After Memorial Day, we start taking not-so-serious pop songs a lot more seriously.

That’s when any old hit single suddenly becomes a contender for The Song of the Summer — that magical swatch of rhythm and melody that will define our hot months, for now and for posterity.

Usher, Rihanna, Pitbull and Justin Bieber all have potentially summer-defining tunes currently loitering on the charts, but 2012’s most promising pieces of summer bubble gum come from new faces — an international smattering of boy bands and party girls from Canada, the U.K. and Sweden (a nation where pop music is taken with summertime seriousness all year round).

What makes a summer song The Song of the Summer? We’ve usually already heard it by April. It often leans toward the rhythms of hip-hop and R&B. It has a chorus that minivan-loads of tweenage girls can — and will — sing along to. Loudly. It can articulate sticky human emotions with a few gloriously melodic syllables, making you feel something deep without asking you to think too hard. Years later, it’s difficult to remember it existing outside of the summer when it arrived, and ironically, it becomes eternal because of that fact.

That’s why we love to argue about The Song of the Summer, even if some think the debate has become a media contrivance. A great pop song is a great pop song, regardless of the heat index, right? It’s not like Beyonce wrote “Crazy in Love” on a boogie board.

But we can’t help ourselves. Last year, perhaps in an attempt to be a little more scientific about it, Billboard published a weekly “Songs of the Summer” chart, which ranked hits by how well they performed on the regular Hot 100 singles chart between June 11 and Sept. 8.

More useful: Billboard’s lists of the biggest hits from summers past. Rihanna and Katy Perry both made chart debuts with breakout summer singles, but most of the past decade’s summertime hitmakers seemed to vanish after Labor Day. (Nina Sky, we miss you!)

Even if summer isn’t starmaking season, it still provides an increasingly rare communal moment for the rest of us. Windows are rolled down, volume knobs are cranked up. These songs drift through the air and braid themselves into our memory. We associate them with the cold splosh of SPF 30 on our backs, the smell of Kingsford briquettes, the taste of sugar-dusted-deep-fried-everything.

Which song will most remind us of the summer that’s about to happen? Here are five leading hopefuls.

THE FRONT RUNNER:

Carly Rae Jepsen, “Call Me Maybe”

Perhaps you’re one of the 9 million YouTubers who have watched the Harvard University baseball team dance to this one during a van ride to an away game. A few months before that video went viral, Carly Rae Jepsen was touring across her native Canada in her own “soccer mom van,” opening for ’90s survivalist boy band Hanson.

“Show by show, we’d start to sneak a box of merch onto the Hanson tour bus so we could get away with a little more leg space,” Jepsen says. “At the same time, I was negotiating the deal with Scooter Braun.”