Thermal, Thermophysical, and Compositional Properties of the Moon Revealed by the Diviner Lunar Radiometer

Transcription

1 Thermal, Thermophysical, and Compositional Properties of the Moon Revealed by the Diviner Lunar Radiometer Benjamin T. Greenhagen Jet Propulsion Laboratory David A. Paige and the Diviner Science Team LEAG /23/12 Greenbelt, MD

2 The Moon is a model of airless solar system bodies but don t forget the infrared!

3 LRO Diviner Overview Observation Strategy Detectors Fields of view Primarily nadir pushbroom mapping Nine 21-element linear arrays of uncooled thermopile detectors Detector Geometric IFOV: 6.7 mrad in-track 3.4 mrad cross track 320 m on ground in track for 50 km altitude 160 m on ground cross track for 50 km altitude Swath Width (Center to center of extreme pixels): 67 mrad; 3.4 km on ground for 50 km altitude Normalized Response Wavenumber (cm-1) Wavelength (microns) Science Goals 1. Characterize the Moon s surface thermal environments: Daytime Nighttime Polar 2. Map properties of the lunar surface: Bulk thermal properties Rock abundance Composition 3. Characterize polar cold traps: Map cold trap locations and temperatures Assess potential lunar volatile resources Determine thermophysical properties

4 Examples of Diviner South Pole Coverage /27 9/20 11/13 1/7 2/28 Des. EQX Lon EQX Time-of-Day :00 Ascending EQX 18:00 12:00 6:00 Descending EQX 0:00 Enhancing diurnal and seasonal coverage is a prime goal of the LRO extended science mission

5 South Pole Temperature Summary Maps Maximum Temperature Average Temperature Minimum Temperature Diviner has observed the lunar poles with a wide range of local times Diviner Polar Resource Products: Which volatiles could be present Where to look for surface and near surface deposits after Paige et al., 2010; Science Paige et al., 2012

6 South Pole Temperature Depth to 1 mm water Summary ice Maps sublimation per BY Maximum Temperature Average Temperature Minimum Temperature Diviner has observed the lunar poles with a wide range of local times Diviner Polar Resource Products: Which volatiles could be present Where to look for surface and near surface deposits after Paige et al., 2010; Science Paige et al., 2012

7 Equatorial Daytime Coverage Ch 7 Brightness Temperature (K) Green Crater 133 E / 3.5 N

8 Equatorial Nighttime Coverage Ch 7 Brightness Temperature (K) Green Crater 133 E / 3.5 N

9 Diviner-revised Thermal Models Highlands: rougher, more scatter Maria: smoother, but with warm rocks Remarkably similar on average Diviner diurnal temperature data reveal effects of thermophysical properties, roughness, and rocks Data are consistent with a near-surface regolith in which density and temp-variable conductivity gradually increase in the upper ~20 cm (Vasavada et al., 2012; JGR-Planets) Leveraged eclipse observations to understand upper ~2 cm (Hayne et al., 2012)

10 Diviner Global Rock Abundance 0 Tycho (~100 Ma) Aristarchus (~170 Ma) Rock Concentration (0-0.05) 0 50 km Copernicus (~800 Ma) Bullialdus (>1100 Ma) Rock Concentration Rock abundance and regolith temperature map level 3 products available at the PDS Methodology and initial science results published at JGR-Planets (Bandfield et al., 2011) Regolith Temperature (Normalized for Local Time) Regolith Temperature (Normalized for Local Time and Latitude)

11 Tsiolkovskiy Crater Diviner Rocks over WAC Mosaic / DEM after Greenhagen et al., 2012; EPSC

12 LROC WAC Equatorial Cold Spots Nighttime Soil Temperature Colder than average nighttime temperatures associated with small, fresh craters No associated albedo or spectral signature Modeling indicates thicker than average highly insulating layer Deposits were likely emplaced via combination of granular and fluidized flow Mechanism is currently uncertain but could include mobilization of volatiles after Bandfield et al., 2012

13 Surface and Buried Rock Populations Surface Rock Fraction Buried Rock Depth 5% 10 cm Model Rock Abundance 2.5% Model Rock Depth 5 cm 0% 0 cm Copernicus Crater Diviner surface rock abundances match LROC NAC images of surface rocks but Mini-RF shows extended regions of blocky materials Radar observed blocky materials must be buried Diviner rock abundance and nighttime soil temperatures with thermal models are used to estimate the burial depth of extended blocky regions potential to constrain lunar burial / regolith formation rate after Ghent et al., 2012

14 Lunar Swirls 50 km Diviner CF Map of Reiner Gamma Feature Off-swirl CF Swirl CF Δ CF Reiner Gamma Airy Ingenii Marginis km CF Shift consistent with solar wind stand-off inhibiting space weathering. CF position not consistent with pure feldspar composition Night-time data reveal weak thermal anomaly thermal modeling is under way. after Glotch et al., 2012

15 Groundtruthing Diviner Data Measured Diviner CF values for each Apollo Site Strong Correlation between Diviner measured CF and some geochemical species (esp. Al 2 O and FeO) Illustrates sensitivity to plagioclase-mafic ratio; complementary to NIR datasets Apollo 15 2 km Al 2 O 3 wt% Apollo 11 Apollo 12 Apollo 14 Apollo 15 Apollo 16 Apollo 17 Apollo 17 2 km CF Position (μm) after Greenhagen et al., 2012; LPSC

16 Diviner observations of crater central peaks (after Song et al., 2012, JGR-Planets) Copernicus Crater. Colorized CF over WAC basemap Copernicus crater (above), E 9.6 N. Central peak CF value of 8.14µm. Northern wall feature CF value is 8.41µm. Eratosthenes crater (right), 348 E 13.5 N. Central peak CF value of 8.48µm, making it the most mafic composition sampled in the central peak survey. 6/135 craters with central peak composition more mafic than typical mare basalt. None that appear to be mantlesourced. Eratosthenes Crater. Colorized CF over WAC basemap

17 Some Additional Ongoing Investigations Constraining lunar heat flow by analyzing data for coldest permanently shadowed craters Investigating Diviner-constrained lunar permafrost locations with neutron data Investigating warmer, off-pole shadowed regions where ice pumping to subsurface may be enhanced Photometric and thermophysical studies using targeted emission phase function observations Understanding the effects of space weathering on Diviner data Compositional studies of a wide range of targets High silica, plagioclase, olivine, pyroclastics, etc. Studying the Earth as an exoplanet using Diviner Earth scans Laboratory experiments to aid the interpretation of Diviner data Incorporating other lunar datasets to enhance Diviner data analyses LOLA, LROC, Mini-RF, M3, Kaguya, Clementine, LP Producing enhanced maps and data products for PDS

18 Conclusions Diviner data are being used to understand in detail the lunar thermal environment and thermophysical and compositional properties The Diviner dataset will be important for future lunar landing site selections Thermal state Global diurnal and seasonal temperatures Polar Resources Potential volatile cold traps and species Thermophysical Properties Rock abundance and nighttime soil temperature Insulating layer thickness Constraints on buried rocks Composition Mineralogical diversity Plagioclase abundances and mixing