Wind-blown dust on volcanic Mars
Sen— Syrtis Major is a familiar dark feature on Mars to amateur astronomers, vaguely resembling the shape of India and about 1,500 km long. It was discovered way back in 1659 by Dutch scientist Christiaan Huygens who used it to tell the speed at which the planet rotates.
New images of the region have just been released, taken by Europe's Mars Express orbiting spaceprobe, which show the region in great detail. They reveal its volcanic features and the effects of windy weather.
Lave flows can be seen which flooded the older highland rock, leaving behind steep-sided hills called buttes. They stand out due to their lighter colours and eroded state. Some show ancient valleys along their flanks.
As well as individual lava flows, and lava-filled craters, the photos also allow space scientists to tell the way the prevailing winds blow in this region of the Red Planet. The direction is apparent from the way lighter-toned dust and darker sand has been dispersed around the craters and buttes in the images. This is particularly clear around the smaller craters.
The largest crater visible in the pictures has a small central peak. A small area of darker-toned dunes can be seen to the east of its floor.
Planetary scientists count the number and size of craters to help them date surfaces in the Solar System because the number of impacts increases over over time. Using this method, they have estaimated that this volcanic region must be more than three billion years old.