Quick Facts - Mercury

  • Age: 4 Billion years old
  • Mercury Day: ~ 58 Days
  • Mercury Year: ~ 88 Days
  • Type of Planet: Terrestrial Planet, Lifeless Planet, Barren Planet
  • Distance from Sun: ~ 58 Million KMs
  • Natural Satellite: 0
  • Named after: Roman messenger god Mercury


Mercury is the smallest and innermost planet in our Solar System, named after the Roman messenger god Mercury. Like Venus, Mercury orbits the Sun within Earth’s orbit as an inferior planet.

The planet can only be seen near the western horizon after sunset or eastern horizon before sunrise, usually in twilight. At this time, it may appear as a bright star-like object, but is often far and more difficult to observe. Mercury has no natural satellite.


Mercury rotates in a unique way; it rotates on its axis exactly three times for every two revolutions it makes around sun. Meaning it appears to rotate only once in two Mercurian years, therefore only one day every two Mercurian years is observed. Mercury’s axis has the smallest tilt of any of the Solar system’s planets (1⁄30 degree).

Surface Geology and Conditions

Mercury’s surface appears heavily cratered (large cavities in surface) Caloris Basin being the largest known carter. It is similar in appearance to the Moon’s; it has been geologically inactive for billions of years. Due to no atmosphere its temperature ranges from 100 K (-173°C) at night to 700 K (427°C) during day across the equatorial regions, while the Polar Regions are constantly below 180 K (-93°C).

Mercury is too small and hot for its gravity to retain any significant atmosphere over long period of time. It contains mostly Hydrogen, Oxygen, Sodium, Calcium, Potassium and others.

Mercury’s magnetic field is about 1.1% the strength of Earth’s. Like that of Earth, Mercury’s magnetic field is dipolar; its magnetic field is strong enough to deflect the solar wind around the planet.


Mercury was heavily bombarded by comets and asteroids during and shortly following its formation 4.6 billion years ago. During this period of intense carter formation was assisted by lack of atmosphere making Mercury volcanically active. Like Earth, the metallic core of Mercury formed first, and then gathered lighter elements around it to form its crust and mantle.

Space Probes sent to Mercury

Mariner 10

Mariner 10 was an American robotic space probe launched by NASA. It flew by Mercury three times and mapped about half of the planet’s surface. It also discovered Mercury’s thin atmosphere and detected its magnetic field.


MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) was NASA’s robotic spacecraft that orbited Mercury between 2011 and 2015, studying Mercury’s chemical composition, geology, and magnetic field.

Amazing Facts

1. Your weight on Mercury would be 38% of your weight on Earth.

2. A year on Mercury takes 88 Earth days.

3. It’s not known who discovered Mercury.

4. Mercury is the second densest planet.

5. Mercury has wrinkles: As the iron core of the planet cooled and contracted, the surface of the planet became wrinkled.

6. Mercury is the most cratered planet in the Solar system.

7. Mercury is the second hottest planet after Venus.

Home | Explore | Units

Curated By: Radhika Bangar