Effects of Mariner IV ionospheric data on Mars atmosphere composition prediction

Johnson, F. S.

English

NASA Technical Reports Server

i;‘ - ‘4 
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The Atmosphere of Mars* 
Francis  S .  Johnson 
D a l l a s  , Texas 
Southwest Center f o r  Advanced ! Studies 
Much new information has become a v a i l a b l e  i n  r e c e n t  years  on the 
Martian atmosphere. Mariner I V  data  have shown t h a t  the su r face  pressure 
i s  below t e n  m i l l i b a r s ,  a r e s u l t  t h a t  i s  not i n c o n s i s t e n t  with t h e  most 
r e c e n t  spectroscopic  s t u d i e s .  
i n t e r p r e t e d  i n  terms of a n  F2 peak, t h e  atmosphere must be very cold a t  
a l l  l e v e l s  and the  exospheric temperature must be near  85 K. 
i s  i n  disagreement wi th  s t u d i e s  of r a d i a t i v e  equi l ibr ium temperatures,  
which i n d i c a t e  a r e l a t i v e l y  warm exosphere, t he  temperature being i n  the 
v i c i n i t y  of 400°K. A s  a consequence of t h i s  inconsis tency and o the r s  of 
a s i m i l a r  n a t u r e ,  t h e r e  is s t i l l  a w i d e  range of specu la t ion  concerning 
t h e  p r o p e r t i e s  of the Martian atmosphere. 
probably be resolved only a f t e r  more d e t a i l e d  observations have been made 
i n  p l ane ta ry  probes,  such a s  the d i s t r i b u t i o n  of resonance s c a t t e r i n g  of 
s u n l i g h t  by atomic oxygen. 
I f  t he  Mariner I V  ionospheric data  a r e  
0 This r e s u l t  
These incons i s t enc ie s  w i l l  
*This paper was presented a t  the COSPAR Seventh InterGLtional  Space Science 
Symposium i n  Vienna, A u s t r i a ,  May 10-19, 1966. 
https://ntrs.nasa.gov/search.jsp?R=19660023012 2020-03-16T21:10:43+00:00Z
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I '  w 
- 2 -  
Mariner I V  da t a  (Kliore e t  a l . ,  1965a) show t h a t  t he  sur face  
pressure  on Mars i n  qu i t e  low,  l e s s  than 10 m b ,  and t h a t  the  atmosphere 
c o n s i s t s  mainly of carbon dioxide. Johnson (1965) has argued t h a t  the 
concept t h a t  t he  e a r t h ' s  atmosphere has a r i s e n  from wi th in  the  p lane t ,  
if appl ied t o  Mars, p r e d i c t s  an  atmospheric composition t h a t  i s  i n  
agreement wi th  the  observat ions.  
On e a r t h ,  t h e  t w o  m o s t  p l e n t i f u l  gases t h a t  have been re leased  from 
5 2 the  e a r t h ' s  i n t e r i o r  a r e  water  vapor and carbon dioxide.  
water  vapor have been re leased ,  and t h i s  has gone mainly i n t o  the  formation 
of t he  oceans. 
t h i s  has gone mainly i n t o  carbonate depos i t s  through chemical processes 
t h a t  depend on the  presence of water. The next most p l e n t i f u l  gas has 
probably been n i t rogen ,  of  which about 10 
however, t h i s  i s  a cons t i t uen t  t h a t  i s  s u f f i c i e n t l y  i n e r t  so  t h a t  it 
can accumulate i n  the  atmosphere, and i t  now makes up the  bulk of the 
atmosphere. Oxygen has a r i s e n  through secondary processes ,  i n i t i a l l y  by 
photochemical decomposition of  wa te r  vapor,  but predominantly through 
photosynthesis  a f t e r  l i f e  on e a r t h  became abundant. 
