Google's recently released Social Search feature, whose raison d'etre is to include content from users' social network contacts in search results, can barely tap into the connections people have made on Facebook, the world's largest social network.

Social Search, which graduated from an opt-in Google Labs experiment to a default feature on Google.com for signed in users, will only access Facebook public profile pages, which at best contain barebones member information.

The problem is that only a small amount of information from Facebook member profiles can be published publicly on the web. To access the rest, people have to log into the site.

Granted, Google's Social Search feature isn't the only search service affected by this situation. Microsoft announced back in October that it would at some point this year begin including Facebook member status updates in its realtime search results. That hasn't happened yet, because Facebook members can't make those status updates available in the open web. Google has also expressed an interest in indexing and returning Facebook status updates in its search results.

Still, the issue is particularly serious for Social Search, a search feature whose value resides squarely on returning relevant links to content from users' social-networking rings. For now, Social Search will miss out on leveraging the content and connections of Facebook's 350 million members worldwide.

"Social Search includes public [social network] connections. Since Facebook's connections aren't public, we can't at this time include them," said Maureen Heymans, the technical lead for Social Search at Google.

The best someone could do would be to point Social Search to their public Facebook profile page. "That's the content Facebook is making public to Google," she said.

If and when Facebook lets its members make more profile content public, Google will evaluate including it in Social Search query results, Heymans said. Ultimately, Social Search seeks to improve the quality and relevance of Google results, and comprehensiveness is a key element in this endeavor.

"It's really important for us to try to bring you all the content you have access to from your [social network] friends," she said.

Social Search will return relevant results for people who are signed into their Google account when they do searches on Google.com and on Google's Image Search. Social Search will take into account contacts and content people have on Google services like Gmail, Picasa, Reader and Blogger, as well as on external social networks like Twitter, Yahoo's Flickr photo sharing site and, ironically, FriendFeed, which Facebook recently acquired. FriendFeed's user culture, like Twitter's and unlike Facebook's, is geared toward public sharing of information. For Social Search to tap into people's social networking connections, Google recommends that people build a Google Profile, where these third-party connections can be listed.

Within Facebook, members can make their profiles completely open to everyone on the site if they wish, or, on the other extreme, only available to specific, handpicked friends. In between the two extremes, Facebook offers a broad variety of privacy settings to establish a wide range of access to profile content. Recently, Facebook began letting members apply a specific privacy setting to every piece of content they post.