2036 asteroid collision ‘effectively ruled out’

The possibility that a 325-metre-wide asteroid will impact Earth in 2036 has been “effectively ruled out” based on new data leading up to yesterday’s flyby, NASA scientists announced.

Asteroid Apophis was discovered on 19 June 2004. Credit: UH/IA

SYDNEY: The possibility that a 325-metre-wide asteroid will impact Earth in 2036 has been “effectively ruled out” based on new data leading up to yesterday’s flyby, NASA scientists announced.

When the asteroid, named Apophis after a demon from Egyptian mythology, was discovered in 2004, scientists estimated a 2.7% chance of impact in 2029 – the highest ever seen for an asteroid.

While the 2029 impact was soon ruled out, a small chance (one in 250,000) remained for a collision with Apophis in 2036 – until yesterday.

Impact odds less than one in a million

“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,” said Don Yeomans, manager of NASA’s Near-Earth Object Program Office, in a statement.

“Our interest in asteroid Apophis will essentially be for its scientific interest for the foreseeable future,” he said.

The scientists used updated information obtained by NASA telescopes in 2011 and 2012, as well as new data from the time leading up to Apophis’ distant Earth flyby yesterday.

Next month’s close shave

When asteroid Apophis does pass Earth again in 2029, it will be the closest flyby of an asteroid of its size, at 31,300 kilometres (19,400 miles) above Earth’s surface.

However much sooner, on February 15 this year, another smaller (45 metre-wide) asteroid, called 2012 DA14, will also pass Earth at less than 30,000 km – closer than the orbit of our geostationary satellites. 2012 DA14 will not be visible to the naked eye.

More information:
NASA Asteroid Watch

The Doomsday asteroid Apophis that could hit Earth in 2036 as it whizzed past us

Pictured: The 'Doomsday' asteroid Apophis that could hit Earth in 2036 as it whizzed past us (but don't worry it was still nine million miles away)

• 1000 foot wide asteroid will brush past the Earth at a distance of 30,000km
• Scientists claim little chance of it hitting us - but scientists warn of 'tiny but real' likelihood it may in 2036
• Name inspired by two of the asteroid's co-discoverers favorite science fiction villain
• 
  

The European Space Agency's orbiting telescope has captured striking new images of the huge 'Doomsday' asteroid Apophis that could smash into Earth in 2036 - revealing it is larger than previously thought.

Long billed as a potential cause of an Extinction Level Event (ELE) for humanity, today ESA officials announced that its Herschel Space Observatory discovered that the asteroid is 1,066 feet wide, 20 percent larger than the previous estimate of 885 feet.

Whizzing past Earth at the relatively close distance of nine million miles tonight, Apophis is being closely tracked because of a 2004 study that predicted the rock has a 2.7 percent chance of hitting Earth in April 2029, which was later revised to 2036.

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ESAs Herschel Space Observatory captured asteroid Apophis in its field of view during the approach to Earth on January, 5-6, 2013. This image shows the asteroid in Herschels three PACS wavelengths: 70, 100 and 160 microns

'The 20 percent increase in diameter … translates into a 75 percent increase in our estimates of the asteroid's volume or mass,' study leader Thomas Müller of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, said in a statement.

In addition to the latest findings two free webcasts will stream live views of the asteroid as it passes, filmed from telescopes in Italy and the Canary Islands.

The video streams from Slooh Space Telescope and Virtual Telescope Project will show Apophis as a moving light streaking across the sky - although scientists have said that sadly the large space rock is too small to be seen through home telescopes.

 

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'Alone among all these near-Earth asteroids that have passed our way in recent years, Apophis has generated the most concern worldwide because of its extremely close approach in 2029 and [chances of a] potential impact, albeit small, in 2036,' said Slooh president Patrick Paolucci.

Indeed, while scientists have ruled out any possibility of a cataclysmic collision - there remains a very real chance of the asteroid Apophis smashing into Earth in 2036.

'Apophis has been one of those celestial bodies that has captured the public's interest since it was discovered in 2004,' said Steve Chesley at NASA's Jet Propulsion Laboratory in Pasadena, California.

