Radar observations made during this week's close encounter with the asteroid Apophis have ruled out the risk of a catastrophic cosmic collision in 2036, NASA says. Experts say it'll be much farther away at that time than it is right now.

The crucial readings came on Wednesday when the space rock, which is thought to measure at least 885 feet (270 meters wide), approached within 9 million miles (14.5 million kilometers) of Earth. NASA is monitoring Apophis with its 230-foot (70-meter) Goldstone radio dish in California. Optical readings also have come in from the Magdalena Ridge Observatory in New Mexico and the Pan-STARRS observatory in Hawaii.

The bottom line? "We have effectively ruled out the possibility of an Earth impact by Apophis in 2036," Don Yeomans, manager of NASA's Near-Earth Object Program Office at the Jet Propulsion Laboratory, said today in the all-clear news release. "The impact odds as they stand now are less than one in a million, which makes us comfortable saying we can effectively rule out an Earth impact in 2036. Our interest in asteroid Apophis will essentially be for its scientific interest for the foreseeable future."

Jon Giorgini, who developed JPL's online Horizons database to keep track of solar system objects, would go even further. He says that according to calculations based on the Goldstone data, Apophis will probably pass by Earth at a distance of 36 million miles (58 million kilometers, or 0.39 AU), and absolutely no closer than 14 million miles (22 million kilometers, or 0.15 AU). "That is a very extreme minimum," he told NBC News. "Nothing else plausible can get you closer."

Apophis, a.k.a. 2004 MN4, created a huge splash when it was discovered in 2004 because the initial assessment of its orbit gave a 1-in-40 chance of Earth impact in 2029. That would be catastrophic: The space rock is big enough to wipe out a city if it struck land, or create killer tsunami waves if it splashed into the ocean.

Additional orbital data quickly eliminated the risk for 2029, but showed that it would pass within 20,000 miles (32,000 kilometers) of our planet at that time. That's so close that Earth's gravitational field will perturb Apophis' orbit. The experts worried that if the asteroid passed through a particular half-mile-wide zone in space, known as a "keyhole," its orbit would be perturbed just enough to set up a smash-up during the 2036 encounter. Fortunately, the latest observations indicate that Apophis will miss the keyhole by a long shot.

Did I just hear a cosmic sigh of relief?

UH / IA

The asteroid Apophis, highlighted here by a white circle, was discovered in June 2004.

There are still a few uncertainties surrounding Apophis: Astronomers don't yet have enough data to determine how the asteroid is spinning or how solar radiation is affecting its orbital path — a phenomenon known as the Yarkovsky effect. Giorgini said that even under the worst-case scenario, the effect won't push Apophis into a collision in 2036. But there could conceivably be other risky encounters in the decades or centuries ahead.

"There's a non-linear amplification that can really move it around more," Giorgini said.

Also, there are questions about Apophis' exact size. Just this week, readings from the European Space Agency's Herschel space telescope suggested that the asteroid may be nearly 20 percent bigger than previously thought. But that larger size estimate is based on the assumption that Apophis is a spheroid, and astronomers already know that it's elongated.

"We're not seeing that larger size in the radar data," Giorgini said.

By the end of next month, continued radar observations from Goldstone as well as the Arecibo Observatory in Puerto Rico should give astronomers a much better fix on Apophis' spin and its size. When those factors are fully accounted for, the Jet Propulsion Observatory will update its official risk assessment for Apophis — and could take this bad boy off the hit list for good.

Update for 6:30 p.m. ET: Clark Chapman, senior scientist at the Southwest Research Institute, weighed in on the current state of the asteroid hunt in an email:

"One thing you should be aware of, and might mention, is that the next Planetary Defense Conference, an every-two-year international meeting, will be held April 15-19 in Flagstaff, Arizona. ... Some presentations are already listed in the program, which should be finalized a week from now, which is the due date for abstracts.

"An interesting tie-in with the new observations of Apophis is that a similar thing happened with 2011 AG5 a few weeks ago, when observations with the huge Gemini telescope in Hawaii showed that it would, in 2023, miss the roughly 350-km-wide 'keyhole' and, therefore, not strike the Earth in 2040.  Prior to these critical observations, the chance of a 2040 impact was unusually high (though still low in everyday terms) at 1 in 500.

"A point to be realized is that while the chances of impact in these cases are very low by ordinary standards, they aren't zero, and the consequences of an impact could be very terrible, so it is important to plan and prepare for the possibility of impact until it is ruled out.

"It was important to get these observations of AG5 in the autumn of 2012, because if it had turned out that AG5 was actually on an impact trajectory, it would have given us an additional year to mount a deflection mission and succeed in deflecting it from the 2023 keyhole. Without making a major observational effort with a very large telescope this autumn, the next routine observational opportunity wasn't until this coming autumn."

Update for 8:30 p.m. ET: One of NASA's experts on the asteroid threat and two former NASA astronauts have weighed in on the report about Apophis. David Morrison of NASA's Ames Research Center sent these comments via email:

"One possible angle is the recent proposal from [NASA Administrator] Charlie Bolden, based on a Keck study, that we retrieve a 7-meter carbonaceous near-Earth asteroid and bring it into lunar orbit. There are many questions about this idea, but the one I have in mind is our assumed ability, without Sentinel, to find 7-meter C-type asteroids in Earthlike orbits. If you can't find them, you can’t protect against them, or do anything with them as potential resources." 

Now here's an email from Ed Lu, a veteran of two space shuttle missions and an extended stay on the International Space Station. Lu now serves as chairman and CEO of the B612 Foundation, which is planning to launch the Sentinel space telescope to track half a million near-Earth asteroids:

"While it is great that Apophis is much better understood, and we know it won't hit us in 2036, the greatest danger from an asteroid strike is from the ones we haven't yet found.  Of asteroids larger than the one that struck Tunguska in 1908, we know of less than 1 percent of them.  And as David Morrison points out, we can't protect ourselves from the unknown asteroids (or make use of them either). The B612 Foundation Sentinel Space Telescope is going to work on finding and tracking these asteroids."

And here are some comments from Apollo 9 astronaut Rusty Schweickart, who has played a key role in raising awareness about the threats and opportunities presented by near-Earth objects. It was Schweickart who warned in the wake of Hurricane Katrina that asteroids like Apophis could spark a much more devastating "cosmic Katrina":    

"I'm hoping that you don’t follow the bad (surprisingly wide) precedent of stating that [the risk from] Apophis has been eliminated.  Please look on the JPL risk page  and especially the more detailed info and note that 1) The 2036 impact possibility is, while significantly reduced, still possible, and 2) that the 2068 impact possibility is now elevated ... to a level that exceeds what the 2036 impact was prior to this apparition.

"There’s certainly good news re the 2036 impact decreasing in probability ... but frankly it was 1 in 234,000 prior to the new observations ... not exactly an impact probability to worry one. (There are many NEOs with higher impact probability ... but no one pays attention to them ... they aren't the 'poster child' that Apophis is.) My personal reaction was one of surprise that the new 2036 impact was not zero!

"But/And ... there are more radar observations to integrate in ... as well as optical tracking both now and for the next several years.  Apophis isn't going away ... the impact possibilities are simply shifting around a bit with refinement of the tracking data. 2036 is now less probable; 2068 is now more probable (but still very low).

