Researchers at NASA/JPL, Caltech, and Arecibo Observatory have released the results of radar observations of the potentially hazardous asteroid 99942 Apophis, along with an in-depth analysis of its motion. The research will affect how and when scientists measure, predict, or consider modifying the asteroid’s motion. The paper has been accepted for publication in the science journal “Icarus” and was presented at the AAS/DPS conference in Orlando, Florida in October of 2007. The Apophis study was led by Jon Giorgini, a senior analyst in JPL’s Solar System Dynamics group and member of the radar team that observed Apophis.

The analysis of Apophis previews situations likely to be encountered with NEAs yet to be discovered: a close approach that is not dangerous (like Apophis in 2029) nonetheless close enough to obscure the proximity and the danger of a later approach (like Apophis in 2036) by amplifying trajectory prediction uncertainties caused by difficult-to-observe physical characteristics interacting with solar radiation as well as other factors.

BACKGROUND

Upon its discovery in 2004, Apophis was briefly estimated to have a 2.7% chance of impacting the Earth in 2029. Additional measurements later showed there was no impact risk at that time from the 210-330 meter (690-1080 foot) diameter object, identified spectroscopically as an Sq type similar to LL chondritic meteorites. However, there will be a historically close approach to the Earth, estimated to be a 1 in 800 year event (on average, for an object of that size).

The Arecibo planetary radar telescope subsequently detected the asteroid at distances of 27-40 million km (17-25 million miles; 0.192-0.268 AU) in 2005 and 2006. Polarization ratios indicate Apophis appears to be smoother than most NEAs at 13-cm scales. Including the high precision radar measurements in a new orbit solution reduced the uncertainty in Apophis’ predicted location in 2029 by 98%.

While trajectory knowledge was substantially corrected by the Arecibo data, a small estimated chance of impact (less than 1 in 45,000 using standard dynamical models) remained for April 13, 2036. With Apophis probably too close to the Sun to be measured by optical telescopes until 2011, and too distant for useful radar measurement until 2013, the underlying physics of Apophis’ motion were considered to better understand the hazard.

RESULTS OF THE STUDY

(1) Extending the “Standard Dynamical Model”

Trajectory predictions for asteroids are normally based on a standard model of the solar system that includes the gravity of the Sun, Moon, other planets, and the three largest asteroids.

However, additional factors can influence the predicted motion in ways that depend on rarely known details, such as the spin of the asteroid, its mass, the way it reflects and absorbs sun-light, radiates heat, and the gravitational pull of other asteroids passing nearby. These were examined, along with the effect of Earth’s non-uniform gravity field during encounters, and limitations of the computer hardware performing the calculations.

One would normally look for the influence of such factors as they gradually alter the trajectory over years. But, for Apophis, the changes remain small until amplified by passage through Earth’s gravity field during the historically close approach in 2029.

For example, the team found solar energy can cause between 20 and 740 km (12 and 460 miles) of position change over the next 22 years leading into the 2029 Earth encounter. But, only 7 years later, the effect on Apophis’ predicted position can grow to between 520,000 and 30 million km (323,000 and 18.6 million miles; 0.0035-0.2 AU). This range makes it difficult to predict if Apophis will even have a close encounter with Earth in 2036 when the orbital paths intersect.

It was found that small uncertainties in the masses and positions of the planets and Sun can cause up to 23 Earth radii of prediction error for Apophis by 2036.

The standard model of the Earth as a point mass can introduce up to 2.9 Earth radii of prediction error by 2036; at least the Earth’s oblateness must be considered to predict an impact.

The gravity of other asteroids can cause up to 2.3 Earth radii of prediction uncertainty for Apophis.

By considering the range of Apophis’ physical characteristics and these error sources, it was determined what observations prior to 2029 will most effectively reduce prediction uncertainties. Observing criteria were developed that, if satisfied, could permit eliminating the 2036 impact possibility without further physical characterization of Apophis.

Such observations could reduce the need for a visit by an expensive spacecraft and reduce the risk of Apophis being prematurely eliminated as a hazard under the standard model, only to drift back into the hazard classification system years later as the smaller, unmodeled forces act upon it.

