Outpost

Outpost can be one of three types Outpost are created by Engineer units, which, like settler ships, are consumed by the creation of the outpost.
 * 1) Mining - Grants a increase in production for your colonies in the system. Can be created in systems that have asteroid belts.
 * 2) Science - Grants a increase in science for your colonies in the system . Can be created in systems that have gas giants.
 * 3) Planet - Can be created on any un-occupied planet.

Outposts of any kind expand the range of your ships. If any planet is within your current fuel range tech of any outpost or colony, your ships can travel to that planet. As outposts are less expensive than colonies, this can be a a way to expand your ships area of operations faster or cheaper. But note that outposts are much more vulnerable than colonies. Any warship can automatically destroy an outpost in a single turn. Colonies have to be bombarded and invaded, by specialised ships.

Outposts, like Colonies, also allow all damaged ships to be fully repaired at the end of each turn. So while fighting for control of a system it is very useful to place an outpost on an unoccupied (or forcibly depopulated) world in the contested system. A colony is better as it is more durable but an outpost can make a huge difference to winning or losing a multi turn battle.

Also note that mining outposts can only be created once you have developed Asteroid Mining Tech.

If there are multiple friendly asteroid Outposts or Science Stations in one system, the Production or Science bonuses are added, not multiplied. So 20% + 10% = 30% (not 1.20 x 1.10 = 1.32).

If you have an outpost in a system but no colonies, there is no benefit, other than extending the range of your ships, and the fact that damaged ships will be repaired there.

An outpost in a system does not appear to give any benefits to colonies of other empires in that system. Though it's hard to tell for sure other than testing in a Hotseat game.