Mercury is the first planet of the solar system, which means it is the innermost and closest planet towards the Sun. It also means it has the lowest mass, and shortest orbital period. Its mass is 3.285 × 10^23 kg, and its orbital period is only 88 days! You may think, that Mercury is the hottest planet. However, it is not! Venus is because there is a lot of carbon dioxide, and Mercury has limited of it. Mercury was first discovered by Timocharis at around 265 BC. Zupus discovered and studied Mercury's orbit in 1639. This planet literally almost has no atmosphere. It contains very small amounts of hydrogen, helium, and much smaller amounts of potassium, sodium, and magnesium. Most of its gas particles are formed by radioactive decay, or solar winds.

Physical Features

Some physical features of Mercury include craters such as Tolstoj, Raditladi Basin, and Beethoven. There are also some plains in Mercury, including Caloris Planitia.


Believe it or not, Mercury has a molten core. Normally planets tend to cool down fast, but when NASA researchers studied the core, that was not the case. Mercury does not cool down. Now, scientists believe the core consists of sulfur, which would lower the melting temperature of the core.