About 3 x 10 g/cm 
4 About 2 x 10 g/cm2 carbon dioxide have been re leased ,  and 
3 2 g/cm have been re leased;  
The temperature of Mars i s  so low t h a t  most of t he  water vapor t h e r e  
would accumulate i n  i c e  depos i t s  which could then become covered and 
obscured by dus t .  Lacking l iqu id  water ,  t he  carbon dioxide t h a t  has been 
re leased  from the  Martian i n t e r i o r  should remain i n  the atmosphere and 
make up most of i t s  bulk. The amount of carbon dioxide on Mars i s  about 
20 g/cm ; t h i s  i n d i c a t e s  t h a t  the amount of gas t h a t  has been released 
from the  i n t e r i o r  of Mars i s  only about 10 t h a t  re leased  on e a r t h  i n  
2 
-3  
terms of mass pe r  u n i t  a r ea .  Thus, t h e  water on Mars can be expected t o  
amount t o  300 g/cm ; t h i s  should be non-uniformly d i s t r i b u t e d  over t h e  2 
p l a n e t  i n  the form of subsurface depos i t s  of i c e .  
atmosphere of Mars should be about 1 g/cm2, and argon only 0.01 g/cm , 
Nitrogen i n  t h e  
2 
assuming i t s  r e l e a s e  on Mars t o  be comparable i n  e f f i c i e n c y  t o  t h a t  of  t he  
o t h e r  gases.  
The ionosphere on Mars was observed a t  t h e  unexpectedly low a l t i t u d e  
of 120 km (Kliore e t  a l . ,  1965a; 1965b), and t h e  r a t e  of  decrease of 
i o n i z a t i o n  with a l t i t u d e  w a s  very r a p i d  above the maximum, the  s c a l e  height  
being about 25 km. D i f f e ren t  i n t e r p r e t a t i o n s  e x i s t  with regard t o  t h e  
i o n i z a t i o n  peak. It has been i d e n t i f i e d  a s  an F2 peak (Johnson, 1965; 
Fjelbo e t  a l . ,  1966), a n  F1 peak (Donahue, 1966) and an E peak (Chamberlain 
and McElroy, 1966). 
The i d e n t i f i c a t i o n  of t h e  i o n i z a t i o n  maximum a s  an F2 peak involves 
t h e  concept t h a t  t h e  peak i s  con t ro l l ed  by downward d i f f u s i o n  of i o n i z a t i o n ,  
t h a t  t h e  ions a r e  O', and t h a t  the predominate l o s s  process f o r  ions involves 
r eac t ions  with n e u t r a l  molecules and occurs mainly below t h e  ion iza t ion  
maximum. The i d e n t i f i c a t i o n  of the ions a s  0 r a t h e r  than heavier  ions + 
r equ i r e s  that a very l o w  temperature be associated with the ionosphere, 
about 85'K above 120 km. The p a r t i c l e  concentrat ion a t  120 km i s  estimated 
on the  b a s i s  of  d i f f u s i o n  theory t o  be about 10 c m  , which can be reached 
only i f  t h e  average temperature up t o  120 km i s  about 13O0K. 
9 -3  
Johnson (1965) 
proposed the  temperature d i s t r i b u t i o n  shown i n  Figure 1 on the b a s i s  of  
t h i s  i n t e r p r e t a t i o n .  
Two d i f f i c u l t i e s  e x i s t  with the F2 i n t e r p r e t a t i o n  discussed above, one 
involving chemical r a t e  constants  and the  o t h e r  r a d i a t i o n  balance. 
- 4 -  
Fehsenfeld e t  a l .  (1966) have measured the  r a t e  constant  f o r  t he  r eac t ion  
+ 0 + co2 -+ 02+ + co 
3 -1 and obtained t h e  l a r g e  value o f  10” c m  sec 
magnitude would convert  O+ i ons  t o  0 +- i ons  very r a p i d l y  and e l imina te  2 
any p o s s i b i l i t y  of forming an F2 peak with g r e a t e r  e l e c t r o n  concentrat ions 
than  those e x i s t i n g  a t  the F1 l eve l  unless  something happens t o  reduce the 
CO concentrat ions.  F j e lbo  e t  a l .  (1966) suggest t h a t  a reduct ion i n  C02 
2 
concen t r a t ion  i n  the F region i s  brought about by the  f r eez ing  out of CO 
by a temperature minimum near 100 km, s o  t h a t  a n  F2 peak can s t i l l  e x i s t  
even with t h e  l a r g e  r a t e  c o e f f i c i e n t  measured by Fehsenfeld e t  a l .  f o r  
removal of 0 ions.  
