An analysis of the magnetic field of the planet Jupiter is presented. The data are based on the information returned by Pioneer 11 space probe. It was determined that the magnetic field stretches across 9 million miles of space at some times and shrinks in volume by three-fourths or more at other times. It was also determined that electrons trapped in the magnetic field of Jupiter are 10,000 times more intense than those in the Van Allen radiation belts which circle the earth. Additional data were obtained on the polar regions, atmospheric circulation, and the nature of the moons

Panagakos, N.

Waller, P.

English

NASA Technical Reports Server

Nicholas Panagakos
Headquarters, Washington, D.C.
(Phone: 202/755-3680)
NATIONAL AERONAUTICS AND
SPACE ADMINISTRATION
Washington, D. C. 20546
(Phone: 202/755-8370)
FOR RELEASE:
THURSDAY -—.
March 6, 1975
Peter Waller
Ames Research Center, Mountain View, Calif,
(Phone: 415/965-5091)
RELEASE NO: 75-49
JOVIAN MAGNETIC FIELD IS COMPLEX, PIONEER 11 'SHOWS
Forces at work in the seething interior of giant
Jupiter are far more complicated than had been previously
believed.
Data returned by Pioneer 11 suggest that the liquid
planet's magnetic field, unlike Earth's, may ba created by
several ring currents—like electric generators—deep
within the planet.
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February 26, 1975
https://ntrs.nasa.gov/search.jsp?R=19750009193 2020-03-22T22:44:51+00:00Z
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Earlier measurements made from a distance of 210,000
kilometers (131,000 miles) by Pioneer 10, Pioneer 11's
predecessor, had indicated only a simple magnetic envelope
with a single "generator", much like Earth's.
But this apparently is not so, according to scientists
sifting through the mountain of data returned by Pioneer 11,
which flew three times closer last December.
It now seems that Jupiter's interior may contain a
large ring current or 'generator, along with many eddies or
smaller generators, rather than a single large one.
Pioneer experimenter Dr. Walker Fillius of the Uni-
versity of California, San Diego, points out that such a
complex field close to the planet would be required to explain
the field's high-energy particle pattern, as well as the
bursts of intense radio energy long-observed to emanate
from Jupiter at long wave lengths.
Planetary magnetic fields are believed to be pro-
duced by motions of the liquid material in planets' in-
teriors, through mechanisms similar to those of electric
dynamos. Earth and Jupiter are the only known planets
with a substantial magnetic field.
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Wobbling and tilting like a plate on top of a juggler's
stick, Jupiter's field sometimes stretches across 9 million
miles of space, and at other times shrinks in volume by
three-fourths or more. Inside this pulsating field are
the belts of intense radiation. Electrons trapped there
are 10,000 times more intense than those in the Van Allen
radiation belts which girdle the Earth, and their energies
range upward to more than 30 million electron volts.
Trapped protons, the nuclei of hydrogen atoms, are also
intense.
Pioneer 11 found that peak intensities of high-energy
electrons were moderately higher than Pioneer 10 experienced.
And the peak proton intensity experienced by Pioneer 11 was
a hundred times stronger than that encountered by Pioneer 10.
But these very-high-energy protons were concentrated in
small and very thin, shallow regions. Pioneer 11 sliced
through these narrow regions so quickly, at a record speed
of 171,000 km (107,000 mi.) an hour, that it received rela-
tively low total radiation.
Neither the Pioneer 11 spacecraft nor its scientific
instruments suffered damage in the belts, although radiation
particles produced effects which resulted in dozens of false
commands to some of the instruments, temporarily interfering
with their operation and causing some loss of data.
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Pioneer 11, renamed Pioneer Saturn, is now headed
upward out of the ecliptic—the celestial plane containing
*
the planets. It will reach a point 160 million km (100
million mi.) above this plane—exploring new regions of
space—in 1977.
The robot spacecraft will continue on to Saturn, arriving
at the ringed planet in September 1979, after a 2.4-billion-km
(1.5-billion-mi.) journey across the solar system. The tar-
get point at Saturn has not been selected. One possibility is
for Pioneer to fly between Saturn's surface and its 'innermost
ring, and to explore Saturn's planet-sized moon, Titan, con-
sidered a possible abode for complex organic molecules, the
building blocks of life.
Besides the new findings on Jupiter's erratic magnetic
field, the flight of Pioneer 11 has provided a number of
new details about the planet, its poles and its moons, and a
greater insight into the nature of cosmic rays from the stars.
The early findings include the following:
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• In making the first observations of Jupiter's
immense polar regions (which cannot be seen from the Earth),
the spacecraft found that the planet's cloud tops are sub-
stantially lower at the poles than at the equator, and are
covered by a thicker transparent atmosphere. The cloud
tops at the South Pole are lower than those in the North
Polar regions.
• Though there is much less evidence of rapid at-
mosphere circulation at the poles than at the equator, the
polar areas unexpectedly showed many small convective cells,
dwarfing similar Earth thunderstorms. "Blue sky" also was
visible at the poles and is attributed to the same cause
as Earth's blue sky—multiple molecule-scattering of light
by gases of the transparent atmosphere at Jupiter's poles.
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• Scientists suggest that Jupiter's relatively stag-
nant polar regions would be the best place to search for
life on the planet. Pioneer 11 infrared measurements show
that the polar regions are about 5 degrees Fahrenheit cooler
