DUSSELDORF, Germany - Former world champion Jenson Button said that Mercedes could possibly challenge the Formula 1 title in 2012.The McLaren driver, who finished runner-up to champion Sebastian Vettel in 2011, said he expected three strong teams next season, "And possibly also Mercedes."Speaking at the Race of Champions in Dusseldorf, Button said he expected Ferrari to be on form in 2012.LACK OF SPEEDButton said: "They are strong as a team, especially with Fernando Alonso at the top."He said he felt the 2011 season was a positive one, "I have really enjoyed this season and I have a car beneath me that I have had a big part in."It was good, but not quite good enough. We did not have the speed to challenge Red Bull and that is a problem. If you don't challenge a team, they do not make mistakes."