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30 Interesting Io Facts: The Volcanic Moon of Jupiter

Io – that’s perhaps the smallest name of any celestial object known to humans. It is one of the 67 moons of Jupiter and is quite an interesting object hanging out there in the void. In this article on Io facts, we are going to share some of the most mind-blowing information about this interesting Jovian moon. So, sit tight. It is going to be one hell of a read…

Interesting Io Facts: 1-5 | About Io – Discovery, Position

1. Io was discovered on January 8, 1610. The discoverer was Galileo Galilei. It was one of the four Jovian moons that were discovered by Galileo and hence, it is often referred to as the Galilean Moon of Jupiter. The other three moons that were discovered by Galileo are:

2. If we are to compare the volume and mass of the four Galilean moons of Jupiter, they ranking they get is:

  • First – Ganymede
  • Second – Castillo
  • Third – Io
  • Fourth – Europa

3. If we are to arrange all 67 moons of Jupiter in order of distance from Jupiter, Io takes the 5th spot. However, if we are to arrange the four Galilean moons in order of distance from Jupiter, Io takes the 1st spot.

4. Actually, Io was not discovered on January 8. It was discovered on January 7, 1610 by Galileo. However, that night, Galileo failed to distinguish between Europa and Io. Things became clear to him on the next night, that is, 8th January. Hence, it is said that the discovery was done on 8th January.

5. Discovery of Io, Europa, Callisto and Ganymede was the first ever discovery of any moon orbiting any other planet but Earth.

Interesting Io Facts: 6-10 | Incorrect Credit, Naming of Io

6. Galileo’s discovery was stunning. It was his discovery of these moons that eventually led people to believe that planets orbit Sun and NOT the solar system orbiting Earth. Galileo gets a lot of credit for this.

7. The truth however is that it was ancient Indian mathematician-astronomer by the name Aryabhata (born 470 CE) who actually told that planets orbit Sun and not the solar system orbiting Earth. His observations and studies are all recorded in his work ‘Aryabhatiya’ – an astronomical treatise. Still, to this day, West refuses to give him the credit he deserves.

8. Nonetheless, coming back to Io, Galileo actually named the Jovian moon as Jupiter I (because it was the first Jovian moon he discovered). The name he gave was used till mid 1800’s when it became clear that using numbers as names will only create a lot of confusion.

9. So, in mid 1800’s the name of Jupiter I was changed to Io. Io comes from Greek mythology where Io was the priestess of Hera – the wife of Zeus. Io was the daughter of Inachus, who was in turn, the King of Argos.

10. According to Greek mythology, Zeus fell in love with Io. However, he was afraid that Hera would catch him with Io. So, to avoid being caught, Zeus turned Io into a cow.

Interesting Io Facts: 11-15 | Numbers and Figures of Io

11. Age of Io: Io is just as old as Jupiter itself. This means that Io is around 4.5 billion years old and was formed around the same time when Jupiter was born.

12. Distance between Io and Jupiter: Io hangs at a distance of 421,700 kilometers. This is the mean distance. The farthest Io goes from Jupiter is 423,400 kilometers (Apoapsis) and the closest it gets to Jupiter is 420,000 kilometers (Periapsis). This is known as the orbital distance of Io from Jupiter.

13. Orbital time and speed: Io orbits around Jupiter in 42.45936086 hours. That is equivalent to 1.769 (or ~ 1.77) Earth days. The moon travels around Jupiter at as speed of 17.334 km/s.

14. Measurements of Io: The measurements here refer to the following:

  • Mean Radius of Io: 1,821.6 ± 0.5 kilometers.
  • Surface Area of Io: 41,910,000 km2.
  • Mass of Io: (8.931938 ± 0.000018)×1022 kg.
  • Volume of Io: 2.53×1010 km3.
  • Mean Density of Io: 3.528 ± 0.006 g/cm3.
  • Minimum Surface Temperature: 90 K or -183.15°C.
  • Maximum Surface Temperature: 130 K or -143.15°C.
  • Mean Surface Temperature: 110 K or -163.15°C

15. Gravity and escape velocity on Io: Surface gravity on Io stands at 1.796 m/s2. That is less than the gravity on Earth. Earth has a gravity of 9.807 m/s2 while our Moon has a gravity of 1.622 m/s2. Escape velocity for Io is 2.558 km/s.

