By Brennan Barrington, INSPIRE Online Learning Community
I have always been fascinated by Jupiter. This is probably related to a large astronomy book with huge color pictures of the gas giants which my father would read to me from when I was young. It was an adult-level book; my grandfather had sent it for me to read when I became older, but I wanted to read it right away. So my dad read it for me at bedtime, as I looked at the pictures and text. Of course, I didn't understand very much of the text, even when he read it, but the pictures alone made quite an impression. The pictures which made the strongest impression upon me were those of Jupiter. The sheer bulk of the planet which the pictures conveyed, the color patterns, the Great Red Spot, and the complex diagrams of the planet's interior captured my imagination--in the same way that kids were and are awed and impressed by buried treasure, comic book heroes, or people who they know, things and people which are far away, powerful, and full of excitement, I was awed by Jupiter and its moons. The other planet pictures in the book seemed inferior by comparison, although I did draw a picture of the view from Charon after I heard about Pluto. Some of the pictures were artists' conceptions, and my dad and I labelled the picture in black pen as "an artist's conception of the view from Charon" and described the objects which I had put in the picture--I included the Sun, Jupiter, Neptune, and Pluto, in about the right sizes.
My fifth grade teacher, Ms. Hunt, took me aside one day. We were about to start a unit about the moon (Luna), its orbit, and its phases. She said, and I agreed, that I already knew all of that, and suggested that I do an alternate project, separate from the rest of the class. I agreed to this, and I decided to create a mobile with Jupiter, its rings, and its moons and write a report about it. I wanted, in fact, to take my own pictures of Jupiter through my dad's old telescope, but it was lost in the office and he did not have time to find it. Jupiter was painted paper-mache, supported by thin wooden rods from a hobby shop. The rings and moons were supported by similar rods. The rings were made of clear tape, and I painted small styrofoam balls from the hobby shop for the moons, using larger ones for the Galilean moons and smaller ones for three others. I did my research thoroughly. The moons were painted correctly and at the right distances relative to one another. The Galilean moon balls were one inch in diameter, and I was careful to inform the class during my presentation that for the mobile to be to scale, the Jupiter sphere would have had to be four feet in diameter (it was closer to two feet--now that I know calculus, I want to calculate the slowed rate of diameter increase which caused be to give up as I approached two feet, as more material was added) and that Europa, for example, would have to be approximately 60 feet from the Jupiter sphere. My Jupiter sphere incorporated the Great Red Spot and the zones of polar calm. I gave an amazing presentation--my teacher and many students were fascinated and told me afterward that I should become a professor. I received an A. Years later, I learned that I had made one mistake: I placed all of the three minor moons at distances beyond Callisto. In fact, Amalthea is closer to Jupiter than Io.
I see Jupiter fairly often in winter mornings while waiting for the school bus, just before sunrise. Recently, it has been about 20 degrees up in the western sky, a brilliant, unwavering light.
Once when I was seven or eight, my dad brought the telescope mentioned above outside, set it up, and found Jupiter (among other planets). (The telescope was stowed in the office and subsequently lost after this.) The telescope was not powerful enough to reveal color, but I was able to see the bands of Jupiter and several moons. It was another experience that caused my fascination with the planet.
Zeus was king of the gods in Greece, and he was associated with that planet. The Romans, who adopted the Greek religion in most respects but changed the names of most of the gods, called him Jupiter. The mythology of the planet is described in the post "Planetary Name Game" by Cecilia Stoner. Some historians claim that a Chinese astronomer--in the Roman alphabet, Gan De--detected one of the moons of Jupiter without a telescope several hundred years before Christ. Each of the moons is bright enough independently to be seen with the naked eye, but is obscured by the glare of Jupiter. By obscuring Jupiter with an object such as a tree limb, it might have been possible, although his description of the moon as "reddish" is puzzling. Io is the only one of the Galilean moons that is remotely reddish, and it is very unlikely that he saw that one because it is the closest one to Jupiter. It occurred to me as I wrote this that by calculating the positions of Earth and each of Jupiter's moons at that time, it might be possible to determine which of the moons he saw; however, there is not sufficiently precise information about when he made this observation to do this. Gan De also calculated the orbital period of Jupiter. His result was within a week of the modern number.
When the planet finally ceased to be a part of myth in Europe, the fact tore a lot of other myths down with it. When Galileo Galilei
Ultimately, he discovered four moons, which were later named Io, Europa, Ganymede, and Callisto. He attempted to have them named the Medician satellites, after the family name of a sponsor of his astronomical research, but later astronomers with no interest in Medici termed them the Galilean moons. He also discovered the bands on Jupiter, which went against the idea that everything in the sky was uniform and perfect. Galileo attempted to set up a system of calculating longitude at sea based upon the positions of Jupiter's moons, but it proved impossible to maintain a telescopic fix on Jupiter from a pitching ship deck. The idea would otherwise have worked.
Jean Picard (1620-1682) observed Jupiter extensively with the limited equipment of the time and used the apparent positions of Jupiter's moons to make an approximate calculation of the speed of light. He was the basis of the fictional character Captain Jean-Luc Picard.
