Which planet is known as Earth's 'sister planet'?

Venus is known as Earth’s “sister planet” because the two worlds are similar in size, mass and overall rocky composition.

Venus is the second planet from the Sun, while Earth is the third. Their diameters differ by only a few hundred kilometres, and Venus has about 82% of Earth’s mass. Both are terrestrial planets with rocky surfaces, iron-rich cores and substantial atmospheres, which is why astronomers often compare them.

The nickname can be misleading, however, because Venus is not Earth-like in its surface conditions. A dense carbon-dioxide atmosphere and powerful greenhouse effect make Venus the hottest planet in the Solar System, with surface temperatures around 465°C. Its atmospheric pressure is roughly 90 times that at Earth’s sea level, and clouds of sulfuric acid surround the planet.

Venus also rotates unusually slowly and in the opposite direction from most planets. One Venusian rotation takes about 243 Earth days, longer than its 224.7-day trip around the Sun. The planet is bright enough to be seen easily from Earth and is often called the Morning Star or Evening Star, although it is neither a star nor Earth’s moon.