"Until JPL and the other guys get more data (enough to really define the Yarkovsky effect), we really won’t be able to get definitive data for longer time scales that we can rely on."

JPL's Giorgini said the risk assessment that Schweickart mentioned won't be full updated until after Goldstone and Arecibo finish their observational campaign in mid-February — so there may still be a non-zero risk listed until then. But Giorgini is confident that the 2036 risk will disappear when all the observations are factored in. (As of this writing, the estimated risk of collision is listed at 1 chance out of 10,989,000.) But you're right, Rusty: In order to eliminate the risk completely, astronomers will have to get more data about Apophis' physical characteristics. And then there are all those other unknown killer asteroids that might be out to get us...

More doomsday worries addressed:

• Asteroid 2012 DA14 won't hit Earth next month
• Asteroid 2011 AG5 won't hit Earth in 2040
• This year's big comets won't pose a threat
• Asteroid-hunting telescope to be launched in 2017

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.

NASA

The view out the front of NASA's Multi-Mission Space Exploration Vehicle simulator features an image of the asteroid Itokawa, which was visited by Japan's Hayabusa probe in 2005. Itokawa serves as the model for the Desert RATS' simulated mission to a near-Earth asteroid.

NASA's Desert RATS team is ready to begin a visit to a near-Earth asteroid next week — a simulated mission, that is.

Since 1997, the Desert RATS crew have conducted summer simulations aimed at trying out the robots and other tools that may come into play during future exploration missions beyond Earth orbit. The "Desert" part of the name refers to the usual locale for the exercises, in the Arizona desert, and "RATS" stands for "Research and Technology Studies."

This year is different: Instead of simulating surface operations on the moon or Mars, the team will focus on a zero-G visit to an asteroid, like the one NASA is planning for the mid-2020s. That means it's not so important to go out into the desert. As a result, this month's simulation is being run out of Building 9 at Johnson Space Center in Texas, the Desert RATS home base.

A mockup of NASA's Multi-Mission Space Exploration Vehicle, or MMSEV, has been outfitted with a display that will show a virtual-reality view of the asteroid Itokawa out the front windows.

"It curves around the windows of the vehicle as a projection," NASA spokeswoman Brandi Dean explained.

Four crew members will take turns living in the MMSEV and exploring their simulated asteroid, using Johnson Space Center's virtual-reality facilities — as well as a setup known as ARGOS (Active Response Gravity Offload System) that can suspend astronauts in the air to make them feel as if they're floating in microgravity.

James Blair / NASA

NASA astronaut Alvin Drew tries out the ARGOS system, which is designed to simulate microgravity.

Communications between the MMSEV and a mock mission control will be tweaked to simulate the light-speed travel time between Earth and an asteroid. There'll be a 50-second delay in voice transmission, going each way. And the MMSEV can move around to simulate the moves that an asteroid-bound crew might feel during a real mission. "We have it on a sled that we can put on an air-bearing floor," Dean said.

The Desert RATS exercise is due to get under way on Monday and run through Aug. 30, with Aug. 31 set aside as a contingency day. After all, even a mission to a make-believe asteroid may require a one-day extension.

To keep up with the RATS pack, check out the team's website, Facebook page and Twitter stream.

Where in the Cosmos
The picture of the MMSEV with a simulated asteroid looming in front of the windshield served as today's puzzle picture for our weekly "Where in the Cosmos" contest on the Cosmic Log Facebook page. It didn't take long for Dug Patnaude and Andrew Russell to figure out that the picture showed a simulated MMSEV — and to reward their quick wits and typing fingers, I'm willing to send them 3-D glasses, courtesy of Microsoft Research's WorldWide Telescope project. Those red-blue spectacles will come in handy for watching this 3-D video of asteroid Itokawa. Want to get in on the fun? Click the "like" button for the Cosmic Log Facebook page and limber up your fingers for next Friday's contest.

More about mission simulations:

• Astronauts complete undersea asteroid mission
• Crew selected to explore food's final frontier
• Pale-faced crew emerges from mock Mars mission

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.

NASA

Crew members for the current NASA Extreme Environment Mission Operations simulation, or NEEMO, float around a porthole 63 feet below the Atlantic Ocean's surface at the Aquarius Reef Base undersea research habitat. The crew is led by NASA astronaut Dottie Metcalf-Lindenburger and also includes Japan's Kimiya Yui, the European Space Agency's Timothy Peake and Cornell astronomer Steven Squyres. Aquarius team member James Talacek peers out from the porthole.

If NASA’s underwater practice session is any indication of what a real space mission to an asteroid will be like, you can expect to follow along with the exploration of a near-Earth asteroid via Facebook, Twitter and the Web — or whatever takes their place by the year 2025. There’s a string of chats and webcasts that let you in on the action at the Aquarius deep-sea habitat during the simulated mission, known as NEEMO 16.

As the "16" suggests, the space agency has been doing NEEMO — NASA Extreme Environment Mission Operations — for more than a decade. The idea is to simulate the logistics associated with an extended space mission, as well as the isolation, by sending an astronaut crew into the Aquarius, 63 feet (19 meters) below the Atlantic Ocean's surface in the Florida Keys, and have them practice the routines they'd be doing in scuba gear.

This summer's 12-day simulation began on Monday with the four-person crew's "splashdown" into the sea. The NEEMO 16 crew is headed by NASA astronaut Dottie Metcalf-Lindenburger, who flew into space on the shuttle Discovery in 2010, and also includes Japanese astronaut Kimiya Yui, British astronaut Timothy Peake and Cornell astronomer Steve Squyres (who's the top scientist on the Mars rover team, the chairman of the NASA Advisory Council, and a veteran of NEEMO 15). Aquarius habitat technicians Justin Brown and James Talacek play support roles underwater.

Last year marked the first time that the NEEMO exercise was designed in line with the space agency's current plan to send a crew to a near-Earth asteroid by 2025. This year, the four-person crew will bring even more of a sense of realism to the simulation: For instance, they're communicating with an onshore Mission Control team on a delayed basis, to reflect the light travel times that would be involved with a deep-space mission.

They're also experimenting with different ways to explore an asteroid-style surface. Because a small asteroid has nearly negligible gravity, astronauts won't be able to tramp across it as if it were Earth or even the moon. One option would be to use attachment points and handholds to move across the asteroid surface. Another option would be to use mini-spacecraft to hover over and touch down on the surface. Both techniques are being tested during NEEMO 16.

During the latter part of the simulation, Nuytco's DeepWorker one-person submersibles will be deployed for underwater excursions by the NEEMO aquanauts. "They get flown around the reef with their personal transporters," Saul Rosser, operations director for the Aquarius Reef Base, told me today.

The crew members also plan to conduct a variety of experiments that play off the fact that the atmospheric pressure inside the Aquarius habitat is equal to the surrounding water pressure at depth — which is about 2.5 times the air pressure at the surface. The experiments will show whether simple tasks such as blowing a bubble or operating a remote-controlled device are tougher at high pressure than they are at normal pressure.

To add a social-media angle, folks who are following the NEEMO mission will be invited to predict the outcome of each experiment. Starting on Thursday, watch for announcements on the following forums: NASA's NEEMO Facebook page and Twitter account, the JSC Education Facebook page and "Teaching From Space" Twitter account, and the European Space Agency's Facebook page and Twitter account. This NASA Web page provides details on how to compete, and what you can win. 

