The playing environment in EVE Online consists of over five thousand star systems, almost all of which can be visited by the player.[1] Each solar system is connected to other systems by one or more stargates, and in this way neighboring systems are organized into constellations and constellations are in turn organized into regions. In total there are 64 regions.[1] The central regions make up most of the so-called high-security space with some low-security systems in between. Surrounding these are regions with no security, or 0.0 (zero-zero).[19] (See section Security index system for more information). In some solar systems a player might be alone. In others more than 600 players might gather, e.g. for a fleet battle or to use a trading hub. Different systems contain different types of celestial objects, making them more or less suitable for different kinds of operations. In a typical solar system the player will find asteroid fields, stations, and moons, the latter two most often orbiting planets. Planets themselves are currently not explorable; however, players can use moons to anchor their parent corporation's structures for production and research or for moon mining. Asteroid fields can be mined for minerals. Other objects that can be found in systems are the aforementioned stargates, complexes or static dungeons for exploration. Occasionally a player may even stumble across a historic site, e.g. one where another player's Titan-class ship was destroyed and the wreck now floats in space. In addition, an area of the galaxy is occupied by the Jovian Empire, and is currently not accessible by players.