 |
| Titel |
Small Scale Impacts as trigger for an avalanche in a low gravity environment |
| VerfasserIn |
Marc Hofmann, Holger Sierks, Jürgen Blum |
| Konferenz |
EGU General Assembly 2014
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250094608
|
| Publikation (Nr.) |
 EGU/EGU2014-10029.pdf |
|
|
|
|
|
| Zusammenfassung |
| The European Space Agency’s Rosetta spacecraft was launched in 2004 and will rendezvous
with comet 67P/Churyumov-Gerasimenko in 2014. On its route towards the comet, it flew by
asteroid (21) Lutetia on 10 July 2010, with a closest approach distance of 3170 km. OSIRIS -
the Optical, Spectroscopic, and Infrared Remote Imaging System on board Rosetta [1] - took
462 images of Lutetia, using 21 broad- and narrowband filters covering a wavelength range
from 240 to 1000 nm [2].
The surface of Lutetia is covered with a thick layer of regolith. On slopes of
several craters this regolith layer collapsed in landslide like events. A possible trigger
mechanism for these low-gravity avalanches is the impact of a small mm to cm-sized
body.
We conducted an experiment where samples of different granular materials were tilted at
different angles with respect to the vector of gravity. We accelerated a small mm-sized metal
sphere to velocities up to 1.5 m/s and shot it into the sloped granular material. The impacts
and any events triggered by the impact were recorded using a high-speed high-resolution
camera.
The experiment was implemented at the center of applied space technology and
microgravity (ZARM) vacuum drop tower in Bremen in August 2012. The experiment was
placed in an evacuated cylinder and mounted on a centrifuge that was spun with varying
rotation rates to accommodate the vacuum and low gravity present on the surfaces of
asteroids.
A total of 20 experiments as described above were realized during 10 drops.
The tilt angle and the magnitude of artificial gravity were varied for two different
materials, a ground HED meteorite and the JSC MARS-1 Martian soil simulant.
Additional ground-based experiments in 1g environment were conducted at a later
time.
We analyzed the images using an image subtraction algorithm to track movement from
one frame to the next. In subsequent steps we observed the behavior of the material
on the surface as well as in deeper layers to characterize the effects of the impact
with changing gravitational acceleration, impactor velocity and tilt angle of the
material.
The analysis of the experimental data indicates that small scale impacts can, under certain
conditions, trigger avalanches in both normal and reduced gravity. Furthermore the
gravitational acceleration influences the limiting slope angle below which no effect can be
observed.
Additional computer simulations using a particle code as well as a hydro code are being
conducted.
[1] H. U. Keller et al., OSIRIS–The scientific camera system onboard Rosetta. Space Sci.
Rev. 128, 433 (2007)
[2] H. Sierks et al., Images of Asteroid 21 Lutetia: A Remnant Planetesimal from the
Early Solar System, Science 334, 487 (2011) |
|
|
|
|
|
|