You can also monitor the NEEMO 16 mission via the this Ustream live-video page or this Aquarius webcam page, and watch for updates on Flickr and YouTube. Web-streamed educational activities are planned every day for the next week and beyond, in cooperation with the Challenger Center for Space Science Education. The interactive webcasts will be supplemented by chat capability.

The Aquarius Reef Base is the world's only undersea research station, situated three and a half miles (5.6 kilometers) off Key Largo on a sandy patch of seafloor sitting next to spectacular coral reefs. It's owned by the National Oceanic and Atmospheric Administration and operated by the University of North Carolina at Wilmington. NEEMO ranks among the highlights of Aquarius' research season, but Rosser said there's more to come.

This year marks the 50th anniversary of Aquarius' founding, and to mark the occasion, Rosser and his colleagues are planning an underwater extravaganza next month. He was reluctant to provide the details, but a sneak peek that was posted online says the golden-anniversary mission will be led by two pioneers of marine science, Sylvia Earle and Mark Patterson.

"Stay tuned," Rosser said.

More about NEEMO and Aquarius:

• Astronauts go deep for undersea 'asteroid' trip 
• NASA halts undersea mission due to hurricane
• Aquanauts live in a scientific fishbowl

Alan Boyle is msnbc.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. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

Space entrepreneurs laid out a lot of the details for their billionaire-backed plan to extract resources from near-Earth asteroids today, but other details — such as how much they've received in investments, or exactly how they'll get their hands on precious water and precious metals — are still being held close to the vest.

If Planetary Resources is as successful as its founders hope, it could be bringing a fortune in platinum and gold back to Earth within the next decade or two, and supplying outer-space filling stations with water, fuel and air for interplanetary travelers. The company could tap into trillions of dollars' worth of space resources. But the venture could also go bust, just as some of the first European trading companies did when they came to the Americas centuries ago.

"There's a significant probability that we may fail," company co-chairman Eric Anderson acknowledged during today's big reveal at Seattle's Museum of Flight.

At least two things are certain: Planetary Resources is already bringing in income, and it's intending to launch real hardware within two years. "This company is not about paper studies. .... We're not just talking about it. We've done enough of that," Anderson said.

The company was founded in 2009 by Anderson and Peter Diamandis, but flew under the radar until last week. Both men have had long experience with space and technology ventures: Anderson heads Space Adventures, the company that has brokered eight private-passenger trips to the International Space Station. He also serves as president of Intentional Software, the company founded by billionaire space traveler Charles Simonyi. Diamandis is co-founder of the X Prize Foundation (which awarded a $10 million spaceflight prize in 2004), Zero G Corp. (which puts passengers on zero-gravity airplane flights) and the Rocket Racing League (which is currently in neutral).

Stephen Brashear / Getty Images

Planetary Resources' president and chief engineer, Chris Lewicki, shows off a full-scale mockup of the Arkyd Series 100 space telescope during a news conference at Seattle's Museum of Flight. "Good morning, everyone. I'm Chris Lewicki, and I'm an asteroid miner," he told the crowd.

This latest venture has the backing of Simonyi as well as other billionaires, ranging from Google's Larry Page and Eric Schmidt to Silicon Valley's Ram Shriram and Texas' Ross Perot Jr. (son of the former third-party presidential candidate). The company's advisers include filmmaker/adventurer James Cameron and astronaut/scientist Tom Jones.

Planetary Resources

An informational graphic explains Planetary Resources' perspective on a future "gold rush." Click on the image for a larger version.

Planetary Resources' executives declined to say how much the backers were putting into the business, but Diamandis touted them as "risk-tolerant investors" who were prepared to support the venture for decades. He also said "the company is cash-flow positive at this point," with about 20 engineers working at the company's headquarters in Bellevue, Wash. And there are still more openings to fill, which is a big reason why the company's executives decided to go public now.

Former Mars mission manager Chris Lewicki, who serves as the company's president and chief engineer, said the company had a contract with NASA to share data about the development a laser-equipped spacecraft system that combined imaging, optical communications and navigation. He hinted that there were other contracts as well, but wouldn't provide details.

Step 1: Launch space telescopes
The system will be used on Planetary Resources' first-generation spacecraft, the Arkyd Series 100 space telescope, also known as Leo. As Lewicki told me in a previous interview, the Arkyd Series 100 will serve as the company's Earth-orbiting survey telescope for identifying asteroids. It will also be sold to other parties for use as a "personal space telescope" or Earth-imaging satellite. He said the price tag for the telescope would be on the order of tens of millions of dollars, and eventually mere millions of dollars.

The Leo telescope would be built to have "multi-tool or Swiss Army knife capability," Lewicki said. Its imager would be capable of doing spectral analysis of near-Earth asteroids, to determine their chemical composition. There'd also be a camera mounted on a boom so it could take pictures of itself. The Museum of Flight's president, Doug King, said he and his institutional colleagues might someday consider becoming customers.

With a mass of 66 to 110 pounds (30 to 50 kilograms), the spacecraft would be small enough to launch as a secondary "rideshare" payload on any of a variety of launch vehicles, including the SpaceX Falcon, the Russian Dnepr or the European Ariane. The first launch is expected within two years, Anderson said.

Planetary Resources' prime targets would be among the estimated 1,500 asteroids that are energetically easier to get to than the moon. The team would be looking for water-rich or metal-rich asteroids that come close enough to Earth for a more detailed survey to be made. 

Step 2: Go beyond Earth orbit
The asteroid survey effort would continue with the Arkyd Series 200 "Interceptor," which would be equipped with a propulsion system and scientific instruments as well as an imager. Such craft could be placed into geosynchronous Earth orbit as a secondary payload — then identify, track and fly past asteroids that happen to come between Earth and the moon. Lewicki told me that the interceptor craft could get "up-close and personal" with a near-Earth asteroid within five years.

Planetary Resources

An artist's conception shows the Arkyd Series 200 spacecraft tracking an asteroid.

Planetary Resources

A swarm of Arkyd Series 300 spacecraft conducts reconnaissance on an asteroid.

Step 3: Swarm around an asteroid
The Arkyd Series 300 "Rendezvous Prospector" spacecraft would incorporate the laser-based communication system, enabling a swarm of probes to surround a distant asteroid for coordinated reconnaissance. "Within a decade, we hope to have identified our first target that we'll start extracting resources from," Diamandis told me. The Series 300 would demonstrate technologies that could be used for interplanetary missions by NASA or other entities.

Lewicki said the mission plan called for sending multiple low-cost spacecraft so that the failure of one probe wouldn't doom the mission. "When failure is not an option, success gets really expensive," he quipped.

Step 4: Get the goods
Later generations of spacecraft would have the capability to extract water from carbonaceous asteroids. If there's power available for a space processing system, the water could be broken down into hydrogen for rocket fuel and oxygen for breathable air. Such materials could be stockpiled in orbital or deep-space fuel depots, to be fed to spacecraft in need of a fill-up. Diamandis said a 165-foot-wide (50-meter-wide) asteroid with 20 percent water ice content could provide enough hydrogen and oxygen to power every space shuttle that ever blasted off.

The first goal for resource extraction would probably be a water-bearing asteroid, Diamandis told me, but eventually techniques would be developed for extracting gold and platinum-group metals from promising asteroids and returning the shipments to Earth. Platinum-group metals are particularly valued because they're used in a wide variety of high-tech devices, ranging from consumer electronics to fuel cells for electric vehicles. Platinum currently goes for more than $1,500 an ounce, which makes it almost as costly as gold.

