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DAWN GRAND MAP VESTA NEUTRON ABSORPTION V1.0 (PDS)

NSSDCA ID: PSSB-00578

Availability: Archived at NSSDC, accessible from elsewhere

Description

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

Data Set Overview #1

A global map of a compositional parameter, delta-C_perpendicular (DCP) and its 1-sigma statistical uncertainty are provided as an ASCII table. DCP varies linearly with the macroscopic thermal neutron absorption cross section of Vesta's regolith. The map data are given for 15-degree quasi-equal area pixels. Equations for converting DCP and uncertainties to physical absorption units are provided (below). The data reduction and analysis methods used to determine corrected neutron counting rates, sensitive to surface compositional variations, are described by PRETTYMANETAL2012. Epithermal and thermal+epithermal (TPE) neutron counting rates measured in Dawn's circular, polar, low-altitude mapping orbit (LAMO), at a mean distance of about 210 km from Vesta's surface were corrected for variations in the flux of galactic cosmic rays (GCR) and solid angle. The data were acquired in early LAMO (Time-interval IA, described in the Supplementary Information of PRETTYMANETAL2012, Fig.1 and Table 2) during a long period (30 days) of continuous instrument operation and steady GCR counting rates. A method to determine neutron absorption variations from thermal+epithermal (TPE) and epithermal counting rates is presented by PRETTYMANETAL2013. A scatter plot of normalized epithermal vs. TPE counting rates is used to derive the compositional parameter, DCP (unitless). The perpendicular distance (DCP, denoted ' delta-C_perpendicular' in PRETTYMANETAL2013) of each data point from a trend line, approximating the variation of epithermal vs. TPE counting rates with hydrogen abundance, is sensitive to neutron absorption. Assuming Vesta's global regolith is well represented by howardite (e.g. see PRETTYMANETAL2012), then the following relationship can be used to convert DCP to physical absorption units: Sigma_Eff = 216.4 * DCP + 66.3, where Sigma_Eff is the macroscopic thermal neutron absorption cross section with units of 10E-4 square-centimeters per gram. The propagated 1-sigma uncertainty in Sigma_Eff is given by Unc_Sigma_Eff = 216.4 * SIGMA_DCP The dependence of Sigma_Eff on elemental composition is described by PRETTYMANETAL2013. Sigma_Eff is a weighted, linear sum of the abundance of neutron absorbing elements in Vesta's regolith. Sigma_Eff is shown to vary linearly with the percentage of eucritic material in howardite. Parameters ========== Each row of the table provides the DCP parameter and 1-sigma uncertainty for a single rectangular pixel. The format for each row is '(i10,6(f7.1),e11.2,e10.1)'. East longitude convention is used (-180 to 180 degrees). The longitudes are given in the Claudia Double Prime coordinate system (see Confidence Level Note). 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 DELTA_LAT (F7.1) Width of the pixel in latitude deg 4 MIN_LON (F7.1) Pixel longitude lower boundary deg 5 MAX_LON (F7.1) Pixel longitude upper boundary deg 6 DELTA_LON (F7.1) Width of the pixel in longitude deg 7 DCP (E11.2) Neutron absorption parmeter unitless 8 SIGMA_DCP (E10.1) 1-sigma uncertainty unitless

Data Set Overview #2

These data are maps of fast neutron residual count rates from the GRaND plus Z BLP sensor. The nominal fast neutron count rates were detrended using the GRaND epithermal neutron map to produced this residual map. The residual map is related to the average atomic mass on Vesta. Details of the map, data reduction, and interpretation are described in LAWRENCETAL2013. Two time-contiguous datasets were used for the fast neutron analysis: period 1 - 2011-12-09T00:00:00 to 2012-01-14T06:48:00 period 2 - 2012-04-03T00:00:00 to 2012-05-01T01:51:29 Parameters ========== Each row of the table provides the abundance of hydrogen for a single rectangular pixel. The format for each row is '(i10,6(f7.1),f8.2)'. East longitude convention is used (-180 to 180 degrees). The longitudes are given in the Claudia Double Prime coordinate system (see Confidence Level Note). 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 DELTA_LAT (F7.1) Width of the pixel in latitude deg 4 MIN_LON (F7.1) Pixel longitude lower boundary deg 5 MAX_LON (F7.1) Pixel longitude upper boundary deg 6 DELTA_LON (F7.1) Width of the pixel in longitude deg 7 FAST_RESID (F7.3) Fast neutron residual counts/s

