por What is Io?
Io It is part of the four Galilean satellites (Io, Europa, Ganymede, Callisto) so called because they were discovered in 1610 by Galileo Galilei with a rudimentary telescope that he himself built.
It is the third in size of those of the Galilean satellites and of the remaining 75 satellites of Jupiter. In order of orbital radius, it is the fifth satellite and the first of the Galileans. Its name comes from Greek mythology, in which Io she was one of the many maidens with whom the god Zeus, also called Jupiter in Roman mythology, fell in love.
Io has a third of the Earth’s diameter and a size similar to that of our satellite the Moon. Compared to the other satellites in the solar system, Io It takes fifth place in size, preceded by the Moon.
the surface of Io It has mountain ranges that stand out on the extensive plains. No impact craters are observed, which indicates that they have been erased by its great geological and volcanic activity, considered the largest of all in the solar system. Its volcanoes produce clouds of sulfur compounds that rise 500 km above its surface.
There are hundreds of mountains on its surface, some higher than Mount Everest, which have been formed due to the intense volcanism of the satellite.
The discovery of Io in 1610 and of the other Galilean satellites changed the perspective of our position in the universe, since at that time it was thought that we were the center of everything.
By discovering “other worlds”, as Galileo called the satellites revolving around Jupiter, the idea, proposed by Copernicus, that our planet revolved around the Sun became more feasible and palpable.
Thanks to Io, the first measurement of the speed of light was made by the Danish astronomer Ole Christensen Rømer in 1676. ÉHe noticed that the duration of the eclipse of Io by Jupiter was 22 minutes shorter when Earth was closest to Jupiter than when it was furthest away.
That was the time it took light to travel the terrestrial orbital diameter, from there Rømer estimated 225,000 km/s for the speed of light, 25% less than the currently accepted value.
General characteristics of Io
By the time the Voyager mission got close to the Jovian system it found eight volcanoes erupting on Io, and the Galileo mission, while unable to get very close to the satellite, returned excellent-resolution images of the volcanoes. As many as 100 erupting volcanoes were detected by this probe.
The main physical characteristics of Io are:
Its diameter is 3,643.2 km.
Mass: 8.94 x 1022 kg.
Average density 3.55 g/cm3.
Surface temperature: (ºC): -143 to -168
The acceleration due to gravity on its surface is 1.81 m/s2 or 0.185g.
Rotation period: 1d 18h 27.6m
Translation period: 1d 18h 27.6m.
Atmosphere composed of 100% sulfur dioxide (SO2).
Summary of the main features of Io
Composition
The most outstanding characteristic of Io is its yellow color, which is due to the sulfur deposited on the essentially volcanic surface. For this reason, although the impacts due to the meteorites attracted by the giant Jupiter are frequent, they are quickly erased.
It is thought that basalts abound on the satellite, as always, colored yellow by sulphide.
In the mantle (see below for details of the internal structure) molten silicates abound, while the crust is composed of sulfur and frozen sulfur dioxide.
Io is the densest satellite in the solar system (3.53 g/cc) and is comparable to rocky planets. The silicate rock of the mantle envelops a core of molten iron sulfide.
Finally, Io’s atmosphere is composed of almost 100% sulfur dioxide.
Atmosphere
Spectral analyzes reveal a tenuous atmosphere of sulfur dioxide. Even though hundreds of active volcanoes spew out a ton of gases per second, the satellite cannot retain them due to low gravity and the escape velocity of the satellite is not very high either.
Additionally, ionized atoms that leave Io’s adjacencies are trapped by Jupiter’s magnetic field, forming a kind of doughnut on its orbit. It is these sulfur ions that print the reddish color to the tiny and nearby satellite Amalthea, whose orbit is below that of Io.
The pressure of the tenuous and thin atmosphere is very low and its temperature is less than -140ºC.
Io’s surface is hostile to humans, due to its low temperatures, its toxic atmosphere and the enormous radiation, since the satellite is within Jupiter’s radiation belts.
Io’s atmosphere turns off and on
Due to the orbital movement of Io there is a time in which the satellite stops receiving the light of the Sun, since Jupiter eclipses it. This period lasts 2 hours and as expected, the temperature drops.
Indeed, when Io faces the Sun its temperature is -143 ºC, but when it is eclipsed by the gigantic Jupiter its temperature can drop to -168 ºC.
During the eclipse the tenuous atmosphere of the satellite condenses on the surface, forming sulfur dioxide ice and disappears completely.
Then, when the eclipse ceases and the temperature begins to rise, the condensed sulfur dioxide evaporates and Io’s tenuous atmosphere returns. This is the conclusion reached in 2016 by a NASA team.