. A r a t e  constant  of t h i s  
2 
+ 
The second d i f f i c u l t y  with the F2 i n t e r p r e t a t i o n  i s  t h a t  t he  l o w  
temperatures a s soc ia t ed  with i t  cannot be reconciled with the  thermal 
balance ca l cu la t ed  on the  b a s i s  of r a d i a t i v e  exchange and molecular 
conduct ivi ty .  Chamberlain and McElroy (1966) and Gross e t  a l .  (1966) 
i n d i c a t e  t h a t  t h e r e  i s  a n  excess of h e a t  i npu t  over h e a t  l o s s  i n  the 
i n f r a r e d  t h a t  r equ i r e s  t h e  temperature i n  the  exosphere t o  be i n  the  
neighborhood of 400 K so t h a t  molecular conduc t iv i ty  can remove the  excess 
h e a t  by downward conduction. With t h i s  cons ide ra t ion  i n  mind, Chamberlain 
and McElroy (1966) i n t e r p r e t  the i o n i z a t i o n  m a x i m u m  a s  a n  E l a y e r ,  and 
conclude t h a t ,  i n  order  t o  suppress by chemical means the  formation of 
an F region with l a r g e r  e l e c t r o n  concentrat ions a t  higher  a l t i t u d e s ,  t he  
atmosphere must be w e l l  mixed up t o  190 km. I n  t h e i r  t reatment ,  they do 
no t  take i n t o  account t h e  e f f e c t s  of eddy t r a n s p o r t ;  t h e i r  conclusion 
0 
- 5 -  
t h a t  t h a t  atmosphere must be well mixed up t o  190 km implies  t h a t  mixing 
must proceed more r ap id ly  than molecular d i f f u s i o n ,  which would be 
cha rac t e r i zed  by a c o e f f i c i e n t  of about 2 x 10 cm sec a t  190 km i f  
t he  concent ra t ion  o f  n e u t r a l  p a r t i c l e s  t he re  had the  value which they 
i n d i c a t e .  
8 2 -1 
I f  t he  eddy c o e f f i c i e n t  were th i s  l a r g e ,  the  downward hea t  
t r a n s p o r t  by eddy motion a t  190 km would be about 0 . 2  e r g  cm -2  s ec  -1 , which 
appears t o  be l a r g e r  than the  t o t a l  h e a t  input  above t h a t  a l t i t u d e  i n  
t h e i r  model. 
f o r  mixing, a downward h e a t  t r anspor t  would have t o  e x i s t  t h a t  would 
completely e l imina te  the  high temperature thermosphere t h a t  they obtained 
while  ignoring the  eddy t r anspor t .  This seems t o  i n v a l i d a t e  the  E region 
i n t e r p r e t a t i o n .  
The i n t e r e s t i n g  conclusion i s  t h a t ,  t o  s a t i s f y  t h e i r  requirement 
I n  t h e  e a r t h ' s  atmosphere, eddy h e a t  t r a n s p o r t  i s  more important than 
r a d i a t i v e  h e a t  t r a n s p o r t  i n  con t ro l l i ng  the  thermal balance between about 
60 and 120 km (Johnson, 1967). The corresponding a l t i t u d e s  on Mars a r e ,  
o f  course ,  not known, but  i t  i s  reasonable t o  assume t h a t  eddy t r anspor t  
i s  of comparably g r e a t  importance i n  the  Martian atmosphere. Eddy t r anspor t  
could produce a temperature minimum such a s  t h a t  involved i n  F je lbo  e t  a l . ' s  
(1966) i n t e r p r e t a t i o n  of t h e  Martian atmosphere. The p a r a l l e l  i s  t h a t  eddy 
t r a n s p o r t  i s  the  dominant energy exchange mechanism a t  the  mesopause, 
and probably i s  pr imar i ly  respons ib le  f o r  producing the  temperature minimum 
a t  80 km i n  t he  e a r t h ' s  atmosphere. 
