Official and fan location Beyond the Solar System
by HåvardAlpha Centauri
Sources: Immortal Set
Distance from Mystara: 4.3 LY
double star system
Fan material by Mystaros postulates that this world became colonized by the Blackmoor Civilsation. It is unknown what happened to the colony after Blackmoor was destroyed.
Sirius
Source: Immortal Set
Distance from Mystara: (8.6 LY),
double star system
Fan material by Mystaros postulates that this world became colonized by the Blackmoor Civilsation. It is unknown what happened to the colony after Blackmoor was destroyed.
Epsilon Eridani
Source: Immortal Set, VotPA
Distance from Mystara: (10.7 LY)
"The closest civilization able to use magic (counting only those outside the home system of humanity) is on several planets orbiting"
Fan material suggests that this world is the original homeworld of the Pytherians, some of whom became pirates in Mystara's Solar system. One break off group settled on Mystara's continent of Davania and founded the nation of Emerond (VotPA, PWA)
Procyon
Source: Immortal Set
Distance from Mystara:(11 LY)
double star system
Fan material by Mystaros postulates that this world became colonized by the Blackmoor Civilsation. It is unknown what happened to the colony after Blackmoor was destroyed.
61 Cygni
Source: Immortal Set
Distance from Mystara:(11.1 LY)
double star system
Fan material by Mystaros postulates that this world became colonized by the Blackmoor Civilsation. It is unknown what happened to the colony after Blackmoor was destroyed.
Tau Ceti
Source: Immortal Set
Distance from Mystara:(11.2 LY)
Fan material by Mystaros postulates that this world became colonized by the Blackmoor Civilsation. It is unknown what happened to the colony after Blackmoor was destroyed.
Note: Frank Mentzer said this was the location of his Aquaria/Empyrea campaign world.
Altair
Source: Immortal Set
Distance from Mystara:(15.7 LY).
Fan material by Mystaros postulates that this world became colonized by the Blackmoor Civilsation. It is unknown what happened to the colony after Blackmoor was destroyed.
Aelos
Source: CM6 Where Chaos Reigns
Note some fan material have interpreted Aelos to be located in Mystara's solar system or even to be Mystara itself, simply at different points in the timeline.
Old Alphatia
Source: M1 Into the Maelstrom
Note: WotI retcons Old Alphatia into another Dimension.
Old Pytheria
See Epsilon Eridani
The Galactic Federation
Source: DA3 City of the Gods. Additional Information in Supplement II: Blackmoor, DA1, DA2, DA4, WotI
Some sources suggest this is a separate dimension
Some fan material assumes this Federation occupies numerous worlds near the Galaxy's Hub
Spillworld, The
Source: DotE
While DotE says this world exists outside Mystara's solar system, the scenario makes more sense if the world is placed a bit closer to Mystara.
Planar Spider Worlds
Source: RC (Speculative)
Planar Spiders appear across Mystara's multiverse, including the Prime Plane travelling in saucer like vessels. They are a trade oriented civilisation.
Adaptor Homeworld
Source: RC (speculative)
Adaptors are a shape changing race said to be native to all planes of existance. They travel across worlds to observe and exchange knowledge with with each other.
Oard Worlds
Source: CM6 (Speculative)
Mek World
Source: RC (Speculative)
The insect-like race of sorcerers who created the constructs known as Meks are extinct on Mystara, but they could easily exist somewhere in the galaxy.
M'Kar World
Source: X6 (Speculative)
Very little is known about the M'Kar, but they have six fingers on each hand.
The Galaxy's Hub
Source: Immortal Set
This region of space is where stars are much closer together meaning space travel is much easier. It is also a reqion of much higher radiactive energy levels meaning travel there is much more dangerous.
It is speculated as a possible locaton for the Galactic Federation.
Nithian Colonies
Source: Gaz2, DotE (Speculative)
We know that the Nithians were powerful enough to contact civilisations across the galaxy (ie Old Alphatia) and invite them to Mystara. It does not seem unlikely that they could have settled other worlds.
Oltec Colonies
Source: HW Boxed Set (Speculative)
There is no official hint of Oltec or Aztec exploration of other worlds, but it does make sense and fits well with the real world inspiration for the cultures.