Journey (without return) in the hellish atmosphere of Jupiter
Mysterious, imposing and austere, Jupiter is the largest and most massive planet in
the entire Solar System.
It is so large (140 thousand kilometers in diameter) that if we put together all the
other planets, including Saturn, we would be able to equal only half of its mass.
It is difficult to describe in words the fascination that this cosmic giant has exerted over the
centuries on entire generations of astronomers, enthusiasts and simply curious.
On Jupiter everything is out of scale, starting from its best known feature, the Great Red
Spot, a huge cyclone that rages in the atmosphere of the planet for at least 350 years.
Like Saturn, Uranus and Neptune, Jupiter is mostly composed of gas - especially hydrogen
and helium - and therefore has no defined surface on which to land.
A hypothetical descent into its atmosphere would look very much like a very long dive
into the depths of the ocean.
Although we do not know all the secrets of Jupiter yet, we know just enough to imagine
the wonderful and terrible spectacle that a hypothetical astronaut would see if he tried
to venture into its turbulent atmosphere...
Alien colors, clouds as big as mountains, immense columns of gas in continuous movement,
lightning so powerful that an entire ocean evaporates in the space of an instant: on
Jupiter every atmospheric phenomenon is taken to the extreme, to characterize one of the
most hostile environments of the Solar System.
An environment that - few remember - we began to explore a quarter of a century ago.
So much time has in fact passed since the day the Galileo probe arrived on Jupiter after
a six-year journey.
Among the main objectives of that mission, in addition to the study of the Medicean satellites
and the Jovian magnetic field, there was also the analysis of the atmosphere, for which
was designed a small probe (called "atmospheric") that would measure pressure, temperature and
chemical composition.
Galileo released the atmospheric probe five months before meeting Jupiter, in July 1995,
and on December 7, 1995 the two ships reached the gas giant together.
The "mother probe" entered into orbit around the planet, while the little one penetrated
its atmosphere at a speed of 48 kilometers per second, after which, in little more than
two minutes it was slowed down to subsonic speed by the density of the air.
The descent lasted a total of 58 minutes, and the connection was interrupted when the
probe, arrived at 150 km of "depth", reached conditions of temperature and pressure so
high that it dissolved in the atmosphere of the planet.
The data collected along the way proved to be of fundamental importance to understand
the dynamics and chemical composition of the upper layers of the Jovian atmosphere, but
did not provide any clue as to what lies deeper.
However, nothing prevents us from putting together what little we know with a bit of
imagination, and fantasize about what we might see as we descend towards the core, obviously
protected by a super pressurized suit.
A dive that will allow us to discover the secrets of one of the most extreme environments
of the Solar System.
Are you ready?
En route to Jupiter!
We are half a million kilometers away from Jupiter, aboard our ship, and the approach
phase is much longer than expected: we are navigating at the maximum speed allowed by
our propulsion system, yet it seems that the planet is not approaching one meter!
The outermost layers of its atmosphere begin to occupy the entire field of view only after
several hours of travel, when we are still 200,000 kilometers away from the apparent
surface of the planet, that is, from the top of its highest clouds.
Now the entire disc of the planet extends into the sky for about 40 degrees of apparent
diameter.
Finally we see in detail the dense clouds of ammonia and hydrogen that rotate in parallel
around the equator forming the characteristic white, red and orange bands.
Jupiter, as well as the Sun and Saturn, is in fact subject to a differential rotation
phenomenon.
Because of its high speed of rotation (9.9 hours), the gases that make up the upper layers
of the atmosphere - mainly hydrogen, helium and ammonia - move at different speeds depending
on their position with respect to the equator, creating the characteristic horizontal bands
of different color.
Usually, the red ones, called "zones", correspond to atmospheric depressions caused by descending
cold air, while the lighter ones, the "bands", are cloudy reliefs formed by rising hot air.
