New imaging data from a European Space Agency spacecraft characterizes the thick vertical layers that compose the atmosphere of Mars. By harnessing light scattering to visualize the layers as colors, the research defines the relationship between particle size and altitude. Nicolas Thomas and colleagues liken the appearance of the layers to mille-feuille, a classic French dessert made from alternating layers of puff pastry and pastry cream. Understanding the present-day atmosphere of Mars can yield insights into the planet’s geologically recent and ancient past. For example, questions swirl around the vertical distribution of aerosols in the Martian atmosphere – and how those layers morph across the seasons and years. Using imaging data from the European Space Agency’s ExoMars Trace Gas Orbiter spacecraft, Thomas et al. characterized the atmosphere above the Martian limb, or the horizon point at which the planet appears to merge with space. They analyzed forward light scattering geometry data collected via the spacecraft’s Colour and Stereo Surface Imaging System (CaSSIS) to produce high-resolution (less than 40-meter) color ratios that represent atmospheric aerosol concentrations. Observations revealed the atmosphere contains tens of sub-kilometer-scale layers. The findings also connected changes in red/blue color ratios to altitude; Decreases in red corresponded with higher altitudes and smaller particle concentrations. Moving forward, Thomas et al. plan to build a database to track how the Martian atmosphere’s layers change in composition and size over time.