The Moon and Mercury
Scorched and Battered Worlds

April 7, 2011, jeb


go to the Moon
go to Mercury

Similar Bodies

The Moon - Earth's only natural satellite
Mercury - Smallest terrestrial planet - closest planet to the Sun
These two bodies are similar in appearance in many respects:

The Moon - General Properties

The Moon's Orbit around the Earth

Moon's Gravity on its Surface

Newton's Law:
F = G (M1)(M2) / R2, where G is a constant

So the force pulling on you (suppose you are M2), on the surface of the Moon, would be proportional to M1 / R2, or the mass of the Moon divided by the distance to the center of the Moon, squared.
Since the Moon has about 1/80 of the mass of the Earth, and it has about 1/4 of the radius of the Earth, gravity on the surface would appear about (1/80)/(1/4)2 = 1/5 as great as on the Earth. (a more accurate estimate comes out to 1/6.)

The Moon's Surface Features and Character

The Moon's Internal Features

Origin of the Moon

Impact Theory

Evolutionary History of the Moon

Phases of the Moon

Lunar eclipses

Other Sources on the Moon

StarDate Guide to the Moon
Views of the Solar System - the Moon
The Nine Planets - the Moon


Mercury is the closest planet to the Sun

Named for the fleet-footed messenger of the gods by the Romans

Observing Mercury from Earth

Character of Mercury's Surface

Mercury - General Properties

Mercury's Spin-orbit Resonance

Mercury's Internal Features

Messenger Mission

Mercury's Basic Properties

Planet order from Sun
Orbital period
Semi-major axis
Surface Gravity
Escape speed
Rotational Period
Surface Magnetic Field
Surface Temperature

0.24 years (88 days)
0.39 AU
0.055 x Earth
0.38 x Earth
5430 kg/m3
0.38 x Earth
4.2 km/s
58.6 days
0.011 x Earth
100-700 K

Golden Globe Awards for Mercury

  • Closest planet to the Sun

  • Lightest planet

  • Surface temperature swings are the most extreme

  • Orbit has largest deviation from the plane of the ecliptic

  • Orbit is most eccentric of the planets

  • Spin-orbit resonance locks 3 rotations every 2 orbits

Other Sources on Mercury

StarDate Guide to Mercury
Welcome to the Planets - Mercury
Views of the Solar System - Mercury
The Nine Planets - Mercury