Significant progress in model analysis of data for the directional features of the Io sodium cloud is reported and appears to provide some support for a satellite emission mechanism that is driven by a magnetospheric wind. A number of model calculations for the two dimensional intensity morphology of the Io sodium (region B) cloud are compared with six observations. Results of this comparison support tentative conclusions regarding the satellite emission conditions, the role of the plasma torus and the sodium atom escape flux. Progress in updating the Titan hydrogen torus model is also discussed

Combi, M. R.

Smyth, W. H.

English

NASA Technical Reports Server

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ATMOSPHERIC AND ENVIRONMENTAL RESEARCH, INC.
CAMBRIDGE, MASSACHUSETTS
https://ntrs.nasa.gov/search.jsp?R=19830011398 2020-03-21T03:51:54+00:00Z
OUTER SATELLITE ATMOSPHERES: THEIR
EXTENDED NATURE AND PLANETARY INTERACTIONS
William H. Smyth
and
Michael R. Combi
Atmospheric and Environmental Research, Inc
840 Memorial Drive
Cambridge, Massachusetts 02139
February 1983
Interim Report for Period
December 1, 1982 to February 28, 1983
prepared for
NASA Headquarters
TECHNICAL REPORT STANDARD TITLE PAGE
1. Report No. 2. Government Accession No.
4. Title and Subtitle
Outer Satellite Atmospheres: Their Extended
Nature and Planetary Interactions
7. Author(s)
William H. Smyth and Michael R. Combi
9. Performing Orgonitotton Nome ond Address
Atmospheric and Environmental Research, Inc.
840 Memorial Drive
Cambridge, Massachusetts 02139
12. Sponsoring Agency Home and Address
NASA Headquarters
Headquarters Contract Division
Washington, DC 20546
3. Recipient 's Cotolog No.
5. Report Dote
February 1983
6. Performing Organisation Code
8. Performing Orgoniiation Report No.
10. Work Unit No.
11. Contract or Grant No.
NASW-3387
13. Type of Report ond Period Covered
Interim Report
December 1982 -
February 1983
14. Sponsoring Agency Code
HW-2
IS. Supplementary Notes
16. Abstract ,
Significant progress in model analysis of data for the directional
features of the lo sodium cloud is reported and appears to provide
some support for a satellite emission mechanism that is driven by a
magnetospheric wind. A number of model calculations for the two-
dimensional intensity morphology of the lo sodium (region B) cloud
are compared with six observations of Murcray (1978). Results of
this comparison support the tentative conclusions, reported last
quarter, regarding the satellite emission conditions, the role of
the plasma torus and the sodium atom escape flux. Progress in up-
dating the Titan hydrogen torus model is also discussed.
17. Key Words (S. Ucted by Author(s)) 18. Distribution Statement
satellite atmospheres
planetary magnetospheres
comets
19. Security Clossif. (of (hit report) 20. Security Clossif. (of this pooe)
Unclassified Unclassified
21. No. of Pages 22. Price*
8
•For sale by the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 221)1.
I. SUMMARY OF RESEARCH PERFORMED IN THE THIRD QUARTER
Research activities in the third quarter have been
directed (1) to continue modeling analysis of the directional
features of the lo sodium cloud, (2) to provide further com-
parison of data for the two-dimensional .intensity morphology
of the region B sodium cloud with model calculations includ-
ing the oscillation of the plasma torus, and (3) to further
the investigations of the neutral hydrogen distribution in
the magnetosphere of Saturn and its relation to Titan and
other possible gas sources.
1. Directional Features of the lo Sodium Cloud
The new sodium cloud model, including the oscillating
plasma torus, has continued to be used this quarter to study
the peculiar directional feature data of Pilcher (1982) with
whom a collaborative effort for this purpose has been estab-
lished. The basic idea currently under evaluation is to
determine if the time varying character of the directional
features observed on the sky plane can be understood in terms
of a gas source produced by the magnetospheric wind moving
past lo and a time-space varying sodium sink produced (through
electron-impact ionization) by the plasma torus as it oscil-
lates about the satellite plane.
A new and more elaborate procedure was devised and
implemented this quarter to analyze the relationship between
the model-calculated, time-varying D-line intensity probabil-
ities on the sky plane and the vector orientation of sodium
atoms emitted from lo. The procedure was then applied to
model calculations appropriate to the observed magnetic X.........
coordinate and the satellite geocentric phase angle for three
sky plane images of the directional feature supplied to us by
Pilcher in our ongoing collaborative effort. The three images
were part of a four image sequence measured on January 6, 1980
which documented the feature changing its direction from south
to north on the satellite plane in a period of four hours.
The analysis procedure showed that to produce a more
dominant south to north intensity probability on the sky
plane and to have the south-to-north phase change observed,
the atom emission velocities from lo would have to have some
limited angular dispersion that is approximately centered at
right angles to the direction of the magnetospheric wind past
the satellite. This conclusion is similar to an independent
study by Dr. Robert E. Johnson (Univ. of Virginia) and his
graduate student, Edward Sieveka who have shown, through
elastic collisional calculations for moving ions and station-
ary neutral sodium atoms, that sodium is preferentially scat-
tered at nearly right angles to the ion flux. Our analysis
