Gliese 581d

Gliese 581 D was one of the first human colonies settled after Earth's population had been evacuated. The planet that supported the colony was 20 light-years from Earth and had twin suns.

When Bill asked the Twelfth Doctor travel to the future with her, he took Bill to Gliese. (TV: Smile)

Landscape
Gliese's sky was blue, and it had two suns. The city that would serve as the home of the colonists was surrounded by vast fields of wheat. The architecture of the city was made up of futuristic and smoothly designed buildings with many windows and an overall white colour. It has numerous plants and bodies of water flowing through the streets. (TV: Smile)

Technology
The colonists that populated Gliese had made a number of technological advancements that participated in the functioning of the colony.

The entire city was made up of Vardy, microrobots that interlocked in order to create solid and complete structures such as the buildings and the machines. They could easily break apart into swarms and attack anyone they perceived as a threat. They would envelop the target and could strip them of clothing and flesh in seconds, leaving nothing but bones behind. The Vardy also carried out daily tasks, such as pollinating the wheat fields that surrounded the city. The city was also equipped with Emojibots, an interface between the human colonists and the Vardy that carried out maintenance.

Humans communicated over long distances through a wireless network that was implanted directly into their ears and used their nervous systems as circuitry.

Mood badges were handed out by Emojibots to the human residents and automatically put themselves on the human's back. They monitored their emotions. (TV: Smile)

Behind the scenes

 * In real life, Gliese 581 D is a possible extrasolar planet that could potentially be habitable.
 * The name of the planet is not stated on screen. However, it is named as the Emojibots and colonists' home on the BBC Doctor Who website,  and is named by the interviewer of writer Frank Cottrell-Boyce in DWM 512 -- though not by Cottrell-Boyce himself.