Kicking off our 5 Facts series we have the littlest member of our planetary family!

  • Mercury is the smallest planet 

Pluto used to be the smallest planet in our solar system but since it was ‘demoted’ to a dwarf planet, Mercury then won the prize for being the smallest planet in our solar system. It has a diameter of 3,030 miles (4,876 kilometres) or for those of you like me who like a comparison, the size of our Moon or the size of the United States! Just because it’s the smallest doesn’t mean it’s boring however… 

NASA – Scale model of the Solar System
  • All hot and cold 

Like our Moon, Mercury has no atmosphere, so the surface is either extremely hot or freezing cold. It gets up to 430 degrees Celsius on the side facing the sun, but on the side facing away from the Sun temperatures get as low as -180 °C. So, Mercury being the closest planet to the Sun does not mean that it is our hottest planet! 

  • Attractive Proposition 

Mercury’s iron core takes up about 75 percent of the planet’s radius. This makes it the planet with the largest iron core. Therefore, Mercury has a very strong magnetic field. The field is quite active and frequently interacting with the solar wind and channels plasma from the sun to the planet’s surface. The hydrogen and helium taken from the solar wind help create part of Mercury’s thin atmosphere. 

Photo credit: NASA 
  • Mysterious Mercury 

It may be the fastest and smallest planet in our solar system but it is the planet we know least about. For a long time, the only data we had on Mercury came from the Mariner 10 probe which went there in 1974. This is due to the complexity of the path it takes to get to Mercury. In 2004, Nasa sent the Messenger mission to the planet and since then it has succeeded in mapping the surface of Mercury. 

NASA. An artist’s impression of Mariner 10 probe. 
  • BepiColumbo 

This mission took off in October 2018 and hopes to arrive on Mercury in late 2025. BepiColombo is named after a Professor of mathematics and engineering, Giuseppe (Bepi) Colombo. He also suggested to NASA how to use a gravity-assist swing-by of Venus to place the Mariner 10 spacecraft in a solar orbit that would allow it to fly by Mercury three times back in 1974. The information obtained when BepiColombo arrives will help us further understanding about the composition and history of Mercury, but also on the history and formation of the inner planets in general, including Earth.

So, watch this space… 


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