Why is Venus called Earth's "sister planet"?

1 Answer

Venus is often called Earth's "sister planet" or "twin" because of 3 major similarities:

  • Size
  • Mass, i.e. how much they weigh
  • Composition, i.e. what material they're made of

Further, Venus is the closest planet to Earth within the solar system.


Earth’s diameter is #"12,756.2 km"#, and Venus's is #"12,103.6 km"#. Earth is only #~~ 5%# larger than Venus, which, in comparison to other size differences between other surrounding planets, is a relatively minute difference in size.

In this image, you have to look carefully to notice that Earth (right) is slightly larger:

enter image source here


As with their sizes, the mass of Venus is only slightly lesser than that of Earth—Earth weighs only #~~ 19%# more than Venus does. Even the force of gravity on the 2 planets is close; you'd experience #90%# of gravity's force on Earth if you visited Venus.


Both Venus and Earth have metal cores surrounded by a mantle of silica rock (also common in rocky moons and asteroids), and then a thin crust.

Despite these similarities, Earth and Venus are also quite different, causing some to nickname Venus "Earth's evil twin."

The major differences are those that make Venus too hostile to support life as Earth does: temperature and atmosphere.

Venus's average temperature is #461.85 °"C"# (higher than that of molten lead!) and the atmospheric pressure is 90 times that on Earth’s surface.

While Earth's atmosphere is composed of oxygen and nitrogen (with only small amounts of #"CO"_2#), Venus’ atmosphere is #96.5%# carbon dioxide. Unlike Earth's fluffy cumulus clouds, Venus has clouds of sulphuric acid that rain down on the planet's surface, adding to the planet's inhospitable environment.