Gravity Wells are a game mechanic on Horizon's End.
A gravity well is generated either by a static body of mass, such as a star or planet, or by a ship or NPC nest.
Natural Well Sizes
All stars, and Horizon, have a gravity well with a radius of 1800.
All planets have a gravity well with a radius of 1000.
NPC nests generate a gravity well with a radius of 1500.
Alien "Watcher" NPCs, Teraliths and Verdoliths spawned by the nest generate a gravity well with a radius of 2400.
Artificial Well Sizes
Ship well radius is determined by a formula.
Civilian Ships
((3000 / sqrt(12000)) * sqrt(block count)) / 2
Warships
(3000 / sqrt(12000)) * sqrt(block count)
Starfighters, Interceptors, Shuttles, Speeders, and Platforms are incapable of creating a gravity well.
Gravity well strength
If a ship is within a gravity well of strength greater than the players jump strength, the player's ship cannot jump through that gravity well.
All planets & stars have a well strength approaching 1,000,000.
As of right now, all player ships have a well strength of 1.
Loci likewise have a well strength of one.
Battlecruisers & barges have a jump strength of two, while all other player ships have a jump strength of one. (Note that cruisers MAY have a jump strength of two, but I don't know)
The equation can be visualized using this graph: