322 research outputs found
A new method to determine the grain size of planetary regolith
Airless planetary bodies are covered by a dusty layer called regolith. The
grain size of the regolith determines the temperature and the mechanical
strength of the surface layers. Thus, knowledge of the grain size of planetary
regolith helps to prepare future landing and/or sample-return missions. In this
work, we present a method to determine the grain size of planetary regolith by
using remote measurements of the thermal inertia. We found that small bodies in
the Solar System (diameter less than ~100 km) are covered by relatively coarse
regolith grains with typical particle sizes in the millimeter to centimeter
regime, whereas large objects possess very fine regolith with grain sizes
between 10 and 100 micrometer.Comment: Accepted by Icaru
The physics of protoplanetesimal dust agglomerates. VII The low-velocity collision behavior of large dust agglomerates
We performed micro-gravity collision experiments in our laboratory drop-tower
using 5-cm-sized dust agglomerates with volume filling factors of 0.3 and 0.4,
respectively. This work is an extension of our previous experiments reported in
Beitz et al. (2011) to aggregates of more than one order of magnitude higher
masses. The dust aggregates consisted of micrometer-sized silica particles and
were macroscopically homogeneous. We measured the coefficient of restitution
for collision velocities ranging from 1 cm/s to 0.5 m/s, and determined the
fragmentation velocity. For low velocities, the coefficient of restitution
decreases with increasing impact velocity, in contrast to findings by Beitz et
al. (2011). At higher velocities, the value of the coefficient of restitution
becomes constant, before the aggregates break at the onset of fragmentation. We
interpret the qualitative change in the coefficient of restitution as the
transition from a solid-body-dominated to a granular-medium-dominated behavior.
We complement our experiments by molecular dynamics simulations of porous
aggregates and obtain a reasonable match to the experimental data. We discuss
the importance of our experiments for protoplanetary disks, debris disks, and
planetary rings. The work is an extensional study to previous work of our group
and gives a new insight in the velocity dependency of the coefficient of
restitution due to improved measurements, better statistics and a theoretical
approach
The stratification of regolith on celestial objects
All atmosphere-less planetary bodies are covered with a dust layer, the
so-called regolith, which determines the optical, mechanical and thermal
properties of their surface. These properties depend on the regolith material,
the size distribution of the particles it consists of, and the porosity to
which these particles are packed. We performed experiments in parabolic flights
to determine the gravity dependency of the packing density of regolith for
solid-particle sizes of 60 m and 1 mm as well as for 100-250 m-sized
agglomerates of 1.5 m-sized solid grains. We utilized g-levels between 0.7
m s and 18 m s and completed our measurements with experiments
under normal gravity conditions. Based on previous experimental and theoretical
literature and supported by our new experiments, we developed an analytical
model to calculate the regolith stratification of celestial rocky and icy
bodies and estimated the mechanical yields of the regolith under the weight of
an astronaut and a spacecraft resting on these objects.Comment: 15 pages, 12 figure
Weniger ist mehr, zuviel ist nicht genug, ein bisschen ist perfekter : Maik und Dirk Löbberts Situationen zwischen Geometrie und Alltag / Less is more, too much is not enough, a bit is more perfect : Maik und Dirk Löbbert's situations between geometry and everyday life
The Suborbital Particle Aggregation and Collision Experiment (SPACE): Studying the Collision Behavior of Submillimeter-Sized Dust Aggregates on the Suborbital Rocket Flight REXUS 12
The Suborbital Particle Aggregation and Collision Experiment (SPACE) is a
novel approach to study the collision properties of submillimeter-sized, highly
porous dust aggregates. The experiment was designed, built and carried out to
increase our knowledge about the processes dominating the first phase of planet
formation. During this phase, the growth of planetary precursors occurs by
agglomeration of micrometer-sized dust grains into aggregates of at least
millimeters to centimeters in size. However, the formation of larger bodies
from the so-formed building blocks is not yet fully understood. Recent
numerical models on dust growth lack a particular support by experimental
studies in the size range of submillimeters, because these particles are
predicted to collide at very gentle relative velocities of below 1 cm/s that
can only be achieved in a reduced-gravity environment.
The SPACE experiment investigates the collision behavior of an ensemble of
silicate-dust aggregates inside several evacuated glass containers which are
being agitated by a shaker to induce the desired collisions at chosen
velocities. The dust aggregates are being observed by a high-speed camera,
allowing for the determination of the collision properties of the
protoplanetary dust analog material. The data obtained from the suborbital
flight with the REXUS (Rocket Experiments for University Students) 12 rocket
will be directly implemented into a state-of-the-art dust growth and collision
model
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