Venus and Mercury have comparable compositions; they are both terrestrial planets consisting of rock and metal. Mercury is denser than Venus and is considered to comprise 60–70% metal, with the remainder being rock. Venus and Mercury are both in Earth's orbit. This implies they are constantly near the sun in the sky. Because they are so close to the sun, these planets experience very high temperatures: 450 degrees Celsius (842 degrees Fahrenheit) on Mercury and 454 degrees Celsius (850 degrees Fahrenheit) on Venus.
These temperatures are too hot for liquid water to exist on their surfaces today. However, when Venus was more like Earth in size, the presence of water has been suggested for several reasons. One idea is that perhaps some of this water may be locked up in a deep underground reservoir similar to the one believed to contain water on Earth.
Another possibility is that there might have been more water early in the history of Venus when it was less hot. The early atmosphere of Venus may have been more likely to dissipate into space, allowing more water to be retained.
Venus and Mercury are also both seen from time to time under the light of the moon. When this occurs, they can only be seen in the west just before sunrise or in the east just before sunset.
These two planets have many similarities but also some differences as well. It is this difference that makes them interesting to study.
At their essence, both share comparable components. Venus and Earth are virtually equal in size, mass, and composition. They orbit the Sun at almost the same distance, and over time their orbits have nearly the same inclination (the angle between their orbital planes and the surface of the Earth).
Earth's atmosphere is important because it allows life as we know it to exist. It provides protection from solar radiation and other dangers such as explosive decompression when exposed to cosmic rays. It also acts as a conductor of heat, which is why we can experience seasons on Earth.
Venus does not have an atmosphere, but it does have clouds that cover most of its surface. These clouds play an important role in shielding Venus from the solar radiation that would otherwise destroy any organic material on its surface. The clouds also change frequently, moving around dramatically on Venus.
It is thought that over time Venus' atmosphere has been depleted by oxygenic organisms that have lived on Venus. This would explain why there is no evidence of past or present life on Venus despite many attempts to find it.
Although similar, Venus and Earth are very different forms of life. Earth supports complex ecosystems that include many different types of animals and plants.
It calculates the distance between two planets as the average of all locations along their respective orbits. As a result, Mercury's orbit does not take it very far from the sun, but Venus's orbit takes it much further away from Earth. As a result, Mercury is closer. The distance between Mercury and the sun is about 0.5 astronomical units (au), while that between Venus and Sun is about 0.7 au.
Mercury has only been visited by one spacecraft so far, Mariner 10, which flew by it in 1974. However many instruments on board were designed to work on Earth-based telescopes instead, so most of its secrets remain hidden in plain sight!
Venus has been explored by several missions including Pioneer 2, 3, 4, Venera 7, 8, and 9. Data from these missions have helped scientists understand more about our planet's history and influence other worlds beyond ours!
Earth also uses Venus and Mercury to shield itself from solar radiation. Without this protection, our atmosphere would be destroyed before Mars can be formed. The next time you look at the night sky, try counting the stars you can see from Earth's moon. The only planet without an atmosphere is Pluto. It's hard to see how any life could exist on such a cold, barren world! But scientists think there might be oceans beneath Pluto's frozen surface. We just haven't reached them yet with current technology!