119 research outputs found
Lunar surface: Dust dynamics and regolith mechanics
The lunar surface is characterized by a collisionally evolved regolith resulting from meteoroid bombardment. This lunar soil consists of highly angular particles in a broad, approximately power law size distribution, with impact-generated glasses. The regolith becomes densified and difficult to excavate when subjected to lunar quakes or, eventually, manned and unmanned activity on the surface. Solar radiation and the solar wind produce a plasma sheath near the lunar surface. Lunar grains acquire charge in this environment and can exhibit unusual behavior, including levitation and transport across the surface because of electric fields in the plasma sheath. The fine component of the lunar regolith contributes to the operational and health hazards posed to planned lunar expeditions. In this paper we discuss the mechanical response of the regolith to anticipated exploration activities and review the plasma environment near the lunar surface and the observations, models, and dynamics of charged lunar dust
2012), Characteristics of a plasma sheath in a magnetic dipole field: Implications to the solar wind interaction with the lunar magnetic anomalies
[1] The solar wind interaction with the lunar surface, especially in regions of crustal magnetic anomalies, remains of great interest for in situ plasma measurements. Small-scale laboratory experiments cannot reproduce the conditions near the lunar surface, but provide a unique opportunity to identify and examine several of the physical processes. We study plasma interaction with a magnetic dipole field at an insulating surface in order to understand the effect of crustal magnetic anomalies on the solar wind-lunar surface interaction. In our experiments, electrons are magnetized with gyroradii r smaller than distances from the surface d (r < d) but ions remain unmagnetized with r > d. The measured potential distribution shows a non-monotonic sheath above the surface and variations on the surface along the axis of the dipole field. The surface near the center of the dipole is charged more positively by ions as the electrons are magnetically shielded away. A potential minimum is found in the shielding region between the surface and the bulk plasma due to collisional and magnetic mirror trapping effects. Potential variations on the surface are the result of the inhomogeneity of the dipolar field, showing an enhancement of the electric field at the cusps. Enhanced electric fields in the regions of magnetic anomalies on the lunar surface may enhance the transport of small-sized charged dust particles, possibly explaining the formation of the lunar swirls. Citation: Wang, X., M. Horányi, and S. Robertson (2012), Characteristics of a plasma sheath in a magnetic dipole field: Implications to the solar wind interaction with the lunar magnetic anomalies
Probing IMF using nanodust measurements from inside Saturn's magnetosphere
We present a new concept of monitoring the interplanetary magnetic field (IMF) by using in situ measurements of nanodust stream particles in Saturn's magnetosphere. We show that the nanodust detection pattern obtained inside the magnetosphere resembles those observed in interplanetary space and is associated with the solar wind compression regions. Our dust dynamics model reproduces the observed nanodust dynamical properties as well as the detection pattern, suggesting that the ejected stream particles can reenter Saturn's magnetosphere at certain occasions due to the dynamical influence from the time‐varying IMF. This method provides information on the IMF direction and a rough estimation on the solar wind compression arrival time at Saturn. Such information can be useful for studies related to the solar wind‐magnetosphere interactions, especially when the solar wind parameters are not directly available. Key Points A new method to probe IMF with nanodust measurements inside the magnetosphere Under changing IMF, ejected nanoparticles can re‐enter Saturn‐s magnetosphere IMF direction and solar wind compression arrival time can be derivedPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/99078/1/grl50604.pd
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Magnetic Field Effect on Antenna Signals Induced by Dust Particle Impacts
The Radio and Plasma Wave Science instrument on Cassini has observed fewer than expected dust particle impacts during the mission's Grand Finale orbits. The relatively strong magnetic field in the close vicinity of the planet has been suggested to affect the intensity of the dust impact generated signals. A laboratory investigation is performed using dust particles accelerated to ≥20 km/s speed impacting onto a previously developed model of the spacecraft and the Radio and Plasma Wave Science antennas. The external magnetic field is generated by two sets of magnetic coils. The recorded antenna waveforms are decomposed into contributions from the electrons and ions of the dust impact generated plasma cloud. A good qualitative understanding of the waveforms is achieved by dividing the electron and ion population into two portions: one that is escaping from the spacecraft and another that is collected by the spacecraft. The experimental results show that the part of the signal corresponding to escaping electrons is affected by the magnetic field and that dust impact signals can be significantly reduced for spacecraft floating potentials close to zero.
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Four years of Ulysses dust data: 1996 to 1999
The Ulysses spacecraft is orbiting the Sun on a highly inclined ellipse (, perihelion distance 1.3 AU, aphelion distance 5.4 AU). Between
January 1996 and December 1999 the spacecraft was beyond 3 AU from the Sun and
crossed the ecliptic plane at aphelion in May 1998. In this four-year period
218 dust impacts were recorded with the dust detector on board. We publish and
analyse the complete data set of both raw and reduced data for particles with
masses to g. Together with 1477 dust impacts
recorded between launch of Ulysses and the end of 1995 published earlier
\cite{gruen1995c,krueger1999b}, a data set of 1695 dust impacts detected with
the Ulysses sensor between October 1990 and December 1999 is now available. The
impact rate measured between 1996 and 1999 was relatively constant with about
0.2 impacts per day. The impact direction of the majority of the impacts is
compatible with particles of interstellar origin, the rest are most likely
interplanetary particles. The observed impact rate is compared with a model for
the flux of interstellar dust particles. The flux of particles several
micrometers in size is compared with the measurements of the dust instruments
on board Pioneer 10 and Pioneer 11 beyond 3 AU (Humes 1980, JGR, 85,
5841--5852, 1980). Between 3 and 5 AU, Pioneer results predict that Ulysses
should have seen five times more ( sized) particles than
actually detected.Comment: accepted by Planetary and Space Science, 22 pages, 8 figures (1
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One year of Galileo dust data from the Jovian system: 1996
The dust detector system onboard Galileo records dust impacts in circumjovian
space since the spacecraft has been injected into a bound orbit about Jupiter
in December 1995. This is the sixth in a series of papers dedicated to
presenting Galileo and Ulysses dust data. We present data from the Galileo dust
instrument for the period January to December 1996 when the spacecraft
completed four orbits about Jupiter (G1, G2, C3 and E4). Data were obtained as
high resolution realtime science data or recorded data during a time period of
100 days, or via memory read-outs during the remaining times. Because the data
transmission rate of the spacecraft is very low, the complete data set (i. e.
all parameters measured by the instrument during impact of a dust particle) for
only 2% (5353) of all particles detected could be transmitted to Earth; the
other particles were only counted. Together with the data for 2883 particles
detected during Galileo's interplanetary cruise and published earlier, complete
data of 8236 particles detected by the Galileo dust instrument from 1989 to
1996 are now available. The majority of particles detected are tiny grains
(about 10 nm in radius) originating from Jupiter's innermost Galilean moon Io.
These grains have been detected throughout the Jovian system and the highest
impact rates exceeded . A small number of grains has been
detected in the close vicinity of the Galilean moons Europa, Ganymede and
Callisto which belong to impact-generated dust clouds formed by (mostly
submicrometer sized) ejecta from the surfaces of the moons (Kr\"uger et al.,
Nature, 399, 558, 1999). Impacts of submicrometer to micrometer sized grains
have been detected thoughout the Jovian system and especially in the region
between the Galilean moons.Comment: accepted for Planetary and Space Science, 33 pages, 6 tables, 10
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