If those valuable metals could be brought back from space at an affordable price, that could create a multitrillion-dollar shift in high-tech markets.

Hurdles to overcome
That's a big "if." In order for Step 4 to succeed, there'd have to be sufficient demand for deep-space refueling. Right now, there's zero demand, but that could change if NASA actually goes through with its current plan to send astronauts to a near-Earth asteroid by the mid-2020s and to Mars and its moons by the mid-2030s.

Planetary Resources' long-term business plan assumes that in the next few decades, there'll be enough spaceship traffic to recover its investment in asteroid-mining infrastructure. The precise shape of that infrastructure is yet to be determined: One illustration provided by Planetary Resources shows swarms of spacecraft doing strip mining, while another shows a water-bearing asteroid being enveloped by a huge inflatable shell.

One option might be to capture a small asteroid and bring it closer to Earth for processing. This month, a study prepared for the Keck Institute for Space Studies at Caltech determined it would be feasible to capture a 500-ton, 23-foot-wide (7-meter-wide) asteroid and transport it to a lunar-scale orbit. Mission cost was estimated at $2.6 billion, which is about the same cost as NASA's Mars Science Laboratory mission. The members of the study group included Lewicki and Jones as well as John Lewis, who has been studying the prospects for asteroid mining for decades and is serving as an adviser to Planetary Resources.

Mining a 23-foot-wide asteroid won't produce as much of a payoff as the 165-foot-wide asteroid that Diamandis had in mind, but the bigger the asteroid, the more difficult it would be to bring it closer to Earth. There might also be risks associated with moving space rocks or even platinum shipments around our planet's celestial neighborhood.

"The energy equivalent of a medium-sized 'ore wagon' in space, if it fell to Earth, would be on the order of a hydrogen bomb," NBC space analyst James Oberg said in an email. (That might be an exaggeration. The fireball that blazed over California and Nevada early Sunday is thought to have been caused by a meteor about the size of a minivan, with the energy equivalent of 3.8 kilotons of TNT. That's roughly a quarter of the explosive power of the Hiroshima atom bomb.)

"Carl Sagan long ago warned that building asteroid-deflecting technologies had a dark side — the same technology could be used to steer asteroids directly at Earth for military threats," Oberg wrote. "Fortunately, Sagan's fears were science-based and not spaceflight operationally based. It turns out to take far too long — years in flight — to actually drop a space rock on Earth. And the ability to deflect space objects safely away from Earth, or into commercial mining zones, is nowhere near accurate enough to do the opposite — aim for Earth itself.

"But the issue is a perfect rallying cry for environmental activists who can be counted on to rally against this looting of heaven's virginal treasures."

If Planetary Resources' long-term plan is successful, that could force nations to face the long-dormant issue of property rights in outer space. Oberg said widescale commercial exploitation of space resources could spark a diplomatic outcry, "at least until the United Nations gets some acknowledged 'tax' on any space-based profits." That issue is at least a decade away, however.

Even if Planetary Resources doesn't hit its long-term goal, the earlier phases of its business plan — the data deals and the spacecraft sales — would still give the billionaires an opportunity to recoup their investment. And it's virtually certain that other companies will eventually join the fray. For example, a venture called Moon Express is chasing after a share of the $30 million Google Lunar X Prize and making plans for mining operations on the moon. Just today, Moon Express announced the expansion of its scientific advisory board.

"We don't believe you have to wait around for a date with a near-Earth object," Bob Richards, the venture's co-founder and CEO, told me in an email. "If you want to mine asteroids, go to the moon  —  they have been bombarding the moon for billions of years."

How would you rate the chances for Planetary Resources, Moon Express and other would-be extraterrestrial miners? Feel free to cast your vote and/or leave a comment.

More about space resources:

• Asteroid mining venture starts with space telescopes
• Google billionaires back space resource venture
• Could legal loophole lead to extraterrestrial land claims?
• Private property in outer space? It's debatable
• To infinity and beyond: Investing in space travel
• How to make the moon pay

Alan Boyle is msnbc.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter or adding Cosmic Log's Google+ page to your circle. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for other worlds.

Planetary Society

Researchers are looking into the possibility of sending a swarm of "laser bee" satellites to deflect a potentially hazardous asteroid, as shown in this artist's conception.

How do you solve a problem like Apophis? For years, researchers have been tracking the asteroid to determine whether or not it could get into a catastrophic smash-up with Earth on Friday the 13th in April 2036. Last week, Russian reports suggested that Moscow is thinking about launching a probe to Apophis as early as 2015 to track the threat, but U.S. experts say it's the wrong idea for the wrong asteroid.

So what's the right idea? They have a modest proposal that just might save the planet someday.

First, here's a little more background on Apophis: The 885-foot-wide (270-meter-wide) space rock was discovered in 2004 and set alarm bells ringing when experts said it had a 1-in-40 chance of hitting Earth in 2036, due to the uncertainty about its orbit. Since then, astronomers have gotten a better fix on Apophis' parameters and set the chances of collision at 1 in 240,000 or so. Some uncertainty remains, because if the asteroid passes through a relatively small region of space known as a "keyhole" in 2029, Earth's gravitational pull would deflect its course just enough to guarantee the hit in 2036.

Last week, the Russian Academy of Sciences recommended sending a small, radioisotope-powered probe with a radio beacon on board, so that astronomers could get a high-precision fix on Apophis' trajectory. "From a technical point of view, the mission could be started for implementation from 2015," the academy was quoted as saying by the RIA Novosti news service.

I ran that idea past several experts on the asteroid threat, and the consensus was that you almost certainly wouldn't need that kind of mission to rule out a collision threat. Retired astronaut Rusty Schweickart, who has become deeply involved in studying potential threats from near-Earth objects and how to address them, noted that there's an excellent opportunity for high-precision, Earth-based observations of the asteroid coming up in early 2013. Another opportunity comes along in 2021. Chances are that the upcoming observations will turn Apophis into a complete non-threat.

"Why, given this circumstance, the Russians would send a probe to Apophis in order to pin down its impact probability is indeed puzzling," he told me in an email.

Scientific value
That's not to say a trip to Apophis would be totally useless. Far from it.

"I would support a mission to study Apophis, either a lander or an 'orbiter' rendezvous mission," David Morrison, director of the SETI Institute's Carl Sagan Center for Study of Life in the Universe, wrote in email. "I wish the Russians luck. This fascinating object is a favorable target mostly because it will come so close to Earth in 2029, so that ground-based observations can be made in synergy with in situ measurements."  

Clark Chapman, a planetary scientist at the Southwest Research Institute, agreed that there are plenty of good scientific reasons for studying Apophis up close. "It is expected that the tidal effects on the body could change its characteristics markedly ... and I know a number of colleagues who would like to see such a mission," Chapman wrote. But based on RIA Novosti's report, the kind of mission that the Russians are contemplating may not fill the bill. In fact, it could do more harm than good.

"I wouldn't totally dismiss the concerns about physically interacting with Apophis during its close approach," Chapman said. "If a spacecraft were actually to dock with it, there is the possibility of interfering with the natural responses that are of interest ... and, in the extremely low-probability case that Apophis were right at the threshold of passing through a keyhole, tampering with it could raise legal issues.  I'm not aware that anyone has deeply thought through these concerns."

