## Lunar Gravity

Relate the lack of atmosphere to the Moon's low gravity

Mass is the amount of matter that a body (such as a table, bar of chocolate or a planet) contains.

The mass of the Moon is just 1/81th of the Earth's.

Gravity means the attraction that a body exerts on another, such as the force that the Earth exerts on a person.

Gravity is just over 1/6th (16.6%) that of Earth's.

This means that if you were able to jump one metre off the ground on Earth, you would, in theory, be able to jump six metres on the Moon.

The spaceperson in the figure on the right jumps higher on the Moon as the gravity there is six times weaker than Earth's.

Without enough gravity a planet or moon would not be able to keep an atmosphere - it would evaporate into space. Saturn's largest satellite, Titan has an atmosphere because it is larger than our Moon and has a greater mass. It is also much further from the Sun and does not experience the strong solar wind that our Moon does.

###### Questions
• Why is the effect of gravity on the Moon much less than on Earth?
• Why does the Moon not have an atmosphere when nearby Earth does?
###### Summary
• The Moon has 1/6th of the gravity that Earth does.
• The Moon cannot keep an atmosphere because of its low gravity and mass.