Thousands of American pensioners are retiring on college campuses

“Are we alone in the universe? That’s the core question we’re trying to answer here,” Meenakshi Wadhwa, a planetary scientist with ties to NASA, tells her spellbound class. As she explains that to answer this “we need to go back to Mars to collect rocks”, one student scribbles notes while another holds up an iPhone to take a snap of the slides. In many ways this lecture hall at Arizona State University (ASU) is like any other. A group of keen women sit attentively in the front row; the men are spread out in the back. But the hearing aids hint at how unusual this class is.