She uses a tool called the PIXL, which she invented as a postdoc: It fires a hair's-width x-ray beam at a rock. That energy stirs up the atoms on the surface, which then shoot back their own distinct x-rays. Combined, those x-rays create finely detailed maps of the rock, potentially revealing the past presence of microbes. She previously used the method to study rocks in Australia's Pilbara region. "I stood barefoot on a seashore that was formed 3.45 billion years ago," she says.
Now she's gearing up to repeat her study—on Mars. Allwood is a principal investigator on NASA's 2020 rover mission, the first woman to oversee a scientific instrument on a Red Planet expedition. "About bloody time!" she says. The PIXL will be one of just seven instruments aboard. "This isn't going to be a shiny-object hunt," she says. "It's not like uncovering a dinosaur bone." Her spectral science is far more subtle—but just as exciting.