To put it another way, Mercury takes around 88 Earth days to complete a single orbit around the Sun. A single year on Mercury is actually shorter than a single day due to its quick orbital period and sluggish rotational period! The reason for this is because of mercury's proximity to the sun. It receives more radiation from the sun than any other planet in our solar system.
Here on Earth, we experience 24 hours of daylight and then darkness when the moon or planets move out of the way. But because of its location right next to the sun, Mercury experiences all sunlight all the time. For example, when the sun is directly over Mercury's equator, it gets as much sunlight as if it were directly overhead on Earth. This is why it is always sunny on Mercury! The only part of the planet that never sees direct sunlight is the far side because it faces away from the sun. Even though it has no real night, there is still a west-to-east shift in gravity that causes objects on the far side to roll over into western Mercury.
The average temperature on Mercury is -180 degrees Fahrenheit. Although this seems like it would be too cold for life, scientists have found that by combining ice with hydrogen (which is what most planets start out as) you get water, which is necessary for life as we know it.
This is due to Mercury's spin around its axis lasting 59 days and its orbit around the Sun taking 88 days. Surprisingly, 59 is precisely two-thirds of 88. This is not by coincidence; it is a result of Mercury's gravitational field being affected by the Sun's gravitational field. The closer together they are, the more their individual gravity fields add up instead of subtracting from one another.
If Mercury were in exactly circular orbits around the Sun, then its average distance would be about 453 million miles (739 million km). But because it travels along in its own path around the Sun, its distance varies between about 442 million and 457 million miles (754 million and 873 million km).
It takes Mercury about 84 minutes to rotate once on its axis. This means that each day, the part of the planet facing the Sun changes orientation relative to the nightside, which faces away from it.
The reason for this is that when Mercury is on the other side of the Sun, it is dark and cannot be seen from the Earth with the naked eye. So the only parts of Mercury that are visible at any given time are those where the northern hemisphere is facing us and the southern hemisphere is facing away from us.
Mercury completes five cycles around the sun in 440 days. It takes 87.5 years for Mercury to orbit the sun once.
The average distance of Mercury from the Sun is 59 million km (37 million miles). At this distance, sunlight strikes the planet at a rate of 500 watts per square meter (5,800 watts per square foot). This is more than enough energy to completely evaporate any water on the surface.
However, because Mercury has no atmosphere or magnetic field, most of this radiation is absorbed by the surface itself. Only a small fraction reaches the interior of the planet where it could have an effect.
This is why Mercury is said to be the hottest planet outside of Earth's moon! Average surface temperature is 450 degrees Celsius (890 degrees Fahrenheit).
It's also why people look weird when they wear sunglasses inside a building on Mercury day! The ultraviolet light would burn your eyes out if you were not wearing protection against it.
Mercury is only 5% water by mass. Most of its mass is made up of iron and nickel with some silicon and phosphorus present as well.
The time it takes a planet to revolve or spin once on its axis is referred to as its day. Because Mercury revolves at a far slower rate than Earth, a day on Mercury is significantly longer than a day on Earth. A day on Mercury lasts 58.646 Earth days (1407.5 hours), whereas a day on Earth lasts 23.934 hours. The difference in length between these two days is 45.32%, which means that for every hour that pass on Earth, Mercury will have spun through nearly two full rotations.
In addition to taking longer to rotate, Mercury has very little atmosphere to act as a cushion against high-speed collisions with space debris. Thus, the surface of Mercury is heavily cratered by many thousands of years of asteroid and comet impacts.
The presence of an ocean beneath Mercury's crust would provide another source of friction that could slow down its rotation even more. However, recent findings suggest that much of this water may be locked up in ice caps or briny deposits rather than being available for erosion to take place.
It is thought that over time, the lack of impact damage to certain regions of Mercury may indicate that they are covered in ice. In 2008, the MESSENGER spacecraft was able to determine that the core of Mercury is mostly iron with some silicon and magnesium present. The amount of iron found in the core suggests that it might be liquid under most conditions, which would make it useful for storing energy like the Earth's core.