According to David J. Tholen, an astronomer, Ph.D., Planetary Sciences, University of Arizona and his team, Apophis will make an extremely close approach to the Earth on 2029 April 13.
Additional observations provided improved predictions that eliminated the possibility of an impact on Earth or the Moon in 2029. A future impact on April 13, 2036, is still possible...but for now, we are worry about the earlier date and time of the event.

"... release more than 100,000 times the energy released in the nuclear blast over Hiroshima. Thousands of square kilometres would be directly affected by the blast but the whole of the Earth would see the effects of the dust released into the atmosphere..."

The computation of Earth impact probabilities for near-Earth objects is a complex process requiring sophisticated mathematical methods.

It is not any easy work!

For now a possible impact Risk from Apophis (MN4) still does exist. The new data slightly raise the odds of an impact in the 2030s to roughly 1 in 8,000. The most probable impact scenario occurs in 2036, off the Pacific coast of North America, and carries the potential of generating a 30-foot-high tsunami that could strike southern California.

Key points:
Impact probability currently at one in forty five according to astronomers
• Threat, at level four on astronomical measure, never before been raised

"IN WHAT could make for the blackest of black Fridays, an asteroid a quarter of a mile long has been given the highest risk of hitting the Earth ever conferred on a heavenly body.

The threat posed by object 2004 MN4 has been graded by astronomers as level four out of ten on their warning scale - the first asteroid ever to be graded higher than level one.
This means it has a one-in-45 chance of impact on Friday, 13 April, 2029. The assessment originally stood at level two.

The level-four threat posed by the asteroid is listed on the Torino scale as "a close encounter, with 1 per cent or greater chance of a collision capable of causing regional devastation".

"This will allow scientists a good window of opportunity to continue observations and refine their understanding of the asteroid’s orbit," he said.
Astronomers expressed concern last year that reports of potential asteroid collisions with the Earth were causing unnecessary panic.
The inventor of the Torino scale, named after the Italian city where it was devised in 1999, was so upset by coverage of asteroid scares that he has proposed toning down the scale’s wording. Dr Rick Binzel, of the Massachusetts Institute of Technology, said the definition of category one, under which most asteroids are initially classed, should be changed from "requiring careful monitoring" to "normal".
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Asteroid may come uncomfortably close to Earth in 2036
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The Association of Space Explorers, a group of former astronauts and cosmonauts, intends to host a series of high-level workshops this year to flesh out a plan and will make a formal proposal to the U.N. in 2009.

An asteroid may come uncomfortably close to Earth in 2036 and the United Nations should assume responsibility for a space mission to deflect it, a group of astronauts, engineers and scientists said.

Astronomers are monitoring an asteroid named Apophis, which has a 1 in 45,000 chance of striking Earth on April 13, 2036. Although the odds of an impact by this particular asteroid are low, a recent congressional mandate for NASA to upgrade its tracking of near-Earth asteroids is expected to uncover hundreds, if not thousands of threatening space rocks in the near future, former astronaut Rusty Schweickart said.

"It's not just Apophis we're looking at. Every country is at risk. We need a set of general principles to deal with this issue," Schweickart, a member of the Apollo 9 crew that orbited the earth in March 1969, told an American Association for the Advancement of Science conference in San Francisco.

Schweickart plans to present an update next week to the U.N. Committee on Peaceful Uses of Outer Space on plans to develop a blueprint for a global response to an asteroid threat.

The Association of Space Explorers, a group of former astronauts and cosmonauts, intends to host a series of high-level workshops this year to flesh out the plan and will make a formal proposal to the U.N. in 2009, he said.

Schweickart wants to see the United Nations adopt procedures for assessing asteroid threats and deciding if and when to take action. The favored approach to dealing with a potentially deadly space rock is to dispatch a spacecraft that would use gravity to alter the asteroid's course so it no longer threatens Earth, said astronaut Ed Lu, a veteran of the International Space Station.

