Mariner IV observations of protons in interplanetary spac

Krimigis, S. M.

Van Allen, J. A.

English

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A 663 J* 65
Observation of -- 500 keV Protons in
Interplanetary Space with Diner IV
by
S. M. Krimigis and J. A. Van: Allen
Department of Physics and Astronom;;
University of Iowa., Iowa City, Iowa
December 1,0b5
2We report herein the observation of protones of kinetic Energy
E
P
 
N 500 keV during a ten morth period of interplanetary flight by
the Mariner IV spacecraft.
The impulsive emission of energetic protons ( P 1 BeV)
from the sun was shown first by Forbush.l Massive studies of the
arrival at the earth of solar cosmic rays (protons, alpha
particies,' and heavier nuclei) in the energy range > 10 MeV
have been made by ionospheric methods 2, by direct detection with
satellite equipment-, 3 and by other-methods. The frequent
occairrence of beams of protons of p ^-1 MeV, below the energy
and/or intensity threshold of previously used techniques, was
inferred by Gregory  from 2.3 Mc/s :_onospheric scatter measurements
in Antarctica during 1959, 1960, and 1961. The inference of
Gregory was confirmed and placed on a firm foundation by an
extended series of direct interplanetary observations in late
1462 by Van Alien et al. 5 using a detector having an energy
threshold p = 0.5 MeV on the Mariner II spacecraft.
The University of Iowa detector complement on the
Mariner IV spacecraft consists of three thin window Geiger tubes
(EON type 6213) and a thin ( ^- 35 micrcn) surface barrier non-
3totally depleted solid state detector (Nuclear Diodes, Inc.).
A descriptian of the detectors and of other experimental details
has been published elsewhere.6 In this note we are concerned
primarily with results from the solid state detector which has-.
two discrimination levels set to count protons i mn the energy
ranges 0.50 < E < 11 'MeV (channel D) and 0.88 < E < 4 MeV
p '	 -	 1	 p'
(channel D^)• Both channels are insensitive to galactic cosmic
rays and to electrons of any energy, in the intensities found to
be present by the Geiger,tubes during the Mariner IV flight.
The detector is equipped with a weak95Ad 	 source of alpha
particles to provide assurance of its proper operatiorr in flight.
10
At	 -
The conical collimator of the detector has a half angle of 30%
and the spacecraft is oriented continuously so as to point the
center line of the collimator toward the inner solar system at
70 0 to the spacecraft-sun line. The absolute value of the
unidirectional geometric factor is 0.065 + 0.003 Cm  sterad.
Simultaneous data from the three Geiger tubes assure that all
protons reported herein are in fact entering the solid state
detector through its collimator and not through the protective
shield.
4Figure 1 shows the-
-
daily averages of the counting rates of
channels D1 and D2 during ten months of interplanetary flight.
Our apparatus performed properly throughout. "Cruise science" was
commanded "off" for days197-214 and days- 243 .245 --of 1965 -in_ y
order to use the spacecraft for other purposes and was finally.
commanded "off" on day 274 for an indefinite period, thus terminat-
ing the present series of observations.
The daily average of the counting rate of the Deep:_River_
neuron monitor (courtesy H. Can_.chael) is also Flotted in
Figure .1 as is the daily sum of the three-hour geomagnetic
disturbance indices Kp . These auxiliary data provide direct
measures of the galactic cosmic ray intensity at the earth and of
geomagnetic activity and thus, inferentially, a measure of the
state of the interplanetary medium.
The observational duty cycle of each channel D 1 and D2
is 11.1610. During a solid day of observations 9643 seconds of
data are obtained from each channel. Hence, the statistical
standard deviation a of the daiiy average background rates of D1
(0.069 count sec) and D2 (0.057 count see) is 0.0025 count/sec.
A 3 a departure from the daily mean corresponds to a detection
5sensitivity for interplanetary-protons having a unidirectional
intensity j of 0.12 (em2 sec sterad) -1 in the energy ra►,ges quoted
above. -Due to incomplete coverage in the preliminary Oxta used
in -this report, -typical values of -a are a-bout 1.5 to 2 times as
- great as that for-an ideal day.
In Table I there are listed 20 resolvable proton events
having clear statistical significance. It is probable that a refined
analysis of the final data will reveal other everits cf lesser
intensity. Three electron events (not listed here) on days
25-28 May, 5-7 June, and 13-14 June 1965 have been reported 
previously and attributed to direct solar emission.
The following summary remarks result from a preliminary
-study of the data:
(a) The counting rate of D1 is significantly above that due to
the calibration source for 10 0 of the period of obotervation
29 November 1964--20 April 1965, for 32°d, of the period of observa-
tion 21 April--30 September 1965, and for 24% of the entire period.
(b) There is a striking general anti-correlation between inter-
planetary proton activity and the intensity of galactic cosmic
rays as measured by the Deep River neutron monitor (Figure 1).
6It is tempting to regard this anti-correlation as physically
significant and to suggest further that May 1965 is the "bottom"
of a solar activity cycle.
(c) --The-most intense event of the series is that of
5_13 February 1965- It is the only one of the 20 events which is
convincingly associated with a specitIc solar flare. In addition
to the low energy protons shown in Figure 1, it contains a maximum
omnidirectional intensity J -0  80 (em2 sec) -1 of protons
P
> 55 MeV as measured with the shielded Geiger tube. The energy
spectrum of the particles in this event is distinctly flatter
than that of any of the other 10 events for which a significant
spectral determination is feasible. The time profile of the
intensity of the hard component in the 5-13 February event is
reasonably well understood on the basis of free diffusion in the
interplanetary medium. But the time profile of the intensity of the
soft component as shown in Figure 1 is not so explicable.?
(d) The time-intensity profiles of most of the other 19 events
reported here are roughly symmetrical and have widths in the
range of one to several days.
7(e) _ Also, in most of the other 19 events, the ratio of the
counting rate of D1 to that of D2 is roughly constant throughout
each event for which the D2 rate is adequate for a significant
determination. The differential energy spectra corresponding to
these ratios can be represented by djfdE x e.Yp (-E/E0) with Eo_
in the range 2oo_to boo keV or by dj/dE E with y in the range
2 to 4.	 -
(f) Despite paragraph (b), in only 5 cases is there a convincing
association between the occurrence of low energy protons at the
spacecraft and a specific Forbush decrease at the earth; and in
only 7 cases is there an associated geomagnetic sudden commencement
(SC) at the earth (Table I). It appears that these associations
weaken as the difference in heliocentric longitude of the space-
craft and the earth increases.
(g) me occurrence of successive events (with the exception of
the first two) has no simple relationship to the period,
of rotation of the sun, as seen from the spacecraft, though it
is possible that rotational periodicity is masked by the
combination of several active centers at different heliographic
longitudes and latitudes. A similar situation prevailed in our
earlier observations5 with Mariner II in late 1962.
-c,_f -protons P >
	
