Solar plasma experiment by Mariner  IV space prob

Bridge, H. L.

Lazarus, A.

Synder, C. W.

English

NASA Technical Reports Server

RELEA 
i ? 
WO 2-41 5 5  
WASHINGTON, D.C 20546 TELS' W o  3-6925 
L7 753--- 
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 
FOR RELEASE: 11 A.M. EST, MO~JDAY 
S 
A p r i l  19, 1965 
SE NO: 65-117-A 
(One t n  a ser ies  of s i x  r e l e a s e s  based on papers presented 
on Mariner I V  experiments a t  t h e  46th convention of t h e  
American Geophysical Union, headquartered a t  the  Nat ional  
Academy of Sciences,  2101 Cons t i t u t ion  Ave,, N.W.,  Washing- 
ton ,  D.C. ,  A p r i l  19, 1965.) 
I . .  v 
SOLAR PLASMA EXPERIMENT 
Professor  Herbert L, Bridge ,  Massachusetts I n s t i -  
t u t e  of Technology w-' 
D r .  Alan Lazarus, Massachusetts I n s t i t u t e  of 
Techno1 ogy 
D r .  Conway W .  Snyder, J e t  Propuls ion Laboratory 
On t h e  f i r s t  day of t h e  mission t o  Mars, Mariner I V  
d e t e c t e d  t h e  shock wave produced by the  " s o l a r  wind" on 
n E a r t h ' s  magnetic f i e l d  a t  a g r e a t e r  a l t i t u d e  than  t h i s  phe- 
nomenon has e v e r  before  been observed. 
A t  a d i s t a n c e  of about 138,000 miles from Ear th ,  t he  
s o l a r  plasma probe aboard the  spacec ra f t  began t o  measure 
a plasma energy spectrum t h a t  i s  c h a r a c t e r i s t i c  of i n t e r -  
p l a n e t a r y  space,  i n d i c a t i n g  t h a t  Mariner I V  had passed out  
through t h e  "bow shock" produced by the  impact. 
This  shock had been observed repeatedly i n  r ecen t  months 
by the  I n t e r p l a n e t a r y  Explorer  ( IMP)  s a t e l l i t e s  b u t  a t  a ig -  
n i f i c a n t l y  lower a l t i t u d e s .  
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Two a d d i t i o n a l  changes i n  t h e  plasma spectrum--at about 
145,000 miles  and a t  154,000 miles--during t h e  first 24 hours 
of t h e  mission a l s o  i n d i c a t e d  shock passages, showing t h a t  t h e  
shock expanded and moved out beyond t h e  Mariner and that  l a -  
t e r  t h e  spacec ra f t  aga in  passed through it .  
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r i o r  t o  making t h e s e  observa t ions  on launch day-- las t  \ Y 
November 28--the instrument  measured the plasma trapped i n  and 
flowing around the Ea r th ' s  magnetic f i e l d .  
So la r  plasma, nicknamed s o l a r  wind because of i t e  high 
v e l o c i t y ,  l e  a n  extremely ho t ,  ion ized  gas  composed of e l e c -  
t r o n s  and t h e  n u c l e i  of t h e  atoms of l i g h t  elements,  p r i n c i -  
p a l l y  hydrogen and helium. The Mariner IV inst rument ,  which 
measures t h e  s o l a r  wind a t  32 energy bands wi th in  a range of 
30 t o  10,000 e l e c t r o n  v o l t s ,  was able t o  s e p a r a t e  the hydrogen 
and helium components of the plasma more a c c u r a t e l y  than  had 
been done In any previous experiments. 
P r o p e r t i e s  of the s o l a r  wind change wi th  t ime a8 plasma 
tha t  o r i g i n a t e d  from d i f f e r e n t  reg ions  of the Sun ' s  cornona 
i s  encountered. Some f l u c t u a t i o n s  i n  the s o l a r  wind are e a s i l y  
d e t e c t a b l e  on Earth,  as i n  the case  of a d i s tu rbance  on t h e  
Sun which r e s u l t s  i n  a geomagnetic storm o r  r a d i o  blackout 93 
m i l l i o n  miles away on Ea r th ,  
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Since the second day of f l i g h t  t he  instrument  has been 
