caltech

An orbital diagram shows the pre-impact orbit of the asteroid that blew up over Russia on Feb. 15, based on the track of its atmospheric entry. The asteroid came at Earth from the sunward side.

"The impactor had likely been following this orbit for many thousands of years, crossing the Earth's orbit every time on its outbound leg," NASA's Near-Earth Object Program Office said in Friday's assessment.

The fresh readings tweaked previous estimates of the object's size and brightness as well: NASA said the meteor was 17 to 20 meters wide (55 to 65 feet wide), and reached peak brightness at an altitude of 14.5 miles (23.3 kilometers), when it was traveling at a speed of 41,760 mph (18.6 kilometers per second). There's also quite a bit of discussion about the energy release — and why the new estimate for impact energy (440 kilotons, which includes energy lost during atmospheric entry) is so much bigger than the fireball's radiated energy (90 kilotons, which applies only to the blast).

From the get-go, astronomers have said that the Russian meteor was not connected with the close flyby of a much bigger asteroid, known as 2012 DA14, which took place later on the same day. Friday's assessment confirms that lack of a connection — not only because the two orbital paths were markedly different, but also because the two asteroids had different compositions.

NASA said a spectral analysis of 2012 DA14, conducted by researchers at the Massachusetts Institute of Technology, suggests that the asteroid is a relatively rare carbonaceous chondrite "with abundant calcium- and aluminum-rich inclusions."

"On the other hand, meteorite fragments being recovered from the fireball event are reported as silicate-rich ordinary chondrites, a completely different and unrelated class of meteorites," NASA said. "About 80 percent of all meteorite falls are in the ordinary chondrite category." 

Andrei Romanov / Reuters

A local resident shows a fragment thought to be part of a meteorite collected in a snow-covered field in the Yetkulski region, outside the city of Chelyabinsk.

Taking pride in a superbolide
Scientists may classify the Russian meteorites as an unremarkable kind of space rock, but they're extra-special to the folks in Chelyabinsk. For one thing, such meteorites could be worth more than their weight in gold on the collectors' market. Some have estimated their value at $2,200 per gram. For another thing, the region's residents are now talking about capitalizing on the international interest generated by the impact.

"Space sent us a gift, and we need to make use of it," Natalia Gritsay, head of the region’s tourism department, told Bloomberg News this week. "We need our own Eiffel Tower or Statue of Liberty."

Among the ideas being debated: building a "Meteor Disneyland" theme park that re-creates the glass-shattering event, or organizing a cosmic music and fireworks festival, or erecting a beacon-tipped pyramid at nearby Chebarkul Lake, where meteorite fragments have been found. Tourist companies are already starting to sell group tours to Chelyabinsk at $800 a person, Bloomberg News reported.

When the meteor exploded, many of the region's residents feared that it was a plane crash, or a missile strike, or even the end of the world. Now it's starting to look as if the superbolide is the best thing to hit Chelyabinsk in years.

“Nobody had heard about us, and now all the world knows,” the region's governor, Mikhail Yurevich, told Bloomberg News. “We can earn some dividends on that."

Slideshow: Meteor streaks over Siberia

Yekaterina Pustynnikova / Chelyabinsk.ru via AP

Click through scenes from Russia's Chelyabinsk region, where a huge meteor fireball set off alarms, injured hundreds of people and caused a factory roof to collapse.

Launch slideshow

More about the meteor:

• Experts get set for the next asteroid
• How to 'hear' the Russian meteor
• NBCNews.com archive on asteroids

Tip o' the Log to space illustrator Don Davis and Spike MacPhee.

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

The meteor that blew up over the Russian city of Chelyabinsk 11 days ago has provided a new focus for the effort to establish an international asteroid warning system, one of NASA's top experts on the issue says.

Lindley Johnson, the executive for the Near Earth Object Observation Program at NASA Headquarters in Washington, said that the Feb. 15 impact is certain to become "by far the best-documented meteor and meteorite in history" — but at the time, he and his colleagues could hardly believe it was happening.