Although Chamberlain and McElroy's (1966) i n t e r p r e t a t i o n  of t he  Martian 
ionosphere a s  an  E region may not be c o r r e c t ,  t h e i r  conclusion t h a t  t h e r e  
should be a temperature r i s e  a t  and above the  temperature maximum i s  
I 
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- 6 -  
s i g n i f i c a n t  and not l i k e l y  t o  be i nva l ida t ed  by the  f a i l u r e  t o  take i n t o  
account t he  eddy h e a t  t r a n s p o r t ,  al though some doubt remains on t h i s  
po in t .  Acceptance of t he  high temperature (d 400°K) exosphere would 
i n v a l i d a t e  the  F2 i n t e r p r e t a t i o n  f o r  t he  i o n i z a t i o n  peak and lead t o  
t h e  requirement f o r  an a l t e r n a t i v e  i n t e r p r e t a t i o n .  This a l t e r n a t i v e  might 
be an  F1 region wi th  a h igh  temperature exosphere,  something t h a t  has been 
suggested by Donahue (1966). 
If the  i o n i z a t i o n  peak i s  an F1 region,  t h e  n e u t r a l  p a r t i c l e  concen- 
10 -3 t r a t i o n  a t  120 km should be about 4 x 10 cm , assuming t h a t  t he  
abso rp t ion  c ross  s e c t i o n  i s  about the  same a s  f o r  t h e  e a r t h ' s  F1 region. 
The i o n i z a t i o n  s c a l e  he ight  above the  i o n i z a t i o n  peak depends on the  
ion izab le  c o n s t i t u e n t ;  i f  i t  were atomic oxygen, a low temperature (n/ 85 K) 
would be ind ica t ed ,  which i s  not  c o n s i s t e n t  with the  high temperature 
exosphere. It seems more l i k e l y  t h a t  carbon dioxide should be the  ion izab le  
c o n s t i t u e n t ,  which would ind ica t e  a temperature of 235 K ,  o r  even higher  
when the  e f f e c t  of the  temperature g rad ien t  i s  taken i n t o  account. The 
p a r t i c l e  concent ra t ion  a t  120 km, compared t o  t h a t  a t  t he  ground, i nd ica t e s  
an  average temperature up t o  120 k m  of 150 K. The temperature d i s t r i b u t i o n  
and p a r t i c l e  concent ra t ions  ca lcu la ted  by Chamberlain and McElroy can be 
used a s  the  b a s i s  f o r  an F1 model i f  they a r e  s u i t a b l y  modified. Thei r  
r e s u l t s  a r e  shown i n  Figure 2 ;  s ince  they ca l cu la t ed  the  v e r t i c a l  d i s t r i -  
bu t ion  assuming a molecular weight of 35, whereas a value near 44 seems 
more l i k e l y ,  a revised a l t i t u d e  s c a l e  based on a moiecular weight of 44 
i s  shown on the  right-hand s i d e  of Figure 2 ,  and t h e  s c a l e  i s  adjusted 
s o  t h a t  t he  p a r t i c l e  concentrat ion a t  the  i o n i z a t i o n  peak a t  120 km i s  
4 x l o l o  ~ m - ~ .  
0 
0 
0 
Also, below 100 km on the  rev ised  s c a l e  (or 150 km on 
- 7 -  
t h e i r  o r i g i n a l  s c a l e ) ,  t h e i r  temperature d i s t r i b u t i o n  and t h e  p a r t i c l e  
concentrat ions have been adjusted s o  a s  t o  agree with the  requirement 
t h a t  t he  average temperature below 120 km be 150 K; t h e i r  o r i g i n a l  curves 
a r e  shown dashed. The concentrat ion curve ca l cu la t ed  by Chamberlain and 
McElroy was f o r  a gas mixture cons i s t ing  of 44% C02 and 56% N2, whereas 
i n  the  modified view the  concentrat ion curve i n  Figure 2 r ep resen t s  only 
t h e  CO concentrat ion;  g r e a t e r  concentrations of l i g h t e r  c o n s t i t u e n t s  2 
(most l i k e l y  atomic oxygen) might e x i s t  near t he  top of t he  diagram. 
