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

2001 Mars Odyssey GRSRDS 1

HEND Workshop 2002May 20th – 22nd 2002

Mars Odyssey Gamma-Ray Spectrometer

Richard StarrNASA/GSFC – Catholic University

and the GRS team



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



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).



Ge vs. NaI



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.



GRS Coverage



Cruise Spectrum



Background Lines

8

104

2

3

4

5

678

105

2

3

4

5

678

106

2

3

4

Cou

nts

per

Cha

nnel

1400keV12001000800600400200Energy (keV)

#075m

Ge76

Ge(p,p'n)132.68 #1

46mSc

136.00

#265

Ga(spal)

~153.60

#371

As72

Ge(p,2n)181.52

#467

Ga70

Ge(p,a)190.39

#571m

Ge72

Ge(p,p'n)194.43

#6212

Pb235.75

#744m

Sc(spal)

269.56

#8214

Pb294.18

#967

Ga70

Ge(p,a)308.91

#10228

Ac337.10

#11214

Pb350.56

#1243

K43

Sc372.29

#1367

Ga70

Ge(p,a)402.69

#1423

Na69m

Zn(n,ng);spal

438.87

#1523

Mg450.71

#1624m

Na472.24

#177Be

(spal)477.17

#18annih

511.00

#1969

Ge70

Ge(p,p'n)584.02

#2074

Ge74

As(SAW)~598.00

#21214

Bi608.71

#2243

K617.39

#2663

Cu670.77

#2772

Ge72

Ge(n,n')~693.00

#2810

B719.02

#2958

Co(spal)

811.24

#3058

Co(spal)

817.97

#3172

Ge(SAW)~835.50

#3227

Al(843.8)27

Mg(844.01)56

Fe(846.7)~843.60

#3369

Ge70

Ge(p,p'n)882.65

#3446

Ti46

Sc889.55

#35228

Ac910.98

#3763

Cu962.50

#38228

Ac969.26

#3925

Mg974.81

#4048

Ti48

V48

Sc(n,ng)983.72

#4227

Al1014.65

#4345

Ar1021.10

#4448

Sc1038.20

#4566

Ga70

Ge(n,na)1048.95

#4668

Ga72

Ge(p,na)1087.00

#4769

Ge1107.00

#4869

Ge70

Ge(p,p'n)1117.70

#5065

Zn(Spal)

1124.50

#5144

Sc(Spal)

1157.00

#5260

Co1173.12

#5422

Na22

Ne1274.44

#5548

Ti48

V48

Sc1312.29

#5660

Co1332.94

#5769

Ge1346.68

#5824

MgAl

24Na

(n,ng)1368.58

#5952m

Mn(Spal)

~1434.30

#6040

K1460.78

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.



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



Detector Configuration

Mars OdysseyGRS Detector



Line Shape and Trapping

100

1000

10000

1300 1310 1320 1330 1340 1350

Coaxial n-Type NC

Co

un

ts [

1]

Energy [keV] MPC MainzLinie n-Typ Detektor

Inside: n-contact Outside: p-contact

Germanium crystal

Hole current



Radiation Damage and Detector Annealing



Comparison of Cruise to Mars Orbit



Orbital Spectrum – High Energy



Orbital Spectrum – Low Energy



Why do we believe it’s H20?

• Hydrogen can combine with many elements, such as sulfur to form H2S, 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.



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 CO2 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.

Documents

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