The so-called Gravity Tractor could maintain a position near the threatening asteroid, exerting a gentle tug that, over time, would deflect the asteroid. An asteroid the size of Apophis, which is about 460 feet (140 meters) long, would take about 12 days of gravity tugging, Lu added. Mission costs are estimated at $300 million.

Launching an asteroid deflection mission early would reduce the amount of energy needed to alter its course and increase the chances of a successful outcome, Schweickart said.

NASA says the precise effect of a 460-foot (140-metre) object hitting the Earth would depend on what the asteroid was made of and the angle of impact. Paul Slovic, president of Oregon-based Decision Research, which studies judgment, decision-making and risk analysis, said the asteroid could take out an entire city or region.

Asteroid threat demands response, experts warn
NewScientist.com news service

If the asteroid Apophis hits Earth in 2036, it could slam into the Pacific Ocean, generating a tsunami that could devastate the west coast of North America (Illustration: Don Davis/NASA)

Kamchatkans and Venezuelans beware. A 20-million-tonne asteroid could be heading your way. Californians have even more reason to worry - the asteroid is more likely to hit the Pacific Ocean, triggering a tsunami that could devastate the west coast of North America.

These are among the scenarios projected for asteroid Apophis, which researchers now say has a 1 in 45,000 chance of hitting Earth on 13 April 2036. Calculations show it would strike somewhere along a narrow track that stretches eastward from Siberia to the west coast of Africa.

Compared to earlier estimates, the new figure represents a further reduction in the threat posed by Apophis (see Risk of asteroid smashing into Earth reduced). But the threat is real enough, experts argue, to merit a United Nations protocol for dealing with the problem.

"Someone will have to make a decision," says Russell Schweickart, a former Apollo astronaut and founder of the Association of Space Explorers. Because any plan for deflecting the asteroid away from Earth will need to be implemented well before an impact site is precisely known, he says, "this is inherently going to be an international decision".

Sky surveys

Beginning in the next few months, Schweickart's group will host a series of meetings to provide the UN with a 'decision process' for assessing and acting on the hazard posed by Apophis and other near-Earth asteroids (NEAs). A draft document ready for consideration by the United Nations Committee on the Peaceful Uses of Outer Space is expected by 2009.

During the past 10 years, a concerted search effort by astronomers has led to the detection of an estimated 90% of the asteroids that could threaten Earth with devastation on a global scale. In the coming decade, a next-generation search is likely to uncover most of the remaining global hazards, as well as many more smaller asteroids, like the 250-metre-wide Apophis, that could threaten millions of lives and cause significant damage on a regional scale.

Currently, NASA's Near Earth Object programme lists 127 objects as potential impact risks. By 2020, Schweickart predicts, the list could number in the thousands. Because of the uncertainties involved in calculating asteroid trajectories, many will initially appear to have a small but real chance of hitting Earth in the next few decades.

Too late

In most cases, those threats will vanish with additional observations that will narrow the range of possible trajectories. However, in some cases the threat of an impact could persist long enough to require action.

"If you wait to be certain, it could be too late," says Schweickart.

Schweickart and others discussed options for dealing with Apophis and other asteroid risks at the annual meeting of the American Association for the Advancement of Science in San Francisco, California, US.

"Apophis forces us to think about what we might do if [an impact threat] reaches our threshold of pain," say Ed Lu of NASA's Johnson Space Center in Houston, Texas, US.

Lu, who led the discussion on asteroid deflection, warned that "simple methods are not so simple" when it comes to moving the mountain-sized chunks of rock that hurtle through our local region of the solar system. Among the least desirable options is the use of a nuclear warhead to blow up an approaching asteroid. "You could make life a lot worse," says Lu, by turning one potential impactor into many.

'Reshaping the solar system'

Lu's favoured option is called a gravitational tractor. It involves placing a relatively massive spacecraft near enough to an approaching asteroid to shift its trajectory using only the minuscule force of gravity between the two objects. Although the method requires significant lead time and will not work in all cases, it has the advantage of controlling a hazardous object "in one piece", say Lu.

