Occasionally, questions are sent to Universe Today, one that we get frequently is: ”what is the closest planet to Earth?”. The answer is Venus. Venus is also the third brightest object in the night sky. Only the Sun and the Moon are brighter. When Venus is closest to Earth it is only 38 million km away.
When Venus and Earth are at their closest approach to each other, it is called opposition. Incredibly, the distance between the planets can vary at different oppositions. 38 million km is the closest opposition possible for the two planets. When Venus and the Earth are the farthest from each other, they can be as far as 261 million km apart. The distance between the planets can vary by as much as 223 million km during their orbits.
Even though Venus is the closest planet to Earth, it is a very inhospitable world. The hottest temperature here on Earth was recorded in the Lut desert in 2005. That temperature was 70.7°C. While that is very hot indeed, the constant temperature everywhere on Venus is 460°C. Where Earth’s atmosphere is dominated by nitrogen and oxygen, the Venusian atmosphere is 96% carbon dioxide. CO2 is a greenhouse gas and holds heat close to a planet’s surface. As if the heat and a complete lack of oxygen were not harsh enough, the planet has clouds of sulfuric acid droplets covering its entire circumference.
Venus may be the closest planet to our own, but no one has ever been able to visualize its surface. The sulfur content of the clouds reflects nearly all visible light, preventing visual observation below the edges of the atmosphere. What knowledge scientists have gained about the surface has come from radar imaging. Those images were not taken until late in the 20th century. Imaging from the Earth and Venusian orbit have shown a surface dominated by large volcanoes. There are over 1,000 craters that are 20 km in diameter or larger. There have been some recent images that suggest the planet is still geologically active.
Venus is the answer to ”what is the closest planet to Earth”. It is similar in diameter, mass, and volume, but you can see how it is a scary world compared to ours. There are several missions headed to Venus. The Venus Express is currently studying the planet, BepiColumbo is going to be launched in 2014, and the Venus In-Situ explorer is in the design phase. Scientists may soon find themselves with more information on their hands than they can digest.
We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.