Mercury has no moons, and there aren't many asteroids that may collide with it, therefore it may never have a ring, but maybe one day. But one thing is certain: there are no Mercury rings today.
The last time something big enough to be detected by astronomers collided with Mercury was 486 million years ago, when Asteroid MD is said to have hit the planet. The impact created a crater about 60 miles in diameter and filled with water.
Today's Mercury is the result of an intense bombardment over millions of years. The solar wind and cosmic rays wear away at the planet's surface, while meteoroids crash into it every hour.
The Earth also gets hit with objects from space, but we have shields against most harmful effects of this collisional evolution. Not Mercury. It can't hide from view, because all its dark side is exposed to the solar wind and its atmosphere is easily stripped away. In fact, the only thing protecting Mercury is its tiny size relative to other planets in the Solar System.
It's estimated that within 100 million years or so, all the water on Mercury will evaporate due to solar heating. After another 3.5 billion years, all that's left will be a dry rocky core with no magnetic field.
Mercury, along with Venus, Earth, and Mars, is a rocky planet. It has a solid surface covered in craters. It does not have an atmosphere and no moons. It completes one revolution around the sun in only 88 days on Earth. The next closest planet to Earth that can be seen with the naked eye is Jupiter. It takes 6 years for Mercury's orbit to completely circle the sun.
Unlike the other three, Mercury has very little influence over its own motion through space. Instead, it gets pulled by the sun in a direction opposite to Earth, because all the other planets lie in the same plane as Earth and they each pull her in different directions. This means that if we looked at Mercury from far away it would appear to be moving away from the sun. But it's not: it's staying still while the rest of the solar system moves closer to the star.
This effect was first noticed by Aristotle and his colleagues, who were trying to understand why some stars seem to move against the night sky when viewed from Earth. They hypothesized that there must be other planets out there that could do this if they were close enough to influence their home planet. Over time, more planets were discovered beyond Neptune (the 8th planet from the Sun) and it was realized that these planets did in fact cause some stars to appear to move.
Mercury does not have any moons. Venus is the only other planet in our solar system that lacks moons. Earth has one, Mars has two, while Saturn may have as many as 82 moons. The other planets in order of distance from the sun are Jupiter, Uranus, Neptune, and Pluto.
The closest approach Venus makes to Earth is when it orbits at approximately 108 million km (67 million miles) away. This occurs about 8 hours after sunrise or before sunset every 584 days.
Mars has a 1.9791 astronomical unit (AU) orbit around the Sun, which means it takes 686.4 million km (420 million miles) to go around the Red Planet once. At this distance, 0.38 degrees Celsius (0.74 degrees Fahrenheit) of warming can be expected during martian summer, and -170.6 degrees C (-274.5 degrees F) in winter.
Neptune has a mean distance of 544 AU from the Sun and takes about 15 years to orbit the Sun. It has 30 moons known so far.
Jupiter is the most massive planet in our solar system and also the most widely distributed across the sky. It occupies about 25% of the sky when it rises in the east and sets in the west—a total area of nearly half.
Mercury's discoverer is unknown.
It, like our Moon, has a solid surface covered with craters. However, due to its proximity to the Sun, most of Mercury's surface is hot enough to melt ice and rock, which then flows into large, deep cracks and fissures on the planet's sun-scorched plains. This process creates new land that may or may not be cratered. The best examples of this are the great volcanic plains of Mercury, including those features we know as Marineris. These features were probably created by lava flowing from many small volcanoes over millions of years.
We know about the big craters on Mercury because they're easy to see from space. So far, 13 features have been identified on the planet's surface. Several of these are large enough to hold water when measured in volume, which could support life as we know it. The largest of these is Caloris, which measures 14 miles in diameter.
Many people are surprised to learn that despite its appearance, Mercury is actually quite different from Earth in many ways. It has no magnetic field, for example. And although it orbits the Sun every 88 days, this planet never gets warm enough for liquid water to exist on its surface.
If you monitor it between July 20th and August 9th, you'll notice Mercury wandering, offering strong evidence that it is, in fact, a planet. Infrared images (center, 2007) can be rebuilt, or the Messenger mission can fly to Mercury and photograph it directly (right).
Why is my teacher saying that Mercury is a planet? Mercury is a planet because the International Astronomical Union (IAU) classified it as such in 2008. Before then, it was called a "planetoid" because astronomers weren't sure if it had cleared its orbit of debris to become a true planet.
Classifying objects within our solar system is very important because it tells us about other planets outside of our own. For example, if an object has been classed as a planet but later found not to be one, this would help rule out some potential Earth-crossing asteroids before they reach Earth's surface. Classifying objects also helps scientists to understand how our solar system formed and evolved over time.
So why don't we see many planets around other stars? It turns out that most stars have a faint red glow when seen from afar with the naked eye. This is because they are covered in dust. If there were no dust, we would be able to see far beyond what we actually do. In fact, we know that some stars are surrounded by disks of gas and dust which are likely to one day form planets.