Interesting Io Facts: 16-20 | Io Characteristics – Inside and Surface

16. Based on data available from various spacecrafts like Galileo and Voyager, scientists have used several computer models to determine that the crust of Io and its mantle are rich in silicate. It’s core on the other hand is either rich in just iron or it is rich in iron-sulfide.

17. 20% of the mass of Io comes from its metallic core. Scientists say that radius of the core is dependent on the sulfur amount present in the core. Here are the two estimates that scientists give:

  • If the core is made entirely of iron, the radius of the core is between: 350 km and 650 km.
  • If the core is made of a combination of sulfur and iron, the radius of the core is between: 550 km and 900 km.

18. Scientists say that 75% of the mantle of Io is made of forsterite – a mineral that is rich in magnesium. The iron content in the mantle is higher than what is present in mantles of our Earth and our Moon. The iron content in Io’s mantle is greater than that of Mars.

19. The surface of Io lacks impact craters. Rather, its surface is covered with smooth plains and lots of tall pits and mountains that significantly vary in size and shape. The surface is also covered with volcanic lava flows.

20. The surface of Io is covered with a wide range of colorful material that are basically sulfur compounds. Scientist compare the surface of Io with either a pizza or a rotten orange.

Interesting Io Facts: 21-25 | Io Characteristics – Surface (Colors)

21. Scientists speculated that the absence of impact crater on Io’s surface is actually caused by continuous lava flows that cover those craters. This speculation was eventually confirmed when scientists received images from Voyager I. That spacecraft managed to capture 9 active volcanoes on the surface of Io.

22. Io’s surface has a very colorful appearance and that’s caused by volcanism that deposits material on its surface. The materials that are deposited on its surface by its volcanoes include sulfur dioxide, sulfur and various silicates such as orthopyroxene.

23. If there is something that is found widely across the surface of Io is the sulfur dioxide frost. Large regions of the surface of Io are covered with gray or white material.

24. Many yellow regions or yellow-green regions seen on surface of Io are basically formed by sulfur. However, the sulfur deposits that are found in polar regions and mid-latitude regions often get radiation damage, breaking up the sulfur and creating the red-brown polar regions.

25. The surface of Io also gets painted with silicate materials and sulfurous materials that come out in form of umbrella-shaped plumes during explosive volcanism. Depending on the sulfur dioxide and sulfur content of the plume, the plume may look white or red.

Interesting Io Facts: 26-30 | Characteristics – Surface Mountains

26. Io is dotted with several mountains as well. So far anywhere between 100 and 150 mountains are assumed to be present on it surface with an average height of 4 miles or 6 kilometers. The Boösaule Montes located at the south reach a maximum height of 17.5 ± 1.5 kilometers of 10.9 ± 0.9 miles.

27. In terms of length, the mountains on pretty long with the average length stretching over 98 miles or 157 kilometers.

28. Since the mountains on Io lack any global tectonic patter that we see on Earth, scientists believe that these mountains are actually not made of sulfur. Rather, the hypothesis is that these mountains are made of silicate rocks.

29. Interestingly the Ioian mountains are tectonic structures. They are formed by compressive stresses at the lithosphere base resulting in uplifting of the crust and thus, formation of mountains. No, volcanoes on the Jovian moon do not form the mountains.

30. Another important feature of the Ioian mountains is they have a lot of plateaus (flat tops). Funny that most of the mountains on Io go through degradation via mass wasting – a phenomenon in which large landslides leads to deposits at the base of the mountains.

That concludes our list of interesting Io facts here. However, we are far from presenting a complete list here. This is the reason why, we will creating another article on Io facts that will cover a few more interesting aspects of Io but mostly focusing on its atmosphere.

Sources: 1, 2