2001 Mars Odyssey GRS RDS 1 HEND Workshop 2002 May 20 th – 22 nd 2002 Mars Odyssey Gamma-Ray...
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Transcript of 2001 Mars Odyssey GRS RDS 1 HEND Workshop 2002 May 20 th – 22 nd 2002 Mars Odyssey Gamma-Ray...
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
2001 Mars Odyssey GRSRDS 2
HEND Workshop 2002May 20th – 22nd 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
2001 Mars Odyssey GRSRDS 3
HEND Workshop 2002May 20th – 22nd 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).
2001 Mars Odyssey GRSRDS 5
HEND Workshop 2002May 20th – 22nd 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.
2001 Mars Odyssey GRSRDS 8
HEND Workshop 2002May 20th – 22nd 2002
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.
2001 Mars Odyssey GRSRDS 9
HEND Workshop 2002May 20th – 22nd 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
2001 Mars Odyssey GRSRDS 10
HEND Workshop 2002May 20th – 22nd 2002
Detector Configuration
Mars OdysseyGRS Detector
2001 Mars Odyssey GRSRDS 11
HEND Workshop 2002May 20th – 22nd 2002
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
2001 Mars Odyssey GRSRDS 12
HEND Workshop 2002May 20th – 22nd 2002
Radiation Damage and Detector Annealing
2001 Mars Odyssey GRSRDS 13
HEND Workshop 2002May 20th – 22nd 2002
Comparison of Cruise to Mars Orbit
2001 Mars Odyssey GRSRDS 16
HEND Workshop 2002May 20th – 22nd 2002
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.
2001 Mars Odyssey GRSRDS 17
HEND Workshop 2002May 20th – 22nd 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 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.