Mercury: The Moon Planet
Mercury was named after the speedy messenger of the Roman Gods by the Romans because it moved across the sky faster than any of the other planets.
Mercury is the smallest of the inner planets at a little more than half the size of Earth and 40 percent bigger than the Earth's moon.
The surface of Mercury is very similar to that of Earth's moon; covered with craters from meteorites bombarding it constantly. You would have fault-cliffs that would reach several kilometers into where the sky would be if the sun hadn't evaporated all the atmospheric gases off the planet. This leaves the sky dark and empty despite the sun looking 2 ˝ times larger, because those gases scatter the light from the sun. Also, depending on which side of the planet you were on (side facing toward or away the sun), you could experience huge differentials in temperature. From 427*C (800*F) on the sun-facing side, to -183*C (-297*F) on the opposite side.
Before Mariner 10 went to Mercury, there was very little known about the planet. This was because that there is an extreme difficulty to observe it from Earth because it is so close to the sun. We now know more about Mercury. We discovered that Mercury had a magnetic field. They thought that because Mercury's core, being as small as it is, would have solidified a long time ago [obviously, it hasn't].
Venus: The Jewel of the Sky
Venus is named after the Roman goddess of love and beauty. It was given this name because it was the brightest of the planets visible to the Romans.
Venus is known to astronomers as Earth's sister planet. It is because Venus has many similarities to Earth, including: mass and density, gravitational pull, and volume. However, that is where the similarities end; the two are very different from one another point of view. Venus has no water, its atmosphere is thicker, mostly made up of CO2 (Carbon Dioxide) with minute amounts of water vapor. The thick clouds on Venus are made up of a deadly poison to humans called Sulfuric Acid. Sulfuric Acid can eat through just about any material known to man. And at the surface, the atmospheric pressure is 92 times that of what is on Earth at sea level [talk about putting the squeeze on things]
Venus is hot; very hot. The surface temperature is 482*C (900*F). The high temperature is due to the greenhouse effect (that's the same thing that keeps getting Earth hotter). The greenhouse effect works in that when heat is brought down to the surface, the CO2 keeps insulates in. This ends up making Venus the hottest of all the inner planets.
A thing that separates Venus from the other inner planets is that it rotates backwards. If you were on Venus watching the sunset (which would hard because of the clouds, but let's forget that), you wouldn't be facing the west to see it, but to the east, the opposite of Earth.
Venus' surface also seems to be younger than most of the other planets. Thanks to NASA's Pioneer Venus mission in 1978, the Soviet Venera 15 and 16 missions of 1983-84, and the NASA Magellan radar mission of the early 1990s, we have learned that Venus' surface is only 300-500 million years old. The surface consists mainly of lava plains and high mountain ranges that can go for huge amounts of distance across the land (the Aphrodite Terra Highlands extend almost halfway around its equator), and 85 percent of the land surface appears to be volcanic rock.
Earth: Our Home
What do you think of our planet from the "creature living here" perspective? You probably think that we live on a large planet with a stable ground and an almost endless supply of air around us. Well… how do I break this to you? From space, the Earth is small, with a thin and delicate atmosphere. If you were to travel from another planet to Earth, you would notice the blue water, the green and brown land and the white clouds. All of this is next to a black background of space. If an interstellar traveler were to come to Earth, they would find life on our lovely abode. They would find trees, frogs, fish, spiders, birds, deer, lizards, snakes, and humans [that's us].
Mars: Another Inhabited Planet?
The most unique feature that you could notice about Mars when looking up on it from Earth is that it is red in color. The color is due to that most of the soil on Mars is made up of iron, which, when corroded, becomes red in color. Because of its red color, the Romans named the planet after their god of war Mars.
Before humans sent spacecraft to travel space, Mars was the most likely planet to have extraterrestials inhabited on it. Why? When astronomers thought they saw straight lines on the surface, people believed they might be irrigation canals that some intelligent aliens had built. Mars was such a huge candidate to be a planet where aliens were living that in 1938 Orson Welles made a radio drama based on H.G. Wells Sci-Fi classic book, War of the Worlds. So many people believed that the broadcast was about a real invasion that it nearly caused a panic [those are some paranoid people].
There was also more evidence that Mars had life on it. On the surface of the planet, there seemed to be seasonal changes in color. That led to the thought of plant life growing in the warmer seasons and then becoming dormant again in the colder months. Also, Mars has a very different atmosphere from Earth, it is mostly made up of CO2 (Carbon Dioxide).
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Chart of the Gases on Mars |
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But in spite of all this evidence, when Mariner 4 returned the close up pictures of the Martian surface, the supposed canals were dry and not straight, meaning that they were dried up river beds and the seasonal color changes were just the color of the amount of ice on the surface. And when the Viking 1 and 2 Landers arrived on the Martian scene and did studies on the soil, they found no sign of microscopic life. Now scientists believe that Mars is self-sterilizing. They think that the combination of the surface being flooded with UV (ultraviolet) Radiation, the dry soil, and the oxidizing nature of the Martian soil contribute in the lack of life being formed on the planet.