"Our first reaction was, 'This can't be. ... This must be some test of a missile that's gone awry,'" Johnson told NBC News.

The Chelyabinsk meteor exploded at an estimated altitude of 12 miles (20 kilometers) over the city of 1.1 million in Russia's Urals Mountains, setting off a shock wave that blew out windows, caused an estimated $33 million in property damage and injured more than 1,200 people.

It was doubly coincidental for Johnson and his colleagues: The meteor was thought to have been caused by the breakup of a 17-meter-wide (55-foot-wide), 10,000-ton asteroid that entered Earth's atmosphere and released the equivalent of 500 kilotons of TNT in explosive energy. All this happened just hours before a 45-meter-wide (150-foot-wide) asteroid, capable of setting off a city-killing blast, passed within 17,200 miles (27,680 kilometers) of our planet. Adding to that coincidence, researchers from around the world were gathered in Vienna for talks aimed at moving forward with an international network to deal with ... asteroid threats!

The spectacle in Russia "certainly brought renewed interest to our efforts here," said Johnson, a leader of NASA's delegation to the Vienna talks.

He said the recommendations from the researchers were "well-received" and are moving up the ladder to the next phase in a U.N.-led process for addressing outer-space threats. An action plan could be considered by the U.N. Committee on the Peaceful Uses of Outer Space during its next meeting in Vienna in June.

Johnson summarized the three main points of the recommendations:

• Set up an international asteroid warning network, or IAWN, supported with existing detection assets but incorporating additional contributions. "The basis of such a network already exists," Johnson said, thanks to NASA, the European Space Agency, the International Astronomical Union's Minor Planet Center and the NEODyS asteroid-tracking center at the University of Pisa in Italy. NASA also has partnered with the U.S. Air Force to share tracking data about near-Earth objects. Just this week, a $25 million Canadian-built satellite known as NEOSSat was launched to look for small asteroids in Earth-threatening orbits.
• Bring the world's space agencies together in a new working group called the Space Mission Planning and Advisory Group — also known as SMPAG (pronounced like "Same Page"). The group's purpose, Johnson said, would be to "get all the agencies on the 'same page' as far as assessing what capabilities could be brought to bear should there be a threatening asteroid detected."
• Put asteroid experts in contact with countries around the world, to advise disaster response agencies about the nature of a potential impact event — that is, the area expected to be affected, the potential effects and the scale of the evacuation if necessary. "It's an offshoot of the warning network," Johnson said. If the asteroid behind the Russian meteor had been detected in advance, for example, the expert network might have advised emergency workers about the potential for a midair blast and the resulting shock wave (although Johnson said he was "surprised" by the shock wave's effect).

Until last year, NASA spent about $4 million a year to track near-Earth objects, or NEOs, and Johnson said the program "has accomplished quite a bit in the relatively short time that it's been in existence." About 95 percent of the potentially threatening asteroids bigger than a kilometer (half-mile) wide have been detected. However, now NASA is working on charting the asteroids down to a width of 100 meters (330 feet). To fund that more difficult task, the annual funding level for NEO research was raised to $20 million a year.

NASA is using that money to beef up its capabilities for spotting smaller asteroids, through programs such as the Asteroid Terrestrial-impact Last Alert System, or ATLAS, which is due to get $5 million over the next five years. Less than a million dollars a year is going toward studies aimed at figuring out what to do if a threatening asteroid is found, Johnson said. After all, you have to identify the risky rocks before you can do anything about them. The potential strategies range from diverting it gently with the aid of gravity tractors or space paintball guns, to blasting it with nukes, Bruce Willis-style.

"It really depends on the scenario that we'd be faced with," Johnson said. "It depends on how big the object is. It depends on how long we have to do something about it. And if we do the search-and-detection job right, we will find a potential hazard many years if not decades before it becomes an immediate threat. There may be technologies available at that time that we never thought about. I don't get too worked up about trying to find an immediate technology that we've got to have right now to do that. Our focus is to find them as early as we can, and have the maximum amount of time to do something about it."

