Volcanoes of Io

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Volcanoes of Io

 After the detailed imaging of Io, the fourth-largest moon in the Solar System, in 1979 by Voyager 1, it was concluded that Io is the most geologically active body in the solar system. It also has the lowest amount of water of any object in the solar system. Discovered by Galileo, the moon has more than 400 active volcanoes. The moon has mountain peaks taller than Mount Everest and its surface is mainly made up of iron and sulphur. Imagine mountains taller than Everest full of sulphur and iron oxides! These volcanoes are responsible for large clouds of gases around Jupiter.

It is one of the only four volcanic active bodies in the solar system after Earth, Enceladus and Triton. Voyager 1 during its close flyby of Io experienced the strong tidal heating from the volcanoes. Also, the gravity of Jupiter changes the amount and direction of tidal heating. Lavas on Io are hundreds of kilometres long and are different from those on Earth. Lava on Earth is mainly made up of iron and magnesium, those on Io has excess sulphur and its oxides. The temperature of lava at the time of eruption is around 1300°C. Volcanic eruption leads to different shades like yellow, red, black, white and green.

Io's core, crust and surface have a large volume of sulphur. Hence during volcanic eruptions, sulphur and sulphur dioxides reach about 500 km into the space from the surface. These fumes even lead to surface changes in spacecraft that have passed by the Io. The volcanoes are also responsible for changes in Jupiter's magnetosphere. Io also has large lava lakes and valleys. 

Gish Bar Patera: 

Gish Bar Patera is one of the many active volcanic sites on Io. The sites cover 9500 sq km and have an 11 km high mountain at its southern base. The volcanic activity on this site was discovered in 1996 by the near-infrared imaging spectrometer of the Galileo spacecraft. The main composition of this crater is silicates. These silicates give patera an orange and yellow shade. There are green channels and orange flow in the centre area of the site, which may be due to the recent volcanic activities. As the lava gets cooled it gets accumulated at the edges of the patera. This means the young, newer lavas are at the centre of the patera and older, cooled lavas are at the edges. This creates a wall-like structure around the patera. As the lava becomes older the surface becomes brighter. This method is used to determine the age of lava. 

The western section of the patera is mostly green which perhaps shows the volcanic activities that occurred in late 1996 or 1997. The smaller sub-patera in the southeast part is also green, which means the lava is similar to that in the western part. The NIMS (Near Infrared Mapping Spectrometer) observed the Gish Bar Patera for straight two years (1996 and 1997).

On August 2, 1999, Galileo observed a very bright eruption during its close flyby of Io. The eruption was short-lived but it was the brightest eruption observed in the last 14 years. The temperature was about 1200 K and its area was around 200 sq km. Its location was somewhere around the east of Gish Pareta. Galileo again returned to Io in 2001-02 and this time its main target was Gish Bar Patera. Much of the patera remained unchanged during those 6 years, but the southeast sub patera was much darker than the previous observations in 1996-97. The southeast part showed many changes and the part with the most activity was the northern part of the sub patera.

A 30 km long new lava flow was also observed this time in the northwestern part. The flow of lava showed that the location of the eruption must be the central area of the patera. A total of 1500 sq km of new lava was seen in the new images. The eruption of the western part continued until late 2001. The detailed study of Gish Bar Patera showed a longer period of low to moderate volcanic activities. The lava flow in the patera showed an excess of sulphur. From these observations, astronomers finally concluded that the lava flow on Io is mostly made up of sulphur only. 

Loki Patera:

Apart from the Gish Bar Patera, Voyager 1's IRIS (Infrared Interferometer Spectrometer and Radiometer) instrument observed the volcanic activities of the Loki Patera. Loki is the largest volcanic site on the Io with a diameter of 202 km. Loki Patera also showed sulphur volcanism, similar to that on Gish Bar. Thermal emission observation showed molten rocks along the margin of the Loki Patera. During the eruption, the lava flows at a rate of 1 km per day. A new eruption will occur as soon as the crust is cooled down and when it becomes so thin to hold the eruption. Such volcanic activities are responsible for the changes in brightness of the patera every 400- 500 days.   

 Observations from the above two paterae helped astronomers to understand the physics behind the volcanic activities on the Io. These volcanoes are different and more vigorous than those on the Earth. 


     

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