This processed color image of Jupiter was produced in 1990 by the U.S. Geological Survey from a Voyager image captured in 1979. Zones of light-colored, ascending clouds alternate with bands of dark, descending clouds. http://photojournal.jpl.nasa.gov/catalog/PIA00343

Guardian of the Universe

Nonfiction by Peter Jekel

What men are poets who can speak of Jupiter if he were a man, but if he is an immense spinning sphere

 of methane and ammonia must be silent? —Richard Feynmann

The universe is a violent place. It is filled with violence on the scale of colliding galaxies, to supernovae, to black holes, to quasars, to blistering radiation and even more locally meteor and comets crashing into worlds. Here in our tiny corner of the cosmos, we have been blessed, with relatively steady sunlight warming our world, a shielding magnetic field to protect us against the radiation hotbed of outer space and a large satellite to stabilize our orbit and axial tilt. However, we are not immune to comet and/or meteor hits. It was a massive asteroid that struck the area of the present-day Yucatan Peninsula that caused the eventual demise of the dinosaurs.

From July 16-22, 1994, our solar system was rocked by an event that had never been seen before: fragments of the Shoemaker-Levy 9 comet collided with the planet Jupiter. That spectacular event gave new vigor to the idea that the giant outer planets, particularly Jupiter, function as "protectors," which prevent smaller objects, such as comets originating from the outer extremities of the solar system, from reaching the inner planets by drawing them into their gigantic gravitational maws. The escape velocity of Jupiter, for example, is an impressive 59.5 kilometers per second, while the Earth's is a relatively paltry eleven kilometers per second. The tremendous gravitational field created by this massive gas giant can either “slingshot” incoming celestial objects back out of the solar system, or even draw these objects directly towards its surface, as in the case of Shoemaker-Levy 9. Ironically it can also draw objects from the extremes of the solar system into the inner solar system as well where they may have a detrimental effect on the inner planets. Even the best security has a possible dark side.

Shoemaker-Levy 9 was the first of several impacts of Jupiter that have been observed since 1994. It is now theorized that Jupiter is impacted by meteors and other debris up to ten meters in size several times every year.

In their book Rare Earth: Why Complex Life Is Uncommon in the Universe, geologist Peter Ward and astronomer Donald Brownlee looked at the conditions necessary for life to evolve to an intelligent level. They make the argument that has been suggested by other scientists, that intelligent life in the universe is probably quite rare due to the fact that a number of variables have to come to together to allow it to happen. One key condition they identified is a stable planetary environment. The protection provided by a gigantic gravitational field in the outer reaches of the system that limits the possibility of catastrophic collisions in the "habitable" inner system is a stabilizing feature that allows life to evolve to its fullest potential. So it seems that Jupiter, aptly named after the chief god of the Roman pantheon, may have been a key factor in the evolution of our species, acting as a distant great protector over the eons.

Until exploration of Jupiter began in earnest (with the NASA spacecraft Pioneer 10 and 11, which flew by in 1973 and 1974, respectively, and the two Voyagers both of which flew by in 1979), much of our knowledge of the planet was speculation and extrapolation from distant astronomical observations.

There have been more recent missions that flew by Jupiter since the Pioneers and Voyagers. There was the joint NASA/European Space Agency Ulysses spacecraft that was launched in 1990. Its main focus was to study the Sun and several comets. During its foray around the Sun which it did three times, it also flew over the north pole of the planet at a distance of 451,000 kilometers, taking measurements of the planet’s magnetic field. 

There was the Cassini-Huygens mission that flew by Jupiter on its way to Saturn. Its closest approach to Jupiter was on December 30, 2000. During its months long flyby, a total of 26,000 images of the planet were taken. Resolution of the photos was incredible, capable of “seeing” features as small as sixty kilometers across.

NASA probe New Horizons used the gravitational assist of Jupiter, making its closest approach to the planet on February 28, 2007, to move onto the outer Solar System. During its study of the planetary system, it took a number of measurements of Jupiter’s moons, its ring system and the planet’s giant magnetosphere. Ironically, though New Horizons will be forever known for its rendezvous with Pluto and the Kuiper Belt, there was actually more data received from the probe regarding Jupiter. 