Update for 7:30 p.m. ET Feb. 26: Looking for a practical tip? The large majority of the people injured by the meteor blast were hurt by flying glass, which led Johnson to give this advice during a Vienna news conference: "When you see a white flash and a large trail in the sky, it's probably not a good time to stand at the window and look at it, because it may be a blast coming."

Update for 8:15 p.m. ET Feb. 26: As reported in Technology Review's Physics arXiv Blog, Colombian researchers used video from dashboard cameras and other sources to reconstruct the orbital path of the Russian meteor — and they classified it as an Apollo asteroid, a type of space rock whose path crosses Earth's orbit. That's consistent with NASA's analysis, which said the asteroid traced an orbit that ranged between the main asteroid belt and the region of outer space inside Earth's orbit.

"The preliminary orbit indicates it takes about 2.1 years to go around the sun once ... so this thing was out at its farthest distance from the sun roughly a year ago," Bill Cooke, head of the Meteoroid Environments Office at NASA's Marshall Space Flight Center, told reporters during a Feb. 15 teleconference.

The space rock was on its way back out toward the main asteroid belt, coming from Earth's sunward side, when it entered the atmosphere and blew up. That's why it wasn't possible to predict the impact in advance: At a width of 55 feet, the object was too small to show up in traditional sky surveys, and it would have been lost in the sun's glare during its final approach.

So far, searchers have recovered just bits and pieces of the shattered space boulder. "The largest I've heard is a kilogram and a half," or about three pounds, Johnson told NBC News. 

Slideshow: Meteor streaks over Siberia

Yekaterina Pustynnikova / Chelyabinsk.ru via AP

Click through scenes from Russia's Chelyabinsk region, where a huge meteor fireball set off alarms, injured hundreds of people and caused a factory roof to collapse.

Launch slideshow

More about asteroids:

• How about blasting 'em with lasers?
• How to 'hear' the Russian meteor
• Asteroids vs. comets: Threats compared
• NBCNews.com archive on asteroids

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

This story was originally published on Tue Feb 26, 2013 6:23 PM EST

A pixelated profile from NASA's Goldstone radar dish makes the passing asteroid 2012 DA14 look a bit like an out-of-control Viper space fighter from "Battlestar Galactica." But the real-life asteroid is almost five times as big, and might well pack a bigger wallop if it ever hit our planet.

NASA's Jet Propulsion Laboratory on Tuesday released a movie combining 73 radar images of 2012 DA14, captured over the course of eight hours on the night of Feb. 15-16. The image resolution is 13 feet (4 meters) per pixel.

In a news release, NASA said the images show the roughly 130-foot-long (40-meter-long) asteroid moving away from us, at a distance ranging from 74,000 miles to 195,000 miles (120,000 to 314,000 kilometers). These readings were made just hours after the time of closest approach, when the asteroid came within 17,200 miles (27,680 kilometers) of our planet.

2012 DA14's close encounter on Feb. 15 was eclipsed by the nuclear-scale impact of a meteor over the Russian city of Chelyabinsk earlier in the day — a widely witnessed event that caused more than 1,200 injuries and did an estimated $33 million in damage. NASA said the asteroid behind Russia's meteoric display was about a third the size of 2012 DA14.

If 2012 DA14 had hit instead, the damage would have been much, much worse. Experts have compared the bigger space rock to the object that blew up over a Siberian forest in 1908, knocking down millions of trees over an 820-square-mile area. As it is, the Russian meteor rates as the biggest observed cosmic impact since Siberia's Tunguska event.

JPL's radar observations, which continue through Wednesday, are aimed at fine-tuning the calculations of 2012 DA14's future orbit by getting a better fix on its size, shape, rotation, surface features and surface roughness. For what it's worth, the asteroid's estimated length of 40 meters along its long axis is between four and five times the length of the Colonial Viper spacecraft that buzzed the Cylons in the "Battlestar Galactica" TV series.

