Although Venus has a similar size, mass, gravity and bulk composition as the Earth, the conditions on its surface are unlike anything on Earth. Venus is characterized by a massive carbon dioxide atmosphere which gives a surface pressure that is over 90 times the sea-level pressure here on Earth and a hellish average surface temperature of 740 degrees Kelvin. Near the surface of Venus, the temperature is above the melting points of metals such as lead, tin and zinc. However, at an altitude of 50 kilometres up in the Venusian atmosphere, the atmospheric temperature and pressure are similar to those found on the Earth at sea-level.
Radar observations of the surface of Venus have shown a brightening of the radar reflection from higher elevation regions on Venus. It is believed that the substance responsible for the higher radar reflectivity formed from a process that is similar to the formation of snow on Earth, albeit at a far higher temperature. The furnace-like environment of Venus’ lower atmosphere means that water is not a possible candidate material for this highly reflective substance. Instead, the highly reflective substance is likely to be a heavy metal frost consisting of one or more types of volatile compounds. In this case, the Venusian highlands serve as areas where the temperature is cool enough for these heavy metal compounds to condense and be deposited as frost. The source of these heavy metal compounds is likely to be volcanic in nature. On Earth, these heavy metal compounds are stable solids but the high temperatures on Venus allow many of these compounds to become volatile.
This is a radar image from NASA’s Magellan spacecraft centred along the eastern edge of Lakshmi Planum and the western edge of Maxwell Montes. The highlands on the right are covered in bright “snow” and are 5 kilometres above the above the adjacent plains in Lakshmi Planum. Credit: NASA/JPL
Standing 11 kilometres high, Maxwell Montes is the tallest mountain on Venus and with a temperature of 650 degrees Kelvin at its summit, the top of Maxwell Montes is the coolest location on the surface of Venus. Radar observations of Maxwell Montes show that most of the mountain is covered a layer of highly reflective substance. For this reason, Maxwell Montes serves as a good example of a cool highland region that is covered by a layer of heavy metal frost and as a “snow-capped mountain” on Earth’s scorching planetary neighbour.