(2) Mitigation

Mitigation was not specifically studied, but the team found small variations in the energy absorption and reflection properties of Apophis’ surface are sufficient to cause enough trajectory change to obscure the difference between an impact and a miss in 2036. Changing the amount of energy Apophis absorbs by half a percent as late as 2018 – for example by covering a 40 x 40 meter (130 x 130 foot) patch with lightweight reflective materials (an 8 kg payload) – can change its position in 2036 by a minimum of one Earth radius.

A change somewhat greater than this minimum would be required to allow for prediction uncertainties. For Apophis, scaling up to distribute 250 kg (550 pounds) of a reflective or absorptive material (similar to the carbon fiber mesh being considered for solar sails) across the surface could use the existing radiation forces to produce a 6-sigma trajectory change, moving at least “99.9999998″ percent of the statistically possible trajectories away from the Earth in just 18 years.

While no deflection is expected to be necessary, the team’s research demonstrates that any deflection method must produce a change known in advance to be greater than all the error sources in the prediction, including some greater than those considered with the standard model.

(3) Impact probability

The study did NOT compute new impact probabilities. This is because important physical parameters (such as mass and spin pole) that affect its trajectory have not yet been measured and hence there are no associated probability distributions. The study characterizes how the Standard Dynamical Model can over or under-estimate impact probability for those objects having close planetary encounters prior to the potential impact.

The situation is similar to having 6 apples (the measured Apophis parameters) and 6 boxes whose contents are unknown (the unmeasured Apophis parameters), then trying to compute the probability one has a total of 12 apples (impact probability). The result reflects back what is assumed about the unknown contents of the boxes, but doesn’t reveal new information. The contents of the boxes must be observed (measured) to learn something new.

For similar reasons, the Apophis study instead uses the minimum and maximum range-of-effect in place of computing impact probabilities to provide reasonable criteria for excluding impact in the absence of detailed physical knowledge, once new position measurements are obtained at six key times.

(4) Non-Apophis Conclusions

Aspects of the study relevant to asteroids other than Apophis:

• The Standard Dynamical Model can misestimate impact risk for the more numerous sub-km objects preceded by close planetary encounter(s). This problem might be addressed by reassessing impact potential after planetary encounters, given new measurements.
• The minimum-maximum effect of unmeasured parameters can provide enough information to exclude threats in certain cases, even if a realistic impact probability cannot be computed.
• Amplification of small trajectory offsets makes valid prediction across a close-encounter difficult without physical knowledge, but offers the potential to redirect the entire uncertainty region and has significant implications for costly spacecraft missions.
• A deflection effort must be known in advance to produce change greater than predicted uncertainties due to ALL parameters, not only the Standard Dynamical Model. For example, if a method produces 10 Earth-radii of change, but prediction uncertainties from all sources are 20 Earth-radii, the deflection would move the asteroid around within the noise, producing an unpredicted result or even a new hazard.

The Apophis situation has predictability problems essentially the same as previously described in “Science” for 29075 (1950 DA), but occurring more severely: in as little as 2-3 decades, rather than the 880 year prediction of that case.

FUTURE

The future for Apophis on Friday, April 13 of 2029 includes an approach to Earth no closer than 29,470 km (18,300 miles, or 5.6 Earth radii from the center, or 4.6 Earth-radii from the surface) over the mid-Atlantic, appearing to the naked eye as a moderately bright point of light moving rapidly across the sky. Depending on its mechanical nature, it could experience shape or spin-state alteration due to tidal forces caused by Earth’s gravity field.

This is within the distance of Earth’s geosynchronous satellites. However, because Apophis will pass interior to the positions of these satellites at closest approach, in a plane inclined at 40 degrees to the Earth’s equator and passing outside the equatorial geosynchronous zone when crossing the equatorial plane, it does not threaten the satellites in that heavily populated region.

Using criteria developed in this research, new measurements possible in 2013 (if not 2011) will likely confirm that in 2036 Apophis will quietly pass more than 49 million km (30.5 million miles; 0.32 AU) from Earth on Easter Sunday of that year (April 13).