The Great Red Spot, so clean and geometric if seen from a distance, slowly begins to
transform, so that after a few hours we find it hard to distinguish the contours.
The enormous vortex, which from space seemed to us a single structure, now appears as a
chaotic set of smaller vortexes, whose circumvolutions reveal new and unexpected details about the
extreme turbulence of the atmosphere.
The mighty columns of gas emerging from the deepest layers of the planet make Jupiter
resemble a huge pot full of bubbling water.
Arrived at 100 thousand kilometers from the surface the electromagnetic bombardment caused
by the Jovian magnetosphere is so intense that we are forced to activate the special
protections of our ship.
If we did not, we would die of radiation poisoning within minutes.
Jupiter is in fact like a giant dynamo: because of its fast rotation period the speed with
which the metallic hydrogen "slides" on the inner core of the planet generates strong
electric currents that give rise to a magnetosphere 20 thousand times more powerful than the Earth.
The magnetosphere then traps solar emissions in huge bands of radiation, generating a radioactive
environment that is a deadly risk both for probes, whose instrumentation must be adequately
shielded, and for astronauts.
0 km.
The descent begins!
Continuing our journey we finally reach the edge of the troposphere, the zero limit from
which we begin to measure the descent, as we would do with the depths of an oceanic
trench.
The long descent to the innermost layers of the gas giant begins here: we disengage from
the spacecraft, protected by our magical spacesuit, and let gravity drag us towards the core.
Because of its enormous mass, at this height Jupiter generates a gravitational acceleration
2.6 times higher than the Earth, so if we want to avoid burning like a meteor we have
to open a parachute to slow the fall.
We do it, and in a few minutes our speed goes from 3200 to 360 kilometers per hour, with
a deceleration that allows us to avoid any risk of supersonic compression or overheating
due to friction.
-10 km.
Among the mists of the Great Red Spot.
Looking around we notice an unusual landscape: the colors vary from bright red to brown and
there is a thick layer of mist that prevents us from pushing our gaze further than a few
hundred meters.
But if we could do it we would see a spectacle without equal: the clouds that surround us,
up to 45 km high and composed mainly of hydrocarbons, hydrogen, methane and ammonia crystals, would
look like huge mountains.
We would immediately notice that ammonia covers the upper surface of the clouds like an oil
film on the water, adding a hue of white to the dominant red color.
Pushing our eyes even further in the direction of the Great Red Spot, we would see a huge
column of turbulent gas soaring over the surrounding clouds, almost as if it were floating above
the troposphere.
-50 km.
Lightning and turbulence.
At the height at which we are now, about -50 km from the beginning of the troposphere,
the conditions of pressure and temperature are similar to those detectable on the surface
of the Earth, but the winds raging around us are dragging us at a speed of over 560
kilometers per hour and the intensity of radiation generated by the Jovian magnetic field could
still kill us in a few minutes, in the absence of protection.
The noise generated by the turbulence is deafening, because here the speed of sound is four times
higher than we are used to.
The sky is continuously crossed by violent lightning tens of kilometers long, thousands
of times more powerful than those generated on Earth.
The lightning is mainly caused by rains of water, sulfuric acid and ammonia, which due
to the gravitational attraction of Jupiter fall at a speed three times faster than the
Earth's rains, creating a huge difference in potential.
-100 km.
Goodbye to the light.
After another five minutes of descent the atmospheric pressure rises to 2 bar and we
begin to cross a new layer of clouds, this time composed of ammonium sulphite and ammonium
hydrosulphide.
The conditions of the environment around us are quite extreme, but at this moment we do
not need any additional protection other than good radiation shielding.
Although the weight of the air above us starts to grow following an exponential curve, the
relatively low fall rate allows the cavities of our body to equalize their internal pressure
without generating undesirable effects.
Another 10 minutes pass and the pressure reaches 4 bar, a value corresponding to what we would
experience on Earth by diving into water at a depth of 30 meters, while the temperature
drops to -40 degrees.
