Mercury is the first planet in the solar system, and it is the closest to the sun.
Did you know that even though Mercury is much closer to the sun, there is no morning on this planet? That's right, it's always night here. The sky is constantly black because there is no scattering of light, since Mercury has very little atmosphere. In fact, Mercury is practically without air. The 'atmosphere' consists of oxygen, sodium and potassium.
An orbit is a revolution around the sun, while a rotation is a circling of the planet around its own axis. One rotation around a planet's axis is one day. The Earth takes 24 hours to complete one rotation, 365 rotations to revolve around the sun. Mercury, on the other hand, rotates just one and a half times during each orbit. Its rotation is extremely slow, and one day on Mercury is equal to 176 earth days. Paradoxically, Mercury was named after the swift and speedy messenger of Roman gods, and the very word 'mercurial' means 'swift'!
Mercury has the highest difference in surface temperature at the same time of all planets or even satellites. The side facing the sun can reach a temperature of 427 degrees Celsius, hot enough to melt most metals, while the surface of the other side has a temperature of -183 degrees Celsius! So, while one side of Mercury bakes, the other side of the planet freezes.
It is very difficult for scientists on Earth to get information about Mercury since the planet is so close to the sun. This makes it difficult to be observed at all hours, and Mercury can only be observed only during limited time frames. Most of our information about this planet has reached us thanks to the MARINER 10 spacecraft.
Sunrise and Sunset
On Mercury, the sun rises twice and sets twice! That's right. The sun appears to rise, set, and rise again during sunrise, and again it appears to set, then it rises again, and sets again at sunset. This is because of Mercury's highly elliptical orbit. The only planet which has a more elliptical orbit than Mercury is Pluto.
Ice on Mercury?
Mercury, being so close to the sun, seems to be the planet least likely to have ice. However, studies suggest that ice may be present on Mercury, on its poles. The poles seem to have deep craters, where the ice is shielded from sunlight, which is why it hasn't yet melted. However, this is a theory which is still to be tested.
The surface of Mercury is filled with craters caused due to impacts with meteoroids or volcanic eruptions. In fact its surface is very similar to the surface of the moon. Mercury has no natural satellites.
Mercury is believed to have a strong magnetic field, which is a little weaker than that of the Earth. This is possibly caused due to a core made up of iron. Mercury has a very dense iron core, and this planet is almost as dense as the Earth, even though it is much smaller.