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2004 MN4

From Biocrawler, the free encyclopedia.

The title of this article is incorrect because of technical limitations. The correct title is 2004 MN₄.

Close approach of 2004 MN4 on April 13, 2029

The white bar indicates uncertainty in the range of positions

2004 MN₄ (also written 2004 MN4) is a Near-Earth asteroid that caused a brief period of concern in late 2004. Initial observations of the asteroid revealed a relatively large probability that 2004 MN₄ would strike the Earth in 2029. However, additional observations provided improved predictions that essentially eliminated the possibility of an impact on Earth or the Moon.

Nevertheless, it is expected that it will 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.

2004 MN₄ remains at level one on the Torino scale because of very low but nonzero probabilities of impact on approaches in 2035, 2036 and 2037. 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 [1] (http://science.nasa.gov/headlines/y2005/13may_2004mn4.htm?friend).

Contents

1 Basic data

2 Discovery

3 History of estimates

4 Possible impact effects

5 See also

6 External links

6.1 Risk assessment
6.2 NASA
6.3 Older articles
6.4 More recent articles

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Basic data

2004 MN₄ belongs to a group called the "Aten asteroids", asteroids with an orbital semi-major axis less than one astronomical unit. This particular asteroid 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 2004 MN₄'s length was estimated at 410 m (1350 ft); a more refined estimate based on radar observations 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 miles) from the Earth's surface on April 13, 2029, slightly higher than the altitude of geosynchronous satellites, which orbit at 35,786 km (22,300 miles). Its brightness will be about magnitude 3.3, with a peak 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.

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Discovery

2004 MN₄ was discovered on June 19, 2004, by Roy 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.

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 2004 MN₄ 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.

The asteroid was precovered to 2004-March 15.1104, and an improved orbital prediction was released on December 27. 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. Some other passes still carry some risk, and the cumulative odds of impact over the entire 21st century is 0.0041 percent (1 in 24,000). As of January 15, 2005, the cumulative Palermo scale rating for 2004 MN₄ is −1.59 and the Torino scale rating is 1.

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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 2004 MN₄ 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 by the Arecibo Observatory on January 27, 28, and 30 refine the orbit still further. Three passes at 1 (Torino Scale) in 2035, 2036, 2037.

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Possible impact effects

Because the odds of impact are now known to be very low, the effects of such an event are largely irrelevant. However, for several days armchair speculation about exactly where 2004 MN₄ would hit and what would happen when it did was common on many internet forums.

NASA initially estimated the energy that 2004 MN₄ 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 kilometers, 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 21:21 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.

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External links

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Risk assessment

These sources are updated as new orbital data becomes available:

2004 MN₄ Impact Risk (http://neo.jpl.nasa.gov/risk/2004mn4.html) (NASA JPL)
2004 MN4 page (http://newton.dm.unipi.it/cgi-bin/neodys/neoibo?objects:2004MN4;main) and 2004 MN4 impactor table (http://newton.dm.unipi.it/cgi-bin/neodys/neoibo?objects:2004MN4;risk) from NEODyS.