Jan. 8, 2013: At about 36 hours from the minimum distance (9.3 million miles from Earth), potentially hazardous asteroid Apophis was imaged again with the Virtual Telescope

'Updated computational techniques and newly available data indicate the probability of an Earth encounter on April 13, 2036, for Apophis has dropped from one-in-45,000 to about four-in-a million.'

The science of predicting asteroid orbits is based on a physical model of the solar system which includes the gravitational influence of the sun, moon, other planets and the three largest asteroids. 

The potential planet killer named after a science fiction villain

• One year after its discovery, the asteroid was given the idenitfication number of 99942 in 2005.
• This made it eligible to be be named and on July 19th 2005, the asteroid was called 'Apophis'.
• Apophis is the Greek name for the the enemy of the Ancient Egyptian sun god Ra.
• He is the Uncreator, and is characterised as an evil serpent who dwells in eternal darkness and tries to consume Ra during his nightly passage.
• Roy A. Tucker, David J. Tholen, two of the asteroids co-discoverers are also fans of the science fiction television series Stargate SG-1.
• A prominent villain in that show is called Apophis, who in the mythology of that particular series, gave rise to the myth of the Egyptian god.

NASA detects and tracks asteroids and comets passing close to Earth using both ground and space-based telescopes. 

The Near Earth-Object Observations Program, commonly called 'Spaceguard,' discovers these objects, characterizes a subset of them and plots their orbits to determine if any could be potentially hazardous to our planet.

This year Apophis, named after an Egyptian mythological demon, will not get closer than around nine million miles.

Doomsday Asteroid? An artist's rendering of the asteroid Apophis as created by the European Space Agency

Experts say the impact if Apophis struck the Earth would generate a blast equivalent to more than 500 megatons of TNT

Scientists will use the encounter to improve their estimate of just how dangerous the space rock really is to life on Earth.

In 2029, Apophis is expected to come uncomfortably close, brushing past the Earth at a distance of just 30,000 kilometres. That will put the asteroid inside the orbit of communication satellites.

Current models predict a tiny but real likelihood of Apophis colliding with the Earth in 2036.

When the asteroid was discovered in 2004 scientists calculated a one-in-45 chance of an impact in 2029.

Improved predictions later lifted the threat.

The asteroid's latest near approach will occur at midnight UK time tomorrow.

Members of the public can view the event online via the Slooh web-based sky-watching service, which collects images from observatories around the world.

'We are excited to cover this asteroid live for the general public.'

Scientists at the American space agency Nasa have calculated that if Apophis struck the Earth it would generate a blast equivalent to more than 500 megatons of TNT.

In comparison, the most powerful hydrogen bomb ever detonated, the Soviet Tsar Bomba, released 57 megatons.

 VIDEO   The 'Doomsday' huge asteroid Apophis passes by Earth 

The huge asteroid Apophis passes by Earth

Possibility of an Earth Impact in 2029 Ruled Out for Asteroid 2004 MN4

Possibility of an Earth Impact in 2029 Ruled Out for Asteroid 2004 MN4

Don Yeomans, Steve Chesley and Paul Chodas
NASA's Near Earth Object Program Office 
December 27, 2004

Over the past week, several independent efforts were made to search for pre-discovery observations of 2004 MN4. These efforts proved successful today when Jeff Larsen and Anne Descour of the Spacewatch Observatory near Tucson, Arizona, were able to detect and measure very faint images of asteroid 2004 MN4 on archival images dating to 15 March 2004. These observations extended the observed time interval for this asteroid by three months allowing an improvement in its orbit so that an Earth impact on 13 April 2029 can now be ruled out.

As is often the case, the possibility of future Earth impacts for some near-Earth objects cannot be entirely ruled out until the uncertainties associated with their trajectories are reduced as a result of either future position observations, or in this case, heretofore unrecognized, pre-discovery observations. When these additional observations were used to update the orbit of 2004 MN4, the uncertainties associated with this object's future positions in space were reduced to such an extent that none of the object's possible trajectories can impact the Earth (or Moon) in 2029.

