IO: active volcanoes and sulphurous lavas

Io is the most active planetary body in the solar system.  Even now, dozens of volcanoes eject gas and debris clouds on it. The eruptions spread into the shape of an umbrella; falling back onto the surface, they form a ring around the volcanic centre. There are many volcanoes from which lava flows out regularly. The volcanoes are not high mountains, like on Earth, because Io’s lava is very fluid and easy to flow away. The surface is covered mostly with lava flows coloured yellow by sulphur and a few collapsed volcanic craters, but no impact craters. The surface is made up of layers of lava flows covering each other. There are approximately one hundred mountains, which are pushed up in one piece from the crust along near-surface cracks; they are not volcanoes, but masses of rock derived from the old surface. Io is the nearest large moon to Jupiter, so the attraction of Jupiter affects it the strongest, along with strong tugs from the three large moons orbiting further from Jupiter. This force produces the heat required for volcanism and gives the pressure which raises the mountains.


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Io is a mythological girl who was so beautiful that Zeus seduced her and changed into a heifer to hide, but Hera, his wife found out about the trick and sent gadflies onto the cow-shaped Io, which chased her all over Greece, where she crossed the Bosporus (= Ox-ford ). Shapes on the surface of Io are named after the places and figures of this story, plus other gods associated with volcanoes. 
What are the six-sided features on Io? No features on Io are actually hexagons, as shown on the map, those the artist’s visual concept to represent Io’s diverse surface features in a more ordered way.
How many volcanoes are there altogether on Io? Approximately 425 calderas can be found on its surface, of which approx. 200 volcanoes are recently active.
Is there life on Io? We do not know, but it is unlikely.
Why is its surface not covered with ice? Io is a moon of Jupiter, yet it is an Earth-like rock planet. Its surface is covered with lava coming from the deep.
Can people fly without a spaceship? On the ISS space station there is a space suit called Extravehicular Mobility Unit (EMU), in which astronauts can travel freely around (outside) the space station.
What are calderas? Magma (hot, fluid rock)  accumulates under the volcano, in a cavity. This material ejects onto the surface when the volcano erupts (this is called lava), and the underground cavity becomes empty and collapses. This collapsed surface is the caldera. From some of them long lava flows emerge.



  • Body type: moon
  • Body composition: rocky
  • Atmosphere: no
  • Liquid: lava
  • Endogenic features: volcanic calderas, lava flows, volcanic plumes and their deposits, tectonic mountain blocks
  • Exogenic features: “snow” fields (bright plains from precipitating gases from volcanic eruptions)
  • Cosmogenic  features: no craters observed, because lava fields are produced faster than impact craters and lavas bury old craters
  • Common features: calderas, mountain blocks
  • Rare features: lava channels, active volcanoes (few dozen)
  • Life limiting parameter: no atmosphere, high radiation (from Jupiter)
  • Nomenclature: Gods of fire and Sun, and places and people associated with the Io myth (in greek mythology).
  • Highest point: Boösaule Montes, a group of mountain peaks
  • Age: less than 10 million years old (volcanically so active that new volcanic material covers all surface).


    Io map: (Illustrator: Dóri Sirály) The map of Io is the most abstract one: its landforms are shown in hexagonal symbols. This approach gives the appearance of honeycomb cells, which is partly related to the yellow color of sulfur and partly to the Io mythology, of which some scenes are also shown. The main task for the graphic artist was to find a balance between scientific accuracy and the needs of the children, all using the minimalist geometric style. The main character is a young astronaut chasing bees (or horseflies). Mountain heights are shown for the highest mountains. Major active volcanic centers are shown as ejecting material. Black calderas are filled with lava, yellow calderas are lava-free. This map has a very simple legend that explains complicated orbital and physical parameters without words, using only visual elements

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