TOKYO (Reuters) - Emperor Akihito will hand over all public duties to his heir  after retiring in what will be Japan s first abdication in nearly two centuries, the monarch s younger son said, responding to worries a former emperor might weaken his successor s status. Japan s constitution defines the emperor as a symbol of the state and the people, without political power. His duties include Shinto religious ceremonies and constitutionally-defined tasks, such as the opening of parliament. The octogenarian Akihito s 29-year reign has also been marked by travels to domestic disaster sites to cheer survivors, and overseas to soothe the wounds of a war fought in the name of his father, Emperor Hirohito, who was considered divine until Japan s defeat in World War Two. Some experts, recalling past examples when ex-emperors kept their influence, had feared the former monarch s existence would undercut the symbolic status of his heir, Crown Prince Naruhito.  The emperor all along has intended to pass all his public duties including state acts to the next emperor,  Naruhito s younger brother, Prince Akishino, said in remarks published to mark his 52nd birthday on Thursday.  Even if there are concerns about  dual authority , if that expression is appropriate, I can clearly say that it is impossible,  he added. A law enacted in June allows Akihito, who turns 84 on Dec. 23, to step down, but details have yet to be worked out. A special panel will discuss possible dates on Friday, with the cabinet to make a final decision. The abdication is expected to take place in 2019. Akihito, who has had heart surgery and treatment for prostate cancer, said in rare remarks last year that he feared age might make it hard to fulfill his duties. Akishino, who is next in line to the throne after the 57-year-old Naruhito, said he wanted his father to rest after retiring.  I hope the emperor will spend relaxing time as much as possible after the abdication,  he said. Akishino said he was willing to take on the crown prince s duties as much as possible after Naruhito ascends the throne but would need to consult his older brother.   This is unprecedented, so there are many things I can not imagine,  he said. Akishino s 11-year-old son, Prince Hisahito, is the emperor s only grandson and will be second in line to the throne after the abdication. Naruhito s daughter, Princess Aiko, who turns 16 on Friday, cannot inherit the males-only throne.   