Think back to the middle of August when you just finished mowing the lawn. The sun was beating down and it felt like it must have been at least 110º F outside. You thought it was probably hot enough to fry an egg on the sidewalk.
Although it might have felt like you were standing on the surface of the Sun, Earth — even on its hottest days — is far more tolerable than the hottest planets in the solar system. So which planet is the hottest?
Since Mercury sits closest to the Sun, Mercury must be the hottest planet. Right? That only makes sense, doesn't it? After all, Mercury receives more sunlight per square foot than any other planet in the solar system. Wrong! Venus is actually the hottest planet in the solar system.
Most friends are probably WONDERing WHY Venus is hotter than Mercury even though it's farther away from the Sun. The answer lies in the atmosphere. No, it's not up there in the sky. The answer IS the atmosphere!
Because Mercury is smaller, sits so close to the Sun, and moves so quickly around the Sun, it doesn't have an atmosphere. When the Sun's rays hit Mercury, they just bounce off into space. There's nothing to reflect them back toward the planet and retain their heat.
Venus, on the other hand, has a very thick atmosphere. Its atmosphere is actually over 90 times denser than Earth's atmosphere. Made up mostly of carbon dioxide, a greenhouse gas, Venus' atmosphere acts like a one-way door: it lets in solar radiation, but it doesn't let it back out.
This creates oven-like conditions on the surface of Venus. Because of this intense heat, no water can be found on Venus. Moreover, carbon dioxide is a noxious gas that creates raging winds that blow constantly across the surface of Venus, making it one of the harshest environments you're likely to find in the entire solar system. Although Earth and Venus are sometimes called “sister" planets because of their similar sizes, they couldn't be more different in so many other ways.
Before scientists could “see" Venus with the help of unmanned probes and space telescopes, many of them thought Venus was a lush, tropical paradise. The truth is that it's a barren rock that looks like Earth's Moon. Its clouds appear yellowish because of the presence of sulfur dioxide alongside the huge amounts of carbon dioxide.
What scientists now know about Venus has come from several unmanned probes sent to Venus over the years. The first craft to land on Venus in 1970 was a Soviet probe called Venera 7. Unfortunately, Soviet astronomers only received data from the probe for about 23 minutes before the planet's heat destroyed the probe's electronics!