According to Lu, Apophis is particularly amenable to this form of manoeuvring. Prior to its threatening approach in 2036, the asteroid will sweep past Earth in the spring of 2029. Any change in the asteroid's position before this will be greatly magnified by the 2029 encounter, which could, in turn, eliminate the chance of an impact in 2036.

Such a mission could succeed with a 1-metric-tonne spacecraft arriving at Apophis as late as 2027, says Schweickart, who envisions a protocol that would allow the UN to 'contract' the world's space agencies to remove the threat.

"We can't prevent a hurricane," says Schweickart. "But we can prevent an asteroid impact by slightly reshaping the solar system to ensure the survival of life on Earth."

Some basic info about Apophis
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99942 Apophis (previously better known by its provisional designation 2004 MN4) is a Near-Earth asteroid that caused a brief period of concern in December 2004 because initial observations indicated a relatively large probability that it would strike the Earth in 2029. However, additional observations provided improved predictions that eliminated the possibility of an impact on Earth or the Moon in 2029. A future impact on April 13, 2036, is still possible, keeping the asteroid at level 1 on the Torino impact hazard scale as of September 2005, with an estimated impact-probability of 1 in 5,560.

Apophis is expected to come close enough that on April 13, 2029 (Friday the 13th) it will become as bright as magnitude 3.3 (easily visible to the naked eye). This close approach will be visible from Europe, Africa, and western Asia. Throughout recorded history, no other closely-approaching objects of this size have been visible to the naked eye. As a result of its close passage, it will move from the Aten (see below) to the Apollo class.

(Close approach of Apophis on April 13th, 2029)

Apophis remains at level one on the Torino scale because of a very low but non-zero probability of impact in 2036. However, the approach in 2029 will substantially alter the object's orbit, making predictions uncertain without more data. "If we get radar ranging in 2013 [the next good opportunity], we should be able to predict the location of 2004 MN4 out to at least 2070." said Jon Giorgini of JPL

In July 2005, former Apollo astronaut Rusty Schweickart, as chairman of the B612 Foundation, formally asked NASA to investigate the possibility that the asteroid's post-2029 orbit could be in orbital resonance with the Earth, which would increase the probability of future impacts. For this to happen, Apophis would have to pass precisely through a certain very narrow region of space during the 2029 close approach, a "gravitational keyhole" no more than about 600 m across. Schweickart asked for an investigation of the necessity of placing a transponder on the asteroid for more accurate tracking of how its orbit is affected by the Yarkovsky effect.

Naming

When first discovered, the object received the provisional designation 2004 MN4 (sometimes written 2004 MN4), and news and scientific articles about it referred to it by that name. When its orbit was sufficiently well calculated it received the permanent number 99942 (on June 24, 2005), the first numbered asteroid with Earth-impact solutions. Receiving a permanent number made it eligible for naming, and it promptly received the name "Apophis" as of July 19, 2005. Apophis is the Greek name of the Ancient Egyptian god Apep, "the Destroyer", who dwells in the eternal darkness of the Duat (underworld) and tries to destroy the Sun during its nightly passage.

Although the mythical Greek god may be appropriate, Tholen and Tucker (two of the co-discovers of the asteroid) are reportedly fans of the TV series Stargate: SG-1. In the first several seasons the show's main antagonist was an alien named Apophis who took the name for the Egyptian god and sought to destroy earth. (see "Asteroid Apophis set for a makeover" by Bill Cooke, Astronomy Magazine, August 18, 2005

Basic data

Apophis belongs to a group called the "Aten asteroids", asteroids with an orbital semi-major axis less than one astronomical unit. This particular one has an orbital period about the Sun of 323 days, and its path brings it across Earth's orbit twice on each passage around the Sun.

