On Mercury, a year lasts only 88 Earth days—less than three Earth months. The planet's orbit is almost exactly perpendicular to the ecliptic, which means that at any given time, half of Mercury is in darkness as far as observers on Earth are concerned. But because Mercury is so close to the Sun, even during its eclipse periods, every day feels like 24 hours when measured against Earth.
A year on Mercury is about twice as long as on Earth. The difference is due to the fact that there are 10 hours instead of 12 hours of sunlight during a Mercury day. Thus, it takes two years for the Sun to complete its annual cycle from Greenwich, England, where most solar observations are made.
It should be noted that an observer on Mercury would see the Sun rise and set twice during their year-long trip around the Sun. The reason for this is that Mercury orbits the Sun in approximately 87 days, but it takes it approximately 60 days to rotate completely around itself. So during those first 87 days, the Sun will have moved west across the sky until it reaches its position opposite to where it started. From then on, it will rise in the east and set in the west, repeating this process forever.
A year on Mercury lasts around 88 Earth days. Mercury's year is the shortest of any planet in the solar system. Earth's year is about 365 days, but because of its orbit around the Sun, it always experiences both spring and fall. Mars' year is approximately 686 days, but because it orbits so far from the Sun, it is very cold and dark for much of that time.
Mercury orbits the Sun every 87.9 days. Because of this close orbit, the planet completes one rotation on its axis in only 24 hours. Thus, all parts of Mercury are exposed to the Sun for almost the entire period between successive oppositions, which occurs when Mercury is on the opposite side of the Solar System from Earth. During these periods of direct sunlight, no part of Mercury is shielded by its own shadow, although there are small regions where rocks have been melted by the heat of the sun (these are called "solar prominences").
The average temperature on Mercury is 450 degrees Fahrenheit (232 degrees Celsius). However, because most of the surface is covered in rock rather than water, most of the energy from the Sun is reflected back into space, rather than being absorbed as it is on Earth and other air-covered planets.
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 87.749 hours.
The spin axis of Mercury is nearly perpendicular to its orbital plane, which means it makes one full rotation every 59.5 days.
Its rotational velocity is very high, at almost 40% of the surface speed of light. As a result, even though it is a relatively small body, it has the greatest gravitational field of any other object in the Solar System except for the Sun itself.
Mercury completes one orbit around the Sun (one year in Mercury time) in just 88 Earth days. Mercury, like the Earth's moon, has a solid, cratered surface. Mercury's thin atmosphere, or exosphere, is largely made up of oxygen (O2), sodium (Na), hydrogen (H2), helium (He), and potassium (K). The origin of hydrogen in the planet's atmosphere is not known.
Although only three percent of the Earth's mass, mercury is responsible for more than half of its solar radiation because it is so close to the Earth. This makes it the most active planet beyond Earth's Moon.
The presence of mercury in our environment comes from two sources: natural emissions and human activity. Natural emissions come from volcanoes and other sources such as meteor impacts. Human activities include mining, artisanal fishing, and disposal of industrial waste. Of the total mercury present in our environment, about 50% is from natural sources and 50% is from human sources.
When atoms of elemental mercury (Hg0) join together they form molecules called mercaptans. Animals can't use these compounds so they pass into the food chain through eating behavior called trophic migration. Humans can eat fish containing high levels of mercury without suffering any long-term effects but still should avoid certain species for reproductive purposes or when trying to conceive children. Fish with high levels of mercury include shark, swordfish, king mackerel, and tilefish.
There are 59 Earth days. Mercury revolves slowly. It takes roughly 59 Earth days to complete one rotation. This means that a day on Mercury is about 24 hours, but because it takes so long for the planet to rotate, most places only experience 12 hours of sunlight per day.
The amount of time it takes for Mercury to rotate is called its revolution period. Because Mercury's mass is less than Earth's, its gravity is weaker than Earth's, so less force is needed in order to keep Mercury in orbit around the Sun. However, due to its proximity to the Sun, every aspect of Mercury's orbit changes very quickly, which means that scientists cannot predict how long it will take for Mercury to rotate next.
In addition to its rapid rotation, Mercury has many other unusual qualities that differ greatly from those of Earth and other planets.
Mercury is a lifeless planet with the most craters in the solar system. Mercury travels around the Sun in 88 Earth days but spins so slowly on its axis that dawn to dusk takes 176 Earth days. A year on this planet is shorter than a day! The reason for this is that it is tipped over on its side, like Nebraska.
It used to be thought that because it is so small, has no magnetic field, and has very little air, then life could not exist there. But we now know that this is not true, because there is water under the surface, locked up in ice caps and frozen gases. And even though 95% of this water is frozen, this still amounts to more than one ocean full!
People have been exploring Mercury since 1577, when Ferdinand Magellan first saw it from Earth during his voyage across the Atlantic Ocean. Since then many more missions have been launched, including two by NASA astronauts (Gary Snyder and Bruce McCandless).
These discoveries have shown that Mercury is a very interesting planet, and it is being studied in great detail. It is also being used as a test bed for technologies needed by future missions to Mars and beyond.
In May 2008, the Mariner 10 spacecraft made the first ever close-up images of another planet outside our Solar System.