Emote representing Carl Sagan, emote was added for an event in 2017 called Science week on Twitch where it began by showing of the Carl Sagan's documentary series "Cosmos".

https://blog.twitch.tv/en/2017/04/21/science-week-is-coming-and-it-starts-with-cosmos-b501136f977a/

The emote is associated with the Twitch user Carl, who is known for his upbeat and friendly personality. The emote itself captures a cheerful expression, making it suitable for conveying joy or support during streams.

CarlSmile is part of the broader trend on Twitch where streamers and users create custom emotes to represent specific emotions or reactions unique to their communities.