The asteroid's path was perturbed by Earth's gravitational field in such a way that it won't come as close in the foreseeable future. However, a better understanding of its orbit and its composition could help scientists prepare for encounters with other asteroids — and figure out the best way to divert potentially threatening near-Earth objects.

The radar observation campaign is led by JPL's Lance Benner and Marina Brozovic.

Here are a more views of 2012 DA14 from other observers:

An international team led by MIT's Nicholas Moskovitz observed asteroid 2012 DA14 with a number of telescopes, including the 2.1-meter telescope at Kitt Peak National Observatory. This animated image shows the asteroid as it was leaving Earth's vicinity. Check out the National Optical Astronomy Observatory's news release for more information. If you missed seeing the animation, click here for a refreshed view.

More about the asteroid:

• Watch a passing asteroid fade out
• How it rates among asteroid hits and misses
• Earth kicks asteroid into safer orbit
• NBCNews.com's asteroid archive

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

This story was originally published on Tue Feb 19, 2013 5:24 PM EST

Slideshow: Meteor streaks over Siberia

Yekaterina Pustynnikova / Chelyabinsk.ru via AP

Click through scenes from Russia's Chelyabinsk region, where a huge meteor fireball set off alarms, injured hundreds of people and caused a factory roof to collapse.

Launch slideshow

Scientists have raised their estimates of the size and power of what turns out to be the most widely witnessed asteroid strike in modern history. The size estimate puts the object that caused Friday's meteor blast over Russia in a troublesome category of asteroids: big enough to cause damage, but small enough to evade detection.

The new estimates, based on additional readings from a sensor network built to detect nuclear blasts, suggest the meteor released the energy equivalent of nearly 500 kilotons of TNT. That's about 30 times the power of the Hiroshima atomic bomb.

Experts have been assessing the level of the meteor explosion using a network of infrasound sensors that were set up under the terms of the Comprehensive Test Ban Treaty to check for changes in atmospheric pressure caused by nuclear blasts.

"These new estimates were generated using new data that had been collected by five additional infrasound stations located around the world — the first recording of the event being in Alaska, over 6,500 kilometers away from Chelyabinsk," NASA's Jet Propulsion Laboratory said in a statement.

NASA now says the Chelyabinsk object must have been about 55 feet wide (17 meters wide) with a mass of 10,000 tons before it entered Earth’s atmosphere.

"We would expect an event of this magnitude to occur once every 100 years on average," Paul Chodas of NASA's Near-Earth Object Program Office said in the statement. "When you have a fireball of this size, we would expect a large number of meteorites to reach the surface, and in this case there were probably some large ones."

Searchers have been focusing on a frozen lake about 50 miles (80 kilometers) west of Chelyabinsk, where they suspect meteorite fragments made a 20-foot-wide (6-meter-wide) hole in the ice. Searchers have found fragments up to a half-inch wide (1 centimeter wide) that might have come from the meteor, but nothing bigger yet, according to reports from Russia.

Experts emphasized once again that the meteor's trajectory was significantly different from the path of asteroid 2012 DA14, a 150-foot-wide (45-meter-wide) space rock that passed harmlessly within 17,200 miles (27,600 kilometers) of Earth later Friday. Thus, 2012 DA14 was "a completely unrelated object," NASA said.

The space agency said Friday's Russian meteor was the largest reported since 1908, when an asteroid roughly the size of 2012 DA14 exploded over a remote wooded area in Siberia's Tunguska region. That blast flattened millions of trees over a 820-square-mile area, but was not widely seen. Friday's event, in contrast, took place over a city of 1.1 million inhabitants, and hundreds of millions more watched the videos that were distributed over the Internet.

As powerful as the meteor blast was, it's on the low end of the asteroid impact scale. Astronomers estimate that there are about a million potentially hazardous near-Earth objects smaller than 100 meters (330 feet) in width, and only about 1 percent of those have been cataloged. For the time being, NASA is focusing on detecting and tracking near-Earth asteroids wider than 100 meters.

