Dear Tom,

I have read that Mercury, the planet closest to the sun in the Solar System, is not the hottest planet. Venus, the next planet farther out, is hotter. Why is Venus hotter than Mercury?

Victor McMell, Rockford

Dear Victor,

What you have stated is correct. Mercury is in a variable orbit around the sun, its distance ranging from 29 million to 43 million miles from the sun. Venus orbits at 67.2 million miles. Earth, the third planet from the sun, orbits at 93 million miles. Mars, the next planet out, at 141.6 million miles. Jupiter, the next planet out from the sun, orbits at 460.3 million miles.

The fact that Venus is hotter than Mercury has to do with the atmospheres of the two planets. Venus has a rather dense atmosphere; Mercury has almost no atmosphere. Mercury’s absence of a significant atmosphere means the planet has almost no capacity to trap and hold heat from sunlight. Venus’ atmosphere is able to do this very well.

  • Mercury’s average temperature: 333 degrees Fahrenheit
  • Venus’ average temperature: 867 degrees Fahrenheit
  • Earth’s average temperature: 59 degrees Fahrenheit
  • Mars’ average temperature: -85 degrees Fahrenheit

The air pressure on Mercury is 10-14 bars; on Venus, it is about 95 bars. On Earth, one bar. (One bar is defined as the Earth’s air pressure at sea level). Mars, 0.0065 bars.