Surface and contours (second part)
The terrain of Venus is very different in each hemisphere: in the north it is more mountainous, with plateaus, in the south there are vast plains of lava.
||Hemispherical view of Venus obtained from data gathered by the Magellan probe, centred on 90 degrees east (longitude). Magellan mapped 98% of the surface of Venus with a resolution approaching 100 m. This image was made from a mosaic of images. The lack of data in certain areas was filled in with those gathered by the Arecibo radar in Porto Rico, as well as altimetric data from the Venera and Pioneer-Venus probes. The image treatment used was chosen to increase the contrast and accentuate details. The colours are given as a function of altitude: low regions are in blue and higher regions are in red.
The Venusian surface is principally composed of vast, undulating plains (70 %), with no more than a 1000m change in height. These were baptised the Planitiae : some of them have a name, like Atalanta Planitia, Guinevere Planitia or Lavinia Planitia. These immense plains are also scattered with large, shallow basins (from 400 to 600 km in diameter but only 200 to 700m deep) that are the remains of impact craters.
There are also numerous plateaus and mountains. Two giant plateaus (each called Terra), resemble our continental plates:
- Ishtar Terra, situated in the northern hemisphere (latitude 70°N). It is the same size as Australia - 1000 km long by 1500 km wide. On the Eastern edge of the plateau we find the highest mountains on Venus (over 9000 m), towered over by Mount (and volcano) Maxwell which reaches 11 800 m tall for a circumference of 750 km. In the central parts and more to the west we find another raised plateau, Laksmi Planum, which, at 3000 to 4000 m, dominates the neighbouring plains. Laksmi Planum is an immense plateau of 2 500 km diameter, or 3 times the size of the Tibetan plateau;
Aphrodite Terra, situated south of the equator. This giant plateau is the size of South America, measuring about 15 000 km. It spreads from mountain ranges 4000m to the East and 9000m to the West (notably Maat Mons, Venus’ second highest summit at 9000m tall). This mountain is also a volcano that could still be active, since the Magellan probe detected a surrounding of recent lava;
Other plateaus rise up from the plains of Venus but are far less impressive than the first 2 described here. We can however still mention Alpha Regio, a region made up of basins, ridges and folds in all directions, with an average altitude of 4000 m; and Beta Regio, remarkable because we have detected here tall volcanic formations whose relatively new summits attain 4000m;
- Deep grooves, sometimes hundreds of kilometers wide, many thousands of meters deep and thousands of kilometers long, score the face of the planet (20 % of the surface of Venus). The North-west extremity of Aphrodite Terra is a large valley 250 km wide and 2250 km long, containing the lowest point of the surface of Venus, 2900m below the average level.