Mercury is a fascinating planet. It is the closest planet to the sun, the smallest planet (4,878 kilometers in diameter), it has no moons, and has the most extreme temperatures of any planet in our solar system.


The gravitational pull on Mercury is actually only 38% of Earth's. A person weighing 45 kilograms (100 pounds) would weigh only 17 kilograms (38 pounds) on Mercury.


Mercury's distance from the Sun is a mere 58 million kilometers (36 million miles) away.

While 58 million kilometers might seem a long way, it is almost three times closer to the Sun than Earth is (at 150 million kilometers). Imagine looking up and seeing the Sun so close!


So it is no surprise that Mercury can get extremely hot.

Temperatures on the surface of Mercury can reach up to 430°C (800°F). The hottest place on earth, Death Valley, in California, has only reached 57°C (135°F), and even your oven at home rarely gets higher than 230°C (450°F).

But when the Sun's rays are not hitting the planet, it gets down to an extremely cold -170°C (-280°F). The Antarctic, the coldest place on earth, only gets down to -89°C (-128°F).

Such extremes!


Because of the solar winds (the stream of charged particles coming from the Sun) that attack the planet, Mercury's atmosphere has been nearly blown away.

What is left contains 95% carbon dioxide, approximately 3% nitrogen, and some argon, oxygen, carbon monoxide, and water vapor.

Mercury's atmosphere has four regions:

  • The lower area is warmed by dust and heat from the surface,
  • The middle area has a layer of winds,
  • The upper area is warmed by solar wind.
  • And above that is the exosphere which just thins out as it heads into space.


Surface and Core

The surface looks like Earth's moon, with many ridges, mountains and valleys.

It is also filled with many craters and holes formed from being hit by millions of meteroids and comets during its lifetime.

Mercury's core is liquid and is has more iron than any other planet. The rest of the planet is made up of rock.


Rotation and Revolution

It takes Earth 365 days to revolve around the sun, but it only takes Mercury 88 days. So Mercury's "year" is only about three Earth months long. You would get a lot of birthday parties!

While Mercury revolves around the sun faster than any other planet, it rotates on its axis slower than earth.

While an Earth day is 24 hours, Mercury's day is 1407 hours long, or about 59 Earth days.

Long days, but short years!

What an interesting place to live, if you could handle the heat and cold.


Mercury (on the far left), is much smaller than the other planets
Venus, Earth, Mars, and the Gas Giants Jupiter, Saturn, Uranus and Neptune

(Images courtesy NASA.)