CREDITS

In addition to Giorgini, co-authors of the report include Dr. Lance A. M. Benner and Dr. Steven J. Ostro of JPL; Dr. Michael C. Nolan, Arecibo Observatory, Puerto Rico, and Michael W. Busch of the California Institute of Technology.

Arecibo Observatory is operated by Cornell University under a cooperative agreement with the National Science Foundation. JPL is managed for NASA by the California Institute of Technology in Pasadena.

Source:

http://neo.jpl.nasa.gov/apophis/

Here is the PDF from http://neo.jpl.nasa.gov/apophis/Apophis_PUBLISHED_PAPER.pdf

Anatoly Perminov, head of the Russian Space Agency, caught scientists off guard back in January when he called for a closed meeting of Russian

ASTEROID1

scientists to counter a killer asteroid headed our way. He said that a potential impact from the asteroid Apothis around 2036 could kill hundreds of thousands of people. Immediately this conjured up images of Bruce Willis and his space cowboys riding the Space Shuttle to blow up a comet in the movie “Armageddon.” Scientists, realizing that the danger is slight but real, have in fact seriously proposed various ways in which to deflect the asteroid.

As asteroids go, Apophis is a whopper, measuring 1,000 feet across, about the size of the Rose Bowl. In 2029 it will make its first pass around the earth, so close that it will travel beneath our communication satellites. In fact, you might see it whiz by overhead with binoculars. Depending on how it whips around the earth, there is a slight chance it might actually hit the earth when it returns in 2036 (but the latest calculations only show a one in a hundred thousand chance of impact).

The Russians take such a threat seriously, since a “city buster” hit Tunguska, Siberia, in 1908, flattening about a thousand square miles of forest, destroying about 100 million trees, and leaving a huge scar in the Earth. The object that struck Siberia was probably only 100 feet across, yet it created a blast about 1,000 times greater than the Hiroshima bomb. The shock waves were so intense they were detected in Europe. It created a strange glow which spread over Asia and Europe so that you could read the London papers at night. If it had hit Moscow, it would have completely flattened that city and beyond. A city-buster like that happens once every 100-300 years, with most of them hitting the oceans.

A hit from Apothis, however, would be another story. It would be a “country buster,” capable of creating fire storms, shock waves, and a rain of fiery debris that would destroy an area almost the size of France, or perhaps the entire Northeast of the U.S. The energy of the impact would be roughly 100,000 times that of the Hiroshima bomb. If it hits the Pacific Ocean, it could also generate a huge tidal wave, a gigantic wall of water that could swamp most coastal cities in the Americas and Asia. An impact from an Apophis-like asteroid is estimated to happen once in a thousand years. (The worst case scenario, however, would be an impact from a “planet buster” as little as six miles across, like the one that hit Mexico and probably wiped out the dinosaurs 65 million years ago.)

Plans to counter such a hypothetical threat, however, are sketchy. A staple of science fiction is to send the Space Shuttle to blow it up. Bad idea.

First, this might only crack the asteroid, so you would have a swarm of deadly mini-asteroids headed your way. Second, the Space Shuttle can only circle the Earth; it is incapable of reaching deep space to intercept the asteroid. And it is going to be phased out this year anyway and a replacement won’t be ready for about five years.

Several proposals made by scientists are currently being studied. One likely scenario is to nudge the asteroid while it is still in deep space so that it eventually misses the Earth. This deflection might be done via rockets to push the asteroid years before it passes the Earth. Or, the gravity of the spacecraft itself may be used to gently tug on its trajectory. Yet another proposal is to use mirrors and even paint to increase the pressure of sunlight so that, over decades, its trajectory is modified.

At present, none of the hardware for such a mission exists, so we will be helpless for years if a real threat emerges. And any serious proposal will require tens of billions of dollars, for new booster rockets and the complex machinery to deflect the asteroid.

But given these hard economic times, money is scarce even to maintain the current space program. The Augustine Report on the future of space travel, commissioned by NASA and presented to President Obama in October, stated that manned missions to the moon and Mars were “unsustainable” without a new injection of funds. However, it did leave open the possibility of landing on an asteroid. So one real possibility is to land a probe on the asteroid in 2029 so that scientists can study its properties as well as get a free ride through the solar system. We know so little about Apothis that it might be a solid object or just a loose collection of rocky debris held together by gravity.

