Home » Space » 20 Io Moon Facts: All About Atmosphere of Io

20 Io Moon Facts: All About Atmosphere of Io

In our last article on Io facts – the Jovian moon, we focused on a few important things like its discovery, its mass, distance of the moon from its host planet, gravity, characteristics like surface, interior composition, mountains etc. What we did not cover was its atmosphere. It is quite interesting. That’s the reason why we decided to create a separate article on Io moon facts, focusing primarily on its atmosphere. We will throw in a few extra information if we can. So, let’s begin…

Io Moon Facts: 1-5 | Atmosphere

1. Since our own Moon has no atmosphere, it is logical to think that this Jovian moon will not have an atmosphere of its own. Quite the contrary, Io has its very own atmosphere. And yes, it is unlike what we have on our Earth.

2. Atmosphere of Io is thin, really thin. The gases that make up Io’s atmosphere include sulfur dioxide as the primary component. Mind it. SO2 is the primary component. This means there are other components as well.

3. The other components that make up Io’s atmosphere include SO or sulfur monoxide, NaCl or Sodium Chloride (yes our table salt) and there’s atomic oxygen as well as atomic sulfur present in the atmosphere.

4. Well, no need to get too excited here. Though there’s oxygen in Io’s atmosphere, it is too scanty to support aerobic life. And scientists don’t yet know if there is anaerobic life present on Io or not.

5. One really interesting thing about Io’s atmosphere is its temperature and density variation depending upon several factors like volcanic activity, latitude, time of the day, abundance of surface frost etc.

Io Moon Facts: 6-10 | Atmosphere

6. Wondering what’s the maximum atmospheric pressure out there on Io? Scientists say that it ranges anywhere between 3.3 x 10-5 pascals and 3 x 10-4 pascals.

7. This maximum atmospheric pressure on Io is present on the anti-Jupiter hemisphere of the Jovian moon and also at its equator. This maximum atmospheric pressure is also seen when the temperature of surface frost is at peak and even during early afternoons.

8. That’s maximum. What about the minimum? The minimum atmospheric pressure comes at night. That’s when the atmospheric pressure dips all the way down to between 0.1 x 10-7 pascals and 1 x 10-7 pascals.

9. Here is something really interesting. The magnetosphere of the host planet, that is, Jupiter, actually strips Io’s atmosphere of the gas.

10. The gas that escapes the atmosphere of Io can land in two possible places:

  • It can land in the neutral cloud that is known for surrounding Io.
  • It can land in the plasma torus of Io.

Wondering what plasma torus is? Plasma torus is a ring created by ionized particles. This ring is known for sharing not only the orbit of Io but also known for co-rotating with Jupiter’s magnetosphere.

Now the question is, what really is a torus? It is a concept in geometry. It is a surface of revolution that is generated by revolving a circle in a 3D space ensuring that the plane of the circle and the axis of the circle are on the same plane (called coplanar). See the image below:


Io Moon Facts: 11-15 | Atmosphere

11. Did you know that the magnetosphere of Jupiter manages to strip out nearly 1 ton of material from the atmosphere of Io?

12. So, the atmosphere must be quickly replenished, right? Exactly that’s what happens. The volcanoes on Io manage to pump in around 104 kilos of sulfur dioxide into the atmosphere of Io every single second. That’s far more than what is stripped off.

13. Here is yet another interesting thing. The SO2 that comes out of the volcanoes are frozen and they fall down as frost. This frost undergoes sublimation (changing state directly into gas from solid) by sunlight.

14. Scientists can say that the atmosphere is mostly sublimation-driven because the atmosphere is densest:

  • In Io’s anti-Jupiter hemisphere.
  • When Io is closer to Sun.

15. The other constituents of the atmosphere of Io comes from three sources namely:

  • Chemical breakdown of SO2 by ultraviolet radiation of the Sun.
  • Direct volcanic outgassing.
  • Sputtering (bombardment with particles from magnetosphere of Jupiter) of deposits found on surface of Io.

Io Moon Facts: 16-20 | Atmosphere

16. Io has been imaged when the moon was in eclipse. The high resolution images show that Io (during eclipse) has aurora-like glow. This happens because charged particles from magnetic field of Jupiter hits the atmosphere of Io.

17. Unlike in case of planets, the aurorae of Io are actually far brighter near equator. This happens because the Jovian moon lacks its own intrinsic magnetic field.

18. The multi-colored aurorae of the Jovian moon is actually caused by the emission from different components of the moon’s atmosphere. For instance, blue comes from emissions from volcanic gases like SO2.

19. The red color is emitted by the oxygen content of the atmosphere of Io. Green on the other hand is because of sodium.

20. Because Io doesn’t have a thick atmosphere, if probes are sent by any space agency for landing on Io, the probe will not required an aeroshell-style heatshield encasement. Rather, retrothrusters for soft landing will suffice.

Io Moon Facts: Some Io Trivia for You

1. Io is tidally locked with Jupiter. This means that one side of Io always faces Jupiter just as one side of our Moon always faces our Earth.

2. Io along with Earth and Venus are the only celestial bodies in our very own Solar System which is known for have active volcanoes that spew out basaltic lava.

Note: There are two type of volcanoes that you can find in the Solar System. They are the normal volcanoes as we know on Earth and then there are colder versions of volcanoes known as Cryovolcanoes. Cryovolcanoes are those volcanoes that do not spew out basaltic lava. Instead they spew other volatile material like water, ammonia etc. Here is a list of different celestial bodies where you can find volcanoes (normal and cryovolcanoes):

Moon (our moon) – There are volcanoes on moon but they are inactive now.

Mars – There are volcanoes but they are inactive.

Earth – There are active volcanoes that spew basaltic lava.

Venus – Astronomers believe that there are active volcanoes on the planet. The probe called Venus Express detected various spots on the planet where temperatures have risen and fallen rapidly, suggesting lava flows that cause the brief temperature spikes.

Titan (the largest moon of Saturn) – It may have cryovolcanoes that erupt ammonia, water and other volatile liquids but not basaltic lava.

Enceladus (another moon of Saturn) – There are over 100 geysers that spew out water and various other chemicals periodically. So, it does have active cryovolcanoes.

Triton (the largest moon of Neptune) – It has very active cryovolcanoes and they spew out ice and other material but not basaltic lava.

3. Io has 400 active volcanoes on its surface. This makes Io the most volcanically active celestial body in our Solar System. Even Earth’s volcanoes cannot match Io.

4. The volcanic eruptions are pretty violent. Some volcanoes on Io can spew materials as high as 330 kilometers above the surface of Io.

5. Pioneer 10, Pioneer 11, Voyager 1, Voyager 2 and Galileo spacecrafts have flown by Io. However, Voyager 1 was the first one to send back Io’s images. The next ones to do so were Voyager 2 and Galileo spacecrafts. So, all the information we have on Io actually comes from Voyager and Galileo spacecrafts.

Sources: 1, 2, 3