Motorola Mobility's patents and "developed property" are worth $5.5 billion, less than half of what Google (Nasdaq: GOOG) spent to acquire the company, the Android maker revealed in a regulatory filing Tuesday.

Google spent $12.4 billion to acquire Moto, a deal that closed in May after regulatory reviews. The driving force behind the merger was Google's need to shore up its patent defenses to fight the lawsuits its handset maker partners are facing. (See Google Closes $12.5B Motorola Deal .)

Of the remaining $6.9 million Google spent, $2.9 billion was for cash acquired, $2.6 billion for goodwill, $730 million for customer relationships and $670 million for other net assets acquired, the SEC filing revealed.

"The acquisition is expected to protect and advance our Android ecosystem and enhance competition in mobile computing," Google wrote in the filing.

The company didn't divulge its plans for Motorola on its second-quarter earnings call last week, only promising changes to come. It reported that Moto contributed $1.25 billion in revenue to the merged company, but it also posted an operating loss of $233 million. (See Google Keeps Quiet on Plans for Moto and Google Posts $2.79B Profit in Q2.)

Why this matters
Given how much it spent on Moto compared to its patents' worth, Gogle may have more in store for Moto than just a patent play -- although it certainly needs that as well.

Google will have to tough task ahead in making Motorola smartphones solid competitors to market leaders like Apple Inc. (Nasdaq: AAPL) and Samsung Corp. , while not alienating any of its other partners. (See Google & Moto: What's Next? and Google Plays Favorites With Moto Buy.)

At the same time, Google is likely to also be shopping around Motorola's cable assets, including its set-top boxs, cable modems, video processing and access network gear. (See Light Reading Poll: Who Will Take Motorola Home?)

For more

— Sarah Reedy, Senior Reporter, Light Reading Mobile