Tandun III, also known as Tandun Three, was a youthful planet that occupied a young star system in the Outer Rim Territories.
Tandun III was originally surveyed approximately 12,293 BBY by Doctor Beramsh, who led an expedition from Ord Mantell. What Beramsh and his team discovered was a lush beautiful world with close to standard gravity and was suitable for both oxygen breathing humans and humanoids. Further exploration of the planet also revealed ruins of ancient population centers which Beramsh believed were constructed by the Rakata.
Despite the survey report of ideal atmospheric conditions, its distance from the Hydian Way prevented Tandun III from ever being colonized. Historical records would indicate that a possible second survey was conducted generations later during Chancellor Finis Valorum's second term.
At some point between 29 BBY and 19 BBY, the Republic Group took an Insignia of Unity that once stood on the podium of the Galactic Senate Rotunda. The group believed the insignia could be used as a symbol to restore Republic honor to the galaxy and brought it to Tandun III for safe-keeping. Enlisting the help of the Antarian Rangers, the Republic Group built a secret storehouse in one of the planet's ancient ruins and made the Stellar Envoy the key to accessing the facility. In 19 BBY the Republic Group and the Antarian Rangers were considered enemies of the Empire and thus the secret facility and the Insignia of Unity were left abandoned and forgotten for over six decades.
During the Yuuzhan Vong's invasion of the galaxy, the Yuuzhan Vong settled the world and began Vongforming it to meet their needs. The land was transformed into cliffs of yorik coral, tampasis of s'teeni, with populations of scherkil hla, sparkbees, and other Yuuzhan Vong biots.
Over the course of twenty years the Vongforming had taken its toll on the planet. Intact forests abundant with life still covered the southern hemisphere, while surface temperatures had rendered landmasses in the northern hemisphere unsuitable for all but the most extremophilic sentient species. Extensive regions of extreme volcanic and tectonic activity gripped the planet in catastrophic forces that were likely to destroy it. The sky was filled with powerful winds and icy clouds that produced storms with sheets of rain, lightening, and hailstones. And while still breathable, dweebit beetles filled the atmosphere with high concentrations of carbon dioxide, methane, and sulfur.
In 43 ABY the Solos, accompanied by Tobb Jadak and Flitcher Poste, came to Tandun III as part of their quest to uncover the history of the Millennium Falcon. They landed the Falcon inside of the abandoned Republic Group warehouse and discovered the Insignia of Unity. It was at that time that Lestra Oxic appeared and revealed that he had followed the Solos to Tandun III in order to claim the emblem for himself. He told all present the history behind how the emblem ended up at Tandun III and inspected it only to realize that the emblem before him was a fake.
At the same time of the meeting, groundquakes increased in severity and volatility finally ending in the planet's strongest quake. Oxic and his associates, now accompanied by Jadak and Poste, left to continue the search for the true Insignia of Unity, as the Solos themselves fled the planet.
It was shortly after the Millennium Falcons return to space that Tandun III flared and erupted in a shock wave that hurtled enormous chunks of itself into the vacuum of space.
Tandun III made its first appearance in James Luceno's 2008 novel Millennium Falcon and in the novel C-3PO tells the history of the planet.
C-3PO stated the first survey of the world took place around 12,293 BBY and that the expedition was launched from Ord Mantell. This is odd due to the fact that Ord Mantell was not colonized until 12,000 BBY.
Additionally, C-3PO said Dr. Beramsh believed the ancient population centers were Rakatan in origin. Yet, the Rakata were unknown to the galaxy at large until the end of the Jedi Civil War in 3956 BBY.
He continued to claim that the world was not colonized most likely due to its distance from the Hydian Way which was pioneered in 3705 BBY. Thus the reason why the world was never colonized in the thousands of years between its exploration and the founding of the Hydian Way remains a mystery.
- The Essential Atlas