In an announcement on BioWare's Mass Effect forums, Community Coordinator Chris Priestly said the new downloadable content would become available on Xbox Live Marketplace on March 10 at 2:00 a.m. PST, for 400 Microsoft points. The DLC will be the first in a series of new content that will expand the Mass Effect universe and let gamers follow the exploits of Cmmander Shepard and his crew even further.
Bring Down the Sky will include a new world populated by the Batarians, a "notorious and feared" alien race. When the Batarians hijack a mobile asteroid station and set it on a collision course with the colony planet Terra Nova, it will be up to Commander Shepard and the intrepid crew of the Normandy to stop the attack and save millions of innocent lives. The add-on will offer roughly 90 minutes of new action, as well as a new Achievement worth 50 Gamerscore points.
More information about Bring Down the Sky, as well as an ongoing discussion thread, is available at the official BioWare forums.