than the equatorial regions, and become steadily cooler with
proximity to the poles themselves. On the other hand, the
temperature difference between the equator and polar regions
on Jupiter is not great as on Earth, because two-thirds of
Jupiter's heat is radiated from the planet's high-temperature
interior and is radiated uniformly over the planet. On
Earth, heat is received from the Sun largely at the equator,
and there is little internal heat generation, so Earth's
equator is much warmer than the poles.
• Biggest obstacle to life on Jupiter, which appears
to have all the necessary organic building blocks, had
been thought to be the planet's rapid vertical circula-
tion in its atmosphere. Huge regions of dense room-tem-
perature atmosphere probably are carried down by this cir-
culation to areas too hot to support life. But the rela-
tively warm and stagnant poles conceivably could harbor
living organisms, because the atmosphere there circulates
more slowly. Pioneer did find less circulation at the poles
than in the equatorial regions.
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• Another feature seen by Pioneer 11's electronic
camera for the first time was an oval cell of down-moving
*
atmosphere, surrounded by a bright ring of upwelling clouds.
• Many more flow features were seen in the clouds
around the Great Red Spot than were seen a year ago by
Pioneer 10. The Great Red Spot is believed to be a
32,000-km (20,000-mi.)wide "permanent hurricane." Within
the Spot, a number of details were seen for the first time,
suggesting convection and circulation. The center of the
Spot, which could easily swallow three Earths, is clearly
brighter than the edges, which form a broad, darker border.
Enhanced versions of the new close-up pictures of the Great
Red Spot should provide a further explanation.
• A Pioneer finding which bears directly on many
studies of our Galaxy concerns electrons. In measuring
electrons close to the planet, scientists found that there
were ten times as many as had been predicted from Earth-
based radio studies of Jupiter. Electrons produce radio
signals as they spiral around the lines of force of
Jupiter's magnetic field.
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Astronomers have made extensive calculations of the
numbers of such particles in stars, pulsars, interstellar
gas clouds, and other celestial objects, using data from
radio emissions similar to those emitted by Jupiter. If
the Pioneer findings stand up, various celestial theories
will have to be reviewed.
Pioneer experimenter Dr. John Simpson, University
of Chicago, points out that Jupiter is a sort of "poor
man's star." Like many stars, and unlike Earth, it is a
fast-spinning body with strong magnetic fields.
• Pioneer 11 determined very accurately the mass of
the Jovian moon Callisto, a possible site for future
manned landings. Callisto"s mass is 1.5 times that of the
Earth's moon. Pioneer also observed for the first time an
extensive white, south-polarcap on Callisto.
• Scientists have found that "magnetic weather" in
Jupiter's enormous magnetosphere is extremely variable-^
much more so than in Earth's magnetosphere. Conditions
when Pioneer 11 passed through the magnetosphere last
December were far different from those found during the
passage of Pioneer 10 a year earlier.
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Jupiter's magnetic envelope, always inflated by hot,
ionized gas, apparently can be squeezed down in volume as
much as eight times by pressure from the solar wind. This
compression, in turn, may churn up the various regions
within the magnetosphere. Jupiter's magnetosphere fluctu-
ates continually in size like a huge, cosmic jellyfish.
• Findings that appear to hold for all magnetosphere
states include the fact that the planet's huge envelope
appears to be relatively blunt as it faces into the solar
wind. Most of the time, this magnetic bubble is probably
about as thick as the distance of its boundary from the
planet, according to Pioneer's project scientist, Dr. John
Wolfe of Ames Research Center, Mountain View, Calif.
• The current sheet, which bisects the outer magnetosphere
horizontally, now appears to be a relatively permanent fea-
ture of the magnetosphere and to extend completely around the
planet. The current sheet is formed by electrified parti^-
cles spun out from the top of Jupiter's ionosphere by the
planet's high-speed rotation. The sheet can become dis-
turbed when the magnetosphere undergoes drastic changes in
size due to pressure changes in the solar wind. Pioneer 11
found that the magnetosphere boundary can move back toward
Jupiter as rapidly as 320,000 km (20,000 mi.) an hour.
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As magnetic lines of force produced by the current
sheet cancel each other out, experimenters suggest, par-
ticles are accelerated to nearly the speed of light. This
makes Jupiter the only other significant source of high-
energy particles in the solar system besides the Sun.
• Pioneer scientists report that all of Jupiter's
large moons "sweep out" particles from the radiation belts,
reducing the belts' intensity. The closest large moon,
lo, absorbs virtually all the low-energy electrons between
its orbit and Jupiter.
The passages of. these moons, each with a different
period, constantly stir up the magnetosphere like "a spade
in a bucket of molasses," says Dr. James Van Allen, of
the University of Iowa, a Pioneer experimenter. As a
result, there are rapid changes in the magnetosphere, shown
by the fact that radiation on Pioneer's outgoing pass was
ten times higher than on the incoming leg.. Distribution
of high-energy particles also was far different, incoming
from outgoing—and far different from the Pioneer 10
findings a year earlier.
The Pioneers are managed for NASA's Office of Space
Science by Ames, They are built by TRW Systems Inc.,
Redondo Beach, Calif.
-end-


Jovian magnetic fields is complex, Pioneer 11 shows

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