Felipe Massa will stay at Ferrari for the 2013 season in an unchanged line-up with Fernando Alonso, the Italian Formula 1 team has said.Massa has struggled for form in recent years but has agreed to a one-year extension amid continued speculation that World champion Sebastian Vettel could join Alonso at Ferrari from 2014.Alonso's contract runs to the end of 2016.FUTURE UNCERTAINMassa said on the Ferrari website: "The team and all the fans can rest assured that I will do all in my power to help the scuderia reach the targets it sets itself each year.”Massa's future has been uncertain through the 2012 season, the 31-year-old suffering an abject run until he took second at the Japanese GP in October, his first time on the podium since 2010.He was fourth at the next GP, South Korea, the following Sunday which meant he had scored more points in those two races than he had in the first 11 of the season.Ferrari's decision was not a great surprise, with Alonso clearly favouring the Brazilian as his team mate since established himself as the clear focus of the sport's most successful team."I’m so happy to continue another year with Massa as a team mate! I'm sure we are the best team!" Alonso said on Twitter after the announcement, which Ferrari had said it would only make the following week.SEVERE HEAD INJURYMassa's poor form in the first half of the campaign hit Ferrari hard in the Constructor's championship, however, where it is second to Red Bull but still 77 points from the lead.Double champion Alonso has scored 209 of Ferrari's 290 points and Massa's fate was determined after a meeting, described by the team as very friendly, with Ferrari president Luca di Montezemolo at the Maranello factory on Tuesday.Montezemolo had said on Monday that Massa, who suffered a severe head injury when hit by a steel car spring in qualifying for the 2009 Hungarian GP, had returned to the level expected of him.He had also said, referring to speculation about Vettel, that he didn’t want "two roosters in the same hen house" but rather two drivers "who race for Ferrari and not for themselves".The decision will be a blow for those who had been touted as possible replacements at the most glamorous team in the sport, notably the Force India pair of Briton Paul di Resta and German Nico Hulkenberg.STILL VACANCY AT SAUBERSeven-times World champion and Ferrari great Michael Schumacher has already announced his retirement at the end of the season and was not an option, even if some diehard supporters hoped he could be.The attention will now turn to the Sauber team which has at least one vacancy, with Mexican Sergio Perez leaving to join McLaren as the replacement for Mercedes-bound Lewis Hamilton, and possibly two if Japan's Kamui Kobayashi is not retained.Hulkenberg is considered a hot favourite to take one of those places.Massa has been a part of the Ferrari family for a decade, starting at Ferrari-powered Sauber in 2002 and serving as a Ferrari test driver before joining as a race driver in 2006 and staying on after Schumacher's first retirement."Ferrari is my racing family and throughout my entire time in F1 I’ve always driven cars powered by engines built in Maranello: I can't see myself driving cars propelled by anything else," he said on Tuesday.He was runner-up in the 2008 championship to Hamilton by a single point and has won 11 GP’s, the most recent in Brazil at the end of 2008.Team principal Stefano Domenicali said: "We’ve always supported Felipe, even in the most difficult moments of his career. We’re certain of his worth and sure he will know how to repay the confidence this renewal proves we have in him.