The beta, which is due to start at the end of this week, will include four story chapters, four competitive multiplayer maps, a "huge world to explore with your own unique Guardian," the letter reads.
PS3 and PS4 owners with beta access will be able to start playing at 1 p.m. ET on July 17, and they'll be able to keep going until the end of the beta period, except for a two-day maintenance window - Destiny developer Bungie will take the beta offline from July 21-22. The studio will open the beta up again on July 23, when it will go live at 1 p.m. ET on Xbox 360 and Xbox One, and continue on PS3 and PS4.
For more on Bungie's post-Halo universe, be sure to read our E3 2014 in-depth coverage, which includes interviews with Destiny's developers.