Clouds on Venus

This week’s guess the planet image comes from Venus. It was taken by the Galileo spacecraft in 1990 and credit goes to NASA’s Jet Propulsion Laboratory. The ultimate destination of the Galileo probe was the Jupiter system, and it became the first spacecraft to enter Jupiter orbit. However in order to get there it had to make several flybys of other planets in order to increase its speed. This is called a “gravity assist” or slingshot manoeuvre and is often used to accelerate spacecraft on route to the outer solar system.

This image, from one of the spacecraft’s flybys shows cloud patterns in the atmosphere of Venus. Clearly this is a false colour image. The write up that accompanies this image in the NASA gallery explains that this is to “emphasize the subtle contrasts in the cloud markings and to indicate that it was taken through a violet filter”. False colour images are often used in planetary science, so it is always important to understand what you are looking at, and how the way in which the data were collected and processed influence what you can see.

The atmosphere of Venus is dramatically different to that of Earth. It is composed primarily of carbon dioxide. The clouds visible in this image are made of sulphuric acid. These clouds are largely opaque and make direct observation of the Venusian surface quite difficult. The atmospheric composition has also resulted in a runaway greenhouse effect, leading to temperatures at the surface being much higher than those on Earth. The pressure at the surface is also extremely high, making it a very difficult environment to explore.

The soviet Venera 7 probe was the first spacecraft to land on Venus, or indeed any other planet. It touched down in 1970 although it had a somewhat rocky landing, and was nearly lost.

This image of the surface was captured by the Venera9 lander in 1975. This was the first spacecraft to return images from the planet’s surface. These landers required an extensive cooling system to remain operational on the surface, and had to be built to resist the high pressure.  

The surface of Venus may not lend itself for human habitation, but ironically the upper atmosphere, above the cloud layer, might be far more hospitable. As there is an elevation, around 50 km above the surface of Venus where the temperature and pressure are quite Earth-like. It has been suggested that floating cities could be constructed here. A breathable mix of gasses is less dense than those that make up Venus’ atmosphere, so could be used as a lifting gas in the same way that hydrogen and helium are on Earth. Humans could live inside a balloon, safely above the hellish surface of the planet.

Image Credits:

Galileo image of Venus: NASA JPL

Surface of Venus from Venera 9: USSR Space Program via Wikipedia.