Some conspiracy theorists have raised the dark possibility that any nation that can deflect an asteroid could also send it hurtling toward its enemies. But such a weapon is simply too unstable and unreliable to be taken seriously.

Indeed, scientists are applauding the Russian Space Agency for addressing the issue, even if the danger from Apophis is very slight. Sooner or later, we will face a catastrophic threat from space. Of all the possible threats, only a gigantic asteroid hit can destroy the entire planet. If we prepare now, we better our odds of survival. The dinosaurs never knew what hit them.

http://online.wsj.com/article/SB10001424052748703580904574638230276797924.html

Yesterday, the Japanese Aerospace Exploration Agency (JAXA) is planning to bring the Hayabusa probe down to Earth in Australia, hopefully bringing bits of an asteroid down with it.

The probe visited asteroid 25143 Itokawa in 2005 and attempted to collect samples of dust and pebbles from the rock. Because of glitches during the sample collection, scientists are unsure exactly what they will find when they open Hayabusa’s sealed sampling chamber.

(Source: Space.com)

The probe visited asteroid 25143 Itokawa in 2005 and attempted to collect samples of dust and pebbles from the rock. Because of glitches during the sample collection, scientists are unsure exactly what they will find when they open Hayabusa’s sealed sampling chamber.

But if successful, this will mark the first time asteroid samples are returned to Earth for analysis.

Although missions to celestial bodies such as Mars or the moon may sound more exciting than a mission to asteroid 25143 Itokawa, scientists say we have much to learn from these irregularly-shaped rocks that roll through our solar system. Here are 5 reasons why we should care about asteroids:

1.  They will tell us about the origins of our solar system.

“The materials in asteroids represent the building blocks of the planets,” said Carol Raymond,
deputy principal investigator on NASA’s Dawn mission, which lifted off in 2007 and will visit asteroid Vesta in 2011 and dwarf planet Ceres in 2015. Because of the position of the asteroid belt that lies between the rocky inner planets and the gas giants of the outer solar system, the materials found there may hold clues as to why the planets are so diverse today.

For example, although Ceres and Vesta formed at roughly the same time – within the first 10 million years of the solar system’s existence – they have very different compositions now. Vesta, at some point, melted completely and then resolidified, so it is now smooth. Meanwhile Ceres does not show signs of having gone through this melting.

It’s possible, Raymond said, that Vesta experienced more collisions, or that it had a high amount of a radioactive form of aluminum that would have given off heat as it underwent radioactive decay. By studying each asteroid, scientists will be able to solve this mystery.

2. They will help us understand more about the origin of life.

Scientists do not fully understand how the first life forms arose on Earth from non-living organic matter, and asteroids may help us learn more about this puzzle.

Asteroids such as 2 Pallas and 10 Hygiea, which are both believed to have had water in the past, appear to have organic (carbon-based) compounds on them, Raymond said. Today, these asteroids have a more primitive chemical composition than Earth has – they are more similar to the conditions that existed in the solar system’s younger years. By studying them, we may learn about how life arose on our own planet.

“There are conditions that may have been conducive to life in the past,” Raymond said.

Plus, scientists think asteroids that landed on Earth long ago may have deposited some of the building blocks that helped start life here.

3. We may want to mine near-earth asteroids for metals.

“There is a keen interest in going to asteroids in the near-earth belt,” Raymond said. “They could be sources of valuable metals.” To investigate the feasibility of such operations, we need to know more about asteroid composition and the technical aspects of traveling to them.

Besides the opportunity for mining, these asteroids are also interesting from a scientific perspective, because studying them complements our studies of the major planets, Raymond said. Analyzing the differences between the planets and the smaller asteroids is like taking slices of the solar system at different times during its formation.

4. They may someday threaten to collide with Earth.

Because some asteroids orbit around the sun in paths shaped like elongated ovals, they cross Earth’s orbit every so often. And sometimes, they come very close to Earth itself. For example, in January, asteroid 2010 AL30 passed within about 80,000 miles (130,000 km) of Earth.

