[meteorite-list] Near-Earth Asteroid 2004 MN4: Improved Situation

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue Dec 28 14:25:25 2004
Message-ID: <200412281924.LAA15811_at_zagami.jpl.nasa.gov>

http://newton.dm.unipi.it/cgi-bin/neodys/neoibo?riskpage:0;main

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.
Received on Tue 28 Dec 2004 02:24:22 PM PST