Early science fiction played on the ignorance of the day and came up with a number of bizarre visions of Jupiter. In 1752, French writer, Voltaire, wrote Micromegas, about a visit to Jupiter with a partner from Saturn, no less, to learn some of the planet’s remarkable secrets. In 1894, American businessman John Astor wrote A Journey to Other Worlds where a stop at Jupiter led to an encounter with dinosaurs. American writer Edmond Hamilton’s 1932 A Conquest of Two Worlds depicts Jupiter as a hot and humid world, much like what was speculated for Venus at the time. Isaac Asimov, too, in 1942, wrote the short story “Victory Unintentional” about a future when we send robots to the surface of Jupiter to make contact with the inhabitants of the planet.

It was only with the launch of NASA’s Galileo on October 18, 1989 and its arrival at Jupiter on December 7, 1995, that we began to learn much more about this mysterious giant. Instead of merely taking pictures of the planet on a flyby, as did her predecessors, Galileo was comprised of an orbiter and an atmospheric probe. Speak of being in the right place at the right time; Galileo was in a perfect position when Shoemaker-Levy 9 entered the Jovian atmosphere, producing some spectacular footage.

Though depicted as a protector, Jupiter could very well have been so much more and the solar system would have looked remarkably different. If Jupiter were about fifty to one hundred times more massive than it is, no small increase, as Jupiter is already a very massive object on the scale of our solar system, it would have had the mass necessary to become a star; in effect, we might have been a part of a binary star system. Imagine what our world would be like if that were the case. Brian Aldiss' Helliconia series explores the possible effects of such a binary system on a life-bearing planet.

In spite of the massive increase of mass that would be required to create a star out of Jupiter, some science fiction authors have envisioned just that. In Arthur C. Clarke's 2010, Odyssey 2, a mysterious alien monolith ignites Jupiter to become the sun, known as Lucifer, for the Jovian system of moons: a solar system within our solar system. Michael James Wilson wrote the novel The Intrepid: Earth’s Moment of Awareness that takes place in the distant future, 48,000 years to be exact, aboard a cruise ship that arrives in the solar system. The main purpose of the mission is to witness the creation of the newest binary star system in the Milky Way galaxy.  

Keeping with its protector status, Jupiter has a spectacular moon system, probably drawing a number of errant asteroids into its gravitational sphere of influence over the millennia. Four of the larger main moons, Io, Europa, Ganymede and Callisto are known as the Galilean moons, named after their discoverer, Italian physicist and astronomer, Galileo. The moons are so unique that they are covered individually in other articles within past NewMyths issues.

In addition to its many moons—95 official moons in 2024—Jupiter has a ring system. It is not as complex as the ring system around the planet Saturn, but it is impressive nonetheless. Jupiter's rings were first discovered by Voyager 1 in 1979. The ring system is comprised of an inner halo, the main ring, and the gossamer rings. The rings themselves are the result of dust from interplanetary meteoroids that smashed into the four innermost moons of Jupiter: Metis, Adrastea, Thebe, and Amalthea. It is not mere chance that the rings' boundaries coincide with the orbital paths of the inner moons: in fact, it is the gravitational influences of these moons that keep the rings' particles in place, and hence these moons are sometimes referred to as the "shepherd moons." 

The innermost halo ring is toroid in shape and extends radially from about 92 to 122,500 kilometers from Jupiter's upper cloud deck. The main and brightest ring extends from the halo boundary to about 128,940 kilometers, just inside the orbit of Adrastea. Voyager 1 showed the gossamer ring only as a single entity, but it was Galileo that found that the ring is actually two rings, one ring embedded in the other. The light and insubstantial-rings are uniform, with the innermost ring extending from the orbit of Adrastea to the orbit of Amalthea at 181,000 kilometers. The fainter Thebean ring extends from Amalthea to the orbit of Thebe at 221,000 kilometers.