But 2010 AL30 was just at 36 feet (11 meters) wide. More worrisome is the prediction that asteroid Apophis will come very close to Earth on April 13, 2036. Although NASA predicts that it will pass no closer than 18,300 miles above Earth’s surface, Apophis is larger than two football fields. While that’s not big enough to create Hollywood-style global devastation, it could cause significant regional damage, were it ever to strike Earth.

5. Astronauts may go visit one, according to Obama’s new plan for NASA.

In April, President Barack Obama announced the next goal for Americans in space: visiting an asteroid by 2025.

In a panel discussion in April, astrophysicist John Grunsfeld – a former NASA astronaut who flew on five shuttle missions – suggested that one goal might be sending humans to purposely move an asteroid, to nudge the space rock to change its trajectory. Such a feat, he said, would show that humanity could deflect a space rock if one threatened to crash into the planet.

“By going to a near-Earth object, an asteroid, and perhaps even modifying its trajectory slightly, we would demonstrate a hallmark in human history,” Grunsfeld said. “The first time humans showed that we can make better decisions than the dinosaurs made 65 million years ago.”

Source:

http://www.space.com/scienceastronomy/5-reasons-care-about-asteroids-100611.html

The Arecibo telescope is located in Arecibo, Puerto Rico, and it is managed by Cornell University on behalf of the National Science Foundation.

Arecibo radar imaging of 2005 YU55 at 25-ft resolution showed that this asteroid is about 400 meters (1,300 feet) in size – about a quarter-mile long – and about twice as large as previously estimated.

On the actual observation at Arecibo, Ellen Howell, a Cornell researcher at Arecibo, was the principal investigator. Other observers include Cornell researcher Patrick Taylor, and Nolan. Jon D. Giorgini of the Jet Propulsion Laboratory (JPL), Pasadena, Calif., conducted the orbital calculations. Lance Benner, Marina Brozovic, both of JPL; Michael Busch of California Institute of Technology, Pasadena; and Chris Magri, University of Maine at Farmington, are collaborators on the project.

This object is on the list of “potentially hazardous asteroids” maintained by the Minor Planet Center, of the Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass.

High-precision radar astrometry reduced orbit uncertainties by 50 percent. This improvement eliminated any possibility of an impact with the Earth for the next 100 years, and it was removed from the “Risk Page” maintained by NASA’s Near-Earth Object Program Office at the Jet Propulsion Laboratory.

After circling the Sun, 2005 YU55 will next approach the Earth to about 0.8 lunar distances on Nov. 8, 2011. It will pose no impact hazard at that time. Robert McMillan of the Spacewatch asteroid detection program discovered the asteroid on December 28, 2005.

President Barack Obama has proposed that NASA’s “Near Earth Object Observations” program be increased from $3.7 million in 2009 to $20.3 million in 2011. NASA has indicated that it intends to provide support to the Arecibo radar program if that funding remains in the budget. Rep. Jose Serrano, D-N.Y., added $2 million to NASA’s near-Earth object research program in 2010 for support of the Arecibo research work. These funds will offset reduced funding from the National Science Foundation.

The Arecibo Observatory is part of the National Astronomy and Ionosphere Center which is managed by Cornell University under a cooperative agreement with the national Science Foundation.

The discovery of significant asteroid ice has several consequences. It could help explain where early Earth first got its water. It makes asteroids more attractive to explore, dovetailing with President Barack Obama’s announcement earlier this month that astronauts should visit an asteroid. And it even muddies the definition between comets and asteroids, potentially triggering a Pluto-like scientific spat over what to call these solar system bodies.

This asteroid has an extensive but thin frosty coating. It is likely replenished by an extensive reservoir of frozen water deep inside rock once thought to be dry and desolate, scientists report in two studies in Thursday’s issue of the journal Nature.

Two teams of scientists used a NASA telescope in Hawaii to look at an asteroid called 24 Themis, one of the bigger rocks in the asteroid belt between Mars and Jupiter. They examined light waves bouncing off the rock and found the distinct chemical signature of ice, said University of Central Florida astronomy professor Humberto Campins, lead author of one of the studies.

