Geoscience Reference
In-Depth Information
the instruments designed to observe meteors from space on the Earth are
also valid for Venus.
3.3.
Meteors on giant planets
Considering the same conditions (mass and velocity of the meteoroids and
atmospheric density), even on giant planets (Jupiter, Saturn, Uranus, and
Neptune) meteors have to be as luminous as on the other planets.
In the case of Jupiter, by using the law of the atmospheres:
ρ
(
q
)=
ρ
0
exp(
−
q/H
)
,
(7)
where
q
is the height,
ρ
0
the density at the atmospheric level with 100 mbar
pressure (
q
=0km),and
H
the atmosphere scale height, we obtain that
the interval 120-70 km for the meteors on Earth corresponds to the inter-
val 290-115 km on the giant of the solar system. These values have been
computed considering as level zero the atmospheric layer at the pressure of
100 mbar.
A meteor trail in the Jupiter atmosphere has been observed during
the Voyager 1 fly-by.
6
From the observations, it results that the bolide
reached the atmospheric level at 3.5 mbar, at about 100 km over the zero
level at 100 mbar, in good agreement with the estimated height range for the
Jovian meteors. The instruments used for the observation of the terrestrial
meteors from orbit are also valid for Jupiter, where the meteor phenomenon
is substantially analogous.
4. Impact Flashes
The Moon, as all the solar system bodies, has undergone a continuous
bombardment by asteroids, comets, and meteoroids since its formation.
Due to the absence of an atmosphere, during the last phases of the fall the
meteor phenomenon does not occur and all the meteoroid kinetic energy is
released on the ground. During the impact a fraction (spanning from 10
−
3
to 10
−
2
) of the impact energy is converted in a luminous flash.
Meteoroid impacts on the Moon have been detected in the past visually
and by the Apollo Lunar Seismic Network. Several observers have claimed
to have detected optical flashes on the Moon, but any of such events has
never been confirmed in an independent way, until the impacts on 18 and
19 November 1999 due to Leonid shower. Unfortunately, different phenom-
ena can cause the appearance of a flash, such as reflection in the instrument
optics, cosmic rays hitting the retina, reflections due to artificial satellite
