After a six year journey through the solar system and being inexorably accelerated to a speed of 170,700
km/hour by Jupiters tremendous gravitational pull, the Galileo Probe successfully entered Jupiters
atmosphere on 12/7/95. During the first two minutes of this most difficult atmospheric entry ever
attempted, near-probe temperatures twice as hot as the Suns surface and deceleration forces as great as 230
times the acceleration of gravity at Earths surface were produced as the spacecraft was slowed down by
Jupiters atmosphere. The Galileo Probe and Orbiter separated on July 13, 1995 and both arrived at Jupiter
on slightly different trajectories. The Galileo Orbiter successfully became the first spacecraft to enter an
orbit around Jupiter a few hours after the probes successful descent into the atmosphere.
The Probe apparently entered a rather special location on a quite non-uniform world. Ground-based
telescopic observations were undertaken to determine the appearance of the Galileo Probe entry site (6.5
degrees North Latitude, 4.5 degrees West Longitude) at the time of entry and to determine the variability of
this location on the planet. An important goal of these observations was to place the Galileo Probe results in
the context of Jupiter as a whole. The Probe entered Jupiter near the edge of a so-called infrared “hot spot”
believed to be a region of reduced clouds.
New Data Suggest Galileo Probe Found a Jovian Dry Spot Amid Wetter Whereabouts. Jupiter has wet and
dry regions, according to the latest images from NASAs Galileo spacecraft, and the discovery may explain
why the Galileo Probe found less water than expected when it dropped into the Jovian atmosphere on Dec.
7, 1995. The Probe, Built by Hughes Space and Communications Company, survived for almost an hour in
Jupiters hostile atmosphere, as it relayed data to the Galileo Orbiter more than 130,000 miles overhead.
The latest data from the Galileo Orbiter also shed new light on the auroras that glow in a narrow ring
around the poles of Jupiter. Auroral arc on Jupiter is thin and patchy, and its altitude is between 300 and
600 kilometers (186 and 372 miles).
The cloud materials are only minor constituents of a much more extensive atmosphere of clear gas. The gas
is mostly hydrogen and helium, whereas the clouds condense from ammonia, water vapor, and other minor
compounds. Jupiters atmospheric composition is about four-fifths hydrogen and one-fifth helium by mass.
The hydrogen and helium are thought to be a ” fossil” atmosphere of the gas that surrounded all the planets
as they formed. Infrared radiation reveals Jupiters temperature in the upper atmosphere to be very cold
because of the planets great distance from the Sun – about 133 K (-220 degrees F), on both the sunlit and
nighttime sides. At a lower level, the poisonous clouds are warmer.
Gaps in the clouds have revealed still lower haze layers with even higher temperatures of around 250 K (-9
degrees F). The lower regions may resemble the hydrogen-compound-rich primordial atmosphere of earth
when terrestrial life originated. A recent model of Jupiters atmosphere calls for temperatures similar to
those at Earths surface at a level of about 60 km below the Jovian cloud tops, where the pressure would be
about 10 times Earths surface pressure. Such conditions might be hospitable to primitive life, but most
scientists doubt that any life forms exist on Jupiter. Future space probes to Jupiter may clarify this.
IOs pictures from the main Spacecraft
Io can be classified as one of the most unusual moons in our solar system. Active volcanism on Io was the
greatest unexpected discovery at Jupiter. It was the first time active volcanoes had been seen on another
body in the solar system. Plumes from the volcanoes extend to more than 300 kilometers (190 miles) above
the surface, with material being ejected at speeds up to a kilometer (.6 miles) per second.
Ios volcanoes are apparently due to heating of the satellite by tidal pumping. Io is perturbed in its orbit by
Europa and Ganymede, two other large satellites nearby, then pulled back again into its regular orbit by
Jupiter. This tug-of-war results in tidal bulging as great as 100 meters (330 feet) on Ios surface.
Io is composed primarily of rocky material with very little iron. Io is located within an intense radiation belt
of electrons and ions trapped in Jupiters magnetic field. As the magnetosphere rotates with Jupiter, it
sweeps past Io and strips away about 1,000 kilograms (1 ton) of material per second. The material forms a
torus, a doughnut shaped cloud of ions that glow in the ultraviolet. The toruss heavy ions migrate outward,
and their pressure inflates the Jovian magnetosphere to more than twice its expected size. Some of the more
energetic sulphur and oxygen ions fall along the magnetic field into the planets atmosphere, resulting in
Cassini scientists have been busy planning what science they will do when they get near Saturn.
Perhaps Cassini will discover new moons of Saturn, or a strange magnetic field anomaly that deserves
However, there are all sorts of opportunities for Cassini. Cassini could go into orbit around Saturns largest
moon. Titan, or even use its gravity assist to escape Saturn altogether. It may even be possible for Cassini
to go to another planet or visit an asteroid (though its likely that this would take many years to do ).
However, the Saturn system is interesting enough — and may even have some mission surprises.
After the probe is released in early November, the orbited performs a propulsive maneuver to target for the
flyby and delay its arrival to Titan so that it can have the proper geometry to view the probe descent region.
During the probe mission, the orbited will fly above Titan and listen with its High Gain Antenna (HGA) for
data transmitted by the probe. This data must be first stored on the orbiters Solid State Recorder before it
can be downlinked to Earth later. The project has a number of strategies, including downlinking the
problem data multiple times, to ensure that the probe data gets to Earth with no problems.
As the Huygens probe breaks through the cloud deck, a camera will capture pictures of the Titan panorama.
Other instruments will directly measure the organic chemistry in Titans atmosphere–providing the
equivalent of a time machine to examine the chemistry of the early Earth. Instruments will also be used to
study properties of Titans surface remotely, and perhaps even directly after landing on the surface.
After the probe mission is completed, the spacecraft will turn the HGA to Earth and begin transmitting the
recorded probe data. The data will even be transmitted twice and be verified on the ground before it can be
overwritten on the data recorders. Once the data is verified, the probe mission is considered to be
Many scientists theorize that Titan may be covered by lakes or oceans of methane or ethane. This remains
a mystery; the laws of thermodynamics say such oceans should exist, while radar studies conducted from
Earth have turned up no evidence of them. Theories from the study of tidal motions suggest that Titan
should either be covered by all oceans or all land, but nothing in between. The resolution of this puzzle is
up to Cassini.