A rocket powered by thin films of nuclear material could get to Mars in as little as two weeks, according to scientists in Israel. With conventional engines, the journey would last almost a year, they say. The new engine, proposed by Yigal Ronen and Eugene Shwageraus at Ben-Gurion University of the Negev in Beer-Sheva, Israel, uses films of a radioactive material called americium which are less than a micron thick.