Mercury revolves slowly. It takes roughly 59 Earth days to complete one rotation. But because of its proximity to the Sun, that rotation is very close to being a perfect circle. At most points over its orbit, Mercury is within 15 degrees of the Sun.
Thus, it gets heated up and evaporated at those places where it is directly exposed to the sunniest side of the planet. The remaining rock cooled down as it receded from the heat source and formed craters all over the surface. Some of these remain today, while others are filled with water. One large crater called Syrtis Major is completely covered by an enormous lake named Marius Crater after the Roman emperor who discovered it in 30 B.C.. He must have been pretty excited about that!
Even though Mercury rotates so slow, there are still four seasons like on Earth. But because all of Mercury is under constant sunlight, there is only ever one season here - day. During the night, the coldest place is always near the Sun. This is why there is no ice or snow on Mercury, only volcanoes and rocks melted by the heat.
The average temperature on Mercury is 450 degrees Fahrenheit (232 degrees Celsius).
88-day period 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 means that every time Mercury orbits the sun, it travels in a straight line for about 58/3 miles (93 km), but then turns around and travel another 3 miles (5 km) back toward the sun.
Mercury is only 105 miles (169 km) in diameter, but because it is so much smaller than Earth, each day on Mercury is almost exactly four days old. At most times of the year, the surface of Mercury is too hot for water to remain in its solid form, but when ice lies beneath the surface, it can change into a gas called helium at the surface. This is why you never find liquid water on the surface of mercury today.
The Earth's moon has been known to influence the tides, but how could something as small as Mercury affect the tide? While orbiting the Sun, Mercury passes through all phases of the Moon's cycle of gravity, from full moon to half moon to new moon. The amount of water on Earth's surface follows these changes with great precision; there are times of high tide and low tide just after a full or new moon, and again several months later after a half moon.
This indicates that a single day on Mercury lasts around 0.646 times as long as a single year on Earth. The equatorial rotating speed of the planet is 10.892 km/h. These times are expressed in solar days. Mercury spins every 58.647 days in sidereal days and circles twice every three revolutions. Therefore, each rotation takes about 87.558 days.
The magnetic field of Mercury is very weak. It has only one pole, which is currently facing away from Earth.
Polar wandering is the movement of the magnetic north pole of the earth over time. Because Mercury's axis of rotation is also its axis of polarization, the orientation of this axis with respect to Earth's surface changes as well. The magnetic north pole traces out a circle on Mercury, called the polar cap. The exact cause of this movement is not known but it may be due to gravitational interactions with Jupiter and Saturn.
In addition, Mercury has a very eccentric orbit around the Sun. So even though it takes 58.647 days for Mercury to make one full rotation, because it takes almost 90 days for it to travel around the sun from perihelion (closest point) to aphelion (farthest point), these two values will never be exactly the same.
Mercury completes five cycles around the sun in 440 days. It takes 87.5 years for mercury to make one full rotation around the sun.
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 (5,778 watts per square foot). This is more than enough energy to completely vaporize mercury ice caps if they existed.
However, because the solar radiation is spread out over time, most of the surface experiences only 3% or 4% of this level for long periods of time. The average global temperature of Mercury is 450°F (232°C), which means that almost all of it is covered by ice caps. These keep a constant temperature despite the changing amount of light they receive from the Sun. But even under the ice there would be hot spots where geothermal energy is released just as on Earth.
It is thought that because of its proximity to the Sun, Mercury has very little atmosphere. However, studies have shown that before it entered its current orbit, Mercury had an atmosphere made up of carbon dioxide, nitrogen, and oxygen.
Mercury rotates on its axis slowly, completing one revolution every 59 Earth days. Mercury's axis of rotation is just 2 degrees inclined in relation to the plane of its orbit around the Sun. That means it rotates nearly exactly upright and, as a result, does not have seasons like many other planets. However, because of the slight inclination of its axis, sunlight falls on different parts of the planet for varying lengths of time each day.
Like all planets except our own, Mercury has two hemispheres that are dark forever trapped in this eternal night. But even though we can't see light from beyond its surface, there is still some activity going on inside Mercury's body. As tides roll across the face of the planet, they cause friction that creates heat. This frictional heating keeps most of the planet's interior liquid iron, which flows back and forth between deep cracks and pore spaces in the rock when the tide goes out and solidifies when the tide comes in. The resulting pressure changes push against the sides of these cracks, which slowly move across the surface.
How do you find out what's happening inside another planet? There are several ways, but none are very direct. The first way is by looking at its shadow on Earth during a total solar eclipse. Because Mercury moves closer in relationship to the Earth than any other planet, it crosses its own shadow every 58 days.
10.892 kilometers per hour The equatorial rotating speed of the planet is 10.892 km/h. Its year is almost identical to Earth's, but its day is slightly shorter.
These values change because of gravitational interactions with Mars and Venus. The most recent update to these values was in 2016 when they were updated again based on new measurements from NASA's MESSENGER spacecraft.
Mercury has no magnetic field, but it does have a very thin atmosphere made up of atoms of helium and oxygen that extends nearly to the surface of the planet. This atmosphere changes constantly due to geologic processes at work under the surface.
In addition to being a smaller planet than Earth, Mercury has only half our mass. So, it rotates faster for its size relative to Earth. It also has less rock than Earth exposed at the surface so it should spin faster too. However, because it has no significant internal gravity, most of the mass is contained within its dense iron core which creates enough pressure to slow down the rotation a little bit.
The last time it was active as a world with a magnetosphere was four billion years ago when it was more like Earth today.