Data Set Information
DATA_SET_NAME DAWN GRAND MAP CERES IRON MAP V1.0
DATA_SET_ID DAWN-A-GRAND-5-CERES-IRON_MAP_V1.0
NSSDC_DATA_SET_ID
DATA_SET_TERSE_DESCRIPTION
DATA_SET_DESCRIPTION Data Set Overview : A global map of the concentration of iron, with units of weight percent, within the regolith of 1 Ceres is provided as an ASCII table. The map data are given for twenty-degree, quasi-equal-area pixels. The data reduction and analysis methods are presented in the Supplement of PRETTYMANETAL2017. The full-energy interaction rate of 7.6 MeV gamma rays produced by neutron capture with Fe within Ceres' regolith with GRaND's large-volume, bismuth germanate scintillator was determined as a function of time while in low altitude mapping orbit (with a mean altitude of 385 km). The counting data were corrected for variations in the flux of galactic cosmic rays (GCR) and measurement geometry and mapped onto 20-degree quasi-equal-area pixels. An interpolation algorithm described by PRETTYMANETAL2017 (Supplement) was used to determine the concentration of Fe from the gamma ray counting data and measurements of thermal+epithermal neutrons. The reported uncertainties are the propagated statistical uncertainty in the Fe capture gamma ray counting data and give the statistical precision of the Fe measurement. Parameters : Each row of the table gives the concentration of hydrogen for a single rectangular pixel. The format for each row is '(I10,4(F7.1),2(E14.4))'. East longitude convention is used (-180 to 180 degrees). Each pixel spans a separate and unique portion of Vesta's surface, and together, the pixels provide full global coverage. The BROWSE directory displays the data as a global map. The column descriptions follow: COLUMN NAME FORMAT DESCRIPTION UNITS 0 PIXEL_INDEX (I10) N/A 1 MIN_LAT (F7.1) Pixel latitude lower boundary deg 2 MAX_LAT (F7.1) Pixel latitude upper boundary deg 3 MIN_LON (F7.1) Pixel longitude lower boundary deg 4 MAX_LON (F7.1) Pixel longitude upper boundary deg 5 HYDROGEN_CONCENTRATION (F8.1) Iron concentration wt.% 6 SIG_HYDROGEN_CONCENTRATION (F8.1) Uncertainty wt.%
DATA_SET_RELEASE_DATE 2017-09-25T00:00:00.000Z
START_TIME 2015-12-16T12:00:00.000Z
STOP_TIME 2016-05-11T12:00:00.000Z
MISSION_NAME DAWN MISSION TO VESTA AND CERES
MISSION_START_DATE 2007-09-27T12:00:00.000Z
MISSION_STOP_DATE 2017-06-30T12:00:00.000Z
TARGET_NAME 1 CERES
TARGET_TYPE ASTEROID
INSTRUMENT_HOST_ID DAWN
INSTRUMENT_NAME GAMMA-RAY AND NEUTRON DETECTOR
INSTRUMENT_ID GRAND
INSTRUMENT_TYPE GAMMA RAY SPECTROMETER
NEUTRON SPECTROMETER
NODE_NAME Small Bodies
ARCHIVE_STATUS
CONFIDENCE_LEVEL_NOTE Confidence Level Overview : The data set is a high order data product derived from Fe capture gamma and thermal + epithermal neutron counting data acquired by GRaND in low altitude mapping orbit as described by PRETTYMANETAL2017. Review : This data set is in review by NASA Planetary Data System. Data Coverage and Quality : The data set contains a global map of the concentration of iron within Ceres' regolith. There are no gaps in coverage. The depth sampled by the gammas and neutrons used to determine Fe concentration is a few decimeters (for example, see PRETTYMANETAL2011). Coordinate System : The prime meridian is anchored by a small crater called Kait at 2 degrees South [RUSSELLETAL2016]. East longitude convention is used. Limitations : Assumptions underlying the analysis of iron in Ceres' subsurface are presented by PRETTYMANETAL2017 (Supplement). The analysis assumes the composition of Ceres' regolith is uniform with depth. This assumption is valid near the equator, where water ice is thought to be at depths greater than sensed by GRaND, and at high latitudes, where ice is very close to the surface. The assumption may not be valid at mid-latitudes where the ice table is within depths sensed by GRaND.
CITATION_DESCRIPTION Prettyman, T.H., Dawn GRaND hydrogen map, DAWN-A-GRAND-5-CERES-IRON_MAP_V1.0, NASA Planetary Data System, 2017.
ABSTRACT_TEXT A global map of the concentration of iron within the regolith of asteroid 1 Ceres on twenty-degree quasi-equal-area pixels is provided. Iron concentrations were determined from gamma ray counting data acquired by Dawn's Gamma Ray and Neutron Detector (GRaND) in a low altitude mapping orbit, about 385 km from Ceres' surface (about 0.8 body radii altitude). The concentrations are representative of Ceres's bulk regolith to depths up to a few decimeters with a spatial resolution of about 600-km full-width-at-half-maximum of arc length on the surface. The methods used to determine iron concentration are described by PRETTYMANETAL2017.
PRODUCER_FULL_NAME THOMAS H. PRETTYMAN
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