Based upon the observed brightness, Apophis's length was estimated at 415 m (1350 ft); a more refined estimate based on spectroscopic observations at NASA's Infrared Telescope Facility in Hawaii by Binzel, Rivkin, Bus, and Tokunaga (2005) is 320 m (1050 ft). Its mass is estimated to be 4.6×1010 kg.

As of February 2005 it is predicted that the asteroid will pass about 36,350 km (22,600 mi) from the Earth's surface on April 13, 2029, slightly higher than the altitude of geosynchronous satellites, which is 35,786 km (22,300 mi). Its brightness will be about magnitude 3.3, with a peak angular speed of 42° per hour. Such a close approach by an asteroid of this size is expected to occur only every 1,300 years or so. The maximum apparent angular diameter will be only 2 arcseconds, which means it will be a starlike point of light in all but the very largest telescopes

(The white bar indicates uncertainty in the range of possible positions.)

Discovery

Apophis was discovered on June 19, 2004, by Roy A. Tucker, David J. Tholen, and Fabrizio Bernardi of the NASA-funded University of Hawaii Asteroid Survey from Kitt Peak National Observatory in Arizona. This group observed for two nights. The new object received the provisional designation 2004 MN4, and naturally did not yet have its current name.

On December 18, the object was rediscovered from Australia by Gordon Garradd of the Siding Spring Survey, another NASA-funded NEA survey. Further observations from around the globe over the next several days allowed the Minor Planet Center to confirm the connection to the June discovery.

At this point the possibility of impact on April 13, 2029 was computed by the automatic Sentry system of NASA's Near-Earth Object Program Office. NEODyS, a similar automatic system at the University of Pisa, Italy and the University of Valladolid, Spain also detected the impact possibility and provided similar predictions.

Over the next several days, additional observations allowed for astronomers to narrow the cone of error. As they did, the probability of an impact event climbed, peaking at 2.7 percent (1 in 37). Combined with its size, this caused Apophis to be assessed at level four out of ten on the Torino Impact Hazard Scale and 1.10 on the Palermo scale, scales scientists use to represent the danger of an asteroid hitting Earth. These are the highest values for which any object has been rated on either scale.

Precovery observations from March 15, 2004 were identified on December 27, and an improved orbit was computed. The 2029 pass will actually be much closer than the first predictions (as close as a geosynchronous satellite), but the uncertainty is so much smaller that the risk of impact then went away. A pass on April 13, 2036 still carry some risk. As of September 2005, the odds of impact on that date is 0.018 percent (1 in 5,560) and the Palermo scale rating for Apophis is -1.35 and the Torino scale rating is 1.

