# Presentation: 071719

## A New Analysis of LACE Data from Apollo 17

- Al Schultz

- January 31, 2008

*http://nssdc.gsfc.nasa.gov/*

## Lunar Atmospheric Composition Experiment 

***LASER Proposal Team***
**PI - **Dr. Alfred B. Schultz (NASA/GSFC)
**Co-Investigators**
- Dr. Paul Lowman (NASA/GSFC)
- Dr. H. Kent Hills (Perot Systems/GSFC)
- Dr. David R. Williams (Perot Systems/GSFC)
- David Han (NASA/GSFC)
**Collaborators**
- Dr. Michael A. DiSanti (NASA/GSFC)
- Dr. R. Richard Hodges (U Texas at Dallas)

## Lunar Atmospheric Composition Experiment 

***Apollo 17 LACE***
**PI/Experiment**
- Dr. John H. Hoffman
- To study the composition and variation in the lunar atmosphere.
**The Instrument**
- a 3 channel mass spectrometer design. Three mass ranges were scanned simultaneously; viz., 1 to 4, 12 to 48, and 27.4 to 110 amu.
- could not be operated in the lunar daytime because the detectors were saturated with artifact gases due to solar heating of residual spaceflight hardware.

**Figure 1: The LACE instrument (foreground) measured the ambient lunar atmosphere at the surface and may also have detected byproducts from the ALSEP RTG (black), shown in the middle of the background with the central station. Also captured in the photo are other ALSEP instruments. (AS17-134-20499)**

## Lunar Atmospheric Composition Experiment 

***Apollo 17 LACE***
**Instrument Design**
- a 3 channel mass spectrometer design. Three mass ranges were scanned simultaneously; viz., 1 to 4, 12 to 48, and 27.4 to 110 amu.
- Sensitivity, ~1 count/sec equals  200 mol/cm3
- Sensitivity varies with mass, ~1 count per 100 40Ar atoms/cm3
- Resolution of the analyzer was set at about 100 for the high-mass channel at 82 (1% valley between equal amplitude at mass 82 and 83).
- Ground calibration, Ar, CO2, CO, Kr, Ne, He, Hydrogen

**Figure 2. Schematic diagram of mass analyzer****. Gas molecules entering the inlet plenum aperture are ionized by an electron ion source. Three ion trajectories are shown through the magnet. Electron multipliers serve as charge amplifiers. An Ion pump is used to check the internal analyzer pressure before application of high voltage to the ion source or the electron multiplier electrodes.**

## Lunar Atmospheric Composition Experiment 

***Apollo 17 LACE***
**Experiment**
- Deployed December 11-15, 1972
- ALSEP placed ~185 m north-west of LEM
- LACE instrument placed 13 meters from central station
- Operation December 27, 1972 to mid-October 1973
**Results**
- He, Hydrogen in equal amounts
- 40Ar (mass 40), radioactive decay of 40K
- CH4 (mass 16), NH3 (mass 17), CO2 (mass 44)
- No O or O2 detected

## Lunar Atmospheric Composition Experiment 

**Figure 3. Deployment of the Apollo 17, ALSEP, showing the relative locations of the central station, radioisotope thermoelectric generator (RTG), and the five instruments.**

## Lunar Atmospheric Composition Experiment 

**Figure 4. LACE data arranged to show specific counting rate for gas species (e.g. CH****3****:mass 15, CH****4****:mass 16, N****2****:mass 28) as a function of normal elevation of the Sun where 0****o**** is at the terminator crossing the Apollo 17 landing site. Sunrise occurs nearly 5****o**** after terminator crossing. Pre-dawn enhancement is indicated by positive slope of lines fitted to data (Hoffman and Hodges 1975)**