We begin to encounter the first clouds of frozen water and in the meantime the ambient
brightness continues to decrease.
The speed of the winds rises to 720 kilometers per hour but we barely notice it, because
the level of turbulence in the atmosphere gradually decreases.
Another 15 minutes of fall and the pressure rises to 10 bar.
At this point, in order to avoid harmful effects on the body we have to modify the air mixture
supplied by the suit's respirator: if we do not do it in a few minutes we would encounter
an oxygen poisoning, or a nitrogen narcosis, because under pressure the two gases become
toxic.
Let's take a last look above us, just in time to see the weak disk of the Sun disappearing
in the orange fog.
Another 25 minutes pass and the situation begins to get complicated.
The special protective suit with which we are equipped must withstand a temperature
above 100 degrees Celsius, continuously and constantly increasing, accompanied by enough
atmospheric pressure to crumple a car.
We find ourselves suddenly immersed in darkness and we can no longer distinguish anything.
The absence of light is due to the density and chemical composition of air: around us
now there are only hydrogen, helium, ammonium sulfide and traces of water vapor, compressed
to the point of absorbing all the electromagnetic radiation coming from the Sun.
Our journey has turned into a slow fall into darkness.
-20,000 km.
Gases become liquid.
We continue to slow down due to the increasing atmospheric density, while incandescent helium
is raining around us.
The gases compress more and more, starting to behave like liquids: if we had to leave
our protective suit we would be crushed and vaporized in a split second.
Now we are no longer even able to determine where we are in relation to Jupiter's core,
because the transition between gas and liquid is so gradual that we can not realize the
change in density.
Below us, at an unspecified distance, we notice a faint luminescence caused by the energy
radiating from the nucleus.
Atmosphere is now almost completely formed by liquid hydrogen that boils at thousands
of degrees centigrade, as on the surface of the Sun.
The pressure rises rapidly from one thousand to two million bar and the atmospheric density
has exceeded the water density by a while, reaching even one thousand kilograms per cubic
centimeter.
At this point the fall stops, because our body, being less dense than the matter around
it, once exhausted the kinetic energy of the fall can no longer sink.
If we want to continue we need a push, so we turn on the propellers of the suit and
start to descend slowly again.
- 30,000 km.
An ocean of liquid metal.
From here on, and for several hours, the journey is particularly boring: darkness and silence
dominate, and the monotony is interrupted only by the imperceptible flashes that emanate
from the deepest regions of the planet.
Continuing on becomes more and more difficult.
After a time that seems endless, however, something unexpected happens: the darkness
is torn by a web of lightning that vaguely resembles a spider's web.
This network of lightning branches out following a very particular geometry, which closely
resembles the way electricity propagates in the water.
We are sailing in a vast ocean of metallic liquid hydrogen!
Under normal conditions of pressure and temperature hydrogen is a gas, but if its density exceeds
a certain critical point it turns into something different, a substance that flows like a viscous
liquid and conducts electricity like a metal.
The lightning we saw in the troposphere are nothing compared to those that cross this
boundless ocean.
Where we are now, pressure and temperature have reached such high levels that they escape
any attempt at understanding.
-60,000 km.
The core!
No matter how hard we try, we can't go any further.
Below us now is the core of Jupiter, an extremely dense and warm core with a mass between 12
and 45 times the Earth's one: astronomers believe that it is mostly solid and contains
most of the heaviest elements of the planet, such as ice, rock, iron and other heavy components,
with a considerable amount of hydrogen.
To be able to walk on its surface we should be able to survive pressures four million
times higher than the Earth's surface and temperatures of over 35 thousand degrees:
a bit too much even for our imagination!
After all, it is only thanks to the latter that we can bear the idea of being forced
to stay here forever, held as we are by a gravity force equal to 130 times that of the
Earth.
A well from which no means of propulsion, no matter how powerful, would ever be able
to pull us out...