Post on 25-Feb-2016
description
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 4
HEND Workshop 2002May 20th – 22nd 2002
Ge vs. NaI
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 6
HEND Workshop 2002May 20th – 22nd 2002
GRS Coverage
2001 Mars Odyssey GRSRDS 7
HEND Workshop 2002May 20th – 22nd 2002
Cruise Spectrum
2001 Mars Odyssey GRSRDS 8
HEND Workshop 2002May 20th – 22nd 2002
Background Lines
8104
2
3
4
5678
105
2
3
4
5678
106
2
3
4
Cou
nts p
er C
hann
el
1400keV12001000800600400200Energy (keV)
#075mGe
76Ge(p,p'n)132.68 #1
46mSc136.00
#265Ga(spal)
~153.60
#371As
72Ge(p,2n)181.52
#467Ga
70Ge(p,a)190.39
#571mGe
72Ge(p,p'n)194.43
#6212Pb
235.75
#744mSc(spal)
269.56
#8214Pb
294.18
#967Ga
70Ge(p,a)308.91
#10228Ac
337.10
#11214Pb
350.56
#1243K43Sc
372.29
#1367Ga
70Ge(p,a)402.69
#1423Na
69mZn(n,ng);spal
438.87
#1523Mg
450.71
#1624mNa472.24
#177Be
(spal)477.17
#18annih
511.00
#1969Ge
70Ge(p,p'n)584.02
#2074Ge74As
(SAW)~598.00
#21214Bi
608.71
#2243K
617.39
#2663Cu
670.77
#2772Ge
72Ge(n,n')~693.00
#2810B
719.02
#2958Co(spal)811.24
#3058Co(spal)
817.97
#3172Ge
(SAW)~835.50
#3227Al(843.8)
27Mg(844.01)56Fe(846.7)
~843.60
#3369Ge
70Ge(p,p'n)882.65
#3446Ti46Sc
889.55
#35228Ac
910.98
#3763Cu
962.50
#38228Ac
969.26
#3925Mg
974.81
#4048Ti48V48Sc
(n,ng)983.72
#4227Al
1014.65
#4345Ar
1021.10
#4448Sc
1038.20
#4566Ga
70Ge(n,na)1048.95
#4668Ga
72Ge(p,na)1087.00
#4769Ge
1107.00
#4869Ge
70Ge(p,p'n)1117.70
#5065Zn
(Spal)1124.50
#5144Sc
(Spal)1157.00
#5260Co
1173.12
#5422Na22Ne
1274.44
#5548Ti48V48Sc
1312.29
#5660Co
1332.94
#5769Ge
1346.68
#5824Mg
Al24Na
(n,ng)1368.58
#5952mMn(Spal)
~1434.30
#6040K
1460.78
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
Cou
nts
[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 14
HEND Workshop 2002May 20th – 22nd 2002
Orbital Spectrum – High Energy
2001 Mars Odyssey GRSRDS 15
HEND Workshop 2002May 20th – 22nd 2002
Orbital Spectrum – Low Energy
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.