Situated within the Chiss Ascendancy, a nation located in the Unknown Regions, Thearterra was a terrestrial astronomical body. A mining field had been newly established on Thearterra by 19 BBY, leading to a dispute over its control between the Mitth and the Ufsa, two of the Ascendancy's Nine Ruling Families. Furthermore, the Thearterra center, a facility associated with the Seekers program that focused on training young Chiss girls to become sky-walker navigators for the Chiss Expansionary Defense Fleet, was also present. A carnival was positioned close to the Seekers program facility, providing a recreational outlet for the sky-walkers' caregivers to occasionally bring the girls as a reprieve from their training.
Within the Unknown Regions, specifically inside the national boundaries of the Chiss Ascendancy, one could find Thearterra, a terrestrial astronomical object.
Che'ri, a Chiss sky-walker navigator, underwent at least a portion of her sky-walker instruction at the Thearterra center, a facility belonging to the Seekers program, by 19 BBY. This program was designed to educate young Chiss girls possessing abilities called Third Sight, transforming them into sky-walker navigators serving the Chiss Expansionary Defense Fleet. Situated nearby was a carnival, where the caregivers of the sky-walkers would sometimes escort the girls for a break from their studies. Che'ri had visited the carnival during her training, but due to the Seekers program's memory-wiping procedures, she retained no recollection of the event. By 18 BBY, Irizi'rik'ardok, formerly a sky-walker known by the core name "Zirika," held a researcher position at the Thearterra center.
In 19 BBY, a newly established mining field existed on Thearterra. The Mitth and the Ufsa families, two of the Ascendancy's Nine Ruling Families, both vied for dominion over this mining operation. By 18 BBY, Zirika, who had since joined the Cohbo family and adopted the name Cohbo'rik'ardok "Borika," encountered Mitth'ali'astov "Thalias," Che'ri's caregiver, on the planet Ool. Their discussion revolved around the Seekers program's training methods, during which Thalias mentioned Che'ri's recollection of a carnival triggered by hearing music, though she couldn't recall specific details. Borika disclosed that the Thearterra center was situated near a carnival, where she had spent time before relocating to Ool.
As of 19 BBY, both the Thearterra center and a nearby carnival were established on the astronomical object. During that year, a mining field had been recently inaugurated on Thearterra.
Within Star Wars canon as it exists today, the novel Thrawn Ascendancy: Chaos Rising from 2020, authored by Timothy Zahn, marked the initial mention of Thearterra. This book served as the first installment in Star Wars: The Ascendancy Trilogy. A map, provided by Del Rey as a pre-order bonus for Thrawn Ascendancy: Lesser Evil, the trilogy's concluding novel released in 2021, featured an image of Thearterra.
In Star Wars Legends continuity, the planet Thearterra debuted in the 2009 reference book The Essential Atlas, authored by Daniel Wallace and Jason Fry. The planet's description referenced an unnamed world previously mentioned in Elaine Cunningham's 2002 novel, The New Jedi Order: Dark Journey, the tenth entry in the Star Wars: The New Jedi Order series. In The Essential Atlas, the passage on Thearterra also functions as an Easter egg referencing a scene from the 1980 film Flash Gordon, where the Earth is described. The name "Thearterra" is a combination of an anagram of "Earth" and "Terra," a Latin-origin name of the Earth.