A dark spot on Mars - Syrtis Major

Topographical image map of an area in the eastern part of Syrtis Major.

Amateur astronomers who on occasion observe Mars through the eyepiece of their telescopes are quite familiar with the region of Syrtis Major; when observing conditions are good, it can be easily identified as a dark spot on Mars.

This large volcanic region just north of Mars' equator covers an area of roughly 1300 by 1500 kilometres - about half the size of Europe.

The High Resolution Stereo Camera (HRSC), operated by the German Aerospace Center, on board ESA's Mars Express spacecraft imaged a 90 by 180 kilometre section of Syrtis Major at a resolution of about 19 metres per pixel during orbit 9487 on 8 June 2011.

Syrtis Major was first observed in 1659 by the Dutch mathematician, physicist and astronomer Christiaan Huygens (1629-1695), who was also the first to recognise Saturn's rings.

The pronounced dark colouring of the region allowed Huygens to determine Mars' rotation through the change in position of Syrtis Major in the course of his telescopic observations; he was thus able to, for the first time, estimate the length of the planet's day - and he did so relatively precisely, arriving at a value of 24.5 hours (in fact it is 24 hours and 37 minutes).

The name Syrtis Major is derived from the Roman name for the Gulf of Sidra on the coast of Libya.

Earth and Mars soon in opposition
At present, Mars is once again approaching opposition to Earth; on 2 March 2012 the Sun, Earth and Mars will be in a straight line with Earth in the middle.

Mars will rise in the east immediately after sunset and stand high in the southern sky at midnight. It is not, however, a very favourable opposition for astronomers because, due to its highly elliptical orbit, Mars will be at its furthest point from the Sun in March.

As a result, the distance between Earth and Mars will be 100.8 million kilometres; during opposition on 28 August 2003 they were only 55.8 million kilometres apart, their closest approach for nearly 60,000 years.

The images shown here were produced by the Department of Planetary Sciences and Remote Sensing at the Institute for Geological Sciences of the Freie Universitat Berlin, using HRSC image data systematically pre-processed by DLR.

They show a section of Syrtis Major at 16 degrees north and 73 degrees east. Visible on the general image map are volcanic lava flows that flooded the older highland material, leaving mesas (flat-topped mountains) behind.