making observa t ions  on the i n t e r p l a n e t a r y  plasma. 
Mariner 11, which flew t o  Venus i n  1962, showed that a 
measurably large s o l a r  wind blows a t  hypersonic v e l o c i t y  
through our  r eg ion  of t h e  s o l a r  system from the d i r e c t i o n  of 
the  Sun. Mariner I1 i s  t h e  only o t h e r  s p a c e c r a f t  that  has 
made prolonged cont inuous plasma observa t ions  a t  g r e a t  d i s -  
t a n c e s  from Earth. Other plasma experiments have been flown 
on a number of Earth satell i tes.  
It i s  be l ieved  tha t  the d e n s i t y  of s o l a r  plasma ou t s ide  
of Earth's o r b i t  decreases  as t h e  d i s t a n c e  from the Sun i n -  
c r e a s e s .  Mariner I1 showed that the d e n s i t y  i n c r e a s e s  as the 
s p a c e c r a f t  neared the Sun. 
Q u a n t i t a t i v e  r e s u l t s ,  which would prove t h i s  v a r i a t i o n ,  
however, are no t  ye t  a v a i l a b l e ,  p a r t l y  because of a r e s i s t o r  
f a i l u r e  i n  the in s t rumen t ' s  high vo l t age  c i r c u i t r y  on t h e  
eighth day of the mission. 
T h i s  malfunction caused the  instrument  t o  sweep over t h e  
plasma energy spectrum i n  a manner not p rec i se ly  known. Since 
t ha t  time, however, a n a l y s i s  of the component f a i l u r e  allowed 
s c i e n t i s t s  t o  recalibrate t h e  Instrument,  and it has been pos- 
s i b l e  t o  i n t e r p r e t  about half t h e  data d i r e c t l y .  The o t h e r  
half r e q u i r e s  a much more ex tens ive  a n a l y s i s  than  that  neces- 
sary had the  f a i l u r e  not  occurred. 
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During the past three months, i t  has been poss ib l e  t o  
d e r i v e  reasonably accu ra t e  va lues  of the s o l a r  wind v e l o c i t y ,  
b u t  i t s  o the r  p r o p e r t i e s  have not  y e t  been c a l c u l a t e d .  
Further a n a l y s i s  of data te lemetered from t h e  Mariner I V  
i s  expected t o  h e l p  r e so lve  a c o n f l i c t  i n  s o l a r  wind data 
from instruments  on o t h e r  s p a c e c r a f t .  
SOLAR PLASMA PROBE INSTRUMENT 
The s o l a r  plasma probe i s  composed of three major par ts :  
a c o l l e c t o r  cup, a h igh  vo l t age  power supply and c i r c u i t r y  
t o  provide a n  output  s i g n a l  t o  the data automation system tha t  
cond i t ions  t h e  data f o r  t ransmiss ion  t o  Earth.  
A mesh of f i n e  tungs ten  wire i n  f r o n t  of t he  c o l l e c t o r  
i s  given a negat ive  vo l t age  t ha t  a l t e r n a t e s  r a p i d l y  between 
two l imits.  Thus,  p ro tons  having a range of ene rg ie s  c o r r e s -  
ponding t o  these limits are a l t e r n a t e l y  repelled and passed 
through t o  the c o l l e c t o r ,  producing a n  i n t e r m i t t e n t  c u r r e n t  
that  i s  de tec ted .  
The vol tage  l i m i t s  on the  mesh are repeatedly cycled 
through 32 vo l t age  l e v e l s  t o  a l low d e t e c t i o n  of pro tons  a t  
32 energy bands w i t h i n  a range of 30 t o  10,000 e l e c t r o n  v o l t s .  
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The plasma probe is mounted 6n t o p  of the spacec ra f t  
bus  a t  an ang le  10 degrees  off the spacecraft-Sun l i n e .  
weighs 
It 
pounds and u t i l i z e s  three watts o f  power, 
-End- 


Solar plasma experiment

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