Facebook and MySpace are holding a joint press conference this afternoon to announce... something.

Leading the event are MySpace CEO Mike Jones and Facebook's VP of partnerships and platform marketing Dan Rose. The fact that Facebook CEO Mark Zuckerberg is not attending should put a damper on any speculation that a merger is pending. So what could the two rivals have in store? Among the possibilities:

- It could be some type of data sharing/compatibility announcement that will let users of both services post one update to both services, as well as share links, content, status, etc. That could be as simple as a Facebook Connect integration or it could be something more unique. There have been rumors for weeks that MySpace plans to incorporate Facebook Connect buttons throughout the site

- MySpace is said to be searching for a new advertising partner. Three years ago it struck a $900 million ad deal with Google, which has had two short extensions, but both sides are believed to be looking for an exit out of that relationship. The company has had talks with Microsoft and Yahoo over the summer, according to past press reports, and Facebook seems like a likely contender as well.

- Maybe it'll be some kind of app development deal in which Facebook apps will also work on MySpace, or MySpace apps of Facebook. That seems less likely because Facebook's development platform is a major factor behind its success and sharing that with a rival - however weakened - doesn't make a whole lot of sense. MySpace has already taken steps to work with Facebook rather than against it with its recent redesign and relaunch. At the time, MySpace said users could sign up for MySpace using Facebook Connect (essentially populating the MySpace registration form with data already stored in Facebook). But that feature was not yet live when the relaunch was unveiled.

However you cut it, the fact that MySpace needs to partner with Facebook to survive is a sign of just how far the once mighty social networking pioneer has fallen. Facebook was once the upstart to MySpace, and has now so fully taken over the social networking space that it now counts the likes of Google as its rivals rather than MySpace. With its narrow focus on entertainment and gossip, MySpace is making the right move to capture what little niche it has left. Swallowing its pride and working with the company that replaced it is a good move.

Meanwhile, rumors persist that NewsCorp is looking to sell MySpace for the right price. Our sources say the parent company is giving MySpace between three to six months to show a meaningful return on the changes implemented in the redesign, and if not satisfied will cut its losses and sell the unit. All the chatter regarding a sale could simply be the result of NewsCorp making early inquires and doing due diligence in preparation for that eventuality.