0 
It i s  c l e a r  from the  foregoing t h a t  w e  a r e  faced with choosing between 
r a t h e r  divergent  views, a t  least  two a t  p re sen t ,  and possibly more a s  t i m e  
goes on. The s u b s t a n t i a l  u n c e r t a i n t i e s  t h a t  e x i s t  i n  t h e  i n t e r p r e t a t i o n  
of t he  Martian ionosphere are not l i k e l y  t o  be f u l l y  resolved without more 
d a t a .  
i d e n t i f i e d  components, f o r  example, t h e  d i s t r i b u t i o n  of atomic oxygen by 
fluorescence s c a t t e r i n g .  This w i l l  give an independent i n d i c a t i o n  of the 
exospheric temperature and should c l e a r l y  discr iminate  between the F1 and 
F2 t h e o r i e s  f o r  the Martian ionosphere. 
Especial ly  valuable w i l l  be d a t a  on t h e  d i s t r i b u t i o n  of s p e c i f i c a l l y  
This work was supported by NASA Grant NsG-269. 
- 8 -  
Figure Captions 
Figure 1. The temperature d i s t r i b u t i o n  through the  Martian atmosphere 
based upon an F2 region i n t e r p r e t a t i o n  f o r  t he  i o n i z a t i o n  maximum 
(Johnson, 1966). 
Figure 2 .  9.e teqerl-trrre distr ih iJt i  on and t o t a l  p a r t i c l e  concent ra t ion  
i n  the  Martian atmosphere based on (a) an  E region i n t e r p r e t a t i o n  tor 
t he  i o n i z a t i o n  maximum (lef t -hand s c a l e ,  and dashed curves below 
150 km), (b) on F1 region i n t e r p r e t a t i o n  (right-hand s c a l e ,  s o l i d  
curves below 100 km). The curves a r e  based on the  c a l c u l a t i o n s  of 
Chamberlain and McElroy (1966) bu t  with a modified a l t i t u d e  s c a l e  
and f u r t h e r  modified below 100 km (right-hand sca l e )  f o r  the  F1 
i n t e r p r e t a t i o n ;  i n  the modified form, the  concent ra t ion  curve app l i e s  
t o  C02, whereas i t  o r i g i n a l l y  appl ied t o  a mixture of 44% C02,  56% 
N2 * 
- 9 -  
Ref e renc e s 
Chamberlain, J. W . ,  and M. B. McElroy, "Martian Atmosphere; t h e  Mariner 
Occul ta t ion Experiment," Science, - 152, 21-25, 1966. 
Donahue, T. M.,  "The Upper Atmosphere of Mars," 1966. 
Fehsenfeld,  F. C . ,  E. E. Ferguson, and A. L. Schmetlekopf, "Thermal Energy 
Ion-Neutral Reaction Rates 111. The Measured Rate Constant f o r  the 
Reaction 0 ( S) + C 0 2 ( ' f )  -9 02'(2m + CO($) ,I1 J.  Chem. Phys., - 44, + 4  
3022-3024, 1966. 
Fje lbo ,  G . ,  W. C. Fjelbo,  and V. R. Eshleman, "Models f o r  t he  Atmosphere 
of Mars Based on the  Mariner I V  Occul ta t ion Experiment," J. Geophys. 
R e s . ,  2, 2307-2316, 1966. -
Gross, S .  H., W. E. McGovern, and S. I. Rasool, "Mars: Upper Atmosphere," 
Science,  - 151, 1216-1221, 1966. 
Johnson, F. S . ,  "Atmosphere of  Mars ,"  Science, - 150, 1445-1448, 1965. 
Johnson, F. S . ,  "Turbopause Processes and Ef fec t s , "  COSPAR Seventh 
I n t e r n a t i o n a l  Space Science Symposium, t o  be published i n  Space 
Research, 1967. 
Kl io re ,  A . ,  D. C. Cain, G. S .  Levy, V. R. Eshleman, G. F j e lbo ,  F. I). Drake, 
"Occultation Experiment: 
Mar's Atmosphere and Ionosphere," Science,  149, 1243-1248, 1965a. 
Result  of the F i r s t  D i rec t  Measurement of  
- 10 - 
Kliore, A., D. L. Cain, G. S. Levy, V. R. Eshleman, F. D. Drake, and 
G. Fjelbo, "The Mariner IV Occultation Experiment ,I' Astronautics, 
- 3 (7), 72-80, 1965b. 
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The atmosphere of Mars

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