The rings and the moons of Jupiter exist in an intensive radiation belt of electrons and ions trapped by the enormous magnetic field of Jupiter. The size of Jupiter's field is larger than that of any other body in the solar system with only the Sun having a more powerful one. Even given its size, Jupiter's field is proportionately larger than what would be expected. The solar wind with the charged particles continually being ejected into interplanetary space shapes the field into a teardrop shape. On the sunward side of the planet, the magnetic field extends from five to twelve million kilometers into space, while on the far side the field stretches outward about one billion kilometers, almost to the orbit of Saturn.

There is another interesting aspect to the magnetic field of Jupiter related to one of its moons, Io. Both the Voyager and Pioneer spacecraft detected a large donut-shaped collection of charged particles in the area of Io. It is thought that this is material from the volcanoes of Io, expelled at a rate of one thousand kilograms per second into the magnetic field of Jupiter that forms the Torus of Io. The Torus is, in effect, the largest electrical circuit that we know of, with a generating capacity of about two trillion watts per second. For comparison, if we were to operate all of the electrical plants in the United States at full power for one year, we would reach one trillion watts. Annual electrical consumption in the United States, however, is around half a trillion watts. This enormous field is generated by a combination of Jupiter's size with a radius of 69,911 kilometers and rapid rotational rate of nine hours and fifty minutes at the equator up to ten degrees latitude north and south latitude and nine hours and fifty-five minutes elsewhere. That is only part of the secret though. What lies beneath holds more clues to the source of Jupiter's enormous magnetic field.

When we look at Jupiter through a telescope, we see a banded planet made up of dark belts and lighter zones. This is only the upper cloud deck of the planet's atmosphere. When the Galileo probe penetrated into the upper icy ammonia clouds seen at the surface of the cloud deck on December 7, 1995, it discovered a range of chemicals, from the most common, hydrogen (comprising about 88 percent of the atmosphere), to helium, methane, ammonia, water, hydrogen sulphide, deuterium, neon, argon, krypton, and xenon.

Taking a look at the proportions of the gases and comparing them to that of the Sun and you might find similarities, further advancing the idea that given more mass, Jupiter could have been another star. The proportions of hydrogen and helium are thought to be close to the composition of the primordial solar nebula that formed our Sun. There are also trace amounts of other gases such as water, ammonia, methane and even silicon compounds. Through infrared observations, even complex organic molecules such as benzene and other hydrocarbons have been detected.

At least one science fiction author, Donald Moffat used the atmosphere of Jupiter as an essential plot element. In the story, “Jupiter Theft,” aliens reveal their reason for coming to our Solar System, to use the hydrogen of Jupiter as fuel.

As the Galileo probe approached the bottom of the cloud deck at around 160 kilometers, the weather had been expected to turn windy, overcast, hot, and humid due to an overwhelmingly presence of water vapour, at five to ten atmospheres of pressure. This turned out not to be the case at all. Evidence of clouds was non-existent; instead, the light was hazy, and the pressure was around 22 atmospheres. The lightning detector on the probe, which was effectively an AM receiver, detected only faint discharges. In summary, the weather on Jupiter was found to be a lot drier and clearer than had been expected. What had happened? The probe had entered one of Jupiter's hot spots (temperature of around 153 degrees Celsius), which act as shunts through which infrared radiation from lower levels leaks out. Jupiter has a number of these spots, and they move around constantly, so there was no way the probe could have avoided this opening.

In hot spots such as the Galileo probe entry site, cold air descends from the upper atmosphere and is as dry as the dry valleys of Antarctica. In other areas, there are wet spots that create the giant lightning flashes. In further support of this model, the orbiter found that the abundances of water and ammonia in the Jovian atmosphere can vary greatly. Though the probe's lightning detector only found distant radio noise, the orbiter observed enormous flashes in the clouds, indicators of massive lightning activity, larger than anything seen on Earth. Like its Voyager predecessors, Galileo found that the lightning was concentrated in a few zones of latitude. The depth of the lightning was estimated from the size of the illumination on the cloud tops, with the theory that the bigger the flash, the deeper the discharge. From these observations, the lightning appeared to be originating in the area where water clouds were thought to be formed, similar to the process on Earth.

