Dubiously Canon
Dirk's depiction of Deltritus.
Deltritus is an “M-Class planet” first mentioned in The Homestuck Epilogues: Candy, Postscript and featuring in Homestuck^2: Beyond Canon.
Name
Deltritus' name fits with several trends among the names of other planets in the Homestuck universe. The name Deltritus appears to be at least partially derived from the Greek letter delta. Delta is the fourth letter of the Greek alphabet, mirroring Deltritus' position as the fourth named planet after Beforus, Alternia and Earth. A river delta is also the part of a river where it starts to form the most branches, reflecting the planet's geography. Deltritus may also be intended to act as the fourth 'Earth', with the alpha and beta Earths being named for the first and second letters of both the Greek and Latin alphabets, and Earth C being named for the third Latin letter.
With the addition of Deltritus, the first five letters of the Latin alphabet are all somehow represented in the names of the Homestuck series' main planets; Alternia, Beforus, Earth C, Deltritus, and Earth (B1 or B2).
The planet's name may also derive from detritus, a Latin noun meaning "waste or debris of any kind".
History
Deltritus was first discovered on the Theseus' sensors by Rose Lalonde, who found it to be the “right size, right age, right distance from the sun”
for Dirk Strider's plans. The two had apparently been searching for such a planet for several years.
It was “well over three years” before the pair arrived with Terezi Pyrope on the planet, failing to land properly and leaving the Theseus totalled. Dirk decided on the name Deltritus without first checking with his daughter; Rose described the name as “insufferable” (“Like "Alternia" or "Beforus"”), but “the perfect name” for the planet nevertheless. Once there, Dirk proposed a game with Rose; “[t]wo gods, two species, one copy of the Game.” Each of the two would take turns using the Ecto-Alchemologizer to create species to populate the planet. Though Deltritus housed “no advanced life” at the time of its discovery, before long it was inhabited by a whole host of Dirk and Rose's experiments.
Habitation
Deltritus as it appeared upon the arrival of the Theseus.
Deltritus' most prominent indigenous lifeform was the arboreal ambulator, which “4R3 PL4NTS IN THE STR1CT S3NS3”, but whose bodies are composed primarily of hollow tubes which catch the planet's breeze and cause the whole plant to move as if walking. This constant uprooting and rerooting causes near constant and instantaneous geological activity such as ravines opening and closing and waterways shifting course.
Once Dirk and Rose's game began, a myriad of new species began to populate the word. Among these were larval insects with lagomorphic heads, plushlike animals with humanoid faces, unicorns with goatlike eyes, rotund dragonlike quadrupeds, chimeraic flying grubs, feline cephalopods, and an equine plant with tentacle-like prehensile vines.
At least some of Deltritus' forests are composed of straight-trunked and immobile trees, with luminous fungi and tall grasses growing in the shade of their canopies; however it is unknown whether these forests developed on the planet naturally or are a result of Dirk and Rose's Ecto-Alchemologizing.