Astronomers have long theorized that hydrogen and oxygen and bits of water locked in clay are in asteroids, but this is the first solid evidence. And what they found on 24 Themis, a rock more than 100 miles wide with temperatures around 100 degrees below zero Fahrenheit, was more than they ever expected. About a third of the rock seemed to be covered in frost.

Furthermore, scientists didn’t just find ice; they found organic molecules, similar to what may have started life on Earth, Campins said.

“This asteroid holds clues to our past and how the solar system and water on Earth may have originated and it also has clues to our future with exploration of near-Earth asteroids,” Campins told The Associated Press.

“We’re showing that they’re wetter than we thought,” Campins said. “We’re showing they have organic molecules that might have been the building blocks of life on Earth.”

Earth, when it formed billions of years ago was dry, scientists say. So where did the water come from? One leading theory is from crashing comets, that are essentially icy snowballs.

But comets come from the outer reaches of the solar system and tend to have more heavy hydrogen than the water in our oceans, said Donald Yeomans, manager of NASA’s Near Earth Object Program office. Icy asteroids between Mars and Jupiter might have the right heavy hydrogen ratio to match what’s on Earth, said Yeomans, who wasn’t involved in the studies.

MIT’s Richard Binzel, also praised the studies, calling the findings “one more piece in the puzzle for an abundance of water arriving on Earth and having available the ingredients for life.”

Normally, the ice on the asteroid should have escaped Themis as a gas over thousands of years, but it’s still there after a billion years or so, Campins said. That means there’s likely a supply of ice inside the rock, replenishing the surface, he said.

And if that’s the case for other similar asteroids – especially those that come closer to Earth – then it would be a boon for visiting astronauts, Campins and others said. The astronauts could use the water to drink and to help make fuel. The new NASA space plan calls for astronauts to head to a nearby asteroid sometime in about 15 years as a stepping stone to Mars.

The icy asteroid also just makes a mess of the differences between asteroids and their cosmic cousin, the comet. The general definition has been that asteroids are dry rocks and comets icy snowballs.

Now it seems to be more a continuum of dry and icy with not much difference between asteroids and comets, Campins and others said.

And that, said Andrew Rivkin of Johns Hopkins University, co-author of the other study in Nature, could wind up another cosmic controversy like the debate a few years ago about whether Pluto was a planet. Pluto wound up demoted and is now called a dwarf planet.

Viewed from San Diego, the fireball of hot vapor from the impact appears slightly larger than the sun. The heat is enough to warm, but not burn, your skin. The earthquake tremors wake many people from their sleep, and nearly everyone in the city notices them. Windows break; unstable objects topple over. A fine dusting of debris falls, with occasional quarter-inch fragments of rock. The air blast noise, as loud as heavy traffic, and 25 mph winds are the final signs of the impact. If Apophis were to land not in L.A. but in the Pacific, San Diego could suffer more; some scientists believe the ocean impact would trigger a tsunami.

Astrophysicists think that Apophis is the common type of asteroid, make of rock. But what if it were the rare sort, made of iron, and it inexplicable changed course and hit the city of Angels? Iron is more than twice as dense as the densest rock, and the impact would be much more devastating.

We should actually take an additional step in learning about asteroids where instead of going far away from Earth and planting a man or women on an asteroid, why not find a very small asteroid and with the help of NASA’s  robotic technology we could literally bring the rock back and place it into a geosnych orbit.

Sure, it is a far fetched idea, but if we did such an experiment we could learn a lot about its structure, flight orbital path, and everything that we could think of. And the good news about this is that we can constantly do research on the asteroid instead of just one lone trip.

Space experts say such a voyage could take several months longer than a journey to the moon and entail far greater dangers.

“It is really the hardest thing we can do,” NASA Administrator Charles Bolden said.

Going to an asteroid could provide vital training for an eventual mission to Mars. It might help unlock the secrets of how our solar system formed. And it could give mankind the know-how to do something that has been accomplished only in the movies by a few square-jawed, squinty-eyed heroes: saving the Earth from a collision with a killer asteroid.

“You could be saving humankind. That’s worthy, isn’t it?” said Bill Nye, TV’s Science Guy and vice president of the Planetary Society.