One thing that the scientists did correctly predict about Jupiter's atmosphere is that Jovian winds achieve velocities of several hundred kilometers per hour. This is similar to Earth's jet stream, but the velocity of terrestrial winds dies down as the winds approach the Earth's surface, while Jupiter's surface is much further below its atmosphere. Prior to Galileo, scientists had long speculated on the causes of the rapid winds of Jupiter. On Earth, the winds are driven by temperature differentials between the poles and the equator, whereas the temperature of Jupiter's cloud tops is relatively uniform, with an average of -145 Celsius. There were two main explanations for Jupiter's winds, depending on the energy source driving the winds. If the energy source were internal, for example, caused by gravitational contraction, winds would be expected to increase in speed, or at least remain the same, with increasing depth. If the source of energy were external, perhaps sunlight, the winds would die down with depth. The Galileo probe discovered that the winds actually increased in speed with depth before leveling off and becoming constant, and thus the energy source driving the enormous winds of Jupiter is internal. Jupiter is, in effect, shrinking because of the gravitational effects of its enormous gravity.

With an active atmosphere such as we find on Jupiter, we can also safely assume that it is a planet of intense storm activity, and indeed it is. Next to Saturn's rings, the Great Red Spot of Jupiter is probably the most well-known and recognizable features of our solar system. The Great Red Spot is, in effect, a giant storm, larger than the Earth itself, and has been raging for about three hundred years. The spot, a high pressure system (unlike Earth storms, which are low pressure zones), rotates in a counter clockwise pattern every six days. Its reddish color is somewhat of a mystery, but there is speculation that phosphorus may be the cause. Some have suggested that the reddish colour may have an organic origin. There is evidence that this ancient storm is waning, but it still packs a punch.

In addition to the Great Red Spot, Galileo found three cold storm systems, called white ovals, that merged to form another powerful storm system, called Oval BA. Recently its colour has also taken on a reddish hue causing it to be nicknamed Red Jr. and Little Red Spot. 

What about rain? Does it rain on Jupiter? Given all the lightning activity and storms, the idea seems plausible, but then again we are talking about Jupiter, which is far different from Earth. Recent speculation, based on the findings of the Galileo probe, suggests the following line of reasoning for a helium rainfall. Helium is present on Jupiter, but in lesser concentrations than it is on the Sun. Scientists believe that something must be draining helium from the atmosphere. So there is a possibility, based on these findings, that Jupiter is deluged with a helium rain. And if that isn't bizarre enough, the relative rarity of neon on Jupiter indicates that neon, too, is being drained away, and the hypothesis that neon is actually dissolving in helium rain has been suggested.

Recent information adds to the weird weather of Jupiter. In addition to the helium rain idea there could also be a diamond rain or more correctly hailstorms. The intense lightning of Jupiter is energetic enough to turn any carbon in the atmosphere into diamonds which fall like hail.

There has been speculation that below the cloud cover lies a metallic hydrogen sea about 40,000 kilometers deep. Metallic hydrogen does not occur naturally on Earth, but under the extreme pressures that exist on Jupiter (up to three million times that of Earth), hydrogen molecules can become so tightly compacted that they break up and become electrically conductive. This electrical conductivity is speculated to be one of the main sources of Jupiter's unusually large magnetic field. Underneath it all, is a core at an estimated temperature of 30,000 Celsius. This heat makes its way up to create the hot spots such as the one the Galileo probe entered. The core was theorized at one time to be solid and estimated to be about 1.5 times that of the Earth's diameter, but ten to thirty times as massive.

 However, recent data from the latest mission to the planet, NASA’s Juno spacecraft which entered an orbit around the planet on July 5, 2016, has changed some of the speculation about the core. Juno not only provided a lot of new information about Jupiter’s lightning, aurorae and magnetic field but it also provided some new insights into the origin of the planet itself including its core. The core of Jupiter is likely not solid as once speculated, according to findings by Juno but rather made up of pieces of rock and metallic hydrogen, likely the result of collisions in the early solar system. 

