HEOS B measurements on particles ejected from comet Kohoutek reflect average particle rate as a function of particle speed and mass in relation to random distribution with known speed from the interplanetary region. The micrometeoroid experiment detector onboard the satellite passed through the orbital plane of the comet and encountered ejected particles for approximately two months

Fechtig, H.

Gruen, E.

Hoffmann, H. J.

Kissel, J.

English

NASA Technical Reports Server

' N76-21091
PARTICLES FROM COMET KOHOUTEK DETECTED BY THE MICROMETEOROID
EXPERIMENT ON HEOS 2
H.-J. Hoffmann, H. Fechtig, E. Gr'un and J. Kissel
INTRODUCTION
The HEOS 2 satellite was launched into a highly eccentric orbit
around the earth on January 31, 1972 and re-entered the earth's
atmosphere after a successful mission on August 2, 1974. Due to
the orbit (apogee: 24O OOO km, perigee: 3OO - 5OOO km) the
satellite spent most of the time in the interplanetary region
where the influence of the earth's gravitation field is ne-
gligible with regard to its effect on interplanetary dust
particles.
The micrometeoroid experiment on board measured the mass and the
speed of dust particles by the plasma produced during their
impact on the sensor. The field of view was a cone with a
semi-angle of 60°. The detector was mounted with the axis
of symmetry parallel to the spin axis of the spacecraft.
By an active reorientation system the viewing direction of
the detector could be turned in any direction perpendicular
to the earth-sun line. A detailed description of the detector
has been given earlier (Dietzel et al., 1973} (Hoffmann et al.,
1975).
About 54 days before the end of the mission the earth and hence
the satellite passed through the orbital plane of comet Ko-
houtek. Prior to this event a study of the orbital mechanics
of the earth, the comet and its dust showed that it should
be possible within the given attitude constraints
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https://ntrs.nasa.gov/search.jsp?R=19760014003 2020-03-22T15:32:35+00:00Z
of the spacecraft to encounter dust released from the comet.
Particles, ejected from a comet which moves on a parabolic
orbit, can be detected by an earth orbiting satellite only
during the transit of the earth through the orbital plane
of the comet, provided that the comet's node is on or within
the earth orbit. In the latter case merely particles with
orbits further outwards are able to encounter the earth.
This applies to particles subject to the repulsive force
of radiation pressure after being released from the comet
nucleus. With B denoting the ratio of the force of radiation
pressure to that of gravity, particles with an appropriate
8 > O can encounter the earth orbit. Due to the radiation
pressure the particles lag behind the comet and can only
be detected if the comet passes its node before the transit
of the earth through the orbital plane of the comet. Thus,
in principle, solely particles with a, specific value of
£ = 3 and a specific heliocentric release distance r = r_
are able to encounter the earth.
During the emission process the outstreaming gas from the
comet nucleus adds a velocity distribution to the initial
speed of the particles given by the comet's speed at the
release time. This effect will permit particles from a
certain range of heliocentric distances around rR and
with values of 6 around 8 to encounter the earth. As
o
demonstrated in figure 1, in the case of comet Kohoutek,
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ENCOUNTER VELOCITIES:
<&* CLOSEST DISTANCEEARTH-DUST
JUN.7 (1974)
Fig. 1: Trajectory of dust particle (B =1) released from
comet Kohoutek at a heliocentric distance of
r_. = 4.3 AU passing the earth close to the comet's
X\
line of nodes and velocity diagram during encounte]
(to the left).
951
particles with 3^1 released at a heliocentric distance
re «* 4.3 AU could encounter the earth. Their heliocentricR
speed at the release point is approximately 20 km/sec.
With 8 = 1 the net force acting on the particle is zero,
so their speed remains constant and they move on a straight
line tangentially to the comet's orbit. Close to their
ascending node they are overtaken by the earth. Their geo-
centric speed is 19 km/sec with the apparent radiant 43
away from the earth's apex towards the sun; hence the best
viewing direction of the detector within the given attitude
constraints is towards the earth's apex. The particles then
would encounter the detector at an angle of incidence of
approximately 40 which is well within the detector's field
of view.
During the transit of the earth through the orbital plane
of the comet, the rate of particles with speeds of
approximately 19 km/sec should increase compared to the.,,
normal rate before and after the transit while viewing
towards the earth's apex for particles with $ #*» 1. Since
the inclination of the comet's orbit is fairly low
