Why the Earth Needs the Moon
Without the Moon, the Earth's axis would swing chaotically. A scientifically proven phenomenon with profound consequences for all life.
What keeps the Earth's axis stable?
The Earth doesn't rotate like a perfect sphere. It is thicker at the equator than at the poles. This equatorial bulge is a point of attack for gravitational forces - from the Sun, from the planets.
Without a counterweight, this force would drive the Earth's axis into chaos.
The counterweight is the Moon.
[Laskar & Robutel] In 1993, Jacques Laskar and Philippe Robutel published a groundbreaking study in Nature. They simulated the evolution of the Earth's axis over millions of years - with and without the Moon.
The results were shocking:
| Scenario | Axis Inclination | Time Period | Consequence |
|---|---|---|---|
| With Moon | 22.1° - 24.5° | Stable over billions of years | Stable Seasons |
| Without Moon | 0° - 85° | Chaotic, Unpredictable | Climate Chaos |
The difference from 22.1° to 24.5° seems small. But it is the difference between ice ages and warm periods.
The difference from 0° to 85°? That is the difference between life and death.
In physics, "chaos" has a precise meaning: sensitive dependence on initial conditions. Small changes lead to completely different outcomes.
For the Earth's axis, that means:
| Axis Inclination | What Happens |
|---|---|
| 0° | No seasons. Equator brutally hot, poles eternally dark and cold. |
| 45° | Extreme seasons. Summer with midnight sun reaching the tropics. |
| 85° | The poles point almost at the Sun. Half year day, half year night - everywhere. |
At 85° inclination, every point on Earth - except a narrow strip at the equator - would experience half a year of continuous light and half a year of darkness.
The Moon is large. Unusually large for a satellite.
| Comparison | Moon/Planet Ratio |
|---|---|
| Earth-Moon | 1:81 (Mass) |
| Mars-Phobos | 1:6,000,000 (Mass) |
| Jupiter-Ganymede | 1:12,000 (Mass) |
The Moon is so large that some astronomers speak of the Earth-Moon System as a "double planet".
This size has consequences:
The Moon forces the Earth to wobble - but it prevents it from falling over.
The Laskar-Robutel study of 1993 became consensus. But science is never finished.
[Lissauer 2012] In 2012, Lissauer and colleagues published a reassessment:
| Study | Result | Limitation |
|---|---|---|
| Laskar 1993 | Without Moon: 0°-85° Chaos | Certain initial conditions |
| Lissauer 2012 | Stability possible at 0° starting inclination | Only if axis perpendicular to orbit |
| Current View | Moon helpful, but maybe not necessary | Depends on initial conditions |
The truth is somewhere in between:
Stability is not just an astronomical curiosity. It is the prerequisite for complex life.
| Stable Planet | Unstable Planet |
|---|---|
| Predictable Seasons | Chaotic Climate Changes |
| Stable Climate Zones | Wandering Temperature Zones |
| Long-term Ecosystems | Constant Adaptation Pressures |
| Evolutionary Continuity | Mass Extinctions Every Few Million Years |
Without the Moon, evolution on Earth might never have advanced beyond single-celled organisms.
Science has answers to this question. But before we look at them, let us pause.
In the following subsections we will examine:
Only after we have seen all these puzzle pieces will we return to the scientific explanation - and ask whether it answers all our questions.
The next subsection examines the Earth Tides - and the energy the Moon pumps into the Earth.
The Moon stabilizes the Earth. But it does more: It deforms our planet - daily, measurably, energetically.
The Moon stabilizes the Earth. But it does more: It deforms our planet - daily, measurably, energetically.