Data Set Overview #3

This data product describes a map of the high-energy gamma-ray (HEGR) count rate across the surface of Vesta. As shown in PEPLOWSKIETAL2013, HEGRS are sensitive to the bulk elemental composition of the near surface material, particularly its heavy major-element content. Parameters ========== Each row of the table provides the high-energy gamma-ray (HEGR) count rate information for a single rectangular pixel. The format for each row is '(i10,6(f7.1),f8.2)'. East longitude convention is used (-180 to 180 degrees). The longitudes are given in the Claudia Double Prime coordinate system (see Confidence Level Note). 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 N/A 1 MIN_LAT (F7.1) Pixel latitude lower boundary deg 2 MAX_LAT (F7.1) Pixel latitude upper boundary deg 3 DELTA_LAT (F7.1) Width of the pixel in latitude deg 4 MIN_LON (F7.1) Pixel longitude lower boundary deg 5 MAX_LON (F7.1) Pixel longitude upper boundary deg 6 DELTA_LON (F7.1) Width of the pixel in longitude deg 7 HEGR_COUNTING_RATE (E14.4) HEGR count rate c/s 8 HEGR_COUNTING_RATE_UNCERTAINTY (E14.4) HEGR count rate uncertainties c/s 9 HEGR_SAMPLES (I10) Number of samples per pixel c/s

Data Set Overview #4

A global map of the abundance of hydrogen (micrograms/g) within the regolith of asteroid 4 Vesta is provided as an ASCII table. The map data are given for half-degree, equal-angle pixels. The data reduction and analysis methods are presented in PRETTYMANETAL2012. Epithermal counting rates measured in Dawn's circular, polar, low-altitude mapping orbit (LAMO), at a mean distance of about 210 km from Vesta's surface were corrected for variations in the flux of galactic cosmic rays (GCR) and solid angle. The data were acquired in early LAMO (Time-interval IA, described in the Supplementary Information of PRETTYMANETAL2012, Fig.1 and Table 2). during a long period (30 days) of continuous instrument operation and steady GCR counting rates. The corrected epithermal counting data were globally mapped on 15-deg equal-area pixels, smoothed using tesseral spherical harmonics and rebinned onto a two degree cylindrical map. Hydrogen abundance was determined from the smoothed epithermal map using Eq. 1 of PRETTYMANETAL2012. Parameters ========== Each row of the table provides the abundance of hydrogen for a single rectangular pixel. The format for each row is '(i10,6(f7.1),f8.2)'. East longitude convention is used (-180 to 180 degrees). The longitudes are given in the Claudia Double Prime coordinate system (see Confidence Level Note). 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 DELTA_LAT (F7.1) Width of the pixel in latitude deg 4 MIN_LON (F7.1) Pixel longitude lower boundary deg 5 MAX_LON (F7.1) Pixel longitude upper boundary deg 6 DELTA_LON (F7.1) Width of the pixel in longitude deg 6 H_ABUND (F8.1) Hydrogen abundance micrograms/g

Data Set Overview #5

These tables provide maps of net counting rates of Fe gamma rays at 7.6 MeV measured by the BGO detector of Dawn's Gamma Ray and Neutron Detector acquired at the low altitude mapping orbit. The data are binned on 0.5 degree equal area pixels. The counting rates were normalized for variations of live time, solid angle of Vesta, and galactic cosmic ray intensity. They were also corrected for variations of neutron number density determined by thermal and epithermal neutrons observed by GRaND. The table contains the original Fe counting rates reported by YAMASHITAETAL2013. The data were acquired during the low altitude mapping orbit (approximately 210 km from the surface) phase (LAMO). Only those when the spacecraft is nadir pointing (less than 5 degrees between the +Z axis of the spacecraft and the center of Vesta) are used to map Fe counting rates. At this altitude, the spatial resolution of the gamma ray spectrometer was about 300 km (PRETTYMANETAL2011). Parameters ========== Each row of the table provides composition information for a single pixel. The format for each row is '(i10,6(f7.1),(1x,e13.3). East longitude convention is used (-180 to 180 degrees) with Claudia (double prime) coordinate systems. The column description follows: 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 DELTA_LAT (F7.1) Width of pixel in latitude deg 4 MIN_LON (F7.1) Pixel longitude lower boundary deg 5 MAX_LON (F7.1) Pixel longitude upper boundary deg 6 DELTA_LON (F7.1) Width of pixel in longitude deg 7 FE_COUNTING_RATE (E13.3) Fe counting rate uncorrected count/s for neutron number density As discussed in YAMASHITAETAL2013, a preliminary scaling factor was derived by scaling the average corrected counting rate to the mean Fe content of 13.8 wt% of howardites such that Fe Abundance (wt.%) = Fe counting rate [count/s] x 189.2 which users can apply. However caution is recommended for its applicability.