History of estimates

• The original NASA report on December 24 mentioned impact chances of "around 1 in 300", which was widely reported in the media. The actual NASA estimates at the time were 1 in 233; they resulted in the Torino scale rating of 2, the first time any asteroid had received a rating above 1.
• Later that day, based on a total of 64 observations, the estimates were changed to 1 in 62 (1.6 percent), resulting in an update to the initial report and an upgrade to a Torino scale rating of 4.
• On December 25, the chances were first reported as 1 in 42 (2.4 percent) and later that day (based on 101 observations) as 1 in 45 (2.2 percent). At the same time, the asteroid's estimated diameter was lowered from 440 m to 390 m and its mass from 1.2×1011 kg to 8.3×1010 kg.
• On December 26 (based on a total of 169 observations), the impact probability was still estimated as 1 in 45 (2.2 percent), the estimates for diameter and mass were lowered to 380 m and 7.5×1010 kg, respectively.
• On December 27 (based on a total of 176 observations), the impact probability was raised to 1 in 37 (2.7 percent); diameter was increased to 390 m, and mass to 7.9×1010 kg.
• On December 27 in the afternoon, a precovery increased the span of observations to 287 days and allowed more accurate calculations to re-rate the asteroid's 2029 approach as level zero on the Torino scale (no threat). The cumulative impact probability was estimated to be around 0.004 percent, a lower risk than asteroid 2004 VD17, which once again became the greatest risk object (a position it had held since late November 2004). A 2053 approach to the earth still poses a minor risk of impact, and Apophis was still rated at level one on the Torino scale for this orbit.
• On December 28 at 12:23 GMT and (based on a total of 139 observations), produced a value of one on the Torino scale for 2044-04-13.29 and 2053-04-13.51.
• By 01:10 GMT on December 29 the only pass rated 1 on the Torino scale was for 2053-04-13.51 based on 139 observations spanning 287.71 days (2004-Mar-15.1104 to 2004-Dec-27.8243).
• By 19:18 GMT on December 29 this was still the case based upon 147 observations spanning 288.92 days (2004-Mar-15.1104 to 2004-Dec-29.02821), though the close encounters have changed and been reduced to 4 in total.
• By 13:46 GMT on December 30 no passes were rated above 0, based upon 157 observations spanning 289.33 days (2004-Mar-15.1104 to 2004-Dec-29.44434). The most dangerous pass was rated at 1 in 7,143,000.
• By 22:34 GMT on December 30, 157 observations spanning 289.33 days (2004-Mar-15.1104 to 2004-Dec-29.44434). One pass at 1 (Torino Scale) 3 other passes.
• By 03:57 GMT on January 2, 182 observations spanning 290.97 days (2004-Mar-15.1104 to 2004-Dec-31.07992) One pass at 1 (Torino Scale) 19 other passes.
• By 14:49 GMT on January 3, 204 observations spanning 292.72 days (2004-Mar-15.1104 to 2005-Jan-01.82787) One pass at 1 (Torino Scale) 15 other passes.
• Extremely precise radar observations at Arecibo Observatory on January 27, 28, and 30 refine the orbit further and show that the April, 2029 close approach will occur at only 5.6 Earth radii, approximately one-half the distance previously estimated.
• A radar observation on August 7 refines the orbit further and eliminates the possibility of an impact in 2035. Only the pass in 2036 remains at Torino Scale

Possible impact effects

It must be stressed that the odds of impact are now known to be very low. Hence, the possible effects of an impact are largely irrelevant.

However, the initial reports resulted in widespread discussion on many Internet forums, including armchair speculation about exactly where Apophis (then known only as 2004 MN4) would hit and what would happen when it did.

NASA initially estimated the energy that Apophis would have released if it impacted Earth as the equivalent of 1480 megatons of TNT (114,000 times the energy from the nuclear bomb Little Boy, dropped by the United States on Hiroshima, Japan). A more refined later estimate was 850 megatons. The impacts which created the Barringer Crater or caused the Tunguska event are estimated to be in the 10-20 megaton range. The 1883 eruption of Krakatoa was the equivalent of roughly 200 megatons.

The exact effects of any impact would have varied based on the asteroid's composition, and the location and angle of impact. Any impact would have been extremely detrimental to an area of thousands of square kilometres, but would have been unlikely to have long-lasting global effects, such as the precipitation of an impact winter.

Based on the predicted time of impact (0.89 of a day, or about 21:20 UTC) and the fact that the asteroid would be approaching the Earth from outside of its orbit, the impact was likely to occur in the Eastern Hemisphere (time zones UTC +3 to UTC +10).

Any potential impact would have occurred at a velocity of 12.59 km/s.

It's called Apophis. It's 390m wide.
And it could hit Earth in 31 years time
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Scientists call for plans to change asteroid's path Developing technology could take decades

In Egyptian myth, Apophis was the ancient spirit of evil and destruction, a demon that was determined to plunge the world into eternal darkness.

A fitting name, astronomers reasoned, for a menace now hurtling towards Earth from outerspace. Scientists are monitoring the progress of a 390-metre wide asteroid discovered last year that is potentially on a collision course with the planet, and are imploring governments to decide on a strategy for dealing with it.

Nasa has estimated that an impact from Apophis, which has an outside chance of hitting the Earth in 2036, would release more than 100,000 times the energy released in the nuclear blast over Hiroshima. Thousands of square kilometres would be directly affected by the blast but the whole of the Earth would see the effects of the dust released into the atmosphere.