(i = 14.3°) it would be possible to detect these particles
for a time-period of approximately two months around the
transit.
952
MEASUREMENTS AND DISCUSSION
Due to refurbishing of telemetry stations the detector could
not be reorientated before May 16, 1974. At that time the rates
were already significantly increased, but the remaining period
until the mission end was sufficient to observe the decrease
of the rate towards the "normal" value. The normal rates were
taken from the two periods in 1972 from day 9O-14O and in 1973
from day 29-214 when the detector also was viewing towards the
earth's apex.
In figure 2a and 2b the average particle rate is shown as a
function of the particle speed and mass, respectively, present-
ing the data from the transit period (period T) on the right
and those under normal conditions (period N) on the left part
of the figures. The rates refer to the randomly distributed
particles with known speed from the interplanetary region
(Hoffmann et al., 1975) and the appropriate effective measuring
time T taking into account the data coverage.
As demonstrated in figure 2a the rates of particles with speeds
less than 15 km/sec are equal within the statistical error
for both periods, whereas during period T a significant excess
of particles is observed in the speed interval from 15-2O km/sec
where the cometary particles were expected. Accordingly, in
figure 2b during period T the mass distribution raises in the
-13 —11
mass range from 10 to 1O g over the normal mass distribution
(background). In figure 2c both criteria established in
figure 2a and 2b have been combined, showing the history
953
HEOS 2 EXP. S 215
oc.
LU
CO
LU
CL
U_
O
0.10
0.05
I \ I
PERIOD N
1972 DAY: 90-UO
, 1973 DAY: 29-2U
T E F F : 9 7 d
0.15
0.10
0.05
0
-
PERK
1974
T
DD T
DAY-.136
BACKC
-214
d
5ROUND
I
I
,
I
51
i
o
in
<N
0 5 10 15 20 0 5 10 15 20
SPEED v (km/s) SPEED v (km/s)
a) SPEED DISTRIBUTION OF APEX PARTICLES
o:LU
0.
00
cr
0.10
0.05
0
i I i i
PERIOD N
1972 DAY:90-UO
1973 DAY:29-2H
0.10
0.05
0
I 1
PERIOD
DAY: 136-
f
T
214
ii
I I
!
1974
t BACK-_
GROUND
I
— h-
10-15 1Q-13 10-11 10-9 1Q-15 10-13 10-11
MASS m (g) MASS m (g)
b) MASS DISTRIBUTION OF APEX PARTICLES
10-9
1972
1973
1974
Y/////^////////A
vZ/y/\
y////////////////////////7RS*** 4
r r r r r r r i i I T i I T i i i i i
Y/7/.
RE -
E N T R Yi ' ' ^ ' i r ' ' • i
—^YEAR/DAY No 50 100 150 200
c) TEMPORAL DISTRIBUTION OF APEX PARTICLES
WITH 15km/s<v<20km/s AND 1(T13g<m< 1(T11g
Fig. 2: Data from the HEOS 2 micrometeorpid experiment
S-215 while facing the earth's apex during the
transit of the earth through the orbital plane
of comet Kohoutek (period T) and under normal
conditions (period N).
954
exclusively of particles matching the relevant mass and speed
intervals. The rate of these "cometary candidates" from period T
is higher approximately by a factor of 3.5 than the rate of
the background particles from period N. For the sake of
completeness it may be mentioned that the rate of these
particles during periods when the detector was facing
directions different from the earth's apex is of the same
magnitude or less than during period N.
Though the number of particles is small, the probability
that 7 particles instead of the average of 2 in the relevant
speed interval (see fig. 2a) and 9 instead of the average
of 4 in the relevant mass interval (see fig. 2b) may be
random is approximately 1O~ . Therefore, an additional
particle source during period T is very likely.
Apart from comet Kohoutek no other sources such as the earth
(Bigg and Thompson, 1969), the moon (Alexander et al., 1973;
Hoffmann et al.,.1975), meteor showers or other comets
fulfil all conditions required by the measurements listed
below:
a) time interval of enhanced particle rate between May 16.
and June 23, 1974 equivalent to ecliptic longitudes
from 235°- 273°,
— 1 3 — 11b) mass range of particles: 1O - 1O gf
955
c) speed range of particles: 15 - 2O km/sec
d) apparent radiants of particles: cone around the earth's
apex with semi-angle of 60 .
Particles with the required speed, originating in the earth,
can be excluded because their trajectories cannot enter the
sensor while it is facing the earth's apex. A lunar origin
can be ruled out since the same argument holds for 5 out of
7 candidates. Meteor showers as sources are unlikely
for two reasons because 1) no increased particle rate has
been observed in the preceding year (1973) and 2) the
radiants of the showers occuring in the relevant time
interval (Daytime Arietids, Daytime £ Perseids and
Daytime 3 Taurids) do not match the required cone of
directions (Whipple and Hawkins, 1959), As the nodes
of all major comets (apart from comet Kohoutek) observed
in 1973 and 1974 , such as comet Bradfield (1974b)
(IAU Circular No. 2636), do not fit in the required inter-
val of ecliptic longitudes or have perihelion distances
of more than 1 AU, they cannot supply these particles
