1. 2001 Mars Odyssey GRS RDS 1 HEND Workshop 2002 May 20 th – 22 nd 2002 Mars Odyssey Gamma-Ray Spectrometer Richard Starr NASA/GSFC – Catholic University and the GRS team

2. 2001 Mars Odyssey GRS RDS 2 HEND Workshop 2002 May 20 th – 22 nd 2002 Mars Odyssey GRS Timeline 2001 April 07 – Launch 2001 June – 7 day warm anneal (~42° C) 2001 June 27 – Begin cruise data collection 2001 August 30 – End cruise data collection 2001 October 23 – Mars orbit insertion 2002 February 09 – Begin mapping phase 2002 March – 10 day warm anneal (~52° C) 2002 March 26 – Resume mapping 2002 May – 10 day hot anneal (~73° C) 2002 May 21 – Resume mapping 2002 June 04 – Boom deployment

3. 2001 Mars Odyssey GRS RDS 3 HEND Workshop 2002 May 20 th – 22 nd 2002 Gamma-Ray Spectrometer The Mars Odyssey gamma- ray spectrometer is a 67 mm diameter × 67 mm long, high-purity, n-type Ge crystal that is encapsulated in a sealed titanium canister. The detector is passively cooled to cryogenic temperatures (<130 K).

4. 2001 Mars Odyssey GRS RDS 4 HEND Workshop 2002 May 20 th – 22 nd 2002 Ge vs. NaI

5. 2001 Mars Odyssey GRS RDS 5 HEND Workshop 2002 May 20 th – 22 nd 2002 GRS Accumulation Times The gamma-ray signal comes from the upper 20 to 30 cm of soil. Thermal and epithermal neutrons are sensitive to composition about a factor of 2 or 3 deeper than gamma rays.

6. 2001 Mars Odyssey GRS RDS 6 HEND Workshop 2002 May 20 th – 22 nd 2002 GRS Coverage

7. 2001 Mars Odyssey GRS RDS 7 HEND Workshop 2002 May 20 th – 22 nd 2002 Cruise Spectrum

8. 2001 Mars Odyssey GRS RDS 8 HEND Workshop 2002 May 20 th – 22 nd 2002 Background Lines Over 100 background lines have been identified. The intensity of many will be reduced after boom deployment. Others, resulting from detector materials like Ge and Ti, will not be affected.

9. 2001 Mars Odyssey GRS RDS 9 HEND Workshop 2002 May 20 th – 22 nd 2002 Solar Proton Events During MO Cruise Event-Integrated Fluences for Solar Particle Events since 7 April 2001 (Fluences, F, are omnidirectional - 4-pi - protons/cm2) Date F>10 MeV F>30 MeV F>60 MeV 4/11/01 2.4E+8 3.3E+7 6.0E+6 4/15/01 4.5E+8 1.5E+8 7.0E+7 4/18/01 1.7E+8 4.8E+7 1.8E+7 5/08/01 2.5E+7 1.3E+6 2.5E+5 5/20/01 5.0E+6 1.8E+6 8.0E+5 6/15/01 1.9E+7 1.7E+6 5.0E+5 8/16/01 2.8E+8 9.8E+7 3.1E+7 9/25/01 7.4E+9 1.2E+8 1.9E+8 10/02/01 9.8E+8 6.5E+7 3.6E+6 10/19/01 1.2E+7 2.2E+6 4.0E+5 10/22/01 1.4E+7 4.5E+6 1.5E+6 11/05/01 1.5E+10 3.0E+9 6.0E+8 11/23/01 8.1E+9 8.0E+8 7.0E+7 12/16/01 3.6E+8 9.0E+7 2.4E+7 12/31/01 2.7E+8 1.5E+7 9.0E+5 1/11/02 1.4E+8 6.0E+6 3.0E+5

10. 2001 Mars Odyssey GRS RDS 10 HEND Workshop 2002 May 20 th – 22 nd 2002 Detector Configuration Mars Odyssey GRS Detector

11. 2001 Mars Odyssey GRS RDS 11 HEND Workshop 2002 May 20 th – 22 nd 2002 Line Shape and Trapping Inside: n-contactOutside: p-contact Germanium crystal Hole current

12. 2001 Mars Odyssey GRS RDS 12 HEND Workshop 2002 May 20 th – 22 nd 2002 Radiation Damage and Detector Annealing

13. 2001 Mars Odyssey GRS RDS 13 HEND Workshop 2002 May 20 th – 22 nd 2002 Comparison of Cruise to Mars Orbit

14. 2001 Mars Odyssey GRS RDS 14 HEND Workshop 2002 May 20 th – 22 nd 2002 Orbital Spectrum – High Energy

15. 2001 Mars Odyssey GRS RDS 15 HEND Workshop 2002 May 20 th – 22 nd 2002 Orbital Spectrum – Low Energy

16. 2001 Mars Odyssey GRS RDS 16 HEND Workshop 2002 May 20 th – 22 nd 2002 Why do we believe it’s H 2 0? Hydrogen can combine with many elements, such as sulfur to form H 2 S, or metals to form hydrides, but these compounds are not likely to be stable given the highly oxidizing conditions on Mars. Many theoretical studies have predicted the regions where water ice should be thermodynamically stable on Mars. –Farmer and Doms (1979) conclude that ground ice should be stable in the regolith where temperatures never exceed 200 K. ~10 cm depth at 80° latitude ~100 cm depth at 50° latitude –Mellon and Jakosky (1993) model water ice stability at various depths below the surface versus latitude.

17. 2001 Mars Odyssey GRS RDS 17 HEND Workshop 2002 May 20 th – 22 nd 2002 Summary The Mars Odyssey gamma-ray and neutron spectrometers have identified a significant water ice component south of -60° latitude. The ice is not uniformly distributed within the soil but is buried under an ice-poor layer. North of 60° latitude there is a thick seasonal CO 2 cap that is opaque to gamma rays. We are detecting many gamma-ray lines from elements on the surface of Mars, in addition to H, that are of geochemical significance: Th, U, K, O, Si, Mg, Cl, Fe … Over the life of the mission (>2 years) many of these elements will be mapped with a spatial resolution of order a few hundred kilometers.