After all, there are considerable distinctions between the two bodies: Mercury, unlike the moon, has a worldwide magnetic field; it has a larger density; there is an abundance of volatile elements such as sulfur; and its surface has significantly less iron, notably in its crustal silicates—indicating that the processes deep beneath both...
The first difference is that Mercury has a global magnetosphere while the Moon's magnetosphere only covers about one-quarter of its surface. This means that any particles from outside the solar system that collide with Mercury should be deflected away from the planet by this magnetic field.
The second difference is that Mercury has a strong magnetic field itself. Scientists think that this is because it receives a large amount of electric current from the Sun every day. The force of this current causes volcanic activity on the planet's surface, creating our magnetic field.
Volcanoes also emit gases into the atmosphere that cause global changes to climate, so they have an important role to play in creating a habitable environment for life. Earth's moon doesn't have a strong enough magnetic field to protect itself from cosmic radiation, which is why astronauts aboard spacecraft often wear space suits when they go outside.
However, the fact that Mercury has a global magnetosphere means that it can shield itself from many of these particles, which would otherwise damage its surface over time.
Mercury is frequently likened to the moon because its surface resembles the moon's backside (the main source of erosion for both is meteorite impact). Both have mild magnetic fields, but unlike the moon, Mercury does not. Furthermore, the density of the moon is significantly smaller than that of Mercury. These facts lead scientists to believe that most if not all of the moon was formed by collision with another object.
Additionally, both planets orbit around the Sun at almost the same distance, about 91 million km or 58 million miles. This similarity leads scientists to believe that both planets may have started out as molten spheres that later solidified into their current states. However many scientists believe that Mars might be a former Earthling that we destroyed.
How do the Moon's and Mercury's atmospheres compare? There is no permanent environment in either body. If the Earth's surface temperature were raised to that of Mercury's day side, the Moon's temperature would be equivalent to that of the Earth's crust, while Mercury's temperature would be similar to that of the entire Earth. The presence of water ice under both bodies' surfaces contributes further weight against escape via radiation.
The Moon has a thin veneer of oxygen gas over a dense layer of dust. The dust particles are small, usually less than 2.5 microns across. Larger particles may reach up to 100 microns or more in diameter. The Moon's atmosphere has a pressure about 1/10th of Earth's at sea level.
Mercury has a very thin atmosphere of gases produced by its rocky core that include hydrogen, helium, and traces of other elements. The average density of Mercury's atmosphere is only about 0.11 grams per square meter (g/m2), which is about 1/100th the density of Earth's.
Earth's atmosphere is about 1015 g/m2. This means that there is 1 kilogram of air for every square meter of earth's surface!
It is estimated that the total mass of Earth's atmosphere is about 5 million billion kilograms (5 × 1021 kg).
In general, Mercury's surface resembles that of the Moon (i.e., heavily cratered due to a lack of a heavy atmosphere to erode away primordial impacts). The only real difference is that Earth's moon has been captured by Earth's gravity, so it experiences a little bit of atmospheric erosion as well.
The most likely explanation for Mercury's appearance is that early in its history, when it was much closer to the Sun, it had an atmosphere similar to Venus' today. As Mercury got farther from the Sun, it lost this atmosphere, which prevented any significant further cooling. The remaining body was then able to reach temperatures low enough to produce the observed features on its surface.
It's interesting to think about what would have happened if Earth had another planet close by with different environmental conditions.
Mercury and the moon both have surfaces, or crusts, that are almost completely made of rock and are riddled with craters. Unlike Earth, which has an element-rich atmosphere that typically burns incoming meteorites, Mercury and the moon have thin atmospheres termed exospheres that store little gas and provide minimal protection. The inner cores of these bodies are probably solid iron, although some scientists speculate that they might contain a small amount of nickel.
The cores of Mercury and the moon are also quite different from one another. While the core of Mercury is probably solid iron, that of the moon is thought to be mostly metal oxygen with some silicon and aluminum mixed in. The reason for this difference is still unknown.
Another interesting thing about the cores of Mercury and the moon is that they appear to be both very fluid. Data collected by NASA's Mariner 10 spacecraft revealed that the core of Mercury is actually a large liquid body that rotates around its axis every 58 days! The core of the moon is also believed to be a large body of molten iron deep inside its center. As you can see, these two important objects are very different from each other but have many similarities. It seems that they were both formed by the impact of a giant body such as a planet or larger space object such as a comet.
People have been wondering whether or not the core of Mercury would burn if it came into contact with air.
Mercury resembles Earth's moon in appearance. Mercury's surface, like our moon's, is riddled with craters created by space rock strikes. But because Mercury is so much closer to the sun, it experiences much higher temperatures than Earth's satellite.
The Earth's moon is always dark because of how far it is from the planet. But because Mercury is so close to the Sun, one quarter of its surface is always exposed to sunlight. The other three quarters are hidden by a thick cloud cover that constantly moves over the planet's surface.
Like Earth's moon, Mercury has been affected by meteoroids and asteroids crashing into it. These impacts have left deposits of material on the planet's surface.
Mercury has two small moons named Phoebe and Io. They were discovered by American astronomers Eleanor Helin and Scott Sheppard in 1978.
Io is Jupiter's largest moon, but it is also its most abusive possession. An object the size of Delaware crashes into Jupiter every seven months or so. This impact blasts away much of the moon's interior, causing it to evolve rapidly over time.
Phoebe is less important than Io, but it has an interesting history of its own.