Kerbol System
The Kerbol System is at the moment the only available solar system. It has Kerbol as the central body which is orbited by 5 planets and 2 dwarf planets. Only Kerbin and Laythe have an oxygen atmosphere and only Kerbin hosts life.
With the outermost dwarf planet Eeloo it reaches up to 113 549 713 200 m (about 113.5 Gm or 0.76 AU) out into space. Compared to our solar system it is a very small system, as Earth's periapsis (or more specific perihelion) is about 147 Gm (or 0.98 AU) and thus outside of Eeloo's orbit.
It is difficult to determine if or where the Kerbol System has an edge. Kerbol itself has a non relativistic escape velocity, so it is possible to escape Kerbol. But itself it is not possible to escape Kerbol's gravitational pull, because the sphere of influence is infinite. Although real world gravity expands into infinity, it does only for Kerbol in KSP so it's unclear if this property can be used for determinate where the edge is.
System
 Kerbol
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 Moho
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 Eve
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 Gilly
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 Kerbin
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 Mun
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 Minmus
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 Duna
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 Ike
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 Dres
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 Jool
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 Laythe
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 Vall
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 Tylo
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 Bop
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 Pol
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 Eeloo
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| (Sizes and distances not to scale) | ||||||