President Barack Obama outlined NASA’s new path during a visit to the Kennedy Space Center on Thursday.

“By 2025, we expect new spacecraft designed for long journeys to allow us to begin the first-ever crewed missions beyond the moon into deep space,” he said. “We’ll start by sending astronauts to an asteroid for the first time in history.”

On the day the president announced the goal, a NASA task force of scientists, engineers and ex-astronauts was meeting in Boston to work on a plan to protect Earth from a cataclysmic collision with an asteroid or a comet.

NASA has tracked nearly 7,000 near-Earth objects that are bigger than several feet across. Of those, 1,111 are “potentially hazardous asteroids.” Objects bigger than two-thirds of a mile are major killers and hit Earth every several hundred thousand years. Scientists believe it was a 6-mile-wide asteroid that wiped out the dinosaurs 65 million years ago.

Landing on an asteroid and giving it a well-timed nudge “would demonstrate once and for all that we’re smarter than the dinosaurs and can avoid what they didn’t,” said White House science adviser John Holdren.

Experts don’t have a particular asteroid in mind for the deep-space voyage, but there are a few dozen top candidates, most of which pass within about 5 million miles of Earth. That is 20 times more distant than the moon, which is about 239,000 miles from Earth on average.

Most of the top asteroid candidates are less than a quarter-mile across. The moon is about 2,160 miles in diameter.

Going to an asteroid could provide clues about the solar system’s formation, because asteroids are essentially fossils from 4.6 billion years ago, when planets first formed, said Don Yeomans, manager of NASA’s Near Earth Object program at the Jet Propulsion Lab.

And an asteroid mission would be a Mars training ground, given the distance and alien locale.

“If humans can’t make it to near-Earth objects, they can’t make it to Mars,” said MIT astronautics professor Ed Crawley.

Also, asteroids contain such substances as hydrogen, carbon, iron and platinum, which could be used by astronauts to make fuel and equipment – skills that would also be necessary on a visit to Mars.

While Apollo 11 took eight days to go to the moon and back in 1969, a typical round-trip mission to a near-Earth asteroid would last about 200 days, Crawley said. That would demand new propulsion and life-support technology. And it would be riskier. Aborting a mission in an emergency would still leave people stuck in space for several weeks.

The space agency may need to develop special living quarters, radiation shields or other new technology to allow astronauts to live in deep space so long, said NASA chief technology officer Bobby Braun.

Even though an asteroid would be farther than the moon, the voyage would use less fuel and be cheaper because an asteroid has no gravity. The rocket that carries the astronauts home would not have to expend fuel to escape the asteroid’s pull.

On the other hand, because of the lack of gravity, a spaceship could not safely land on an asteroid; it would bounce off the surface. Instead, it would have to hover next to the asteroid, and the astronauts would have to spacewalk down to the ground, Yeomans said.

Once there, they would need some combination of jet packs, spikes or nets to enable them to walk without skittering off the asteroid and floating away, he said.

“You would need some way to hold yourself down,” Yeomans said. “You’d launch yourself into space every time you took a step.”

Just being there could be extremely disorienting, said planetary scientist Tom Jones, co-chairman of the NASA task force on protecting Earth from dangerous objects. The rock would be so small that the sun would spin across the sky and the horizon would only be a few yards long. At 5 million miles away, the Earth would look like a mere BB in the sky.

“It’s going to be a strange alien environment being on an asteroid,” Jones said.

But Jones, a former astronaut, said that wouldn’t stop astronauts from angling to be a part of such a mission: “You’ll have plenty of people excited about exploring an ancient and alien world.”

The ‘fireball in the sky’ was seen by hundreds, causing a flood of social networking activity. Said one Facebook user, Renee DeVries, “It looked like a red flare and then it changed to a yellowish color and looked as if it was falling from the sky.”

The AP reports that the meteor led to “rattling houses and causing trees and the ground to shake.”

Am I just imagining it or have there been many more meteors coming to earth than normal in the last several years? Even I saw two the same evening last September, while I was watching an outdoor music concert. The first one was huge and was proceeding across the sky horizontally, the second was the standard high up flash of light burning out. I don’t remember so many meteors or meteorites being spotted in such a short time span.