So, the atmosphere of Io is not formed by the gases of the volcanoes, but by the sublimation of the ice on its surface.
Translation movement
Io completes one revolution around Jupiter in 1.7 Earth days, and each time the satellite is eclipsed by its host planet, during a period of 2 hours.
Due to the enormous tidal force Io’s orbit should be circular, however this is not the case due to the interaction with the other Galilean moons, with which they are in orbital resonance.
When Io turns 4 times, Europa turns 2 and Ganymede 1. The curious phenomenon can be seen in the following animation:
This interaction causes the orbit of the satellite to have some eccentricity, calculated at 0.0041.
The minor orbital radius (periastrum or perihelion) of Io is 420,000 km, while the major orbital radius (apoastro or aphelion) is 423,400 km, giving a mean orbital radius of 421,600 km.
The orbital plane is inclined with respect to the Earth’s orbital plane by 0.040°.
Io is considered to be the closest satellite to Jupiter, but there are actually four more, albeit extremely small, satellites below its orbit.
In fact, Io is 23 times larger than the largest of these small satellites, which are probably meteorites trapped in Jupiter’s gravity.
The names of the tiny moons, in order of closeness to their host planet are: Metis, Adrastea, Amalthea, and Thebe.
After Io’s orbit, the next satellite is a Galilean satellite: Europa.
Despite being very close to Io, Europa is completely different in composition and structure. It is believed that this is so because this small difference in the orbital radius (249,000 km) makes the tidal force on Europa much less.
Io’s orbit and Jupiter’s magnetosphere
Io’s volcanoes spew ionized sulfur atoms into space that are trapped by Jupiter’s magnetic field, forming a plasma-conducting donut that coincides with the satellite’s orbit.
It is Jupiter’s own magnetic field that pulls the ionized material out of Io’s tenuous atmosphere.
The phenomenon creates a current of 3 million amps that intensifies Jupiter’s already powerful magnetic field to more than double what it would be if Io did not exist.
Rotatory motion
The period of rotation around its own axis coincides with the orbital period of the satellite, which is caused by the tidal force that Jupiter exerts on Io, its value being 1 day, 18 hours and 27.6 seconds.
The inclination of the axis of rotation is negligible.
Internal structure
Since its average density is 3.5 g/cm3, it is concluded that the interior structure of the satellite is rocky. Spectral analyzes of Io do not reveal the presence of water, so the existence of ice is unlikely.
According to calculations based on the collected data, it is believed that the satellite has a small core iron or iron mixed with sulfur.
followed by a rocky mantle deep and partially molten, and a thin, rocky crust.
The surface presents the colors of a poorly made pizza: red, pale yellow, brown and orange.
Originally it was thought that the Cortex It was sulfur, but infrared measurements reveal that volcanoes erupt lava at 1500ºC, indicating that it is not just sulfur (which boils at 550ºC), there is also molten rock.
Other evidence of the presence of rock is the existence of some mountains with heights twice that of Mount Everest. Sulfur alone would not have the strength to explain these formations.
The internal structure of Io according to theoretical models is summarized in the following illustration:
Geology of Io
The geological activity of a planet or satellite is driven by the heat from its interior. And the best example is Io, the innermost of Jupiter’s largest satellites.
The enormous mass of its host planet is a great attractor for meteorites, like the remembered Shoemaker-Levy 9 in 1994, however Io does not show impact craters and the reason is that the intense volcanic activity erases them.
Io has more than 150 active volcanoes that spew enough ash to bury impact craters. Io’s volcanism is much more intense than Earth’s and is the largest in the entire solar system.
What powers the eruptions of Io’s volcanoes is the sulfur dissolved in the magma, which when released its pressure propels the magma spewing ash and gas up to 500m high.
The ash returns to the satellite’s surface, producing layers of debris around the volcanoes.
Whitish areas are observed on the surface of Io due to frozen sulfur dioxide. In the cracks of the faults, molten lava flows and erupts upwards.
Where does Io’s energy come from?
Since Io is slightly larger than the Moon, which is cold and geologically dead, one wonders where the energy for this small Jovian satellite comes from.
It cannot be the remaining heat of formation, because Io is not large enough to retain it. Nor is it the radioactive disintegration of its interior, since in fact the energy dissipated by its volcanoes easily triples the radiation heat emanating from a body of such size.
Io’s power source is tidal forcedue to the immense gravity of Jupiter and due to its proximity to it.
This force is so great that the surface of the satellite rises and falls 100 m. The friction between the rocks is what produces this enormous heat, much greater by the way than that of the terrestrial tidal forces, which barely move the solid surface of the continents by a few centimeters.
The huge…