Download Ingrid Mann Dust- plasma processes in the vicinity of planetary

Ingrid Mann
Dust- plasma processes in the vicinity of planetary objects and spacecraft
A large amount of solar system dust forms when dust particles collide with other dust, or hit the
surface of planetary objects. Dust impacts on spacecraft influence the particle and field
measurements made onboard. Dust particles that hit the atmospheres of planets disintegrate
and produce meteors. In each of these impact processes, cloudlets of plasma, neutral particles,
and nanometer-sized dust are formed. The surrounding environment controls the dynamics of
the impact-generated populations, for example through electric- and magnetic fields and
radiation pressure. At the same time, the impact-generated ions, neutrals and dust particles
affect the local space environment.
Active asteroids are assumed to emit dust in a similar way as comets. This phenomenon has so
far been observed at a little less than 20 objects and they are detected at a rate of about two per
year. The activity typically lasts a few weeks, but the cause of the activity is not yet understood.
Similar to comets, the activity could be caused by sublimation of ices in the asteroids, but also
fragmentation due to e.g. rotation, or impact events are possible reasons for the activity.
Dust impacts on spacecraft generate signatures in field measurements that have been observed
already since the early days of the Voyager space mission in the 1980s. The dust impacts
generate a small crater on the spacecraft. Some material is ejected and the electric potential of
the spacecraft changes. Dust and spacecraft material form a cloudlet of electrons, ions and
charged dust that induces an electric field. A fraction of the charged particles is collected onto
the spacecraft while another fraction expands into space. The combination of these effects is
seen in the measurements of the electric field instruments operated on the spacecraft.
Dust particles also form in atmospheres when meteors are observed. Cosmic dust particles that
enter the Earth’s atmosphere are heated, producing evaporated material that dissociates and
ionizes at about 140–60 km altitude. Small meteoroids and dust particles, gaseous species that
originate from the meteoroids, and small meteoritic smoke particles re-condense from the gas.
Cosmic dust and meteoroids and their fragments play an important role in the physical and
chemical processes of the upper atmosphere.
Ejection of dust grains from the lunar surface have been suggested as an explanation for
sunlight scattering across the lunar horizon, yet the mechanism to release enough dust grains to
high altitudes has not been explained. Electric fields near the lunar surface are thought to play
an important role for the lunar dust dynamics and may cause dust transport across the day-night
terminator, or even sorting of dust grains by size in areas of lunar crustal magnetic fields.
To study these processes the distribution of ejecta particles needs to be simulated taking into
account the acting forces and estimating and evaluating the influence of other processes like
variable charge states, dust interactions with electron and ions, electron-kinetic scale processes
and photo ionization. The results from model calculations should be compared to in-situ and
brightness observations available.
The outcome of the project should also contribute to prepare for the data analyses of upcoming
space missions to the inner solar system inside 1 AU, where 1 AU is the average distance
between Sun and Earth. The ESA mission Solar Orbiter will make observations of the Sun and insitu measurements from elliptic orbits coming as close as about 0.28 AU to the Sun. The NASA
mission Solar Probe Plus will move to less than 0.1 AU from the Sun. The launches of Solar
Orbiter and Solar Probe Plus are scheduled for 2018.