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Venus: the second planet of the Solar System

Uncover the past and present of Earth's co-called 'sister planet'

By Eloise Smith

Venus has always been romanticised in fiction from early history to the 20th century. Named after the Roman goddess of beauty and love (Greek: Aphrodite; Babylonian: Ishtar), it is also sometimes referred to as the ‘morning star’. It’s a similar size to Earth – albeit slightly smaller, with a mass of 4.869 x 1024 kilograms, (roughly 80% of Earth’s mass) and a radius of 6,052 kilometres. At the beginning of the 20th century, it was discovered that Venus had a similar chemical composition to Earth, and it was also thought to have a habitable atmosphere as well. As such, many science-fiction stories that depicted Venus (especially in the 1930s), described it as how Earth was during the Carboniferous and Permian periods – a prehistoric place with jungles, deserts, oceans, volcanoes and dinosaurs. Venus was the exciting new frontier to be colonised.

However, this imagining of Venus as a habitable planet was proved false after a spacecraft flew by the planet. NASA’s Mariner 2 was the first to fly by Venus in 1962 and took basic measurements of the atmosphere. The Magellan (also a NASA spacecraft) mapped 98% of Venus’s surface by radar, showing that most of the planet’s surface is covered by volcanic flows. Venus has the most volcanoes of any planet in the known solar system.

Venus has average surface temperatures of 462°C and it has a surface pressure of 90 atmospheres– the equivalent of being 1.6 kilometres underwater on Earth. It’s theorised that Venus may have had a shallow liquid water ocean and a survivable surface temperature it its early history, but the ocean has now boiled off and contributed to its thick atmosphere. Venus’s atmosphere is mainly composed of carbon dioxide with small amounts of nitrogen gas. There are clouds of sulphuric acid and sulphur dioxide that are up to 80 kilometres thick, contributing to the greenhouse effect that results in extreme surface temperatures. These clouds also give Venus its bright white appearance from space. Although further from the sun, Venus has a hotter surface than the planet Mercury; it’s so hot that spacecrafts that land on the surface don’t last long – Venera 13 (Soviet Union) lasted the longest, at just over 2 hours before its electronics overheated.

Recently, it’s been thought that if there is life on Venus, it may be in the cloud layer 50 kilometres above the surface, where the temperatures are cooler and more typical of Earth’s surface. However, at the top level of clouds, the wind speed is about 350 kilometres per hour.

To date over 40 spacecraft have visited Venus, with the most recent being the JAXA (Japanese Aerospace Exploration Agency) Akatasuki, which entered Venus’s orbit in December 2015 to study its atmosphere and surface conditions in order to further our understanding of how Earth’s atmosphere formed and to predict how it may develop in the future. As such, although we may not be able to live on Venus, the data we gather from it will still be useful in determining how we can continue to live on our own planet or others in the future.

From Issue 17

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