The right target
All three of the experts are giving deep thought to another potentially threatening asteroid, a 460-foot-wide (140-meter-wide) rock that's been designated 2011 AG5. Right now, the rock has been given a 1-in-500 chance of hitting Earth on Feb. 5, 2040, due to the uncertainties about its orbit and its location relative to a cosmic keyhole in 2023.

Schweickart has been calling on NASA to start making preliminary plans for a mission to 2011 AG5, just in case we need to get a better fix on its orbit between now and 2023. If observations over the next couple of years eliminate the possibility of a threat, hallelujah! But if they don't, and if we're still worried about AG5, we'll have a head start on the asteroid deflection campaign.

"So it would seem that Russia is heading toward the wrong object!" Schweickart wrote. "There could hardly be a better example of the need, not currently in place, for international coordination when it comes to NEO [near-Earth object] impact analysis and deflection planning. So why aren't we?? Ask NASA. Please."

Chapman had a similar assessment: "I agree with Rusty that precisely determining the orbit of Apophis seems like a low priority at this time.  And I also agree that, as of now, 2011 AG5 is the near-Earth asteroid of interest."

Back in February, NASA's Jet Propulsion Laboratory issued a statement noting that there'll be good opportunities for observations of 2011 AG5 in late 2013 and late 2015. "I fully expect we will be able to significantly reduce or rule out entirely any impact probability for the foreseeable future," said Don Yeomans, manager of NASA's Near Earth Object Program Office.

Zapping vs. whacking
Even if Apophis and 2011 AG5 turn out to be totally harmless, it's not such a bad idea to have the plans for a "reference mission" to a worrisome asteroid ready to put into effect. And if it turns out that a future asteroid really is on a collision course, what should we do about it?

That brings us to another angle in the debate over near-Earth impacts: Some have suggested sending in the nukes. Others have proposed launching a "gravity tractor" to shepherd a threatening asteroid into a non-threatening orbit. Researchers at the University of Strathclyde in the Scottish city of Glasgow have been working on a different approach: using a swarm of solar-powered, laser-equipped satellites to blast away at the rock and deflect it.

They say their system could be effective with objects that are smaller than Apophis — say, 150 feet (50 meters) across, like the object that is thought to have blasted a Siberian forest to bits in 1908.

"We could reduce the threat posed by the potential collision with small- to medium-size objects using a flotilla of small agile spacecraft, each equipped with a highly efficient laser which is much more feasible than a single large spacecraft carrying a multi-megawatt [laser]," engineering professor Massimiliano Vasile said in a news release. "Our system is scalable, a larger asteroid would require adding one or more spacecraft to the flotilla, and intrinsically redundant. If one spacecraft fails, the others can continue."

Schweickart said researchers have been talking about zapping asteroids  for a few years. "I've never been able to convince myself that they've ever done any cost-effectiveness investigation ... assuming that they can actually solve the multitude of other technical issues inherent in the concept," he wrote.

It may well be that crashing one of the swarming satellites into an asteroid would have more of an effect on its trajectory than having the whole flotilla aim lasers at it, Schweickart said. In his email, he laid out the more likely scenario:

"It is difficult to take this proposal seriously when compared with the already available kinetic impact [KI] solution.  About the only advantage it has over a simple kinetic impact is that it would presumably be able to execute a precise orbit change (vs. the KI approximate orbit change).  However, in the last few years it has become generally accepted in the NEO deflection 'community' (such as it is!) that a gravity tractor capable 'observer' spacecraft would be pre-positioned to observe, verify, and ultimately precisely adjust (if necessary) the KI-generated orbit change.  The cost, current availability and simplicity of the KI/GT deflection concept is still the 'standard' against which other systems will have to be compared... and especially re their cost effectiveness."

Morrison agreed: "What is needed for deflection is to change the momentum of the asteroid in a controlled way. Surely a simple impact by a fast-moving interceptor is the most efficient way to do that, since the spacecraft is not required to brake and rendezvous, and then fly in formation with, the target."

Former astronaut Ed Lu, president and CEO of the B612 Foundation, also cast a vote for hitting an asteroid with something, if that's what needed to be done: "I couldn't agree more with Rusty's comment about how the real-life feasibility of such schemes needs to be taken into account.  The same could be said of suggestions that asteroids could simply be 'painted.'"

So it sounds as if the right course of action is to draw up the plans for a quick trip to a potentially hazardous asteroid, just in case we need some up-close reconnaissance, and working out a strategy for giving it a good whack if necessary. NASA's OSIRIS-Rex mission, due for launch in 2016, might serve as a good first step. The target for that $800 million mission is the asteroid 1999 RQ36, which has an ever-so-slight chance of threatening Earth in 2182. By then, we should have our anti-asteroid strategy well in hand. And who knows? We might even have to put the strategy into practice long before then.

Are we on the right track to avoid the dinosaurs' fate? Where would you rank the asteroid threat on your list of worries? Feel free to register your opinion in the vote above, and/or the comment space below.

Update for 1:40 a.m. ET April 13: I've made a few tweaks to the story in consultation with Schweickart. In an email, he said a successful asteroid deflection campaign requires two missions: first, an observer spacecraft to monitor the asteroid's position, and then a kinetic impact spacecraft to do the whacking:

"The observer spacecraft is more properly designated a 'transponder/gravity tractor' spacecraft ... the gravity tractor being potentially needed to adjust the NEO orbit slightly after the KI impact. Not either/or, but both/and. There should never be a KI deflection without a transponder/GT spacecraft in place before, during and after the KI impact. It's both/and."

Got it? On it!

More about asteroids:

• Asteroid debate rises to next level
• To fight off asteroids, humans must cooperate
• Largest digital camera hunts killer asteroids
• Here's how to counter a killer asteroid
• Interactive: Close encounters of the asteroid kind

Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter or following the Cosmic Log Google+ page. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

Bill Merline / SwRI / W.M. Keck Observatory

An infrared image produced by the W.M. Keck Observatory in Hawaii shows the asteroid 2005 YU55 as it receded on Nov. 8. Measurements suggest that the space rock was not as wide as originally thought.

The asteroid that had everybody excited on Tuesday is just another space rock today, but 2005 YU55 brought a surprise or two to scientists as it passed by.

As expected, YU55 zoomed harmlessly past our planet at a distance of roughly 198,000 miles (319,000 kilometers) on Tuesday, and made its closest approach to the moon hours afterward.

If the asteroid were on a collision course, Tuesday would have been a very bad day, marked by a cosmic blast equivalent to a 4,000-megaton super-duper nuclear bomb. Instead, it was a very good day for astronomers. They can use the insights gained during this flyby to figure out how near-Earth objects might behave during closer, potentially more dangerous encounters to come.

Scientists tracked the receding asteroid from the Keck Observatory in Hawaii, using an adaptive-optics imaging system, and produced some great infrared pictures (including the one you see above).

Over the next few days, the full data set will be analyzed and perhaps turned into a time-lapse movie, similar to the sequence created from radar imagery during YU55's approach, said Larry O'Hanlon, spokesman for the Keck Observatory. The pictures confirm that the asteroid looks more like an elongated potato than a beach ball, with its side-to-side diameter estimated at 240 meters (787 feet).

"Note that this puts the asteroid at about half the diameter of what previous researchers thought it was," O'Hanlon wrote in an email.