Jupiter is not likely to be an ocean teeming with life, but then one has only to read Robert Forward's Dragon's Egg which speculates about life on a neutron star, another astronomical entity ,with (even more) enormous gravitational and magnetic fields, to find an imaginative depiction of life existing under extreme conditions. A few science fiction writers have speculated on the possibility of life existing in Jupiter's turbulent atmosphere. Arthur C. Clarke's short story “A Meeting With Medusa” which has been expanded by Alistair Reynolds and Stephen Baxter in their official sequel, The Medusa Chronicles and Ben Bova's novel Jupiter and its sequel Leviathans of Jupiter all envision creatures that "swim" in the currents that flow through the Jovian atmosphere.  A short story by Timothy Zahn, “Manta’s Gift,” describes the atmosphere of Jupiter as being populated by intelligent Qanska. Ian Stewart and Jack Cohen wrote the novel, Wheelers, about an intelligent life form that lives in Jupiter’s atmosphere. It is particularly interesting in that one of the authors, Ian Stewart, is a mathematician. Mathematics plays a significant role in the storyline. Perhaps the most interesting spin on the idea of life in the atmosphere of Jupiter is found in Kim Stanley Robinson’s Galileo’s Dream. In the story, human colonists from the 29th century learn that Jupiter’s atmosphere is itself, one vast intelligence.

We do know today that Jupiter is an extreme environment and requires extreme technologies to survive those extremes; Galileo’s atmospheric probe lasted a full fifty-eight minutes as it ventured into the interior of the atmosphere before being crushed by the enormous pressures. In spite of extreme technology required to explore Jupiter, some science fiction authors have envisioned exploration of the planet through the use, not of technology, but of biological manipulation. Clifford Simak wrote the City series early in the 1950’s. It is essentially a loosely connected series of short stories packed together as a novel. One of the stories takes place on a Jupiter inhabited by humans. The humans have been transformed into entities that are able to survive the extremes of Jupiter. Similarly, Pat Cadigan, in his short story, “The Girl-Thing Who Went Out for Sushi,” describes humans as being biologically changed into octopus-like creatures able to live and function in planetary conditions found not only on Jupiter but on the other gaseous worlds of the outer solar system.

According to modern theories of planetary formation, Jupiter emerged from the primordial nebula in two stages. First, icy planetisemals condensed out of the cloud of dust and gas, and as the protoplanet grew so did its ability to gather more material. At a certain point in the process of agglomeration, a critical mass was reached that promoted a rapid growth spurt as the cumulative gravitational effect of the conglomerated protoplanet became sufficient to trap all the nearby hydrogen and helium. Jupiter is somewhat similar to the primordial Sun in chemical content; however, krypton, xenon, and argon are found at higher levels on Jupiter than in the Sun. This suggests that Jupiter's material of formation may have come from the outer reaches of space, since trapping these gases at the levels found on Jupiter would require the gases to be "frozen out," which isn't possible in Jupiter's present location. Thus, it may have formed further out in the solar system and drifted to its present distance of 778 million kilometers from the Sun

Jupiter is certainly presenting itself as being worthy of further exploration. Future missions to the planet will focus on its moons and not as much on the planet itself. One, the European Space Agency’s Jupiter Icy Moon Explorer, scheduled to launch in 2022 did not launch until April 14, 2023. It is scheduled to arrive in the Jovian system in 2031.

The Europa Clipper mission was launched on October 14, 2024, due to enter the Jupiter system in approximately 5.5 years. As indicated by the name of the mission, Europa is the true target of the mission; however, being in such close proximity to Jupiter, will allow for new information to be garnered about the planet.

The guardian of our solar system does not really bear any resemblance to the rest of the planetary family of our solar system. It can be difficult to grasp the scale of Jupiter: at over 300 times the mass and 1300 times the volume of Earth, its immensity renders our human yardsticks barely adequate for the task. Its uniqueness is what makes it worth the visit, and hopefully there will be plenty more visits to follow Juno, particularly when given the possibility that we have Jupiter to partially thank for our existence as an intelligent species, Jupiter is really a solar system neighbour worth knowing.

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