President Barack Obama\'s 2013 budget request for Nasa would slash spending on Mars exploration and shift funds to human spaceflight and space technology. As reported by BBC News last week, this means the US will pull the plug on its joint missions to Mars with Europe. If approved by Congress, the budget request would reduce funds available for planetary science by about 21%. But spending on human exploration and space technology would rise by 6% and 22% respectively. \"There\'s no doubt that tough decisions had to be made,\" said Nasa\'s administrator Charles Bolden told journalists. But he added: \"This is a stable budget that enables us to support a diverse portfolio.\" Overall, Nasa would receive about $17.7bn for next year, with a flat budget envisaged over the next few years. While the budget is flat, the agency needs to pay for its flagship James Webb Space Telescope project, whose budget is projected to rise from $476.8m in 2011 to $659m in 2014. ExoMars prototype The ExoMars project was formally initiated by European space ministers in 2005 It also has a major commitments going forward to fund the development of a huge new rocket and capsule system to take astronauts beyond low-Earth orbit to destinations such as the Moon and asteroids. The biggest loser in this re-prioritisation is planetary science in general and Mars exploration in particular which will receive $360.8m, a reduction of almost 40% from the FY 2012 estimate. As a result, Mr Bolden said: \"We will not be moving ahead with the 2016 and 2018 ExoMars opportunities that we had been exploring with the European Space Agency.\" The Planetary Society, a California-based space advocacy group, commented: \"The US Administration is proposing a budget for fiscal year 2013 that would force Nasa to walk away from planned missions to Mars, delay for decades any flagship missions to the outer planets, and radically slow the pace of scientific discovery, including the search for life on other worlds.\"