'Puzzling' readings
Meanwhile, researchers are analyzing the radar readings gathered by the Goldstone radio antenna in California.

"The animation reveals a number of puzzling structures on the surface that we don't yet understand," radar astronomer Lance Benner, the principal investigator for the YU55 observations, said in a news release from NASA's Jet Propulsion Laboratory. "To date, we've seen less than one-half of the surface, so we expect more surprises."

Radar observations from the Arecibo Observatory in Puerto Rico will be factored in as well.

Well-equipped amateurs captured some great shots in the visible-light spectrum. Mike Renzi combined hundreds of images from his Starhoo Observatory in Massachusetts to create this video, showing YU55 as a fast-moving dot among the stars:

Rick Fienberg, press officer for the American Astronomical Society, snapped this time-exposure picture of YU55's track through the night sky:

Richard Tresch Fienberg / AAS

This time-exposure picture from Rick Fienberg shows 2005 YU55's track through the star field. The contrast has been boosted to emphasize the track.

Here's what Fienberg said about the picture:

"I shot this at Phillips Academy in Andover, MA, using my Canon DSLR and the school's 80mm Orion refractor piggybacked on a 16-inch telescope. Asteroid (in Pegasus) is moving lower right to upper left (north is up, east is left), and each streak is 1 minute long, separated by 1-minute gaps (during which the camera was making dark frames). This is a stack of three 1-minute exposures."

For more pictures of YU55, check out SpaceWeather.com's post-encounter roundup — and mark your calendar for June 26, 2028, when an even bigger asteroid, 2001 WN5, is due to even come closer to Earth.

Update for 10:15 p.m. Nov. 9: Asteroid-hunting can be hazardous to your health, even if the space rock is 198,000 miles away from causing a catastrophic cosmic collision. Just ask the six teenagers who said they were held at gunpoint in Marion, Ohio, while trying to catch a glimpse of YU55.

Update for 2:30 a.m. Nov. 11: A member of the Cosmic Log Facebook community, John Giroux, sent along this time-lapse picture of YU55 streaking across the sky. "Thirty-seven images stacked, contrast and brightness adjusted, color removed," Giroux writes. "Seven minutes worth of tracking, from right to left. Note how the brightness periodically varied. The time frame is from approximately 21:23 EST until 21:30 EST, in the constellation Pegasus."

John Giroux

Asteroid 2005 YU55 shows up as a series of short streaks in this picture from John Giroux.

More about the encounter:

• Passing asteroid puts on a show
• Your guide to the asteroid encounter
• How to save our planet from a killer asteroid
• Could the asteroid destroy the moon? (No)
• Why radar's the best for tracking near-Earth objects
• Interactive: Close encounters of the asteroid kind

Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter or following the Cosmic Log Google+ page. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

Astronomers watched the asteroid 2005 YU55 spin as it zoomed harmlessly past Earth, and everybody else was looking over their shoulders. You can expect to see a huge pile of pictures now that the coal-dark space rock has passed by.

Even before the closest pass, NASA's Jet Propulsion Laboratory provided a six-frame "movie" based on radar data acquired by the Goldstone radio telescope on Monday. This sequence was captured from a distance of 860,000 miles (1.38 million kilometers).

The closest approach to Earth came at 6:28 p.m. ET Tuesday, when the quarter-mile-wide (400-meter-wide) asteroid slipped just barely within the orbit of the moon at a distance of 198,000 miles (319,000 kilometers). YU55 is due to come closest to the moon at 2:14 a.m. ET Wednesday, NASA said.

Neither the moon nor Earth was at risk during this flyby, but the information gathered this time around could help astronomers know what they're dealing with during potentially riskier encounters.

Here's a parting shot of YU55 from the 25-inch telescope at the Clay Center Observatory in Massachusetts, which tracked the asteroid as it swept past at 29,000 mph:

Clay Center Observatory

The speck near the center of this image is 2005 YU55 at the time of closest approach. The bright streaks are background stars.

In a Twitter update, NASA said that YU55 will make its next Earth flyby in 2015, "but at a greater distance than today." Today's encounter wasn't close enough to perturb the near-Earth asteroid's orbit, but experts are wondering whether a close flyby of Venus in 2029 will change its orbital path slightly.

Even if that Venus encounter does cause a change, Earth is in no danger from this particular space rock, at least for the next 100 years or so. Which is a good thing. If an object the size of YU55 were to hit land, experts say it would blast a 4-mile-wide, 1,700-foot-deep crater and set off a 7.0 earthquake. If it hit at sea, it would create a catastrophic tsunami with 70-foot-high waves.

The last time an asteroid as big as YU55 came this close was in 1976, and the next time will be in 2028 — or could it be sooner? Scientists recently estimated that thousands of asteroids around the size of YU55 remain to be discovered, so learning about this rock's composition and motion could help us deal with many other rocks to come. 

YU55 is particularly interesting because it has a high carbon content, which makes it coal-black. Such carbonaceous chondrites have been found to contain amino acids, and may have played a role in the origin of life on Earth. NASA's Osiris-Rex mission, due for launch in 2016, will target a carbonaceous asteroid called 1999 RQ36 and try to bring a sample back to Earth for study.

NASA's current space vision calls for sending astronauts to a near-Earth asteroid sometime in the mid-2020s, and the head of NASA's Near Earth Object Program, Don Yeomans, said that if he got the chance to decide the destination, he'd pick a carbon-bearing rock like YU55.

"This would be an ideal object," he told The Associated Press.

Still more about the encounter:

• Your guide to the asteroid encounter
• How to save our planet from a killer asteroid
• Could the asteroid destroy the moon? (No)
• Why radar's the best for tracking near-Earth objects
• Interactive: Close encounters of the asteroid kind

Correction for 3:45 p.m. ET: I originally wrote that the Clay Center Observatory's telescope was a 15-incher, but it's actually a 25-incher.

Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter or following the Cosmic Log Google+ page. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

Last updated 5:25 p.m. ET Nov. 8

The asteroid 2005 YU55 will pose no threat to Earth when it zooms by on Tuesday, but it will spark a frenzy of picture-taking and online chatting. So where do you find the good stuff?

The hottest action will be up in the sky: This space rock (which we'll call YU55 from here on out) is about a quarter-mile (400 meters) wide, which makes it wider than an aircraft carrier. It's due to zoom past us at 30,000 mph (50,000 kilometers per hour) at a minimum distance of 198,000 miles (319,000 kilometers) at 6:28 p.m. ET. That would bring it just within the orbit of the moon. But don't worry: YU55 is on course to miss the moon as well as Earth, and even if it did hit the lunar surface, the only thing that'd happen would be a fantastic fireworks show.

If YU55 did smash into Earth, it could conceivably turn a city into a smoking crater, or stir up a destructive tsunami. But the asteroid's orbital path doesn't pose any risk in the foreseeable future. It's not expected to have any effect on Earth's tides, or on seismic activity. From the cosmic perspective, this is no big deal. In fact, YU55 has come even closer to Earth over the centuries, but went undetected until just six years ago.

The fact that YU55 went unnoticed for so long does raise a question, however: What else are we missing out there?

The science team for NASA's Wide-field Infrared Survey Explorer recently estimated that more than 90 percent of the near-Earth asteroids wider than a kilometer (0.6 miles) have been identified, but that thousands of asteroids in YU55's size range still remain to be detected. That's why astronomers around the world are so interested in watching for YU55 during this go-round. Getting a close look at this space rock should provide good practice for monitoring other potentially hazardous asteroids.