either. Therefore, the authors believe that the excess
of particles during the transit of the earth through the
orbital plane of comet Kohoutek is due to dust particles
ejected from this comet.
The direct measurements of the individual mass and speed
of the particles supply new knowledge about cometary dust
956
which supplements the data derived from photometric studies
(Finson and Probstein, 1968, Sekanina and Miller, 1973 and
Sekanina, 1975). A direct measurement of cometary dust by
a collection experiment during the transit.of the earth
through the orbit plane of comet Giacobini Zinner has been
reported by Hemenway (1973).
INTERPRETATION
For further evaluation of the measured data, orbit calcu-
lations have been performed for particles ejected from comet
Kohoutek encountering the earth at a time of observation t_
around the date of the earth's transit through the orbital
plane of the comet on day 16O in 1974,
Figure 3 shows an instant picture of the particles' positions
as a function 1) of the magnitude of 3 (syndyne) and 2) of
the release time t (synchrone) and the corresponding helio-
K
centric distance r_, respectively, at t.. = day 160 (1974).
•K w
The additional velocity distribution arising from the gas
streaming away from the comet nucleus has been neglected
in this picture. Due to the additional velocity component AV,
particles with values of B different from 1,OO have a
chance to encounter the earth as long as their AV is
sufficient to cover the missing distance to the earth
during the time interval At = t-.'-t . The magnitudeO R
of Av is presented in figure 4. It shows the minimum
957
\ \ \
v v
1.0
Fig, 3: Position of particles from comet Kohoutek for
constant values of _ 1) g (syndyne: broken lines)
, and 2) release times t (synchrone: solid lines)
or the corresponding heliocentric distances r_
during the transit of the earth through the
orbital plane of the comet at t_ = day 16O, 1974
958
JOOO
160 180 200
DAY OF OBSERVATION 10 (day in 1974)
Fig. 4: Minimum ejection speed ^yv f°r constant values
of 1) & "(broken lines), 2) release times t or
the corresponding heliocentric distances
r_ (solid lines) and envelope (fat line) as a
ix
function of the observation time t_ and temporal
distribution of the cometary particles.
220
959
ejection speed AV required to reach the earth as a function
of the time of observation t and the parameters 6 and r0U K
or t . The envelope (fat line) indicates the absolute
I\
minimum speed at the various days of observation. Using the
time history of the candidates (on the bottom of the figure)
ejection speeds can be derived.
If the candidate from day 192 (1974) is a descendent of
comet Kohoutek it must have been released with Av } 400 m/sec.
On the other hand, AV cannot be much larger because other-
wise further particles should have also been observed at
later times. Particles arriving at the earth at day 137 (1974)
must have been released with AV £450 m/sec. However, in
this caseAV may be more than 450 m/sec because the rise
of the candidates' rate apparently occurred before day 136
which would require a higher ejection speed. Thus, from
figure 4 can be deduced tha,t the parameters of the observed
candidates range from 3 <& .90 at f._ &• 5.4 AU with ^v «400 m/secA
to 0 ft? 1 .10 at rR «• 3.8 .AU and AV > 450 m/sec.
ACKNOWLEDGEMENT
This project was supported by the "Bundesministerium fur
Forschung und Technologic". We also acknowledge the excellent
cooperation with ESTEC and ESOC.
960
REFERENCES
Alexander W.M., Arthur G.W., Bohn J.L. and Smith J.C. (1973)
"Four Years of Dust Particle Measurements in Cislunar
and Selenocentric Space from Lunar Explorer 35 and
OGO 3". Space Research XIII, Akademieverlag Berlin,
1035
Bigg E.K. and Thompson W,J. (1969) "Daytime Photograph of a
Group of Meteor Trails". Nature 222, 156
Dietzel H., Eichhorn G., Fechtig H., Griin E., Hoffmann H.-J.
and Kissel J. (1973) "The HEOS 2 and Helios
Micrometeoroid Experiments". J. of Phys. E:
Sci. Instrum 6, 209
Finson M.L; and Probstein R.F. (1968) "A Theory of Dust Comets.
II Results for Comet Arend-Roland". Astrophys. J.
154, 353
Hemenway C.L. (1973) "Collections of Cosmic Dust" paper
presented at "Whipple Memorial Symposium",
Cambridge, Massachusetts
Hoffmann H.-J., Fechtig H., Grxin E. and Kissel J. (1975)
"First Results of the Micrometeoroid Experiment
S-215 on the HEOS 2 Satellite". Planet. Space
Sci. 23, 215
Sekanina Z. (1975) "Progress in Our Understanding of Cometary
Dust Tails".Proceedings of IAU Colloquium No. 25
Sekanina Z. and Miller F.D. (1973) "Comet Bennett 1970 II".
Science 179, 565
Whipple F.L. and Hawkins G.S. (1959) "Meteors". Handbuch der
Physik, Vol. 52, ed. S. Flvigge, Springer-Verlag
Berlin, Gottingen, Heidelberg, 519
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Particles from comet Kohoutek detected by the micrometeoroid experiment on HEOS 2

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