Dana Hurley Crider

The plasma environment of Mars

When the supersonic solar wind reaches the neighborhood of a planetary obstacle it decelerates. The nature of this interaction can be very different, depending upon whether this obstacle has a large-scale planetary magnetic field and/or a well-developed atmosphere/ionosphere. For a number of years significant uncertainties have existed concerning the nature of the solar wind interaction at Mars, because of the lack of relevant plasma and field observations. However, measurements by the Phobos-2 and Mars Global Surveyor (MGS) spacecraft, with different instrument complements and orbital parameters, led to a significant improvement of our knowledge about the regions and boundaries surrounding Mars.

Variability of the altitude of the Martian sheath

Received 31 March 2005; revised 18 August 2005; accepted 25 August 2005; published 24 September 2005. [1] Using electron energy spectra, we identify time periods when the Mars Global Surveyor (MGS) spacecraft is in or above the Martian magnetic pileup boundary (MPB). We use more than five years of data to develop a statistical picture of the location of the MPB relative to the MGS mapping altitude near 400 km. We show for the first time that the MPB location is sensitive to interplanetary magnetic field (IMF) orientation and to Martian season, and confirm a dependence upon solar wind pressure. We confirm that crustal magnetic sources raise the altitude of the MPB, and demonstrate that sheath electrons populate magnetic cusp regions in the southern hemisphere. During southern summer strong crustal fields near the subsolar point raise the altitude of the MPB over the entire dayside, implying that Martian crustal fields modify the solar wind interaction globally. Citation: Brain, D. A., J. S. Halekas, R. Lillis, D. L. Mitchell, R. P. Lin, and D. H. Crider (2005), Variability of the altitude of the Martian sheath, Geophys. Res. Lett., 32, L18203,

The solar wind as a possible source of lunar polar hydrogen deposits

We investigate the solar wind as a source for the deposits of hydrogen at the lunar poles. We create a Monte Carlo model that simulates the migration of atmospheric particles through the lunar exosphere. Making the model general enough to incorporate any physical process that might affect the particles, we develop a tool that estimates the number and form of particles that reach and stick to lunar cold traps. Each particle is allowed to follow a series of ballistic trajectories as it hops around the surface of the Moon. We trace the path of the particle until it is removed from the system by photo-processes such as ionization or dissociation, by thermal escape, or by reaching a cold trap. Accumulating statistics on the outcomes for various input particles, we determine the amount and form of hydrogen able to migrate to the lunar cold traps over time for a typical solar wind input flux. We find that although the fraction of hydrogen delivered to the Moon that ultimately reaches the poles is small, a slow steady source like the solar wind has provided enough hydrogen over 83 Myr to account for the observed deposits. Also, we find that an enrichment in the [D/H] ratio occurs by the migration process. The amount of fractionation is dependent on the molecular form of the migrating hydrogen. Atomic deuterium/hydrogen is enriched by a factor of 4 over the delivered fraction by the migration process.

Space weathering of ice layers in lunar cold traps

Abstract There are several mechanisms acting at the cold traps that can alter the inventory of volatiles there, including micrometeoroid bombardment, solar wind and magnetospheric ion sputtering, photon-stimulated desorption, and sublimation. We investigate the effects of these space weathering processes on ice layers in a lunar cold trap. We simulate the development of hydrogen content in a column of material near the surface of the Moon by a Monte Carlo model. Each column is initialized with an ice layer existing within otherwise very immature soil. Time is allowed to run for 1 billion years and all changes to the column are calculated. We find that an ice layer must be > 10 cm thick or > 10 cm deep to have a detectable water enhancement.After 1 billion years, the ice layer is buried below the range of the neutron detection technique.For thinner or shallower deposits, the ice becomes indistinguishably mixed with the enriched soil from steady source delivery. A total of 40 cm deposit of water ice at a concentration of 10% is required to equal the hydrogen content resulting from the solar-wind steady source alone. The saturation level of the regolith is 3.7% water ice by mass.

On the role of charge exchange in the formation of the Martian magnetic pileup boundary

In the magnetic pileup boundary (MPB) of Mars a steep increase in the magnitude of the magnetic field is observed in the data from the magnetometer on board Mars Global Surveyor, and the growth of the field is more precipitous than common solar wind-ionosphere models predict. Analysis of both Venus and Mars magnetic field data has strongly implied that plasma pressure is exchanged for magnetic pressure in the magnetic pileup field. To explain this, effects of the Martian exosphere must be included. Then charge exchange between the shock-compressed solar wind protons, which dominate the thermal pressure, and neutral exospheric atoms (mainly H and O) should play a crucial role in the formation of the MPB, as is also inherently required by the conservation of momentum flux. To test this idea, a model of the solar wind interaction with the Martian upper atmosphere, with charge exchange included, is constructed to reproduce the observed magnetic field of the MPB of Mars. The simulation results show that charge exchange is able to account for the sudden buildup of the magnetic field in the Martian MPB, with the implication that the same mechanism produces the magnetic field increase at Venus and comets.

LAMP: the Lyman Alpha Mapping Project aboard the NASA Lunar Reconnaissance Orbiter mission

The Lyman Alpha Mapping Project (LAMP) is an ultraviolet imaging spectrograph recently selected for NASAs Lunar Reconnaissance Orbiter (LRO) mission. Its main objectives are to (i) identify and localize exposed water frost in permanently shadowed regions (PSRs), (ii) characterize landforms and albedos in PSRs, (iii) demonstrate the feasibility of using natural starlight and sky-glow illumination for future lunar surface mission applications, and (iv) characterize the lunar atmosphere and its variability. The LAMP UV spectrograph will accomplish these objectives by measuring the signal reflected from the nightside lunar surface and in PSRs using both the interplanetary HI Lyman-α sky-glow and FUV starlight as light sources. Both these light sources provide fairly uniform, but faint, illumination (e.g., the reflected Lyman-α signal is expected to be ~10 R). Thanks to LAMPs sensitivity, by the end of the 1-year LRO mission the SNR for a Lyman-α albedo map will be >100 in polar regions exceeding 1 km2 (and >15 for 100×100 m2 polar regions), allowing the characterization of subtle compositional and structural features. The LAMP instrument is based on the flight-proven ALICE series of spectrographs that are flying on Rosetta and built for flight on NASAs New Horizons Pluto-Kuiper Belt Mission.