Feldman has continued work using the Mars Odyssey Neutron Spectrometer (MONS) data to map and understand the distribution of water near the surface of Mars and the seasonal variability of the CO2 ice polar caps. I have worked with Josh Bandfield of ASU to inter-compare our maps of the burial depths of water ice at high northern and southerly latitudes and those derived from the thermal inertias derived from TES and THEMIS. Both maps agree quantitatively to a remarkable degree. A paper was written and has been accepted for publication in JGR. Another side result of this work is that the burial depth is found to vary inversely with the mass fraction of water in the buried permafrost layer. This finding is most unusual but probably indicates the existence of ice wedges in the soil and/or ice lenses that grow bigger in volume as the surface is approached from below. A paper has been submitted to JGR for publication but it is still under review. Work on documenting the ability to determine the hydrogen layering in the top meter of Mars using thermal and epithermal neutrons was also conducted. This study was led by Benedicte Diez, a French graduate student. A paper was written and submitted to Icarus, where it is presently under review.
Feldman has continued work using the MESSENGER Neutron Spectrometer data measured during the recent flybys of Venus (June 5, 2007) and Mercury (Jan. 14, 2008). Both flybys were overwhelming successes and our neutron data are beautiful. The cruise data measured after Venus closest approach at 0.7 AU and during cruise phase past the first perihelion of the MESSENGER heliospheric orbit at about 0.32 AU, were reported at the Fall AGU meeting in Dec. 2007. We were looking for evidence of quiet-time solar fast neutrons but saw nothing at the 1 to 2% level, perhaps because the Sun was at minimum activity and was totally clear of sunspots. We are now working up the data during the first Mercury flyby and it looks very promising. Current results are under embargo, but much of them will be reported at special MESSENGER sessions at the 2008 LPSC in March, 2008.
Feldman has continued work in support of the NASA Discovery mission, DAWN, which was successfully launched on 27 Sept, 2007. He is a Co-I (and Tom Prettyman of PSI is the P-I) of the Gamma-Ray and Neutron Detector (GRaND) aboard DAWN. The instrument is working very well. Our work will be to track the variation in detector background due to the depletion of the DAWN Xe fuel load that is used for thrusting the spacecraft. This task will be accomplished by turning on the detector periodically at intervals of about 6 months. The next big event will be a flyby of Mars on about 10 Feb., 2009. This flyby will be important to inter-calibrate the GRaND and MONS instruments during this flyby. Such an intercalibration will be feasible because the flyby periapsis should occur at about 60 degrees southern latitude at an Ls of 205 degrees, or just after winter solstice in the south. The seasonal CO2 ice cap should be near its maximum extent at that time and therefore provide a very clear signal in neutrons to both GRaND and MONS.
Feldman, W.C., M.T. Mellon, O. Gasnault, B. Diez, R.C. Elphic, J.J. Hagerty, D.J. Lawrence, S. Maurice, T.H. Prettyman, Vertical distribution of hydrogen at high northern latitudes on Mars: The Mars Odyssey Neutron Spectrometer, Geophys. Res. Lett., 34, L05201, doi:10.1029/2006GL028936, 2007.
DETERMINATION OF THE LAYERING OF HYDROGEN IN THE TOP METER OF MARS. B. Diez1, W. C. Feldman2, S. Maurice1, O. Gasnault1 and T. H. Prettyman3, 1Centre d’Etude Spatiale des Rayonnements, Toulouse, France, 2Planetary Science Institute, Tucson, AZ, 3Los Alamos National Laboratory, Group ISR-1, Los Alamos, NM (benedicte.diez@cesr.fr), 3rd International Mars Conf., July, 2007.
TEMPORALLY AND SPATIALLY VARYING NEAR-SURFACE WATER VAPOR PRESSURE ON MARS. S. M. Nelli1, W. C. Feldman2, and J. R. Murphy3, 1University of Michigan, Space Research Building, 2455 Hayward St., Ann Arbor, MI 48109, snelli@umich.edu, 2Planetary Science Institute, Tuscon, AZ, feldman@psi.edu, 3New Mexico State University, P.O. Box 30001/MSC 4500, 1320 Frenger Street, Las Cruces, NM 88003, murphy@nmsu.edu. 3rd International Mars Conf., July, 2007
INTERCOMPARISON OF HYDROGEN DISTRIBUTIONS AT HIGH LATITUDES ON MARS. W.C. Feldman1, B. Diez2, S. Maurice2, R.C. Elphic3, D.J. Lawrence3, 1Planetary Science Institute, Tucson, AZ, 2Centre d’Etude Spatiale des Rayonnements, Toulouse, France, 3Los Alamos National Laboratory, Group ISR-1, Los Alamos, NM (Feldman@psi.edu), 3rd International Mars conf., July, 2007.
Constraints on the Structure and Composition of Sand Dunes within Olympia Undae using Mars Odyssey Neutron Spectrometer Data W.C. Feldman1, M.C. Bourke1, R.C. Elphic2, S. Maurice3, T. H. Prettyman2, D. J. Lawrence2, J.J. Hagerty2, 1Planetary Science Institute, Tucson, AZ USA (Feldman@psi.edu), 2Los Alamos National Laboratory, Los Alamos NM USA, 3Centre d’Etude Spatiale des Rayonnements, Toulouse, Fr, LPSC 38, March, 2007
Reduction of Mars Odyssey Neutron Data S. Maurice1, W. Feldman2, T. Prettyman3, 1B. Diez, 1Centre d’Etude Spatiale des Rayonnements, Observatoire Midi-Pyrénées, Toulouse (sylvestre.maurice@cesr.fr), 2 Planetary Space Institute, Tucson. 3Los Alamos National Laboratory, New Mexico, LPSC, 38, March, 2007.
First measurements of neutrons at Venus using the MESSENGER Neutron Spectrometer, D. J. Lawrence1, W. C. Feldman2, W. V. Boynton3, J. O. Goldsten4, E. A. Rhodes4, and the MESSENGER Science Team 1Los Alamos National Laboratory, Space and Atmospheric Sciences, Los Alamos, NM, 2Planetary Science Institute, Tucson, AZ. 3University of Arizona, Tucson, AZ. 4John Hopkins University Applied Physics Laboratory, Laurel, MD, Fall AGU, Dec., 2007.
Search for solar neutrons using the MESSENGER Neutron Spectrometer between 0.7 and 0.32 AU, W.C. Feldman1, D.J. Lawrence2, R.L. McNutt, Jr.2, J.O. Goldsten2, E.A. Rhodes2, F. Vilas3,1, and the MESSENGER Science Team, 1Planetary Science Institute, Tucson, AZ., 2John Hopkins University Applied Physics Laboratory, Laurel, MD., 3MMT, Mount Hopkins, AZ, Fall AGU, Dec., 2007.