The Avalanche and Senators announced the trades after Duchene was pulled out of Colorados game at the Islanders midway through the first period.
Duchene won't have to wait long to face his former team - the Senators' next two games are in Sweden against Colorado as part of the NHL Global series. Rantanen, who registered 20 goals as a rookie last season, shares the scoring lead on the Avalanche with Nathan MacKinnon and defenseman Tyson Barrie with 12 points. The third overall pick in 2009 has 178 goals and 250 assists in 586 games. Colorado gets two prospects and a 2018 second-round draft pick from Nashville, and prospect Shane Bowers, goaltender Andrew Hammond and 2018 first- and 2019 third-round picks from Ottawa.
"We feel this deal brings us some top prospects as well as some high draft picks as we continue to build for both the short and long-term future", Avalanche general manager Joe Sakic said in a statement.More news: Daylight Savings Time ends November 4
Bowers, 18, was Ottawa's first selection (first round, 28th overall) in the 2017 draft. That's way down from the previous season, in which he put up 30 goals and 29 assists in 76 games.
Matt Duchene has been traded. During the 2014-15 season, Hammond helped launch Ottawa into the playoffs by posting a 20-1-2 regular-season record, all of which took place between February 16 and the regular-season finale on April 11.
Duchene is coming off a disappointing season on a team where just about every player struggled.
Duchene is moving to the Eastern Conference.