Spectroscopic Measurements of Water Vapor in Mars Atmosphere

A.L. Sprague, D.M. Hunten, R.E. Hill, B. Rizk
Lunar and Planetary Laboratory
University of Arizona, Tucson, AZ 85721
sprague
fax 520-621-4933

ABSTRACT

(Mars Telescopic Observations Workshop II, 1997)

We report partial results of systematic measurements of water vapor abundance in the Martian atmosphere. As in our previous work (Rizk et al. 1989, Sprague et al. 1996) measurements are made with the LPL echelle spectrograph on the 1.5 m telescope at the Catalina Observatory, a short distance North of Tucson (see Table 1). For this report we include observations made between October 4, 1996 and July 12, 1997, just 8 days after the joyous landing of Mars Pathfinder. We use a new method of modeling the continuum that results in greater equivalent width measurements (see Table 2) than in previous work. General seasonal trends between apparitions remain similar but a reanalysis of the previous data (Sprague et al. 1996) with our new technique will be required before comparison of actual abundances can be made. Our measurements at the Pathfinder site do not coincide with the IMP measurements in local time but water vapor measurements (~10 ppt m) are consistent when diurnal trends are taken into consideration.

 
1.   Rizk, B., W.K. Wells, D.M. Hunten, C. Stoker, R. S.
Freedman, T. Roush, J. B. Pollack and R. M. Haberle.  Icarus, 90,
205 - 213, 1991.       2.  Sprague, A.L., D.M. Hunten, R.E. Hill,
B. Rizk and W.K. Wells.  Martian water vapor, 1988 - 1995. JGR,
101, 23,229-23,241, 1996.

 
   Table 1.  Observations of Martian Water Vapor Abundance
                              
  Date     Time    Ls      Slit        MPF     Arcsec   Doppler
          h   m          Geometry     Site ?    Diam.    Shift
                                                      (Angstroms)
  1996                                                 
Oct. 4
  #44     11 34   18.5      EW          no      4.9     -0.32
  #45     11 55             NS          no                
                                                       
Dec. 3
  #38     10 30   45.9      EW          YES     6.5     -0.44
  #49     11 42             NS          YES                

  1997                                                 
Jan. 2
  #29     09 45   59.1  NS offset +2    YES     8.3     -0.45
  #42     11 44         NS offset -2    no                
                                                                                  
Feb. 1
  #35     09 58   72.3      EW          no      10.7     -0.38
  #46     11 55             NS          no                
                                                       
Feb. 15
  #33     08 56   78.4      EW          YES     12.1     -0.31
  #48     10 48             NS          YES                
                                                       
 May 5
  #21     05 09   113.7     NS          no     11.1      0.32
                                                               
May 29
   #7     04 34   124.9     NS          no      9.3      0.35
  #16     06 08             EW          no                
                                                       
June 22
  #14     03 20   137       NS          no      7.9      0.35
  #19     04 04             EW          no                
                                                       
July 12   
  #14	  03 19   146.4  NS offset -1"  YES     7.9      0.33
  #15     03 32             EW          YES