In the accompanying diagram, the most likely position of asteroid 2004 MN4 is shown at the end of the blue line near the Earth on 13 April 2029. However, since the asteroid's position in space is not perfectly known at that time, the white dots at right angles to the blue line are possible alternate positions of the asteroid. Neither the nominal position of the asteroid, nor any of its possible alternative positions, touches the Earth, indicating that an Earth impact in 2029 is ruled out.

Updated Set of Possible Positions of 2004 MN4 on April 13, 2029

The passage of the asteroid by the Earth in 2029 alters its subsequent trajectory and expands the asteroid's position uncertainty region (i.e., the line of white dots increases in extent) so the asteroid's subsequent motion is less certain than it was prior to the 2029 close Earth approach. However, our current risk analysis for 2004 MN4 indicates that no subsequent Earth encounters in the 21st century are of any concern.

NASA - NASA Refines Asteroid Apophis' Path Toward Earth

NASA Refines Asteroid Apophis' Path Toward Earth

 

 

PASADENA, Calif. -- Using updated information, NASA scientists have recalculated the path of a large asteroid. The refined path indicates a significantly reduced likelihood of a hazardous encounter with Earth in 2036. 

The Apophis asteroid is approximately the size of two-and-a-half football fields. The new data were documented by near-Earth object scientists Steve Chesley and Paul Chodas at NASA's Jet Propulsion Laboratory in Pasadena, Calif. They will present their updated findings at a meeting of the American Astronomical Society's Division for Planetary Sciences in Puerto Rico on Oct. 8. 

"Apophis has been one of those celestial bodies that has captured the public's interest since it was discovered in 2004," said Chesley. "Updated computational techniques and newly available data indicate the probability of an Earth encounter on April 13, 2036, for Apophis has dropped from one-in-45,000 to about four-in-a million." 

A majority of the data that enabled the updated orbit of Apophis came from observations Dave Tholen and collaborators at the University of Hawaii's Institute for Astronomy in Manoa made. Tholen pored over hundreds of previously unreleased images of the night sky made with the University of Hawaii's 88-inch telescope, located near the summit of Mauna Kea. 

Tholen made improved measurements of the asteroid's position in the images, enabling him to provide Chesley and Chodas with new data sets more precise than previous measures for Apophis. Measurements from the Steward Observatory's 90-inch Bok telescope on Kitt Peak in Arizona and the Arecibo Observatory on the island of Puerto Rico also were used in Chesley's calculations. 

The information provided a more accurate glimpse of Apophis' orbit well into the latter part of this century. Among the findings is another close encounter by the asteroid with Earth in 2068 with chance of impact currently at approximately three-in-a-million. As with earlier orbital estimates where Earth impacts in 2029 and 2036 could not initially be ruled out due to the need for additional data, it is expected that the 2068 encounter will diminish in probability as more information about Apophis is acquired. 

Initially, Apophis was thought to have a 2.7 percent chance of impacting Earth in 2029. Additional observations of the asteriod ruled out any possibility of an impact in 2029. However, the asteroid is expected to make a record-setting -- but harmless -- close approach to Earth on Friday, April 13, 2029, when it comes no closer than 18,300 miles above Earth's surface. 

"The refined orbital determination further reinforces that Apophis is an asteroid we can look to as an opportunity for exciting science and not something that should be feared," said Don Yeomans, manager of the Near-Earth Object Program Office at JPL. "The public can follow along as we continue to study Apophis and other near-Earth objects by visiting us on our AsteroidWatch Web site and by following us on the @AsteroidWatch Twitter feed." 

The science of predicting asteroid orbits is based on a physical model of the solar system which includes the gravitational influence of the sun, moon, other planets and the three largest asteroids. 

NASA detects and tracks asteroids and comets passing close to Earth using both ground and space-based telescopes. The Near Earth-Object Observations Program, commonly called "Spaceguard," discovers these objects, characterizes a subset of them and plots their orbits to determine if any could be potentially hazardous to our planet. 

