2010 Annual Research Report

Tom Prettyman's projects include: the NASA Dawn mission (Co-I, Lead for GRaND and Geochemistry); research on Mars' polar science; modeling cosmogenic radionuclide production in meteorites; development of advanced neutron sensors for homeland security and planetary science; and the development of radiation dosimeters for NASA's manned exploration program.

During FY10, the GRaND team completed the final submission of data acquired during Earth-Mars cruise and Mars Gravity Assist (MGA) to the Planetary Data System, including Level 1 experimental and reduced data records (EDR & RDR).  The data sets and accompanying documentation were peer reviewed and their release is anticipated in early CY11.  

In addition, the Dawn project continued preparations for Vesta encounter.  Activities included detailed simulations of low-altitude orbital measurements of GRaND at Vesta (Prettyman et al., 2010).

"Virtual Vesta" simulations were used for operational planning at Vesta and to guide the development of data analysis methods that will be used to determine Vesta's chemical composition (Prettyman & McSween, 2011).  Results show that, at a minimum, GRaND will  distinguish and map the abundance of elemental end members of the howardite, eucrite, and diogenite (HED) meteorites, thought to be representative of the composition of Vesta; however, there are hints from the meteorite collection that Vesta may have some surprises in store.

Potassium-rich impact glasses in howardites suggests that potassium-rich rocks may be mixed with HED compositions on some portion of Vesta‚Äôs surface.  Outcrops of Vesta's olivine-rich mantle may be present in a giant impact basin at Vesta's south pole.

In addition, mesosiderites (basalts mixed with metals) may originate from Vesta, for example if Vesta was impacted by the partially-molten core of a disrupted asteroid. If so, then Ni-metal deposited by the impact could be detectable by GRaND.  While Dawn will arrive at Vesta in the summer of 2011, the chemical composition of Vesta will not become apparent until after GRaND acquires data in low altitude mapping orbit (LAMO) starting in December of 2011.  

The data acquired by GRaND in LAMO will provide new information about the origin and thermal evolution of Vesta, the abundance and distribution of of surfical hydrogen (delivered by the the impact of carbonaceous meteoroids and by solar wind), and how Vesta's crust was shaped by impacts.

Papers: 

Stapels, C.J., E.B. Johnson, X.J. Chen, T.H. Prettyman, E.R. Benton, J.F. Christian, Space neutron spectrometer design with SSPM-based instrumentation, Nucl. Meth. Phys. Res. A, 2010, doi:10.1016/j.nima.2010.10.050.  

Lawrence, D.J., R.C. Elphic, W.C. Feldman, H.O. Funsten, T.H. Prettyman, Performance of Orbital Neutron Instruments for Spatially Resolved Hydrogen Measurements of Airless Planetary Bodies, Astrobiology. March 2010, 10(2): 183-200. doi:10.1089/ast.2009.0401. 

Abstracts:

Prettyman, T.H., H.Y. McSween, Jr., C.A. Raymond, W.C. Feldman, J.-Y. Li, L.A. McFadden, C.T. Russell, P. Tricarico (2010), Dawn's GRaND to reveal the complex geochemistry of Vesta, 41st Lunar and Planetary Science Conference, Abstract #2299.

Prettyman T, McSween H & Feldman W, Dawn’s GRaND to Map the Chemical Composition of Asteroids Vesta and Ceres, Goldschmidt conference, Knoxville, June 13-18, 2010

Co-author on various abstracts for LPSC, IEEE Nuclear Science Symposium, DPS, and AGU.