The planet often referred to as Earth's "twin" is Venus. This nickname arises from their similar size, mass, and proximity to the sun. Both planets have terrestrial structures, which means they are composed mostly of rock and metal. However, they have drastically different atmospheres and climates. Venus has a thick, toxic atmosphere rich in carbon dioxide and sulfuric acid clouds, leading to extreme greenhouse effects and surface temperatures hot enough to melt lead. In contrast, Earth supports life and has abundant liquid water, showcasing the vast differences that exist despite their similarities.