Orbiting spacecraft have peered inside the swirling vortex which encircles Mars’ north pole during winter and found an unexpected surge in ozone, raising questions as to whether the Red Planet once had a protective layer like Earth. “The atmosphere inside the polar vortex, from near the surface to about 30km high, is characterised by extreme cold temperatures, about 40°C colder than outside the vortex,” says Dr Kevin Olsen of the University of Oxford, UK. A view of the north pole of Mars, created by taking images as seen by the European Space Agency’s Mars Express spacecraft and applying topographic data from the Mars Orbiter Laser Altimeter that was on board NASA’s now defunct Mars Global Surveyor mission. These conditions gives rise to a vortex of extremely cold and dry air that encircles the north. A schematic of temperature measurements shows how it is 40°C colder inside the north polar vortex (indicated by the green line) compared to outside the vortex.