Asteroid experts say the last time a space rock as big as YU55 came this close was in 1976, and the next time will be in 2028.

Watching it pass by
You won't be able to see YU55 zoom by with your naked eye. Even at its closest approach, the asteroid will be no brighter than magnitude 11 — much dimmer than the magnitude-6.5 threshold for naked-eye observations. Astronomers say you'd need something on the order of a 6-inch telescope, and you'd have to know exactly where to look.

Sky & Telescope's editors have offered viewing advice as well as charts that show YU55's progress through the constellations. If you have your telescope aimed in the right place, you should be able to see a starlike point moving from west to east. "It will be gliding fast enough to move along in real time as you watch using a moderately high-magnification eyepiece," Sky & Telescope says.

Sky & Telescope

Best seen from North America, the asteroid 2005 YU55 will race far across the constellations in just 11 hours on the night of Nov. 8-9. The times shown on this chart are GMT. Subtract five hours for Eastern Standard Time. Click on the image for a larger view.

Some amateur astronomers are involved in an effort to monitor variations in the asteroid's brightness during the encounter. Those variations can be used to determine how YU55 is rotating as it flies by. Check out this Sky & Telescope webpage for details.

Most of us won't be peering through telescopes when 6:28 p.m. ET rolls around. Instead, we'll be looking for pictures from the professionals. The best pictures are expected to come from radar observations: NASA's Goldstone radio telescope in California and the Arecibo observatory in Puerto Rico are the big guns in this field, but the National Radio Astronomy Organization will be putting other assets on the case as well, including the Green Bank Telescope in West Virginia, the Very Large Array in New Mexico, and the Very Long Baseline Array.

Other telescopes around the world will be watching as well. The Clay Center Observatory in Massachusetts, which became known for its telescopic imagery of high-flying SpaceShipOne, is planning to track the asteroid on video. Stay tuned for that imagery, which will be streamed online via msnbc.com as well as on Ustream and other outlets.

Watching it on the Web
NASA is offering two main portals to asteroid imagery: Asteroid and Comet Watch on the main NASA site, and Asteroid Watch on the Jet Propulsion Laboratory's website. Both those sites should feature the latest and greatest images available to the space agency, and you should be able to see movies of YU55's encounter by late Tuesday or Wednesday.

NASA has just released a new radar view of the asteroid, produced from Goldstone data at 2:45 p.m. ET Monday when it was about 860,000 miles (1.38 million kilometers) from Earth. The image looks pretty pixellated, but it nevertheless reveals what appear to be lumps and craters on the surface. Arecibo is due to join the observing campaign on Tuesday, and the pictures should get progressively better as the asteroid zooms closer.

NASA / JPL-Caltech

The radar image at left shows the asteroid 2005 YU55, as imaged by NASA's Goldstone radio telescope from a distance of 860,000 miles. At right, a diagram shows the asteroid's trajectory past Earth and the moon.

Another popular place to look for space imagery is SpaceWeather.com, which is already passing along intelligence for the flyby. If amateurs come up with cool pictures of YU55, you can bet some of them will appear on that website. Space.com is keeping close watch on the asteroid encounter, and we'll be sharing the best of their coverage.

French astrophotographer Thierry Legault has made a name for himself as the chronicler of fast-moving space phenomena, ranging from space shuttles and the International Space Station to high-flying satellites. I'd be surprised if he didn't at least attempt to catch YU55 on video as it flies by. And if you can read German, you'll enjoy science writer Daniel Fischer's live blog of the flyby.

Share what you see
Have you got questions about the asteroid, or about asteroids in general? The Washington Post's website is hosting a live online chat at 1:30 p.m. ET Tuesday with Thomas Statler, a planetary scientist with the National Science Foundation. The chat follows up on last week's online encounter with NSF's Scott Fisher and NASA's Don Yeomans.

There's a growing buzz about the YU55 encounter on Facebook: You can easily find a whole bunch of event pages. And some wag has already set up a Twitter account for @AsteroidYU55 ("Uncomfortably Close"). For the real lowdown in tweets, do a search on YU55 or #YU55.

If you've made a great sighting, or even if you've found a great site on the Web, I hope you'll share it with the rest of the class. You can pass along links or observations in your comments below. You can also share comments or pictures via the Cosmic Log Facebook page or our brand-new Google+ page. We may use your submissions in our own follow-up coverage of the Great Asteroid Encounter.

Update for 11 p.m. ET: Discovery News' Ian O'Neill lets fly with an "Angry Asteroid" mashup.

More about the encounter:

• How to save our planet from a killer asteroid
• Want to see the space rock? Look fast!
• Could the asteroid destroy the moon? (No)
• Why radar's the best for tracking near-Earth objects
• Interactive: Close encounters of the asteroid kind

Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter or following the Cosmic Log Google+ page. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

Lockheed Martin

Lockheed Martin's proposed "Plymouth Rock" mission would target a near-Earth asteroid. Our planet and the moon are in the background of this artist's conception.

To the moon? Or to an asteroid? Both destinations have been in NASA's sights — the moon during the George W. Bush administration, and a near-Earth asteroid during the Obama administration. Now a "Global Exploration Roadmap" being drawn up by NASA and its counterparts around the world lays out a 25-year scenario for each of the two paths leading beyond Earth orbit.

Both of the paths are aimed at the same eventual destination: Mars. And some observers are suggesting the best course is to aim directly at the Red Planet, rather than starting with closer destinations.

The moon vs. asteroid debate was brought back into the spotlight during the deliberations of a panel known as the International Space Exploration Coordination Group, or ISECG. The group, which includes representatives from Britain, Canada, the European Space Agency, France, Germany, Italy, Japan, Russia, South Korea and the United States, was established as a coordination forum for space exploration back when NASA was aiming for a return to the moon by 2020.

Over the past year, the group has retooled the long-term global strategy for space exploration. "It begins with the International Space Station and expands human presence throughout the solar system, leading ultimately to human missions to explore the surface of Mars," NASA said today in a news release. "The roadmap flows from this strategy and identifies two potential pathways: 'Asteroid Next' and 'Moon Next.'"

NASA said "each pathway represents a mission scenario over a 25-year period describing a logical sequence of robotic and human missions." That scenario would be consistent with the plan that President Barack Obama laid out two years ago, with a goal of sending astronauts to a near-Earth asteroid by 2025 and pushing out to Mars and its moons by the mid-2030s. The new twist is that the moon is back on the table as the initial destination beyond Earth orbit.

NASA

An artist's conception shows NASA's Orion exploration vehicle and a lander docked in lunar orbit.

Senior space officials gave their go-ahead to the two-pathway plan today during a meeting in Kyoto, Japan, NASA said.

"NASA is confident that the release of this product, and subsequent refinements as circumstances within each space agency evolve, will facilitate the ability of space agencies to form the partnerships that will ensure robust and sustainable human exploration," said Bill Gerstenmaier, NASA's associate administrator for human exploration and operations.

Gerstenmaier is the outgoing chair of the ISECG. The incoming chairman, Yoshiyuki Hasagawa of the Japan Aerospace Exploration Agency, said the group's members were "very happy with the progress of the Global Exploration Roadmap."

