Two Masks Are Better Than One Masks have been a big issue throughout the pandemic, from supply shortages to debates about when they should be required to be used. This week, the Centers for Disease Control and Prevention put out research and guidance on the effectiveness of double masking—wearing one mask over another. Engineer and aerosol scientist Linsey Marr talks about how a face mask traps a virus, the effectiveness of double masking, and other other questions about face masks.   Next Week, A Return To Martian Soil It’s a busy time on Mars. This week, spacecraft from both China and the United Arab Emirates successfully maneuvered into position in Martian orbit. And next week, if all goes according to plan, the Mars 2020 mission will deliver the Perseverance rover to its new home in Jezero Crater on the planet’s surface. Scientists hope to use it there for at least two Mars years, exploring the geology and chemistry of what once was a catch-basin for a river delta on the Red Planet. Lori Glaze, head of the Planetary Science Division of NASA’s Science Mission Directorate, joins Ira to give a preview of the landing process, and an overview of some of the experiments on board Perseverance—from a ground-penetrating radar system to an experimental helicopter that may make the first controlled, powered flight on another planet.   Some People Had COVID-19 For So Long That It Mutated Inside Them COVID-19 variants have been front and center in the news over the past few months. Mutations are a natural part of the course of life for viruses. But to us humans, they’re adding more unknowns to an already stressful time. Groups of researchers around the world have found something interesting in a select few COVID-19 patients: individuals who seem to be reservoirs for coronavirus mutations. Essentially, these patients were infected with COVID-19 for so long that the virus was able to mutate inside them. Experts are scratching their heads at these strange cases, and now are looking into what this means for our efforts to fight the virus. Meanwhile, South Africa has suspended the use of the AstraZeneca vaccine because it doesn’t clearly stop the coronavirus variant that originated in the country. This is a problem for AstraZeneca and the University of Oxford, which planned on deploying this vaccine en masse in developing countries. Joining Ira to break down these stories and other science news of the week is Maggie Koerth, senior science reporter for FiveThirtyEight.