However, by the end of the 19th century, we had reached the limit of what could be done with Earth-based telescopes. Fortunately, science fiction of the time began to discuss ways to reach space, and the Space Age began with the launch of Sputnik in 1957.
On March 2, 1972, the Pioneer 10 spacecraft was launched. It made its closest encounter to Jupiter, about 50,000 miles from the cloud tops, in December 1973. The NASA web page about Pioneer 10 reads: "During its Jupiter encounter, Pioneer 10 imaged the planet and its moons, and took measurements of Jupiter's magnetosphere, radiation belts, magnetic field, atmosphere, and interior. These measurements of the intense radiation environment near Jupiter were crucial in designing the Voyager and Galileo spacecraft." By the standards of Voyager, the images were small and crude. The probe broadcast various clear pictures of Jupiter from a distance, and detailed, close-range pictures, but the latter were patchy and incomplete because of damage to the probe caused by Jovian radiation. However, for the time, the pictures were incredibly detailed and clear, and the pictures and instrument readings produced an explosion of research and analysis. The probe had equipment which: analyzed magnetic fields, measured solar wind, measured cosmic rays, detected small, nearby asteroids and particulates, and measured the composition and temperature of Jupiter. The probe continued past Jupiter and into space, but its last signal was lost in 2003, long before it reached the heliopause. I have not scratched the surface of the information available about this mission; I recommend http://www.nasa.gov/centers/ames/missions/archive/pioneer.html and http://en.wikipedia.org/wiki/Pioneer_10#Encounter_with_Jupiter.
Pioneer 11 was launched on April 5, 1973. Its mission plan included flybys of Jupiter and Saturn. It had similar scientific equipment and took more readings on Jupiter, but the main objective of the mission was information about Saturn. It did determine the mass of Callisto and took a few pictures of Io, but observations of the moons were still almost nonexistent--Pioneer 10 had furnished only a few blurry pictures of the moons. The probe also photographed the poles of Jupiter, which are in a state of perpetual calm, like the eye of a hurricane (this appears as a black spot because of the decreased reflectivity, which I made sure to incorporate in my mobile). It used a Jovian gravity assist to make its encounter with Saturn.
The Voyager probes are special to me because most of the gas giant pictures in that astronomy book were from the Voyager probes, and the Voyagers were frequently mentioned in its pages. Each Voyager was in the shape of an elongated 10-faced figure, with a large, dished high gain antenna for transmitting measurements and receiving commands, and was powered by decaying radioisotopes.
Voyager 1 was launched September 5, 1977. It made observations of Jupiter and Saturn. Voyager 1's closest approach to Jupiter was about 128,000 miles from the cloud tops (I apologize for the English units, but I think that the best understanding can be supplied by using units which we are intuitively familiar with). Voyager 1 discovered Jupiter's ring system, which had not been previously discovered because it was tenuous and composed largely of non-reflective dust, as opposed to the icy rings of the other gas giants. It took the first good photographs of the moons. Scientists were awed by the volcanic plumes of Io, intrigued by the craters of Callisto, and were literally rendered speechless as the first pictures of Europa crawled onto the screen. (The silence was broken by: "Lowell was right! Only, the canals are on Europa!") It took various measurements of energetic particles emitted by Jupiter, made infrared spectrometry measurements, received radio emissions from Jupiter (NASA is currently selling to any schools, for about a hundred dollars each, kits to build radio telescopes which can receive radio emissions from Jupiter), measured radiation and cosmic rays (which provided information about the Jovian magnetosphere), and had a polarizing telescope which could get information about atmosphere properties and planetary composition. Voyager 1 is now headed out toward the heliopause, which it may reach before it stops transmitting. A running count of its (and Voyager 2's) current distance from the Earth and the Sun, and the two-way lightspeed delay (to and from Sol), is at http://voyager.jpl.nasa.gov/. (Don't expect to watch that last number ticking up--it will increase by a second at an interval around 25 minutes (I didn't calculate exactly).)
Voyager 2 was launched August 20, 1977. At the time, all of the gas giants were roughly lined up on one side of the solar system in such a way that Voyager 2 was able to make close flybys of all four: Jupiter, Saturn, Uranus, and Neptune. Voyager 2 made its closest passage 350,000 miles from Jupiter to avoid being deflected from its flight path by Jupiter's gravity, and to make observations of the moons. Voyager 2 transmitted the first detailed pictures of the moons, including massive volcanic plumes shooting up from Io (which a researcher had predicted in a paper published a week before the first Io photos). While Io does not have enough internal heat to be volcanically active, the strong and constantly changing gravitational stress upon Io's core creates an incredible amount of heat. The pictures of Europa showed a surprisingly flat surface, leading scientists to the conclusion that the surfaces photographed were covered in ice, with liquid water below. Of course, there were other explanations, and the Galileo mission was needed to make this theory the consensus. Several new, smaller satellites were discovered by the probe. Voyager 2 is now serving a similar purpose to Voyager 1, although there was an odd glitch in 2010 when the probe began sending back information in an incorrect format. If you have ever attempted to open a file made by a program which your computer does not support, tried to use a notepad, and obtained something like "##129@!49-0ja%%ajkl## ##", that is what the probe was effectively doing. Some people began to speculate that aliens had found the probe and were monkeying with it. NASA eventually traced the problem to a bad bit in the memory, possibly caused by a cosmic ray, and fixed it. Voyager 2 had similar equipment to Voyager 1.