-keV (using data from the -Geiger tubes, not
shown herein).
There is little doubt that the observed low-energy protons
owe their existence -to the sun, either (A) by direct emission at
essentially the energy observed or (B) by generation in turbulent
regions of the solar wind in interplanetary space. 10
Alternative (A) has been suggested 11 as an explanation
of the low energy "storm protons" which were observed by satellites
Injun I and Explorer XII on 30 September 1961. The gyro-radius P
(in A.U.) of a non-relativistic proton of kinetic energy E (in MeV)
in a magnetic field B (in gammas) is given by
corona.
Parker 10 rejects A_ternative (A) on the grounds of "adiabatic
deceleration in the expanding volume of the blast wave" and favors
to
Alternative (B), which presumably involves cooperative plasma
phenomena, although he does not develop Alternative (B) to a
convincing level. In a later, detailed paper 15 he shows that:
adiabatic deceleration is not necessarily of importance and we
have al so proposed a physically plausible model of interplanetary
propagation which effectively circumvents the "adiabatic
deceleration" objection to Alternative (A).
In the magnetospheric transition region and tail, which
ma;- be thought to be known examples of Alternative (B) on a
pertinent physical scale, the intensities of electrons of
E  > 40 keV are at least several orders of magnitude greater
than those of protons of F > 500 keV13,14 (as is also the case
in aurorae), contrary to observed fact (h) of the preceding
summary.
We conclude that both Alternatives (A) and (B) and perhaps
some combi ration of t; survive this gaalitative discussion but
we contin^eil to favor (A) as a working hypothesis.
Phis work was supported in .art by Contract 95o613 with
the Jet Propulsion Laboratory and Grant NsG 233 -62 from the
Nat onal Aeronautics and Space Administration.
The authors thank Dr. D. r.. Montgomery for a number of
_i-o	 scussions .
11
References
1I. Lange and S. E. Forbush, Terr. Mag. 47, 331-334 (1942).
2D. K. Bailey, Planet. Space Sci. 12, 495-541 (1964).
3W. C. Lin and J. A. Van Allen, Proc. Int. School of Physics
"Enrico Fermi" Course XIV Space Exploration and the Solar
System, pp. 194-235 Academic Press (1964) (B. Rossi,
editor).
4J. B. Gregory, J. Geophys. Research 67, 3829-3841 (1962).
5J. A. Van Allen, L. A. Frank, and D. Venkatesan, Trans., Am. Geophys.
Union 45, 80 (1964).
6J. A. Van Alley, and S. M. Krimigis, J. Geophys. Research 70,
5737-5751 (1965).
7S. M. Krimigis, r .D. Dissertation, University of Iowa, August 1565
(unpublished) [cf. J. Geophys. Res., 70, 2943-2960 (1965);.
8D. A. Bryant, T. L. Cline, U. D. Desai, and F. B- McDonald,
Phys. Rev. Letters 11, 14: (1963).
9D. A. Bryant, T. L. Cline, U. D. Desa , and F. B. McDonald,
Phys. Rev. Letters 13, 481-484 (1965).
10E. N. Parker, Phys. Rev. Letters 14, 55--57 (1965)
11J. A. Van Allen, W. G. V. Rosser, and W. A. Whelpley,
J. Geophys. Research 67, 3606 (1962).
t
12
References
continued
1 .N. F. Ness and J. M. Nilcox, Phys. Rev. Letters l3, 461-464
(1964)
13L. A. Frank and J. A. Van AUen, J. Geophys. Research 6^,
4923-4932 (1964).
14A. Konradi, Goddard Space Flight Center X-611-65-465
 