procedure also suggests that more atoms may be scattered near
the equator than near the poles of the satellite. In order
to better define the character of this latitudinal dependence
and the velocity dispersion of the high speed sodium emitted
by Io, further analysis and comparison of model calculations
with other sky plane images of Pilcher are required.
2. Region B of the Io Sodium Cloud
The sodium cloud model, including the oscillating plasma
torus but excluding solar radiation effects, has continued to
be used this quarter to calculate the two-dimensional inten-
sity morphology of the cloud on the sky plane. Initial ef-
forts reported last quarter, where one observation by Murcray
(1978) was compared to our model results, have been expanded.
A sequence of 10 images of the region B cloud measured by
Murcray on January 27, 1977 is under study and model runs
appropriate to six of these observations have been performed
this quarter. The three tentative conclusions reported last
quarter, based upon only one observation of Murcray, have !
been further confirmed by the six model runs this quarter.
These three conclusions are stated below:
(1) the presence (at non-critical Io phase angles)
of a predominantly forward sodium cloud and
the absence of a predominantly trailing sodium
cloud may be understood in terms of an isotropic ',
emission of sodium from Io and the radial^ struc-
ture of an oscillating plasma torus which pro-
duces a very asymmetric electron-impact ioniza-
tion sink for sodium
(2) the length of the forward sodium cloud is deter-
mined naturally by the plasma torus and occurs
when the orbital paths of sodium atoms in the
forward cloud have their second ionization
encounters with the plasma torus somewhat
ahead of lo
(3) the flux of sodium from lo necessary to produce
the measured two-dimensional intensity morph-
ology of the B-cloud and also the much larger
intensity values very near lo is approximately
8 ~2 — 15x10 atoms cm sec (i.e., a total source
26 — T
of about 2 x10 atoms sec , with a more
refined value to be achieved when a more
explicit description of the initial exospheric
velocity dispersion is deduced or otherwise
measured).
Model calculations performed this quarter for the six
observations also exhibit ^-rj-r dependent structure in the
forward cloud. Some of the observations of Murcray also
seem to suggest slight ^ I:II dependence in the forward cloud.
Improved sky plane images, such as may be available from
Goldberg (1983), are however required to ascertain if the
model k-r-r-r dependence has a true counterpart in the data.
In addition to the model runs, the computer code has
been improved by rearranging information inside of Cray 1
vector loops so that the CPU execution speed is now about
30% faster. Further potential improvements to the code are
also under evaluation.
3. Neutral Hydrogen Distribution in Saturn's Magnetosphere
Progress this quarter has been made in obtaining infor-
mation to describe the plasma in the Saturn magnetosphere.
New information for the density and temperature of the pro-
tons, heavy ion and electrons has been acquired from the
Voyager PLS group (McNutt, 1983). Additional information
is however needed in order to be able to adequately calculate
the lifetime of H atoms in the Saturn environment. In addi-
tion to this, an analytical fit for the electron impact ion-
izztion of H has also been acquired (Shemansky, 1983) for use
in updating the Titan torus model. Efforts to incorporate
this information into the old code have been initiated and
will be pursued more fully in the next quarter.
II. PROGRAM FOR THE NEXT QUARTER
Research activities in the next quarter will provide
(1) further model studies of the directional .features of
the lo sodium cloud in an effort to understand the exo-
spheric conditions that are important in their formation,
(2) more model calculations for the two-dimensional morph-
ology of the lo sodium (region B) cloud and comparisons of
model results with observations to further evaluate the
three conclusions reported herein, and (3) additional pro-
gress in modifying the Titan hydrogen torus model to include
the spatial lifetime structure of H atoms in the Saturn
magnetosphere.
REFERENCES
Goldberg, B.A. (1983) Private Communication.
McNutt, R.L. (1983) Private Communication.
Murcray, F.J. (1978) Observations of lo's Sodium Cloud.
Ph.D. Thesis, Dept. of Physics, Harvard Univ.,
January 1978.
Pilcher, C.B. (1982) Private Communication.
Shemansky, D.E. (1983) Private Communication.


Outer satellite atmospheres:  Their extended nature and planetary interactions

Significant progress is reported in early modeling analysis of observed sodium cloud images with our new model which includes the oscillating Io plasma torus ionization sink. Both the general w-D morphology of the region B cloud as well as the large spatial gradient seen between the region A and B clouds are found to be consistent with an isotropic flux of sodium atoms from Io. Model analysis of the spatially extended high velocity directional features provided substantial evidence for a magnetospheric wind driven gas escape mechanism from Io. In our efforts to define the source(s) of hydrogen atoms in the Saturn system, major steps were taken in order to understand the role of Titan. We have completed the comparison of the Voyager UVS data with previous Titan model results, as well as the update of the old model computer code to handle the spatially varying ionization sink for H atoms

Outer satellite atmospheres: Their extended nature and planetary interactions

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