But what about the smaller ones?

"Defending the Earth against tiny asteroids such as the one that passed over Siberia and impacted there is a challenging issue. That is something that is not currently our goal," Chodas told reporters on Friday.

The asteroid behind Friday's meteor blast would have been particularly hard to spot during its final approach, because it was coming from Earth's daylit side. The asteroid would have been lost in the sun's glare and undetectable by ground-based telescopes, said Bill Cooke, the head of the Meteoroid Environment Center at NASA's Marshall Space Flight Center.

Several programs on the horizon hold the promise of finding the smaller asteroids that could threaten Earth:

• NASA has just started funding the Asteroid Terrestrial-impact Last Alert System, or ATLAS, which aims to establish two telescopes in Hawaii dedicated to scanning the skies for potential threats.
• The non-profit B612 Foundation has been raising money to launch its Sentinel Space Telescope as early as 2018. Sentinel would scan Earth's surroundings from an outward-looking position in a Venus-like orbit, interior to Earth's orbit. Such a project could provide advance warning for asteroids like the one that blew up on Friday. Former Apollo astronaut Rusty Schweickart, one of the foundation's founders, said he was "overwhelmed" by requests for information after Friday's blast. "It's pretty bonkers at the moment," he told NBC News.
• Planetary Resources, a commercial venture, is developing a fleet of Arkyd-100 space telescopes to identify near-Earth asteroids, in hopes of sending mining operations to them in the decades to come. "As the company ultimately develops the capability and infrastructure for intercepting and mining asteroids, Planetary Resources expects to be able to help in the (slight) redirection of these rocks to keep the Earth safe," Peter Diamandis, the company's co-founder and co-chairman, said in a blog posting.
• Another commercial space-mining venture, Deep Space Industries, is proposing its own set of asteroid-hunting space telescopes. "Placing 10 of our small FireFly spacecraft into position to intercept close encounters would take four years and less than $100 million," David Gump, the company's CEO, said in a statement. "This will help the world develop the understanding needed to block later threats."

More about asteroids and meteors:

• Meteor? Asteroid? Terms get tangled
• Russian meteor blast outshone the sun
• System to vaporize asteroids is in the works
• NBCNews.com archive on asteroids

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

What exactly fell on Russia's Chelyabinsk region on Friday? Was it an asteroid, meteor, meteoroid, meteorite or fireball? You could make a case for "any of the above," depending on your definitions and the precise part of the phenomenon you're trying to describe.

The Chelyabinsk incident is the biggest known cosmic impact since another Russian blast that occurred a century ago, the Tunguska incident of 1908. There's good reason for that notoreity: Hundreds of injuries were reported. NASA estimated that the energy released by the Chelyabinsk impact amounted to 300 kilotons of TNT, which suggests the blast was more than 10 times as powerful as the atom bombs that were dropped on Japan at the end of World War II.

NASA's assessment put the Chelyabinsk object's width at 15 meters (50 feet), and its mass at 7,000 tons. Much of that mass burned up during the object's atmospheric entry at a velocity of 40,000 mph (18 kilometers per second). "The fireball was brighter than the sun," the space agency said in a statement.

Astronomers use different terms to describe cosmic objects of different sizes: When the rock is no wider than a meter (3.3 feet), it's known as a meteoroid. But once you start getting into the 1- to 10-meter range, the term "asteroid" applies. Earlier estimates suggested the Chelyabinsk object was a meteoroid, but the latest assessment would put it in the class of a small asteroid.

Bill Cooke, who heads the Meteoroid Environment Office at NASA's Marshall Space Center, said the object was "a small asteroid or a large meteoroid, depending on how you want to define it."

When pieces of the meteoroid (or asteroid) survive their fiery fall through the atmosphere and hit the surface, those pieces are called meteorites. Russian authorities say a hole in the ice on Chebarkul Lake, near Chelyabinsk, marks a spot where at least one meteorite left its mark. There are already reports of Chelyabinsk meteorites turning up on online auction sites, but those are more likely to be "meteor-wrongs" — rocks wrongly assumed to be meteorites.