of
November 1965 (unpublished).
i5F. N. Parker, Planet. Space Sci. 13, 9-49, 1965.
!able I
Proton Events Observed aith nrrimer n
28 november 196h--1 October 1965
Dates pays Ealloemtrie nedial Urrerenee is neltocentric IrdasIN aidireetiamal Possibly Pertinent Solar
1955 1965 Ddatsmce of Spacecraft Ecliptic Paagitades of Matematty, j Activity as Even
(Marl.) (Intl.) (A.U.) Spacecraft and Earth 0.50:5 _=	 11 New_< from the Earth
(mss) (ei aw sterad)'1
8-12 Jaooary 8-12 1.06 *1.7 4.3 • 0.3 IV. 
2 Flare
6 Jan. 0810 Ur
5-15 PAwuary	 36JA IF- 1.15 -1.9 lie Fe	 2+ FlareFeb. 1750 0!
Za April 11.J	 *F 1.39 -24.5 0.k + 0.1 Lap. 
2	 Flare
15 Apr. 0915 Ur
7-8 Rp I27-128 1.44 -32-0 0.-5+0.2 -----
26 My 146 1.48 -40.3 0.9 + 0.3 -----
27 Pity 147 1.48 -W.8 1.1 + 0.3 ----
1-5 Jane 152-156 * 1.50 -S4 2 3-0 +0.2 28 many `0916 Ur
12-19 Jame IQ =170 R 1.52 -50.4 1.7 +0.5
-
Imp. 3	 Flare
9 Jane 0559 Or
21 June 172 1.53 -53-2 0.6+0.2 -----
28 Jume i79-182 1.54 -57.0 a.2 + C.2
-
up. a Flare
28 June 1020 Ur
--I July
2-3 July 183-194 1.54 -58-4 1.1+0.2 ----
4.6 July 185-187 * 1.55 -59-7 2-1+0.2 -----
10 July 191	 * 1.55 -62-2 u 'L + 0.1 -----
13-15 July 194-196 F 1.55 - 64.3 6.4+0.3 -----
b Observations 19..	 4
--
----I£ July--2 Aug-
3-4 August 215-2i6 1-57 - 7..4 1.4+0-2 -----
6-9 Aag-t 218-2=1 1.57 - 76-+ 6.6 + U-3 -----
17 August 229	 *F 1.57 - 31.0 0.4 +0.1
-
Imp. 2 Flare
15 Aug. 0615 uT
26-30 August 238-242 1.57 - 86.9 6.0 +0_3 -----
No Observations
31 Augus-t 243-245 ---- ---- ----- -----
--2 Sept.
22-24 Sept- 265-267 i.56 -100.0 0.8 +0.2 -----
25-26 Sept. `68-269 1.56 -101.6 0.5 +0_1 -----
notes:
	 (a) $eliocentric ecliptic longitude is measured mmterclocMse as viewed from the north ecliptic pole.
(t) Nsxl - intensity is derived from the highest four-Dour average taunting rate during the event.
(e) The right hano crop is extracted from the monthly 'Compilations of Solar-Geophysical Data° of the U. S. Department of
Comme:x NW/CRFL, Boulder, Colorado.
(d) Positional coordinates are from Jet Propulsion Laboratory ephemeris I&IYS-JPrW 5FP80 111464 of 15 December 1964.
(e) In the second column s eenotes a magnetic SC and F denotes a clear Forbuzh decrease in galactic cosmic ray intensity
observed approximately simultaneously at the earth.
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Observation of about 500 KeV protons in interplanetary space with Mariner IV

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