Venus: Earth’s sister

Look at the sky right after sunset or before sunrise and you might notice an especially bright object. It looks like it could be an unusual star, or maybe a satellite... But it’s actually the planet Venus! At a distance of nearly 109 million kilometers from the Sun, Venus is the second planet of our solar system, and Earth’s closest neighbour. Venus and Earth aren't just close by — they also resemble each other in many ways!

Venus is a bit smaller than Earth, but their mass, density, and gravitational force are very similar. That’s why Venus is often described as Earth’s sister planet! And because their exteriors are so alike, scientists believe that their interiors must also be similar. Venus probably has a metallic core surrounded by a rocky mantle, covered with a solid rocky crust. Scientists think that Venus’s core is a bit larger than Earth’s, and it might contain some less dense elements, such as sulfur.

The mantle makes up the bulk of the planet, and the crust is only about 20 to 50 km thick. But despite the many similarities, Venus and Earth are also very different. Unlike Earth, Venus is a barren, fiery place. The main reason for that is Venus's atmosphere. It is primarily composed of carbon dioxide, with small amounts of nitrogen, argon, sulfur dioxide, and water vapour.

It is very thick and dense — the atmospheric pressure on the surface of Venus is about 90 times more than that on Earth! Sulfur dioxide in the atmosphere mixed with water vapour, forms clouds of sulfuric acid. These clouds and the atmosphere are so dense that about 85% of sunlight that reaches Venus is reflected back into space. Yet, Venus is the hottest planet in our solar system. How come?

Carbon dioxide, which is a greenhouse gas, traps the heat in the atmosphere and prevents it from escaping back to space. The planet can’t cool off and it continues to heat up, causing even more greenhouse gases to form. This is known as the runaway greenhouse effect. As a result, the temperature on Venus is more than 460 °C! There is no liquid water on the surface of Venus — any water that might have been there has evaporated, contributing to the greenhouse effect.

So, Venus’s surface is dry. It has a reddish brown colour, and it’s mostly composed of volcanic or igneous rock. Large volcanoes are scattered all over the planet. Some might be active. Studies of Venus's surface show that it is very young, possibly only 150 million years old.

This means that at some point, for an unknown reason and in an unknown manner, the planet might have resurfaced itself entirely! One year on Venus is about 225 Earth days — that’s how long it takes for Venus to make one full orbit around the sun. It actually takes more time for Venus to rotate around its own axis — one full rotation takes 243 Earth days. Fast rotating planets are normally slightly squashed at the poles and bulging at the equator. But with the slowest rotation in the whole solar system, Venus keeps its nearly perfectly spherical shape.

Venus is also the only planet that rotates clockwise. On Venus, the sun rises in the West and sets in the East. Shining so bright in the night sky, Venus has been observed since ancient times. But the thick atmosphere and hostile conditions on the surface make it difficult to study. There is still much to learn about Earth’s sister planet.