Tvashtar Catena is one of the most interesting features on Jupiter’s moon Io. It is an active volcanic region located near the moon’s north pole. This ever-changing, extremely active volcanic field consists of a chain of giant volcanic paterae (caldera-like depressions).
This chain has exhibited highly variable volcanic activity in a series of observations. Tvashtar was studied by the Galileo spacecraft over several years, from late 1999 until early 2002. In December 2000, the Cassini spacecraft had a distant and brief encounter with the Jupiter system en route to Saturn, allowing for joint observations with Galileo.
During this time, a 25 kilometres (16 mi) long, 1 to 2 kilometres (0.62 to 1.2 mi) high curtain of lava was seen to erupt from one crater, a lake of superheated silicate lava erupted in the largest crater, and finally a plume of gas burst out, rising 385 kilometres (239 mi) above the moon and blanketing areas as far away as 700 kilometres (430 mi).
Therefore scientists expected that the lava flow margins or patera boundaries within Tvashtar would have changed drastically. However, the series of observations revealed little modification of this sort suggesting that the intense eruptions at Tvashtar are topographically confined.
Another eruption on Tvashtar on February 26 2007 was photographed by the New Horizons probe as it went past Jupiter en route to Pluto. The probe observed an enormous 330 kilometres (210 mi) high plume from the volcano, with an as-yet unexplained filamentary structure, made clearly visible by the background light from the sun.
In these images, taken by NASA’s Galileo spacecraft, we can see Tvashtar Catena just after an active volcanic eruption. The left one is taken on 26 Nov 1999 and the right one on 22 Feb 2000. The red and yellow lava flows we see are illustrations based upon imaging data.
The two small bright spots are sites where molten rock is exposed to the surface at the toes of lava flows. The larger orange and yellow ribbon is a cooling lava flow that is more than 60 kilometers (37 mi) long. Dark, diffuse deposits surrounding the active lava flow were not there during the November 1999 flyby of Io.