Venus

Venus has been hard to miss in the evening sky over the last few months. It is named Venus after the Roman goddess of love or beauty. You can see why when you see Venus blazing away in the sky.

Venus shining brightly in May 2020 Credit: Paul Smith

The reason Venus is so bright in the sky, is that it has a very thick atmosphere and reflects large amounts (about 70%) of the sunlight that falls on it. But what is below the clouds of Venus?

Venus Cloud Tops Viewed by Hubble. This is a NASA Hubble Space Telescope ultraviolet-light image of the planet Venus, taken on January 24 1995, when Venus was at a distance of 70.6 million miles (113.6 million kilometres) from Earth. Credit: NASA

Venus is often referred to as Earth’s evil twin. The reason for this, is that Venus and Earth are similar size and mass but they are vastly different in other ways. The atmosphere on Venus is the thickest of all of the rocky planets. It is 96% carbon dioxide and the air pressure at the surface is 92 times that on Earth. This is equivalent to the pressure at nearly 1km under the sea! Scientists think the atmosphere of Venus was much more similar to Earth in the past, and there were once liquid water oceans on the surface.

As the Sun ages it slowly gets bigger. Scientists think that as the Sun grew Venus heated up. Eventually the heat started to evaporate the water from the oceans, and this extra water in the atmosphere acted as more insulation trapping even more heat. This made the problem even worse, with more water evaporating and in turn trapping more heat. The process is known as a runaway greenhouse effect. Earth has tectonic plates which float around on the molten core of the planet. you can imagine them as a layer of cracked ice on a frozen lake. As these moved around very slowly, they sink under, move over and grind past each other. These movements cause events like volcanoes and earthquakes. However, this has another vital function as part of the carbon cycle. On Earth volcanoes erupt and release carbon dioxide. Through other processes the carbon gets trapped in rocks. These rocks then get pulled into the core of the Earth by the movement of the tectonic plates, completing the cycle. The water in the oceans acts as a lubricator for the tectonic plates, allowing them to move.

This was the situation on Venus too until the runaway greenhouse effect got so bad that the oceans dried up and the plates stopped moving. Once the plates stopped moving the carbon cycle stopped and the carbon dioxide built up in the atmosphere making a really bad situation even worse. The result was the thick atmosphere we see today. The atmosphere is so thick and insulates the planet so well, that the mean surface temperature is 462oC. The Sun continues to grow, and in roughly 1 billion years the Earth will meet the same faith as Venus. Unless we do nothing about global warming, in which case it could be a lot sooner.

The surface of Venus has large, smooth volcanic planes. There are a lot of very large volcanoes on the planet. There are also some mountains, ridges and valleys. Most of the surface features on Venus are named after mythological or historical women. However, there are some exceptions that were named before this convention was adopted. Another interesting fact, is that Venus spins in the opposite direction to the rest of the planets. Looking down from what would be the Earth’s north pole, the most of the planets appear to spin an anticlockwise direct but Venus spins in a clockwise direction. Scientists think that when Venus formed it did spin in the same direction is as the other planets. It is thought that atmospheric tides slowed down the spin of the planet until it eventually stopped, and started to spin backwards.

Venus (middle right) and the crescent Moon in May 2020 Credit: Paul Smith

Venus is closer to the Sun than the Earth, so it always seen in the sky either before sunrise or after sunset. In ancient times, people thought that the morning appearance of Venus and the evening one were two different stars. When viewed through a telescope, Venus shows phases similar to the Moon. Galileo observed these phases in early 17th century for the first time. The only way Venus could have phases like this was if it orbiting the Sun and this was more evidence that the Earth was not the center of the Solar System. Making observations of Venusian surface is difficult. If you observe Venus directly, the thick atmosphere blocks most of the view. Other techniques, such as imaging the planet in infrared light and ultraviolet light as well as radar measurements have been used to study it.

Since the 1960s there have been a number of attempts to study Venus using robotic spacecraft. First by the Russians, using the Venera spacecraft and then followed by the US, using the Mariner missions. During these trips scientist discovered a lot about the temperatures, atmosphere and weather on Venus as well as capturing some images from the surface. The images showed the surface to be a rocky. It took a number of attempts to successfully land a probe on the surface of Venus. Initially, scientists misjudged the high temperatures and pressures the landers would experience. Some of them crashed before landing due to the parachute lines melting, some were crushed due to the high pressure and some melted in the high temperatures. Eventually they succeeded by sending a design more similar to a submarine than a spacecraft!

The surface of Venus from Venera 14

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