JPL manages the Near-Earth Object Program Office for NASA's Science Mission Directorate in Washington. Cornell University operates the Arecibo Observatory under a cooperative agreement with the National Science Foundation in Arlington, Va. 

For more information about asteroids and near-Earth objects, visit: 

http://www.jpl.nasa.gov/asteroidwatch

For more information about NASA, visit: 

http://www.nasa.gov

 

- end -

Predicting Apophis' Earth Encounters in 2029 and 2036

Predicting Apophis' Earth Encounters in 2029 and 2036

SUMMARY

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).

Arecibo Radar Image of Apophis

Apophis Position Uncertainty

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.

Present era through 2029 Small factors 2029-2036

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.

Apophis Trajectory Change

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.

UPDATE NOTES

2009-Apr-29:
This animation illustrates how the unmeasured physical parameters of Apophis bias the entire statistical uncertainty region. If Apophis is a RETROGRADE rotator on the small, less-massive end of what is possible, the measurement uncertainty region will get pushed back such that the center of the distribution encounters the Earth's orbit. This would result in an impact probability much higher than computed with the Standard Dynamical Model. Conversely, if Apophis is a small, less-massive PROGRADE rotator, the uncertainty region is advanced along the orbit. Only the remote tails of the probability distribution could encounter the Earth, producing a negligible impact probability. Although measurements in 2010-2011 may cut the size of the measurement uncertainty region greatly and result in an "all clear" using the Standard Dynamical Model, it may not be until Arecibo radar in 2013 provides a spin direction that Earth's passage through the probability distribution center can be ruled out.

2008-Jul-10:
An equivalent way of describing the problem of computing an impact probability for Apophis is that the true 2029 "keyhole" leading to a 2036 impact -- as compared to the theoretical keyhole derived from the Standard Dynamical Model -- is not known in the absence of knowledge of the complete dynamics. The problem is acute enough for Apophis that, IF impact hasn't been previously excluded, AND there hasn't been a through physical characterization, it can't be known for certain it will impact until during or after the 2029 encounter, even if a spacecraft is accompanying Apophis and providing position measurements good to 2 meters. That is, the keyhole could be determined only retrospectively, after passage through it.

2008-Apr-16:
In response to inquiries, accidental impact with an artifical satellite in 2029 is vanishingly unlikely. As mentioned above, (1) Apophis does not pass near the zones where most satellites are located and (2) man-made satellites and Apophis both have small cross-sectional areas. Even if a high-velocity impact occurred, at most a large satellite could change Apophis' position 7 years later (in 2036) by only 100's of km. This is less than 1/10th the size of the smaller issues considered in the study, very much in the noise of the calculations, and can have no meaningful effect on Earth impact probability estimation (which already incorporates more than 30 million km of uncertainty). At such a late date, impact with an artificial satellite would be like a bug on the windshield of Apophis. Deflection efforts are dependent on being early enough to leverage the dynamics of the 2029 encounter. Events during the encounter lack such leverage.

2008-Feb-22:
Paper received JPL's 2008 Edward Stone Award for Outstanding Research Publication.

2007-Dec-13:
The paper will be published in the January 2008 issue of Icarus. Reference: Giorgini JD, Benner LAM, Ostro SJ, Nolan MC, Busch MW, Predicting the Earth encounters of (99942) Apophis, Icarus 193 (2008), pp. 1-19.

MN4 will come scarily close to Earth on April 13, 2029

Friday the 13th, 2029

Asteroid 2004 MN4 will come scarily close to Earth on April 13, 2029, but it will not hit.

Friday the 13th is supposed to be an unlucky day, the sort of day you trip on your shoe laces or lose your wallet or get bad news.

But maybe it's not so bad. Consider this: On April 13th--Friday the 13th--2029, millions of people are going to go outside, look up and marvel at their good luck. A point of light will be gliding across the sky, faster than many satellites, brighter than most stars.

What's so lucky about that? It's asteroid 2004 MN4 ... not hitting Earth.

For a while astronomers thought it might. On Christmas Eve 2004, Paul Chodas, Steve Chesley and Don Yeomans at NASA's Near Earth Object Program office calculated a 1-in-60 chance that 2004 MN4 would collide with Earth. Impact date: April 13, 2029.

