By Peter Forrester | March 29, 2019
I previously wrote about observation of the planet Jupiter. I thought as a bonus, some of you might like to read some more about the fifth planet from the Sun.
Jupiter is the largest of the eight planets in our Solar System. It is named after the king of the gods in Roman mythology. It is made up mostly of gases, and has a prominent storm called the Great Red Spot that has persisted for hundreds of years and is bigger than the Earth. But everyone knows these facts, right? What about some facts about the Red-spot planet that you might not know about?
Some other interesting facts about the largest planet:
Jupiter is mostly made of the lightest element, hydrogen, although about 25% of its mass is helium, the second element (only about 10% of the molecules).
The first spacecraft to fly near Jupiter was called Pioneer 10, in 1973. Pioneer 11 then flew even closer in 1974, followed by the Voyager 1 and 2, both of which flew further away in 1979 but used its gravity to speed them up on the way to the more distant planets.
Jupiter is currently being orbited by a space orbiter called Juno, which entered into orbit in 2016 and will continue until 2021, when it will be intentionally steered into the planet’s outer gas layers (to protect the moons from a collision).
This is the second spaceship to orbit the king of the planets – the previous one, Galileo, orbited from 1995 to 2003, and is named after the Italian astronomer Galileo Galilei, who improved on a recent (1608) invention: the refracting telescope, and is one of the first people known to have used it for astronomy.
Through his telescope in January 1610 he discovered the four largest moons of Jupiter, the first group of objects ever to be discovered that were definitely orbiting an object other than the Sun or Earth. The discovery of the Galilean moons provided evidence to Galileo that all objects in the solar system do not orbit the Earth (this evidence spelled the doom of the Geocentric model of the solar system, although it took a while for the theory to be fully abandoned by scientists). I will let you read for yourself of the religious controversy this caused, which led to Galilei being obliged to recant any belief that the Earth is not the center of the universe, and also spending the end of his life under house arrest.
For a long time Galileo was credited as the sole discoverer of these moons, and hence they are called the Galilean moons after him (though they were also independently discovered by Simon Marius in Germany, a month or two before that, who proposed their individual names when he published his findings in 1614). Galileo also made the first telescopic observations of several other amazing things: craters on the Earth’s Moon, analysis of sunspots, and the phases of Venus, though the telescope only magnified 30 times, much less than the powerful ones used now. He also may have seen the planet Uranus in 1612 (discovered to be a planet in 1781), and also wrote on physics and engineering.
The Galilean moons are called Callisto, Ganymede, Europa, and Io (all named after mythological lovers of the god Jupiter). Ganymede is the largest moon and 9th largest object in the Solar System, being larger than the planet Mercury. It is also the largest object in the Solar System that does not have a substantial atmosphere. Three of the four moons are larger than our Moon (all except Europa). All four are also rounded by their own weight unlike the smaller ones, and hence would be considered “dwarf planets” if they orbited the Sun.
The space mission called Galileo made some amazing discoveries, mostly about Jupiter and its moons. For example, it discovered evidence of a liquid ocean under the surface of the moon Europa, now widely considered to be the most likely place in the solar system, outside of Earth, for life to still exist (though it is likely it once existed on Mars). It also found evidence to explain the origins of Jupiter’s thin rings (much less visible than Saturn’s famous ones).
On its way to Jupiter, the probe also observed the collision of comet fragments into Jupiter in 1994 (the first impacts were not visible from Earth), as well as discovering the first known asteroid-moon system in 1993.
Speaking of moons, there are now 79 known moons of Jupiter with stable orbits, the most satellites discovered around a single object to date other than the Sun. The four Galilean ones are much bigger than all the rest of Jupiter’s moons. No more moons for Jupiter were discovered until 1892. This moon, Amalthea’s largest dimension of 250 km is less than one tenth the diameter of Europa, the smallest of the Galilean moons. Amalthea was the last planetary moon to be discovered by direct visual observation.
If Jupiter was 75 times more massive, it would be capable of nuclear fusion and be considered a star, and give off light. However, if it got just a little more massive than it is now, it is thought that it would start shrinking and become denser (in other words, its radius would actually decrease). However, it gives off more heat than it receives from the Sun, and actually does shrink by about 2 cm per year. Jupiter has 2 and a half times the mass of the other 7 planets combined. Its mass is often used as a comparison when talking about extrasolar planets that have been discovered.
It is theorized but unknown whether Jupiter has a solid core.
Jupiter could fit 10 times across the diameter of the Sun.
Every 398 days Earth overtakes Jupiter in its orbit, and then it appears to move backwards for a few days.
Jupiter rotates about every 10 hours (the fastest of any planet in the Solar System). The cloud layers at the poles orbit at a different rate than those at the equator of Jupiter, about 5 minutes longer, although the planet’s official rotation rate is based on measurements of its magnetosphere by radio waves.
I could go on and on, but you can all read as much of this as you want over on Wikipedia or Google other sources. Until next time, adieu!
References:
Wikipedia. (2019, March 15). Comet Shoemaker-Levy 9. Retrieved from https://en.wikipedia.org/wiki/Comet_Shoemaker%E2%80%93Levy_9 .
Wikipedia. (2019, March 13). Galileo (spacecraft). Retrieved from https://en.wikipedia.org/wiki/Galileo_(spacecraft).
Wikipedia. (2019, March 18). Galileo Galilei. Retrieved from https://en.wikipedia.org/wiki/Galileo_Galilei.
Wikipedia. (2019, March 22). Juno (spacecraft). Retrieved from https://en.wikipedia.org/wiki/Juno_(spacecraft).
Wikipedia. (2019, March 26). Jupiter. Retrieved from https://en.wikipedia.org/wiki/Jupiter.
Milton Observer 