A planet's Defense stat proportionally modifies the amount of damage done by incoming attacks from enemy planets.
For example, if an incoming attack has an arrival energy of 1.5K and the target planet has a Defense stat of 120, the attack will reduce the target planet's energy by
(1.5K * 100) / 120 = 1.25K. Conversely, if the target planet's Defense is below 100 the damage done will be increased proportional to the arrival energy (from previous example:
(1.5K * 100) / 80 = 1.875K).
Defense does not affect energy sent between two planets owned by the same player.
A planet's Defense may be increased to make it harder for opponents to capture by upgrading its Defense rank.
A planet's defense is shown on the information panel by a shield icon:
The maximum defense a single planet is capable of would be a level 1 Nebula planet that has: a x2 defense comet; 3 upgrades into defense; equipped with a mythic planetary shield - giving a total of 8985 defense.