The Unknown planet on the Cepheus-Draco border is the planet from which the Solomons come. It is 14 light-years and 3 billion galaxies away from Earth. ("See Dick Run, Part 1," "Pickles and Ice Cream")
The species of aliens that the Solomons belong to and who call this planet home are a race of beings of which little is known about, with everything that is known about them coming from descriptions given by the Solomons. They are described as gelatinous "Purple Tubes" (the most common description for their kind) with prong-like limbs that are capable of shapeshifting and making new bodies for themselves with parts to spare, a trait which they use to blend in with other species. The only exception to this rule is the Big Giant Head, who is, as his name indicates, a giant alien head, however as they are shapeshifters, this may simply be his preferred form.
The species is ruled by the fearsome Big Giant Head who is described as the king of the known universe. All purple tubes obey the BGH without question lest they face his wrath. It is common to salute within his presence and the BGH can execute anyone he wishes even for so much as annoying him.
Little is known about the culture of purple tubes, but almost everything about Earth culture is completely foreign to them, including emotions and basic social norms. What is known is that members of this species value order and obedience, being faithful to their superiors, but most of all to the Big Giant Head. Their primary goal is to learn about the universe and not interfere in the development of primitive life, only to observe.
It seems life on their planet is dull and uneventful, as Dick Solomon described his youth with an almost miserable tone, having been forced to work for most of his life as a color spectrum particle separator at the Assemblage Dome.
For some peculiar reason, purple tubes have an intense fear of jello.
They appear to be a genderless species (although they are capable of taking on male and female forms of other species) that reproduces artificially, with Harry Solomon in particular describing his "mother" as a "cold receptacle" and his "father" as "just a machine", showing that they are grown artificially and cared for by machines. The notion of "families" is also foreign to them initially.
However, later episodes indicate that natural reproduction is possible among purple tubes, as despite seemingly being a genderless species, it is indicated that males and females do exist among their kind, however this inconsistency may simply be due to them considering males and females of other species different from their own gender differences. Their method of reproduction involves one partner launching a protoplasm capsule into the other partner's receptor port, at which point the first partner has to wait for an impact summary. The Big Giant Head and a few others are later revealed to have relatives of their own, with the Solomons occasionally referring to uncles and cousins on the home planet, and with the BGH having fathered a son in the form of Dick Solomon and even having a niece in the form of Janet. They are also capable of producing hybrid offspring with other species thanks to being able to mimic other lifeforms, and the resulting offspring will look like an ordinary member of the species the purple tubes have mimicked.