NASA spokesman Michael Braukus told me that the roadmap was not yet available for public release, but space officials agreed that an initial version of the document would be issued sometime in the next few weeks. Based on viewgraph presentations prepared in advance of this week's meeting in Kyoto, both paths would eventually get to the moon as well as asteroids. It's more a question of which destination is targeted first.

One suggested strategy would start by sending a deep-space habitat to an Earth-moon gravitational balance point known as L-1. Later missions would go to the moon, as preparation for eventual Mars trips. Another scenario calls for reaching the lunar surface first. The lessons learned there would be applied to asteroid missions, and then to Mars-bound missions. A variant would focus on testing the deep-space habitat, then taking trips to the moon, then going to an asteroid, and finally flying to Mars. It's not yet clear how all these possibilities are wrapped up into the ISECG's "Asteroid Next" and "Moon Next" scenarios.

NASA

An artist's conception shows the Orion exploration vehicle and habitation modules in Martian orbit.

Are these 25-year plans necessary, or is it possible to send humans to Mars on a shorter, more direct timetable? SpaceX's millionaire founder, Elon Musk, says a 10-year plan could suffice for a mission to Mars. Rocket scientist Robert Zubrin, president of the Mars Society, made a similar case for an early Red Planet rendezvous last week in a Washington Times commentary:

"We’re ready. Despite its greater distance, we are much better prepared today to send humans to Mars than we were to send men to the moon in 1961, when President Kennedy started the Apollo program - and we were there eight years later. Contrary to those seeking indefinite delay of any commitment, future-fantasy spaceships are not needed to send humans to Mars. The primary real requirement is a heavy-lift booster with a capability similar to that of the Saturn V launch vehicle employed in the 1960s. This is something we fully understand how to create.

"The issue is not money. The issue is leadership. NASA’s average Apollo-era (1961-73) budget, adjusted for inflation, was about $19 billion a year in today’s dollars, just 5 percent more than the agency’s current budget. Yet the NASA of the '60s accomplished 100 times more because it had a mission with a deadline and was forced to develop an efficient plan to achieve that mission. If NASA were given that kind of direction, we could have humans on Mars within a decade. If not, as the rudderless agency continues to drift into the coming fiscal tsunami, we may soon end up with no human spaceflight program."

Gearing up for missions to Mars would likely require a significant boost in space spending, as well as more serious efforts to solve the problems of interplanetary spaceflight, including radiation exposure and zero-G health hazards. The ISECG's deliberations are a sign that deep-space exploration is too expensive for any one country to take on by itself. But the latest reports about the roadmap suggest that the path beyond Earth orbit is not yet set in stone — which means there's still ample opportunity for you to weigh in on the debate.

Click your choice in the poll at right, and feel free to weigh in at length in the comment space below.

In related developments:

• Caltech's Keck Institute of Space Studies has invited students from around the world to participate in a competition to design a mission that would send astronauts to a near-Earth asteroid and return a sample. The team exercise will bring at least 30 students to Caltech from Sept. 12 to 16. The Caltech Space Challenge was created by two Caltech students, Prakhar Mehrotra and Jon Mihaly. "We have more than 275 applications from exceptional students at 100 universities worldwide, including all the top-rated schools," Mehrotra said in a Caltech news release. "Selecting is going to be very hard."
• China's Chang'e 2 spacecraft has left lunar orbit and traveled about a million miles (1.5 million kilometers) from Earth to settle into orbit around the sun-Earth gravitational balance point known as L-2. Chang'e 2's new location was announced today by China's State Administration of Science, Technology and Industry for National Defense. China's Xinhua news agency said Chang'e 2, which spent about eight months orbiting the moon, will carry out exploration activities around L-2 during the coming year. L-2 already serves as the locale for the European Space Agency's Herschel space telescope and NASA's Wilkinson Microwave Anisotropy Probe. It's also the intended destination for the James Webb Space Telescope, which is currently under construction and due for launch around 2018.
• Instead of sending astronauts to an asteroid, how about bringing the asteroid to us? In the journal Research in Astronomy and Astrophysics, scientists at Tsinghua University in Beijing say "it is possible" to nudge an asteroid into temporary Earth orbit, and they provide a list of near-Earth asteroids that just might serve. One possibility is the 10-meter-wide (33-foot-wide) asteroid 2008 EA9, which could be placed in an orbit about twice as far away as the moon for study or for mining over the course of a few years. "Interesting idea," Technology Review's arXiv blog notes. "What could possibly go wrong?"

More about deep-space exploration:

• Gallery: Seven out-of-this-world destinations
• Europe and Russia take aim at Mars
• Counting down to a mission to Mars
• NASA retools spaceship for deep space

Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter or adding me to your Google+ circle. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for other worlds.

The team behind NASA’s Dawn probe has released a video showing the asteroid Vesta spinning in space with a mysterious shadowy spot on its surface. It's really just the beginning of a weeks-long stream of images climaxing with Dawn's rendezvous with Vesta next month.

Dawn has been en route to Vesta for almost four years, but the $357 million mission is just now starting to get good. When the 5.4-foot-long (1.6-meter-long) spacecraft enters orbit on July 16, it will mark the first time any spacecraft has come so close to an asteroid so big. Earlier probes have landed on smaller asteroids, during NASA's NEAR-Shoemaker mission to Eros in 2001 and Japan's Hayabusa sample-return mission to Itokawa, which ended last year. But with a mean diameter of 329 miles (529 kilometers), Vesta is so big that some astronomers have wondered whether it ought to be classified as a dwarf planet.)

In terms of mass, Vesta is second only to the dwarf planet Ceres in the asteroid belt. Dawn is due to spend a year studying Vesta, and then will move on to a rendezvous with Ceres in 2015.

Right now, Dawn is about 170,500 miles (274,400 kilometers) from Vesta and closing in at a speed of 370 mph (170 meters per second). The images released today roughly match the best pictures previously taken of the asteroid by the Hubble Space Telescope. Twenty pictures, taken for navigation purposes over the course of a half-hour on June 1, were assembled in sequence to create the video you see above. One of the most notable features is a dark spot that rolls across the field of view from left to right.

"Like strangers in a strange land, we're looking for familiar landmarks," the University of Maryland's Jian-Yang Li, a member of the Dawn science team, said in a news release from NASA's Jet Propulsion Laboratory. "The shadowy spot is one of those — it appears to match a feature, known as 'Feature B,' from images of Vesta taken by NASA's Hubble Space Telescope."

The images also give you a sense of Vesta's irregular shape, which is due to a huge crater at the asteroid's south pole.

All these features will come into sharper focus in the weeks leading up to the rendezvous. NASA says it will be releasing images from Dawn's approach on a weekly basis, which should come as a relief to planetary scientists and space fans. For weeks they've been urging the Dawn team to release more such imagery, and now Vesta is finally ready for its close-up.

Update for 5:30 p.m. ET: I had Dawn's position with respect to Ceres and Vesta scrambled up for a little while, but now I have the correct current figures. 

More about asteroids and other worlds:

• Could life on Earth have come from Ceres?
• Vesta: Scientists find a protoplanet's guts
• Pallas: Protoplanet frozen in time
• Smorgasbord includes Vesta fiesta
• Interactive: The new solar system

You can connect with the Cosmic Log community by "liking" the log's Facebook page or following @b0yle on Twitter. Also, give a look to "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.