44
orbits. These changes include radiation pressure acting in the direction of the
Poynting vector (radially outwards from the sun), Poynting–Robertson drag
(a resistive force proportional to the tangential velocity of the particles), braking caused by the electrostatic interaction between the solar plasma and the
charged zodiacal dust particles, and forces deriving from the existence of the
magnetic field in interplanetary space, all of which tend to augment the inclinations of the particle orbits, one component being radial and the other polar.
For certain particle sizes some of these processes will force the grains to leave
the Solar System in time periods of less than a year. But even the slow effects
of gravity, acting over billions of years, are capable of clearing interplanetary
space of dust of cosmic origin.
There is no choice but to seek effective processes of particle injection in
order to explain the permanence of the zodiacal light (likewise for exozodiacal
light). Among the main processes proposed are cometary disintegration, collisional fragmentation of asteroids, capture of interstellar grains, and condensation of interplanetary gas. It is now fifty years since we proposed the existence
of and looked for transitory ‘trails’ or ‘scars’ in the zodiacal cloud (regions of
altered density) to track the effects of both injection and ejection.
The key questions to resolve are the size and nature of the tiny interplanetary particles, along with their origin and evolution, all of which is of great
importance for modelling the formation and evolution of exoplanetary systems. This matter is of the greatest interest now that there is a growing suspicion that there are few stars without a retinue of planets, all of which means
that zodiacal light studies have achieved a new importance. Of course, to
make headway in this topic, improved polarization and spectroscopic measurements are needed at all wavelengths made from the Earth’s surface and
space. But it is now many years since the author and the IAC abandoned this
line of research.
F. Sánchez
orbits. These changes include radiation pressure acting in the direction of the
Poynting vector (radially outwards from the sun), Poynting–Robertson drag
(a resistive force proportional to the tangential velocity of the particles), braking caused by the electrostatic interaction between the solar plasma and the
charged zodiacal dust particles, and forces deriving from the existence of the
magnetic field in interplanetary space, all of which tend to augment the inclinations of the particle orbits, one component being radial and the other polar.
For certain particle sizes some of these processes will force the grains to leave
the Solar System in time periods of less than a year. But even the slow effects
of gravity, acting over billions of years, are capable of clearing interplanetary
space of dust of cosmic origin.
There is no choice but to seek effective processes of particle injection in
order to explain the permanence of the zodiacal light (likewise for exozodiacal
light). Among the main processes proposed are cometary disintegration, collisional fragmentation of asteroids, capture of interstellar grains, and condensation of interplanetary gas. It is now fifty years since we proposed the existence
of and looked for transitory ‘trails’ or ‘scars’ in the zodiacal cloud (regions of
altered density) to track the effects of both injection and ejection.
The key questions to resolve are the size and nature of the tiny interplanetary particles, along with their origin and evolution, all of which is of great
importance for modelling the formation and evolution of exoplanetary systems. This matter is of the greatest interest now that there is a growing suspicion that there are few stars without a retinue of planets, all of which means
that zodiacal light studies have achieved a new importance. Of course, to
make headway in this topic, improved polarization and spectroscopic measurements are needed at all wavelengths made from the Earth’s surface and
space. But it is now many years since the author and the IAC abandoned this
line of research.
F. Sánchez