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2.2. Bolides and superbolides
Due to orbital perturbations with Jupiter, Saturn, and Mars, and also under
the influence of radiative mechanisms like the Yarkowsky effect, meteoroids
originating in the asteroid main belt can be inserted into orbits crossing
those of the terrestrial planets: Mercury, Venus, Earth, and Mars. There-
fore, there are a lot of small bodies, having dimensions of some meters,
which can interact with our planet. If the meteoroid has a size larger than
about 20 cm, during the passage in the atmosphere the meteor head can
reach a high luminosity. When the zenithal apparent magnitude is lower
than
8 magnitudes, the meteor is called bolide . If the bolide magnitude
is lower than
17, this is called a superbolide . Bodies having mass larger
than 1,000 kg generate superbolides. For meteoroids having diameter of
some tens of meters the bolide can be brighter than the Sun (apparent
magnitude
27). Superbolides are rare events, which would need a global
observing network, in order to be studied in a systematic way. 5
Often the meteoroid undergoes multiple fragmentations, generating a
multiple bolide. If the meteoroid is big enough, it can survive the ablation
process. When the velocity decrease below 3 km/s, the mass loss and the
radiation emission end, and the meteoroid enters the so-called dark flight
phase. From this moment a cooling process begins, while at the same time
the body trajectory becomes more and more vertical.
2.3. Meteor observations from space
Still to be explored is the systematic monitoring of meteors from satellites
in orbit around Earth. The USA military surveillance satellites reveal 30-50
superbolide explosions in the atmosphere per year, but frequently the data
on these events, especially the less bright, are discarded. A satellite network
equipped with dedicated cameras is thus necessary to observe in a global
and systematic way these phenomena.
If q is the height in km of the satellite from the Earth surface, and
M the meteor absolute magnitude, the apparent magnitude of the meteor
observed from orbit is given by:
m = M
10 + 5 log( q
100) .
(2)
Considering the sensor limit magnitude on board the satellite +6.0 and the
height 400 km, from Eq. (2) it follows that from orbit only meteors having
absolute magnitude lower than M =+3 . 6 will be detectable. The trends of
Eq. (2) in function of the height and for different M values are plotted in
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