The Galileo probe was intended to orbit Jupiter and make better photographs of the moons, among other mission goals. It was equipped with a visible-light camera, IR and UV spectrometers, a radiometer, a magnetometer, a particle measurement system (measuring the size and energy of particles contacted) and instruments for charged particle analysis. After the immensely successful Voyagers, this might seem to be a piece of cake. It was not.
Galileo was a mission that seemed jinxed. It went through an incredible list of failures, defects, and confusion; the spacecraft seemed to be determined to single handedly prove Murphy's Law--and O'Toole's correlary to it. At long last, the launch was scheduled: it would be the launch immediately after the Challenger launch in 1986. Of course, the Challenger blew up, causing all launches to be delayed. The probe finally launched on October 18, 1989. It reached Jupiter in December 1995. The ground sent the command to open the high gain antenna, which would be used to transmit the huge amounts of data that the probe would be able to gather back to Earth. The antenna did not open. Mission Control tried to use rapid acceleration and deceleration of the spacecraft to jerk the antenna open, and then they tried spinning it rapidly. Neither of these plans worked. The low-gain antenna which had been used for commands and telemetry had to be pressed into service to transmit the readings, which it did at a much lower rate than the high-gain antenna could have. This drastically reduced the amount of data that could be gathered. However, the probe almost completely confirmed the existence of a European ocean, measured a magnetic field around Ganymede and the temperature of Io's volcanoes, helped explain the low visibility of the Jovian rings, and indicated that there might be liquid water on Callisto as well.
Powerful telescopes have recently discovered a huge number of additional moons of Jupiter, some only a few miles in diameter. As of the time when I made that mobile, several years ago, the count was at 63 moons orbiting Jupiter.
The Juno probe was launched August 5, 2011. It is now on its way to Jupiter, and will arrive in about five years if all goes well. Its scientific payload includes: infrared and radio radiometers (measuring radio with wavelength 1.3 to 50 cm, or about 23 GHz to 6 GHz), a fluxgate magnetometer, a UV sensor which can block out areas of field to eliminate glare, and an ordinary visible light camera (which is expected to fail well before the other instruments). To protect the systems from Jovian radiation, the electronics and computer systems are sealed within a 1 cm thick titanium box and the final orbit will be highly elliptical to avoid long-term radiation exposure.
Jupiter is more massive than all of the other planets combined, but its gravitational acceleration is "only" 24.4 meters per second per second at the cloud tops. This is because it is much less dense than the terrestrial planets. It has a comparatively thin upper atmosphere consisting of hydrogen and helium with clouds of dihydrogen sulfide, ammonia, and ammonium hydrosulfide. Below this are three layers which form the bulk of the planet: a layer of liquid hydrogen (at a very high temperature, but also a very high pressure), a transition zone, and then liquid metallic hydrogen. (The pressure is so immense at that depth that hydrogen can no longer form molecules, and electrons become communal, creating an electron sea. Electron seas are normally only found in solid metals, forming metallic bonds, and that is the reason for the name.) The inner three Galilean moons are in an "orbital resonance", meaning that Europa's orbital period is twice that of Io, and Ganymede's is four times that of Io. Callisto's orbit is becoming closer to 8 times Io's.
Future missions to place a lander on Europa and explore its seas for life are under consideration. However, Clarke overestimated--by a lot--human ingenuity and determination. At the height of its first triumph, our progress to the stars was all but halted by the apparent need for inordinate defense spending and a shortsighted government. A manned mission to Jupiter may not happen for another century if current trends continue. However, some unprecedented technological breakthrough--such as controlled fusion, or even wilder possibilities such as controlled wormholes or Casimir effect energy--could shorten that schedule considerably. Some writers have speculated about the possibility of terraforming some of the moons of Jupiter, usually Europa or Ganymede. Whether that is possible or not, permanent bases on Europa (assuming we don't get complaints from the inhabitants that we're invading their territory), Ganymede, and Callisto, and possibly one day cities, could be present by 2150 or earlier. Io and Amalthea are likely to remain uninhabitable for a long time to come. It may be possible to create lighter-than-atmosphere hot hydrogen cities in Jupiter's atmosphere (which would be an interesting reversal of the normal oxygen-hydrogen interaction--oxygen would be the dangerous substance, which explodes in the normal atmosphere and shouldn't have sparks anywhere near it). However, the radiation, and the weight of the shielding that would be required to protect the inhabitants from it, might be prohibitive. But in whatever form, I for one will continue to support the exploration and future settlement of the king of the planets.
