Know your Solar System – Mercury

We all have learnt about our solar system and its planets in high school. Like, its mass, size and blah blah the things we know. But there’s so much more than what we learnt. So many discoveries have been made and still being in the making. Hence this article. There’s going to be one article for every planet in the solar system every week or every other week. 

Let’s go in the Nature’s chronological order. Mercury. Named after the messengers of the Gods, its the smallest planet in the solar system which closely resembles our Earth’s Moon. Until 1543, astronomers didn’t realize Mercury was a planet.

Interesting facts about this terrestrial rock:

  • It’s one of five planets that’s visible to the naked eye from Earth – usually appears in the horizon during dusk/dawn.
  • The gravitational lock with the Sun which has slowed down the rotation of the planet. Thus a year is 88 Earth days approx and yet, a day in Mercury is 176 Earth days approx. Fun fact: If a person standing on Mercury’s surface would see the sun start to rise, then briefly set and then rise again – all within the same day. This is due to its orbital speed being higher than the rate at which it rotates on its axis.
  • It has an eccentric orbit – that is, elliptical. Fun fact: It’s orbit was so important in proving Albert Einstein’s General Theory of Relativity. 
  • It has about only 1/30 degree tilt – the smallest tilt, hence it doesn’t experience any seasons.
  • It is 36 million miles away from the Sun and the Sun would appear more than three times as large as it is seen from the Earth. Now, that’s majestic! Despite being closer to the Sun, Mercury isn’t the hottest planet in our solar system. Shocking? Yeah. I know. That’s because Mercury doesn’t have an atmosphere to trap heat. Sad times.

Mercury’s visitors:

Due to where it is located, its harder for any spacecraft to reach. In spite of that, two missions have visited this rocky planet. Mariner 10 and MESSENGER.

Mariner 10

Mariner 10 – Part of the Mariner program, and the last one of it, this spacecraft was launched in 1973 by NASA with the mission to flyby Mercury and Venus. Its the first spacecraft to use the concept of slingshot, use another planet’s gravity to reach its destination – in this case, Venus. The kind that has now become so common and helpful. This mission conducted three flybys in 1974 and 1975. It flew by Mercury and photographed about 45 percent of the planet’s surface and helped mapping it. It is believed to be orbiting the Sun after it ran out of fuel on March 24, 1975.


MESSENGER – Short for MErcury  Surface, Space ENvironment, GEochemistry, and Ranging – NASA’s mission became the first probe to orbit Mercury. Its mission was to study Mercury’s chemical composition, geology and its magnetic field. It completed its mission in 2012. It used its last of its propellant to deorbit and plunge itself into Mercury’s surface in April, 2015.  This mission gather significant data, including details about its magnetic field and the discovery of water ice at the planet’s north pole.


BepiColombo – Its a joint mission by European Space Agency and Japan Aerospace Exploration Agency, the probe was launched in October 2018 consisting of three components – Mercury Transfer Module for propulsion, Mercury Planetary Orbiter and Mercury Magnetosphere Orbiter built by JAXA. Its expected to arrive at Mercury in December 2025 after a flyby of Earth, two flybys of Venus and six flybys of Mercury itself.

Temperature depiction

Mercury is a tough place for life to survive. Its atmosphere is composed of oxygen (O2), sodium (Na), hydrogen (H2), helium (He) and potassium (K); most of these are blasted off by solar winds causing the thin atmosphere that it has. The daytime temperature can reach up to 430 degree Celsius and drop to -180 degrees Celsius.

That’s more than enough about Mercury, watch out for Venus next. Drop a text in my inbox if you wanna know more!

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