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.