Slideshow: Meteorite showers in Siberia

Yekaterina Pustynnikova / Chelyabinsk.ru via AP

A huge meteor flares through the skies over Russia's Chelyabinsk region, triggering a powerful shock wave that injured nearly a thousand people, blew out windows and reportedly caused the roof of a factory to collapse.

Launch slideshow

The term "meteor" refers to the fiery aerial display created by a falling meteoroid or asteroid. Meteors are called fireballs if they shine brighter than the planets in the night sky (magnitude -4), and bolides if the blast is even brighter (around magnitude -14). There's no question that the Chelyabinsk meteor qualifies as a bolide.

Some asteroids are made of iron and nickel, and survive their fall more easily. However, the fact that the Chelyabinsk object appeared to break up into pieces while it was still miles high indicates that it was made of less dense stuff. The stresses of atmospheric entry caused the rock to break apart explosively, creating the midair flash and generating a shock wave. The shock wave produced the loud "bang" that set off car alarms, blew out windows and apparently collapsed the roof of a zinc factory warehouse. Flying glass from all those broken windows caused many of the injuries that were reported.

What about the asteroid flyby?
The Chelyabinsk object streaked through Russian skies just hours before a 150-foot-wide (45-meter-wide) asteroid known as 2012 DA14 was due to make a remarkably close approach, coming within 17,200 miles of Earth's surface. However, the two objects were in dramatically different orbits, and that's one of the factors that led NASA to conclude that the two cosmic events were "not related."

"It's clearly coincidental, but it's a pretty amazing coincidence," said former Apollo astronaut Rusty Schweickart, a co-founder of the B612 Foundation. For years, Schweickart and his colleagues have been trying to raise awareness about the hazards posed by asteroids, and Friday's double dose of cosmic reality certainly serves as a consciousness-raiser.

"It's a torpedo across the bow," Schweickart told NBC News, "and it serves as an indication that these things really do happen."

Objects as small as the Chelyabinsk asteroid are difficult to detect — but the feat is not impossible, given the right circumstances. In 2008, a 2- to 5-meter-wide asteroid known as 2008 TC3 was spotted using the Catalina Sky Survey 1.5-meter telescope in Arizona, 20 hours before its impact in the Sudanese desert. The Chelyabinsk object would have been particularly hard to spot because it came in from the blind spot on Earth's sunlit side.

The Chelyabinsk object is no more, but there are still lots of other space rocks to be found. In 2011, NASA estimated that there are a million potentially hazardous near-Earth asteroids smaller than 100 meters (330 feet). Several organizations — including NASA, the B612 Foundation and Planetary Resources — are working on plans to detect and track more of the threats that are out there. To learn more about those efforts, click on the links below:

• Asteroid activists seek funds for space telescope
• Asteroid mining venture starts with space telescopes
• Asteroids vs. comets: NASA expert assesses threats

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

This story was originally published on Fri Feb 15, 2013 1:34 PM EST

Asteroid 2012 DA14 has made its closest pass of Earth, just a scant 17,200 miles from our surface, and now astronomers are watching it recede harmlessly into the cosmos. You can watch it, too, thanks to a variety of webcasts.

The time of closest approach came at 2:25 p.m. ET, as scheduled, when the asteroid was zooming above the eastern Indian Ocean at a speed of almost 17,500 mph (7.8 kilometers per second). It was too dim to see with the naked eye, but observers in Australia, Asia and Europe could follow it with binoculars or small telescopes.

"It's on its way out now," said Paul Chodas, an astronomer with the Near-Earth Object Program Office at NASA's Jet Propulsion Laboratory in Pasadena, Calif.  

Read: Meteor vs. asteroid? Terms get tangled when describing space rocks 

Chodas and his colleagues monitored 2012 DA14 with high-powered optical telescopes and huge radar dishes to learn more about the asteroid's color, shape, spin and reflectivity. Such data could tell them what the object is made of, and perhaps provide insights into how similar objects could be diverted if they were on a threatening course.

