April 25, 2017

Venus

Tailles relatives de Vénus et de la Terre

Until the beginning of the Space Age, Venus was considered to be Earth’s twin sister due to several similarities between the two planets (more in the table below):

  • They were formed at the same time, in the same gas and dust cloud, 4.6 billion years ago
  • They are both internal planets
  • They both present a diverse terrain: mountains, plains, plateaus, valleys, volcanos, and impact craters
  • Both planets show little craters, which indicates a relatively young surface
  • They both have an atmosphere with dense clouds
  • Venus is the closest planet to Earth

Venus is similar to Earth in size (it is 12,092 km in diameter compared to Earth’s 12,742 km) and in density (5.26 versus 5.52, respectively), which is why we can deduce that they have similar internal structures.

Venus’s crust is about 20 km thick, which makes it thicker than Earth’s oceanic crust but thinner than out continental crust (which is 30 km thick on average). The thickness of Venus’s crust was deduced from the many lava flows observed around the impact craters. That crust would represent only 0.34% of the planet’s radius, and analyses carried out by the various Venera probes have shown that the material on its surface is very similar to Earth’s granite and basalt (silica and metal-rich rocks).

Due to these common characteristics, it has long been thought that under its dense clouds Venus could be very similar to Earth and perhaps even harbour life. But in many aspects, Venus is radically different from our planet.

Venus’s rotation speed is very slow: it takes the planet 243.0185 Earth days to complete one rotation. Furthermore, Venus has a retrograde rotation, meaning opposite of that of most planets in the solar system, including Earth. It takes Venus 243 Earth days to complete one rotation and 224.7 to revolve around the Sun; one Venusian year lasts a little less than 1 sidereal Venusian day (precisely 0.924). This means that if one were to spend an entire year on Venus, one wouldn’t even see an entire sidereal day!

Typically, the presence of an external spinning molten iron core creates a magnetic field like on Earth and on Mercury. However, Venus’s rotation is likely too slow for the dynamo theory to apply. The planet’s magnetic field is indeed very weak, and the only observable magnetic phenomena are the result of direct interaction between the atmosphere and solar wind.

A few comparative figures about Earth and Venus

 VénusTerre
Average distance to the Sun0,72 UA1 UA
Planetary diameter0,951
Mass (in Earth mass)0,821
Axial tilt-2,6°23,5°
Year duration225 Earth days365 jours
Sidereal day duration243 Earth days, retrograde1 day = 23 h 56 min
Solar day duration116 Earth days and 18 h1 day = 24 h
Average surface temperature460°C15°C
Surface pressure (in bars)921

Read further in our Solar system file, specifically on the  Venus page.