One of the first objects in the night sky seen by the naked eye that was recognized as a planet was Jupiter. In fact, though it is almost eight times further away from the sun as is the earth, it is the fourth brightest object in the night sky when it is visible.
Part of this is due to its immense size. At over 300 times the size of the earth, sunlight reflects brightly off layers of clouds made mostly of hydrogen, helium, and methane. So well does light reflect off the hydrogen, helium and methane crystals in its atmosphere that Galileo using only a small telescope identified the four inner moons, none of which is especially large for a moon, as actual moons.
Indeed it was this that got Galileo in trouble with the church, who believed at the time (and for roughly 1500 years prior to his observations) that the sun, planets, moon, stars, and in fact the entire universe, all revolved around the earth. Galileo reasoned, correctly, that since Jupiter’s moons clearly revolved around Jupiter, Earth could not be the center of the universe.
Galileo was censored by the church and was forbidden from teaching because of his blasphemous views. Only in the last couple decades did the church officially lift the censure, and by then, Galileo’s observations were no longer in doubt.
Scientists believe that at the very heart of Jupiter, there is a core of rock and metal not more than two or three times the size of the earth. Around this, they surmise, is a larger sphere of metallic hydrogen.
Metallic hydrogen is a remarkable substance. It is a liquid, but because of the huge pressures, it has metallic properties, which make it a super conductor. Since it is liquid, it moves at a different rotational speed than the rocky iron core, and this produces the greatest magnetic field in the solar system, not counting the sun. It is basically a dynamo on a planetary scale.
Jupiter, like all of the outer gaseous planets, also has rings. These were only recognized relatively recently, and the composition is believed to be ice crystals of various substances.
The outer atmosphere of the giant planet makes a full revolution in only a little less than 10 hours. With the enormous size of Jupiter, if the earth were spinning as fast, a day here would be less than an hour long. This produces extremely intense winds in the atmosphere of Jupiter, many times greater than anything ever experienced on this planet.
The gravitational pull of the planet is also far greater than the earth’s, though in a large enough pool of water, Jupiter would float.
Jupiter is also unusual in that since it is still contracting, it is generating its own heat. Jupiter’s moons are receiving more heat from Jupiter than they are from the sun, in fact.
One of the moons of Jupiter, Io, is also being stretched and squeezed between the gravity of the giant planet and another moon. The result is that Io is the most geologically active body we’ve found in the solar system, and regularly sends out volcanic plumes of sulfur.
There is so much more information about Jupiter that large books have been devoted to it. It is a truly fascinating planet and is worthy of study. Information about Jupiter and its planets continues to grow, and new surprises are being found all the time. It is worthwhile for anyone with a thirst for astronomic information to study the planet. Jupiter isn’t just the largest planet in the solar system; it is one of the most fascinating.