Experts estimate that asteroids the size of 2012 DA14 hit our planet every 1,200 years or so, exploding with the energy of a 2.5-megaton atomic bomb: The last such impact struck a remote region of Siberia without warning in 1908, flattening 820 square miles of forest. If an object that big were to hit in just the wrong place, it could wipe out a city. Coincidentally, a much smaller space rock came down over Russia on Friday, sparking a fireball and a glass-shattering shock wave.

Even though the 150-foot-wide (45-meter-wide) asteroid 2012 DA14 is the biggest object of its kind to be seen coming this close to Earth, its orbit is so well-known that NASA's Near-Earth Object Program can rule out any chance of collision in the foreseeable future. And even though 2012 flew 5,000 miles closer than satellites in geosynchronous orbit, NASA said its mostly south-to-north orbital path went through a "sweet spot" that kept it far away from those satellites — as well as from other spacecraft that are in closer orbits, including the International Space Station.

Astronomer hope their observations of 2012 DA14 will provide insights into subtle phenomena such as seismic disturbances that are induced by Earth's gravitational kick, or characteristics of the asteroid's spin that are affected by radiation absorption and emission.

This animated set of three images shows 2012 DA14 as it was observed by the Faulkes Telescope South in Australia on Feb. 14 at a distance of 465,000 miles. The asteroid is the moving bright spot in the middle. NASA's website provides details. Credit: LCOGT / E. Gomez / Faulkes South / Remanzacco Observatory.

Radar readings provide the best way to get a fix on the asteroid's shape and spin, in part because observations from multiple radio telescopes can be combined to produce a clearer picture. During the 2012 DA14 encounter, scientists used radio telescopes in California and New Mexico to produce new sets of radar imagery.

The first pictures from NASA's 230-foot (70-meter) dish at Goldstone, Calif., are due to be released on Saturday, and eventually those radar images will be combined to produce a 3-D map of the space rock.

Other telescopes, spread out from Australia to Israel to the Canary Islands to the U.S., gathered optical data — and the images from some of those telescopes were shared over the Internet on Friday. NASA's Jet Propulsion Laboratory has been passing along pictures from a variety of telescopes via its Ustream video channel. Here's a rundown of other post-encounter webcasts:

5 p.m. ET: The Virtual Telescope Project 2.0 presents live video of the asteroid flyby from a telescope in Italy, weather permitting. Video site: Watch Virtual Telescope Project's webcast.

6 p.m. ET: Weather permitting, the Clay Center Observatory in Massachusetts will stream real-time, high-definition video from 6 p.m. ET until 4 a.m. ET Saturday. Watch Clay Center video on Ustream.

9 p.m. ET: Slooh Space Camera plans to present several live shows about the asteroid flyby, accompanied by expert commentary. Weather permitting, imagery will be beamed to Slooh HQ from telescopes on the Canary Islands and in Arizona. Watch the show on Slooh.com.

9 p.m. ET: A video feed of the flyby from a telescope at NASA's Marshall Space Flight Center will be streamed for three hours. During the live-streaming event, viewers can ask researchers questions about the flyby via Twitter or the Ustream chat window. Watch Marshall's Ustream channel.

Chodas said the initial observations confirmed scientists' estimates of 2012 DA14's size, but other revelations will have to wait until astronomers have had a chance to analyze the data collected on Friday. By that time, the asteroid will be long gone. Earth's gravitational influence has changed 2012 DA14's orbit to keep it farther away from our planet during future orbits.

"It won't return for many, many years," he said.

More about the asteroid encounter:

• How 2012 DA14 rates among asteroid hits and misses
• Would-be miners say asteroid is worth $195 billion
• Hooray! Earth will kick asteroid into a safer orbit
• Flash interactive: Close encounters of the asteroid kind
• NBCNews.com's archive on asteroids

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

This story was originally published on Fri Feb 15, 2013 7:51 AM EST