According to comScore’s most recent numbers, the list of the ten most popular mobile apps in the US is ruled by Google and Facebook. That’s not a complete surprise to those who understand just how popular Android has become and how ubiquitous the Facebook app is in 2013. It’s still impressive to see how far down the list the two’s closest challengers sit. Pandora is the closest, but it’s nearly 8% behind YouTube. iTunes comes next, sitting in the eighth spot.There’s just no keeping up with Facebook, but that’s bound to happen when your service has an active base of around one billion users. Mobile traffic now accounts for around 54% of all traffic on Facebook, and its mobile penetration generally hovers between 60 and 80 percent.Google’s showing has a lot to do with Android’s rise, but that doesn’t take anything away from the significance of having five of the top ten apps. Maps has a lock on second place, and Google should give Apple a heartfelt thank-you for that. Cupertino’s inability to deliver a usable Maps app in iOS 5 paved the way for a massive exodus when Google Maps landed in the App Store.It’s curious to see comScore include numbers for Google Play and iTunes. comScore is counting unique visitors, so Play isn’t stuffing the ballot box just because Android relies on it for apps, music, movies, books, and magazines. iTunes, on the other hand, is only pushing music and video. It’s not quite fair to list the two on this chart, at least without combining App Store and iTunes numbers.Perhaps the most amazing thing about this chart? The fact that Yahoo’s Messenger is one of the ten most popular apps in the United States.