Facebook has sent invitations — by physical snail mail — to members of the press announcing a media event scheduled for June 20th. Joanna Stern of ABC News received one such invite, with Facebook's letter claiming "a small team has been working on a big idea." The event will take place at the company's Menlo Park headquarters. As for what Mark Zuckerberg and Co. have in store, the rumor mill has been fairly quiet of late following the high-profile launches of Graph Search, a redesigned news feed, and Facebook Home. We've reached out to the company for more details on the June 20th event.