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DAWN GRAND MAP CERES HYDROGEN MAP V1.0 (PDS)

NSSDCA ID: PSSB-00678

Availability: At NSSDC, Ready for Offline Distribution (or Staging if Digital)

Description

This description was generated automatically using input from the Planetary Data System.

Data Set Overview

A global map of the concentration of hydrogen, with units of weight percent water equivalent hydrogen (WEH), 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. Thermal+epithermal counting rates measured in Dawn'scircular, polar, low-altitude mapping orbit (LAMO), at a mean distance of about 385 km from Ceres' surface were corrected for variations in the flux of galactic cosmic rays (GCR) and measurement geometry. The corrected epithermal counting data were globally mapped on 20-deg equal-area pixels. Hydrogen concentration was determined from the counting data using calculated trends for compositional models [PRETTYMANETAL2017, Supplement]. The map gives a lower bound on the concentration of hydrogen on Ceres. The reported uncertainties give the systematic error in the spatial distribution of hydrogen due to assumptions regarding model composition. Contributions from statistical variations in counts are small in comparison. Consequently, the reported uncertainties represent the total error in the spatial distribution of hydrogen.

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) Hydrogen concentration [a] wt.% WEH 6 SIG_HYDROGEN_CONCENTRATION (F8.1) Uncertainty wt.% WEH [a] The concentratation of hydrogen is expressed as weight percent (wt.%) Water Equivalent Hydrogen (WEH) The concentration of hydrogen can be determined by dividing wt.% WEH by 9.

Data Set Overview

A global map of 7.6 MeV gamma rays produced by neutron capture with Fe within Ceres' regolith is provided as an ASCII table. The data were acquired by GRaND while the Dawn spacecraft was in a low altitude mapping orbit (LAMO) around Ceres. 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 map of 7.6 MeV counting data given here appears in Fig. 1 of the main text 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 produces a peak in the spectrum. The net peak area of this peak was determined as a function of time while Dawn was in LAMO. The time series was corrected for variations in the intensity of galactic cosmic rays and the solid angle subtended by Ceres at the spacecraft. Bad data and data not meeting pointing requirements were excluded from the analysis. The data were binned at the subsatellite point on 20-degree quasi-equal area pixels. For each pixel, the mean counting rate and the statistical uncertainty in the mean is reported along with the number of times the pixel was sampled.

Parameters

Each row of the table gives 7.6 MeV counting rate for a single rectangular pixel. The format for each row is '(I10,4(F7.1),2(E14.4),I10)'. 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 TPE_COUNTING_RATE (E14.4) Mean 7.6 MeV counting rate counts/s 6 SIG_TPE_COUNTING_RATE (E14.4) Uncertainty in the mean counts/s 7 TPE_SAMPLES (I10) Number of samples

These data are available on-line from the Planetary Data System (PDS) at:

https://sbnarchive.psi.edu/pds3/dawn/grand/DWNCGRD_2/

Alternate Names

  • DAWN GRAND MAP CERES IRON 7.6MEV GAMMA COUNTS V1.0
  • DAWN-A-GRAND-5-CERES-HYDROGEN-MAP_V1.0
  • DAWN-A-GRAND-5-CERES-IRON-COUNTS_V1.0

Discipline

  • Planetary Science: Small Bodies

Additional Information

Spacecraft

Experiments

Questions and comments about this data collection can be directed to: Dr. David R. Williams

 

Personnel

NameRoleOriginal AffiliationE-mail
Dr. Thomas H. PrettymanGeneral ContactPlanetary Science Instituteprettyman@psi.edu
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