Right: The orbits of Earth and asteroid 2004 MN4. [More]

The asteroid is about 320 meters wide. "That's big enough to punch through Earth's atmosphere," devastating a region the size of, say, Texas, if it hit land, or causing widespread tsunamis if it hit ocean, says Chodas. So much for holiday cheer.

Asteroid 2004 MN4 had been discovered in June 2004, lost, then discovered again six months later. With such sparse tracking data it was difficult to say, precisely, where the asteroid would go. A collision with Earth was theoretically possible. "We weren't too worried," Chodas says, "but the odds were disturbing."

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This is typical, by the way, of newly-discovered asteroids. Step 1: An asteroid is discovered. Step 2: Uncertain orbits are calculated from spotty tracking data. Step 3: Possible Earth impacts are noted. Step 4: Astronomers watch the asteroid for a while, then realize that it's going to miss our planet.

Killer Asteroid! headlines generally appear between steps 3 and 4, but that'sanother story.

Astronomers knew 2004 MN4 would miss Earth when they found pictures of the asteroid taken, unwittingly, in March 2004, three months before its official discovery. The extra data ruled out a collision in 2029.

Instead, what we're going to have is an eye-popping close encounter:

On April 13, 2029, asteroid 2004 MN4 will fly past Earth only 18,600 miles (30,000 km) above the ground. For comparison, geosynchronous satellites orbit at 22,300 miles (36,000 km). "At closest approach, the asteroid will shine like a 3rd magnitude star, visible to the unaided eye from Africa, Europe and Asia--even through city lights," says Jon Giorgini of JPL. This is rare. "Close approaches by objects as large as 2004 MN4 are currently thought to occur at 1000-year intervals, on average."

Above: The trajectory (blue) of asteroid 2004 MN4 past Earth on April 13, 2029. Uncertainty in the asteroid's close-approach distance is represented by the short white bar. [More]

The asteroid's trajectory will bend approximately 28 degrees during the encounter, "a result of Earth's gravitational pull," explains Giorgini. What happens next is uncertain. Some newspapers have stated that the asteroid might swing around and hit Earth after all in 2035 or so, but Giorgini discounts that: "Our ability to 'see' where 2004 MN4 will go (by extrapolating its orbit) is so blurred out by the 2029 Earth encounter, it can't even be said for certain what side of the sun 2004 MN4 will be on in 2035. Talk of Earth encounters in 2035 is premature."

In January 2004, a team of astronomers led by Lance Benner of JPL pinged 2004 MN4 using the giant Arecibo radar in Puerto Rico. (Coincidentally, the Arecibo dish is about the same size as the asteroid.) Echoes revealed the asteroid's precise distance and velocity, "allowing us to calculate the details of the 2029 flyby," says Giorgini, who was a member of the team along with Benner, Mike Nolan (NAIC) and Steve Ostro (JPL).

More data are needed to forecast 2004 MN4's motion beyond 2029. "The next good opportunities are in 2013 and 2021," Giorgini says. The asteroid will be about 9 million miles (14 million km) from Earth, invisible to the naked eye, but close enough for radar studies. "If we get radar ranging in 2013, we should be able to predict the location of 2004 MN4 out to at least 2070."

Right: The Arecibo radar in Puerto Rico is coincidentally about the size of asteroid 2004 MN4. [More]

The closest encounter of all, Friday the 13th, 2029, will be a spectacular opportunity to explore this asteroid via radar. During this encounter, says Giorgini, "radar could detect the distortion of 2004 MN4's shape and spin as it passes through Earth's gravity field. How the asteroid changes (or not) would provide information about its internal structure and material composition." Beautifully-detailed surface maps are possible, too.

The view through an optical telescope won't be so impressive. The asteroid's maximum angular diameter is only 2 to 4 arcseconds, which means it will be a starlike point of light in all but the very largest telescopes.

But to the naked eye--wow! No one in recorded history has ever seen an asteroid in space so bright.

Friday the 13th might not be so bad after all.