Mariah Carey is celebrating her 55th birthday — or, anniversary, as she calls it — in a new photo posted to Instagram. "Anniversary adventures commence," Mariah captioned the photo of her smiling while relaxing on a boat. Friends Jennifer Hudson and Paris Hilton sent Mariah well wishes on her special day. "Happy anniversary, @mariahcarey! 'Anytime you need a friend, I will be here!!! Love u!!!" Jennifer wrote on her IG Story, while Paris wrote, "Happy Birthday to an absolute icon @MariahCarey."