27 Dec 2004
(Source: NeoDys Risk Page (Italy))
Near-Earth Asteroid 2004 MN4: improved situation
Andrea Milani, Maria Eugenia Sansaturio, Giovanni B. Valsecchi
NeoDys Risk Page (Italy)
December 27, 2004
The asteroid 2004 MN4 will have a very close approach to Earth in 2029. However, the observations collected by the astronomers, both professionals and amateurs, have provided enough information to exclude the possibility of an impact in 2029. This asteroid has an estimated diameter of 400 meters, and the nominal orbit solution results in a close approach to the Earth at 64,000 Km minimum distance on April 13, 2029. The actual distance could even be smaller, as small as 8 times the radius of the Earth. At the time of closest approach, the asteroid should be as bright as a fifth magnitude star, thus from some areas it will be visible to the naked eye.
The sharp decrease in the estimated risk from this object was the result of the enormous work done by astronomers from all over the world. Notwidstanding the Christmas holidays, many dedicated people went to work in their observatories, in the archives of past observations and at their computers, as it was the case for the staff of NEODyS. More than 200 new observations of 2004 MN4 were obtained in the last 5 days. The discovery observations of June have been painfully remeasured, the impact monitoring computer programs have been run more than 30 times. Finally today some prediscovery observations from March 2004 were found and extracted from the archives of the Spacewatch survey. These allowed to extend significantly the observations time span, thus the confidence region for the orbital elements was sharply reduced and many impacts compatible with the previous data turned out to be incompatible with the extended observations.
However, given the current knowledge of the orbit, we cannot yet exclude that there could be an impact at a later date, e.g., in 2044 and 2053. We have every expectation that further monitoring and further analysis on this object will entirely eliminate its potential hazard.
The amount of risk we estimate from this asteroid, given the new data, is not significant in comparison with the background probability of impact (from the asteroid population, known and unknown). This can be expressed by means of the Palermo Scale (PS), which encodes, e.g., the ratio of the risk from the 2044 encounter to the background risk for the time span from now to 2044: the value of the PS is -1.76, that is the risk from this case is almost two orders of magnitude below the background risk. For details please consult the risk page of 2004 MN4.
In accordance with the rules agreed upon by the International Astronomical Union and by the operators of the impact monitoring systems, the announcement that the 2029 impact has been ruled out was posted only after the computations, done automatically by software robots CLOMON2 in Pisa/Valladolid and Sentry in Pasadena, were assessed by the scientists in charge and cross checked between the two systems.
The coworkers of NEODyS/CLOMON2 will continue, in the next days, to process additional observational data as they become available, hoping to remove the remaining Virtual Impactors as soon as possible.