As on Earth, the surface temperature of Venus changes with altitude: in the lowland plains, the temperature is higher, while in the mountains it is lower. Armed with the knowledge of how high a region is, it is possible to forecast the temperature there. In the Lada Terra uplands, close to the South Pole, it was possible to prove the existence of minor variations in the forecast temperature using readings from extinct volcanoes.
The process of ascertaining the actual temperatures was carried out with readings from the VIRTIS (Visible and Infrared Thermal Imaging) spectrometer on board the ESA Venus Express probe. VIRTIS records heat radiation from wavelengths between 1.0 and 1.2 µm (near infra-red). Before that can happen, it must penetrate the cloud cover of the (on average) 460°C surface of Venus. Yellow, orange and red areas reflect the difference between the heat-flow reading and the altitude-based temperature (green), which can be in excess of ten per cent. The blue areas, on the other hand, are colder than predicted. The white areas are those for which the Magellan radar mission elicited no information, hence the absence of a correlation between forecast and measured heat radiation.
The best-surveyed area during the two-year VIRTIS mission (pictured here) stretches along the zero meridian from 50 degrees latitude (top of picture) south to near the South Pole. It was possible to take a total of 297 infra-red pictures. Due to the anomalies in temperature, it may be the case that the structure of Cocomama Tessera are the eldest, followed by the volcanic complexes in the Quetzalpetlatl Corona and Otygen Coronae, and the solidified lava flows of Juturna Fluctus and Mylitta Fluctus.
Credit: ESA/VIRTIS VenusX-Team.