1. Mercury is the closest planet to the sun.
2. Mercury is the smallest of the eight planets. It is slightly larger than Earth's moon.
3. Mercury is the fastest planet to orbit the sun. It takes 88 Earth days for Mercury to fully orbit the sun.
4. Mercury's day is longer than it's year! Mercury rotates slowly but it's orbit is faster than the other planets which means that it's day is longer than it's year. In a day on Mercury there 1,407h, 30m and 14 seconds/176 Earth days. (Imagine waiting for a day to pass on Mercury only to find out that it has been about 2 years)
5. It is named after the roman god, Mercury, the messenger to gods, most likely related to the orbiting speed of the planet.
6. Mercury has been known to humanity since ancient times and although its discovery date is unknown, the first mentions of the planet are believed to be around 3000 BC by the Sumerians.
7. After the Earth, Mercury is the second densest planet. Despite its small size, Mercury is very dense because it is composed mainly of heavy metals and rock.
8. Astronomers didn’t realize that Mercury was a planet until 1543 when Copernicus published his Sun-centered model of the Solar System – putting the Sun as the centre of the solar system rather than the previously believed centre, the Earth.
9. The planet has just 38% of the gravity on Earth. This means that Mercury isn’t able to hold the atmosphere it has and it instead gets blown away by solar winds. However those same solar winds are also bringing in new gases, radioactive decay and dust from micrometeorites – replenishing the atmosphere.
10. Mercury has no moons or rings because of its low gravity and lack of atmosphere.
11. Mercury is the second hottest planet in the solar system.
12. Mercury does not experience any seasons. The axis of Mercury has the smallest tilt of all other planets, and this results in a lack of seasons on its surface.
13. Mercury is the only planet which doesn’t rotate exactly once every year – instead rotating three times for every two orbits of the Sun. This is because it is nearly tidally locked to the Sun.
14. Mercury has a large iron core that is around 40% of its volume (compared to a core volume of 17% for Earth) in its centre whose radius is 1800 to 1900 kilometers (1100 to 1180 miles). Scientists believe the core of Mercury is probably molten.
15. Mercury has a very thin atmosphere, which is made up of atoms from the surface of the planet that have been blown away by solar winds. As Mercury is so hot, these atoms quickly escape into space and so its atmosphere is constantly being replenished.
16. The outer shell of Mercury is only 500 to 600 kilometers (310 to 375 miles) thick. Earth’s outer shell (the mantle and crust) is 2930 kilometers (1819 miles) thick.
17. Mercury has a weak magnetic field whose strength is about 1% of the magnetic field on Earth.
18. Only two spacecraft have ever visited Mercury. It is difficult to reach the planet due to its proximity to the Sun and any spacecraft visiting would need to travel 91 million kilometers into the Sun’s gravitational potential well. The Mariner 10 visited during 1974-75, flying by Mercury three times and mapping half its surface. On March 24, 1975 it ran out of fuel and is still believed to be orbiting the Sun. The MESSENGER probe was launched in 2004 to explore Mercury’s high density, its geological history, the nature of its magnetic field and more. Another mission, BepiColombo, is to be launched in 2015 by the European Space Agency and Japan is expected to reach Mercury in 2019.
19. Mercury has more craters and impact marks that any other planet. The surface is similar to that of the Moon, as unlike most planets, Mercury isn’t geologically active and cannot “self heal” from impacts with asteroids and comets. Most of the Mercurian craters are named after famous writers and artists. If a crater is larger than 250 km in diameter, it is known as a Basin. The largest Basin on Mercury, the Caloris Basin, is around 1,550 km in diameter and was discovered by the Mariner 10.
20. Mercury is one of five planets that can be seen without using a telescope, Mercury, Venus, Mars, Jupiter and Saturn. When you look at the sky at night, the planets do not twinkle in the way that stars do.
Adjectives: Mercurian, Mercurial