Data Set Overview #6

These tables provide maps of net counting rates of Fe gamma rays at 7.6 MeV measured by the BGO detector of Dawn's Gamma Ray and Neutron Detector acquired at the low altitude mapping orbit. The data are binned on 30 degree equal area pixels. The counting rates are accompanied by their 1-sigma standard errors of the mean and average numbers of 5-deg pixels used to derive the 30-deg counting rates and errors. The counting rates were normalized for variations of live time, solid angle of Vesta, and galactic cosmic ray intensity, but were not corrected for variations of neutron number density. The table contains the original Fe counting rates and errors reported by YAMASHITAETAL2013. The data were acquired during the low altitude mapping orbit (approximately 210 km from the surface) phase (LAMO). Only those when the spacecraft is nadir pointing (less than 5 degrees between the +Z axis of the spacecraft and the center of Vesta) are used to map Fe counting rates. At this altitude, the spatial resolution of the gamma ray spectrometer was about 300 km (PRETTYMANETAL2011). Parameters ========== Each row of the table provides composition information for a single pixel. The format for each row is '(i10,6(f7.1),2(1x,e13.3)),i10'. East longitude convention is used (-180 to 180 degrees) with Claudia (double prime) coordinate systems. The column description follows: 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 DELTA_LON (F7.1) Width of Pixel in latitude deg 4 MIN_LON (F7.1) Pixel longitude lower boundary deg 5 MAX_LON (F7.1) Pixel longitude upper boundary deg 6 DELTA_LON (F7.1) Width of Pixel in longitude deg 7 FE_COUNTING_RATE (E13.3) Fe counting rate uncorrected count/s for neutron number density 8 SIG_FE_COUNTING_RATE (E13.3) 1-sigma uncertainty in the count/s uncorrected Fe counting rate 9 FE_SAMPLES (I10) Average number of 5-deg pixels per 30-deg pixel used to determine the uncorrected Fe counting rate and uncertainty

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

http://sbn.psi.edu/archive/dawn/grand/DWNVGRD_2/

Alternate Names

  • DAWN GRAND MAP VESTA FAST NEUTRON RESIDUAL V1.0
  • DAWN GRAND MAP VESTA GAMMA FE CORRECTED COUNTS V1.0
  • DAWN GRAND MAP VESTA GAMMA FE UNCORRECTED COUNTS V1.0
  • DAWN GRAND MAP VESTA HEGR COUNTS V1.0
  • DAWN GRAND MAP VESTA HYDROGEN ABUNDANCE V1.0
  • DAWN-A-GRAND-5-VESTA-ABSORPTION-V1.0
  • DAWN-A-GRAND-5-VESTA-FAST-RESIDUAL-V1.0
  • DAWN-A-GRAND-5-VESTA-GAMMA-IRON-COR-V1.0
  • DAWN-A-GRAND-5-VESTA-GAMMA-IRON-UNC-V1.0
  • DAWN-A-GRAND-5-VESTA-HEGR-COUNTS-V1.0
  • DAWN-A-GRAND-5-VESTA-HYDROGEN-MAP-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. William C. FeldmanData ProviderLos Alamos National Laboratorywfeldman@lanl.gov
Dr. Thomas H. PrettymanGeneral ContactPlanetary Science Instituteprettyman@psi.edu
Dr. Patrick N. PeplowskiGeneral ContactApplied Physics Laboratoryyamashita@psi.edu
Mr. Naoyuki YamashitaGeneral ContactPlanetary Science Instituteyamashita@psi.edu
Dr. David J LawrenceGeneral ContactPlanetary Science Institutedavid.j.lawrence@jhuapl.edu
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