A human space explorer will be able to set foot on Mars no later than the year 2020 and visit other planets of the Solar system in the following decades, the head of the US space agency announced Wednesday. In an address reminiscent of late US president John Kennedy’s 1962 speech announcing a mission to the Moon before the end of that decade, National Aeronautics and Space Agency Administrator Daniel Goldin said the United States would be able to send a man to Mars in no more that two decades.