Showing papers by "Eberhard Grün published in 2012"

3 MV hypervelocity dust accelerator at the Colorado Center for Lunar Dust and Atmospheric Studies

Abstract: A hypervelocity dust accelerator for studying micrometeorite impacts has been constructed at the Colorado Center for Lunar Dust and Atmospheric Studies (CCLDAS) at the University of Colorado. Based on the Max-Planck-Institut fur Kernphysik (MPI-K) accelerator, this accelerator is capable of emitting single particles of a specific mass and velocity selected by the user. The accelerator consists of a 3 MV Pelletron generator with a dust source, four image charge pickup detectors, and two interchangeable target chambers: a large high-vacuum test bed and an ultra-high vacuum impact study chamber. The large test bed is a 1.2 m diameter, 1.5 m long cylindrical vacuum chamber capable of pressures as low as 10−7 torr while the ultra-high vacuum chamber is a 0.75 m diameter, 1.1 m long chamber capable of pressures as low as 10−10 torr. Using iron dust of up to 2 microns in diameter, final velocities have been measured up to 52 km/s. The spread of the dust particles and the effect of electrostatic focusing have bee...

On the applicability of laser ionization for simulating hypervelocity impacts

Abstract: In-situ measurements, the direct interception and analysis of dust particles by spacecraft-based instrumentation, provide insights into the dynamical, physical and chemical properties of cosmic dust. The most sensitive detection methods for dust particles in space are based on impact ionization. Laser ionization is used for the test, development, and calibration of impact ionization instruments and to complement laboratory based particle impact experiments. A typical setup uses a 355 nm Nd-YAG laser with a pulse length of about 5 ns. It is necessary to investigate the properties of both processes with respect to their comparability. A study was performed to find out to what extent laser ionization can be used to simulate impact ionization. The findings show that laser ionization and impact ionization show similarities, which can be used to test the functionality of dust impact detectors, especially time-of-flight instruments. Our paper provides information on what extent these similarities hold and where ...

Spacecraft charging near Enceladus

Abstract: [1] In the vicinity of Enceladus, a geologically active moon of Saturn, the modeled spacecraft potential is significantly more negative than indicated by the Cassini Langmuir probe measurements To understand this potential difference, we introduce two new dust–related charging currents: a) the dust ram current; and b) the dust impact–plasma current, in addition to the customary collection of electrons and ions, and photoemission Our results show that these dust currents are important at high relative speeds between the spacecraft and the dust, or in regions with a low plasma-to-dust ratio, and can lead to reduced spacecraft charging

SARIM PLUS—sample return of comet 67P/CG and of interstellar matter

Abstract: The Stardust mission returned cometary, interplanetary and (probably) interstellar dust in 2006 to Earth that have been analysed in Earth laboratories worldwide. Results of this mission have changed our view and knowledge on the early solar nebula. The Rosetta mission is on its way to land on comet 67P/Churyumov-Gerasimenko and will investigate for the first time in great detail the comet nucleus and its environment starting in 2014. Additional astronomy and planetary space missions will further contribute to our understanding of dust generation, evolution and destruction in interstellar and interplanetary space and provide constraints on solar system formation and processes that led to the origin of life on Earth. One of these missions, SARIM-PLUS, will provide a unique perspective by measuring interplanetary and interstellar dust with high accuracy and sensitivity in our inner solar system between 1 and 2 AU. SARIM-PLUS employs latest in-situ techniques for a full characterisation of individual micrometeoroids (flux, mass, charge, trajectory, composition) and collects and returns these samples to Earth for a detailed analysis. The opportunity to visit again the target comet of the Rosetta mission 67P/Churyumov-Gerasimeenternko, and to investigate its dusty environment six years after Rosetta with complementary methods is unique and strongly enhances and supports the scientific exploration of this target and the entire Rosetta mission. Launch opportunities are in 2020 with a backup window starting early 2026. The comet encounter occurs in September 2021 and the reentry takes place in early 2024. An encounter speed of 6 km/s ensures comparable results to the Stardust mission.

Identification of Crystalline Material in Two Interstellar Dust Candidates from the Stardust Mission

Abstract: NASA's interstellar collector from the Stardust mission captured several particles that are now thought to be of interstellar origin We analyzed two of these via nanodiffraction at the European Synchrotron Radiation Facility (ESRF) and found them to contain crystalline components The unit cell of the crystalline material is determined from the diffraction patterns and the most likely mineral components are identified as olivine and spinel

A linear tof mass spectrometer as a tool for the investigation of impact ionisation plasma

Abstract: The generation of charge during hypervelocity impacts of microparticles provides one of the most sensitive methods for the detection and characterisation of dust particles in space. Linear time-of- flight (TOF) mass spectrometry provides an opportunity for investigating the thermodynamical properties of an impact ionisation plasma, e.g. the velocity distribution of the ions. The dependence of the plasma properties on the impact parameters were studied at the Heidelberg dust accelerator laboratory using impacts speed from 1 to 90 kms-1 and particle sizes form 30nm to 4μm. The results imply that the defining parameter of impact ionisation is either the impact velocity or the energy density and not the total impact energy.