## Lunar Atmospheric Composition Experiment 

**Figure 5. LACE data arranged to show specific counting rate for gas species (e.g. ****40****Ar:mass 40, CO****2****:mass 44) as a function of normal elevation of the Sun where 0****o**** is at the terminator crossing the Apollo 17 landing site. Sunrise occurs nearly 5****o**** after terminator crossing. Pre-dawn enhancement is indicated by positive slope of lines fitted to data (Hoffman and Hodges 1975)**

## Lunar Atmospheric Composition Experiment 

**Figure 6. Argon concentration at the lunar surface was highly variable, as shown by this model for the distribution of ****40****Ar as a function of longitude (with the sub-solar point at 0****o****) fitted to the Apollo 17 LACE data (Hoffman and Hodges 1975).**

## Lunar Atmospheric Composition Experiment 

|  mass (amu) | Cts | CH4 | NH3 | H20 | N2 | CO | O2 | CO2 | Total |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| 12 | 2±2 | 0.2 | - | - | - | 0 | - | 0.3 | 0.5 |
| 14 | 2±1 | 0.5 | 0.02 | - | 0.3 | 0 | - | - | 0.8 |
| 15 | 5±2 | 5 | 0.07 | - | - | - | - | - | 5 |
| 16 | 8±2 | 6 | 0.8 | 0.3 | - | 0 | 0.4 | 0.5 | 8 |
| 17 | 4+2              -1 | - | 1 | 1 | - | - | - | - | 2 |
| 18 | 3±3 | - | - | 3 | - | - | - | - | 3 |
| 28 | 4±4 | - | - | - | 4 | 0 | - | 0.6 | 4.6 |
| 32 | 5±5 | - | - | - | - | - | 5 | 0 | 5 |
| 40 | 90±10 | - | - | - | - | - | - | - | 90 |
| 44 | 7±5 | - | - | - | - | - | - | 7 | 7 |

**Table 1 Pre-Dawn Enhancement. Summary of data from Figures 4 and 5. Column 2 is the increase in counting rate at sunrise over background. Error bar is a best estimate from the slope of the lines. Next columns possible parent molecules (Hoffman and Hodgers 1975).**

## Lunar Atmospheric Composition Experiment 

***Apollo 17 LACE***
**Table I**
- Last column, total accumulated counts, parent plus fragmentary peaks
- Except for mass 12 and 14, peaks are accounted for from listed molecules
- Total counts all within error bars stated in column 2
- Evidence to support CH4, 40Ar
- Possibly small amounts of NH3 and CO2 at terminator
**Note – Figure 4 & 5**
- 40Ar has peaked and turned over at sunrise
- Molecular species count rates continue to rise all the way to sunrise
- Molecular gases affected by surface temperature differently than 40Ar
- Possibly, concentration of molecular gases higher after sunrise
- 12-27 amu, electronic noise from high voltage, local contaminates

## Lunar Atmospheric Composition Experiment 

***Apollo 17 LACE***
**Mystery I**
- Assume mass peak at 40 is Argon
- Could mass peak at 40 be 40Ca? (raised by Tobias Owen 30yr ago)
- Ca II resonance lines 3933 Å, 3968 Å, large oscillator strength
- Ca I resonance line 4227 Å, lower oscillator strength
**Mystery II**
- CH4 detected, abundance exceeding low
- Formed by interaction of solar wind protons and C in regolith?
**Mystery III**
- After billions of years of asteroid and comet impacts, where did the water go?
- Moon rocks, regolith, and dust were found to be dry, no hydrous minerals

## Lunar Atmospheric Composition Experiment 

***Apollo 17 LACE***
**Mystery IV**
- Transient event on February 23, 1973
- Mass peaks 1, 13, 14, 15, 16, 28, 29, and 30 amu
- Dominant mass peaks were 14 and 28 amu
- Reported as artifact due to hardware outgassing?
- Luna 21 (Jan 15, 1973 to May 15, 1973)
- 172 km between Luna 21 and Apollo 17 landing sites
**Recommendation**
- Build a better *in situ* Lunar spectrometer
- Need to detect volatiles
- Need to detect metalic ions