Who is called the brother of Earth

Venus is often referred to as Earth's "sister planet" rather than brother, due to similarities in size, mass, composition, and proximity to the Sun. However, the term "brother" isn't commonly used in astronomical contexts regarding Earth's planetary relationships. Venus and Earth are nearly identical in size, with Venus having about 95% of Earth's diameter and 80% of its mass, and both are rocky terrestrial planets formed from similar materials in the inner solar system.

Despite these similarities, Venus and Earth developed dramatically different conditions—Venus has a crushing atmosphere of carbon dioxide, surface temperatures hot enough to melt lead, and sulfuric acid clouds, while Earth harbors abundant liquid water and life. This stark contrast despite similar beginnings makes Venus a crucial case study for understanding planetary evolution and climate dynamics. Some scientists also consider Mars as a planetary "relative" due to its position in the solar system and evidence that it once had liquid water. The sibling metaphor helps convey the comparative planetology concept that studying other planets provides insights into Earth's past, present, and potential future, particularly regarding climate change and atmospheric evolution.