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Feb - Mar 98
Astronomical
Feature of the Month
SINUOUS RILLES
One feature common to large rocky bodies in our solar system are volcanoes, and with volcanoes comes lava. As lava flows down a volcano it can form into “rivers” which can harden over and make “tubes.” The cooled lava on top of a flow acts as an insulator keeping the lava in the tube molten, thus allowing it to stay liquid and travel for long distances. When the source of the lava runs out, the lava drains out of the end of the tube, leaving it hollow. As time passes, erosion wears down the roof of these tubes, which collapse and reveal the space below. These structures are called sinuous rilles. Rilles are common in the inner solar system. To the right is a photo on the Mare Imbrium region of the Moon taken by the Surveyor probe. Below left is a Magellan image of the Ovda Regio portion of Venus and below right is an image taken by Viking of the Ceraunius Tholus region on Mars. Lava tubes are common on Earth too. Hawaii, Iceland, and north-western America have them (just ask any of the Mt St Helens workshop attendees about hiking down one!). It has been suggested that a lava tube could be the ideal place to built a habitat on Mars. Lava tubes have also featured in several science fiction stories, including one by IAAA member Bill Hartmann. As common as sinuous rilles are, they undoubtedly exist on extra-solar planets too. For artistic views, how about an image of lava coursing down a rille, or a view looking out of a collapsed semi-molten tube? The possibilities are endless…
Lunar Rille Martian Rille Venusian Rille
International Association of Astronomical Artists