And, scientists insist, there is actually very little time left to decide. At a recent meeting of experts in near-Earth objects (NEOs) in London, scientists said it could take decades to design, test and build the required technology to deflect the asteroid. Monica Grady, an expert in meteorites at the Open University, said: "It's a question of when, not if, a near Earth object collides with Earth. Many of the smaller objects break up when they reach the Earth's atmosphere and have no impact. However, a NEO larger than 1km [wide] will collide with Earth every few hundred thousand years and a NEO larger than 6km, which could cause mass extinction, will collide with Earth every hundred million years. We are overdue for a big one."

Apophis had been intermittently tracked since its discovery in June last year but, in December, it started causing serious concern. Projecting the orbit of the asteroid into the future, astronomers had calculated that the odds of it hitting the Earth in 2029 were alarming. As more observations came in, the odds got higher.

Having more than 20 years warning of potential impact might seem plenty of time. But, at last week's meeting, Andrea Carusi, president of the Spaceguard Foundation, said that the time for governments to make decisions on what to do was now, to give scientists time to prepare mitigation missions. At the peak of concern, Apophis asteroid was placed at four out of 10 on the Torino scale - a measure of the threat posed by an NEO where 10 is a certain collision which could cause a global catastrophe. This was the highest of any asteroid in recorded history and it had a 1 in 37 chance of hitting the Earth. The threat of a collision in 2029 was eventually ruled out at the end of last year.

Alan Fitzsimmons, an astronomer from Queen's University Belfast, said: "When it does pass close to us on April 13 2029, the Earth will deflect it and change its orbit. There's a small possibility that if it passes through a particular point in space, the so-called keyhole, ... the Earth's gravity will change things so that when it comes back around again in 2036, it will collide with us." The chance of Apophis passing through the keyhole, a 600-metre patch of space, is 1 in 5,500 based on current information.

There are no shortage of ideas on how to deflect asteroids. The Advanced Concepts Team at the European Space Agency have led the effort in designing a range of satellites and rockets to nudge asteroids on a collision course for Earth into a different orbit.

No technology has been left unconsidered, even potentially dangerous ideas such as nuclear powered spacecraft. "The advantage of nuclear propulsion is a lot of power," said Prof Fitzsimmons. "The negative thing is that ... we haven't done it yet. Whereas with solar electric propulsion, there are several spacecraft now that do use this technology so we're fairly confident it would work."

The favoured method is also potentially the easiest - throwing a spacecraft at an asteroid to change its direction. Esa plans to test this idea with its Don Quixote mission, where two satellites will be sent to an asteroid. One of them, Hidalgo, will collide with the asteroid at high speed while the other, Sancho, will measure the change in the object's orbit. Decisions on the actual design of these probes will be made in the coming months, with launch expected some time in the next decade. One idea that seems to have no support from astronomers is the use of explosives.

Prof Fitzsimmons. "If you explode too close to impact, perhaps you'll get hit by several fragments rather than one, so you spread out the area of damage."

In September, scientists at Strathclyde and Glasgow universities began computer simulations to work out the feasibility of changing the directions of asteroids on a collision course for Earth. In spring next year, there will be another opportunity for radar observations of Apophis that will help astronomers work out possible future orbits of the asteroid more accurately.

If, at that stage, they cannot rule out an impact with Earth in 2036, the next chance to make better observations will not be until 2013. Nasa has argued that a final decision on what to do about Apophis will have to be made at that stage.

"It may be a decision in 2013 whether or not to go ahead with a full-blown mitigation mission, but we need to start planning it before 2013," said Prof Fitzsimmons. In 2029, astronomers will know for sure if Apophis will pose a threat in 2036. If the worst-case scenarios turn out to be true and the Earth is not prepared, it will be too late. "If we wait until 2029, it would seem unlikely that you'd be able to do anything about 2036," said Mr Yates.