PARK CITY, Utah -- Asked to describe Emily Cook, a teammate called her the "mother hen" of the U.S. aerials team.

That was five years ago, before Ashley Caldwell came along. Caldwell, precocious and candid, joined the team in 2008. She was just 14. Cook was 28. Mother hen had her pullet.

Cook and Caldwell evolved into sisters the next three years, training together, rooming together and learning from each other. They are the U.S. women's aerials team this season, the only two to compete regularly on the international World Cup tour. They hold their own, but the high-flying, flipping and twisting freestyle skiing discipline is dominated by Chinese. No U.S. woman has won an aerials medal at a world championship or an Olympics since 1999.

This week's world championships provided a prime opportunity for either to break through. Caldwell was coming off her first World Cup victory, and Cook, who lives in Salt Lake City, circled this event quite a while ago.

They were first (Cook) and third (Caldwell) after the first of two jumps in Friday night's finals. Both botched their second jumps and paid dearly. Caldwell slipped to fourth. Cook's second-jump score was 14th best out of a field of 15. She plunged to seventh place.

"Sometimes you land them, sometimes you don't," said Caldwell, still smiling and satisfied for her first world championship.

Cook appeared to take the disappointment more emotionally. That's no surprise.

She cried when Caldwell won a World Cup event in January and then wrote a 1,885-word article for a skiing website about the experience

Caldwell calls Cook her "surrogate mom." They have a Newlywed Game-type of knack for each other. Asked separately about their favorite story from living together, and they'll both point to one of their first encounters when Caldwell noted that Cook was twice her age.

They both do schoolwork while abroad, where Caldwell helps Cook with her college algebra. In turn, Cook instilled positive habits into the teenager.

"From the beginning, I was like, 'We go to bed at 10,'" Cook said. "The little things that as a kid, sometimes you forget. She is young, and it's important to build those."

Like nutrition. Caldwell now eats her vegetables, "but [Cook] still frowns at me when I eat a bunch of M&Ms before a contest, like I did [Friday]," Caldwell said.

"How to be a professional athlete, that's basically what she's taught me how to do. I came into this sport a 14-year-old little punk. Her and [men's aerialist] Ryan St. Onge basically molded me into a professional athlete."

St. Onge taught Caldwell how to drive stick and also benefits from Cook's benevolence. For years, she's cooked Italian dinners for the U.S. aerials team.

Led by St. Onge, 2009 world champion, and Jeret "Speedy" Peterson, 2010 Olympic silver medalist, the men generated most of the headlines for the U.S. aerialists the last decade. St. Onge is taking an untimed break from the sport after failing to qualify for the men's finals at Deer Valley. Peterson hasn't competed since Vancouver, and nobody seems to know when he'll be back.

That opens the door for Cook and, even more, young Caldwell. Cook, too, is unsure how long she'll keep competing. She was the only skier of the 37-member U.S. world championships team born in the 1970s and seems ready to pass the torch.

"[Caldwell] will be able to carry the team," Cook said. "Not only that, but guide the next generation."

But it won't be the same without mother hen.

"Not as much fun," Caldwell said. "I'll be pretty bummed."

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