With little to go on, speculation has run rampant as to what will be announced at tomorrow's (Tuesday's) mystery Facebook event, with new gadgets and M&A activity topping the list.

The social networking giant sent reporters an invitation last week that simply said to "come and see what we're building" on Jan. 15.

The initial buzz ignited quite a rally in Facebook stock, sending shares up more than 9% last week after the invitations went out. Since the start of 2013, FB shares have been on a tear, up some 20% year-to-date.

Cantor Fitzgerald just made Facebook Inc. (Nasdaq: FB) one of its "highest conviction calls" for 2013. Plus, JPMorgan Chase & Co. (NYSE: JPM) elevated FB shares as a "top large-cap pick" for the Internet sector. Both firms are upbeat on the traction Facebook is making in the mobile arena.

While some are excited about Tuesday's secretive event, others are not expecting much. In that camp is Wedbush analyst Michael Pachter, who has closely been following the company since before its initial public offering.

"I have low expectations," Pachter told MarketWatch, citing the proximity to Q4 earnings, which the company will announce Jan. 30 after the close.

On the other hand, Topeka Capital's Victor Anthony is more expectant and believes the announcement could be "meaningful."

Here are five things that could happen at Tuesday's Facebook event.

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