"Journey through time and space to learn the secrets of Osiris, avert a dark future, and rebuilt the tites between the legendary Warlock and his greatest student-Ikora Rey". However, it was accessible only through the highly competitive Trials of Osiris event, which pitted two teams of three players against each other.
The expansion's description simply reads, "Curse of Osiris continues your Guardian's journey with all-new story missions and adventures set in a new destination, Mercury".
For those who were disappointed by the lack of content that followed the release of the first game in the series, Bungie has previously stated this won't be the case with Destiny 2. The expansions as Mercury as an explorable world and features new story missions, gear, co-op, and Crucible content. It sounds like Curse of Osiris will offer much more to players than The Dark Below, which was Destiny's thinnest expansion even though it included a new raid.
A Kotaku report from last week was the first to reveal details about the first DLC of Destiny 2, with sources claiming that Osiris will be at the center of the upcoming expansion. Though that's unlikely to be the focus of Curse of Osiris, it's perhaps entwined in the story.
Destiny 2 just came out a few days ago, and already more information about its upcoming content came out in the past few days. The Xbox Store listing notes that Curse of Osiris will only be available as part of that season pass, so if you want to play it, you'll need to plop down $34.99 - a price that promises a second expansion in spring 2018.
A representative for Activision told Polygon that information about Curse of Osiris will be posted to Destiny's official website later today.