In a new experiment, Helmut Wiesemeyer from the Max Planck Institute for Radio Astronomy in Bonn/Germany and his colleagues have measured the 18O fraction of the upper mesosphere/lower thermosphere for the first time. They used the GREAT receiver aboard the airborne observatory SOFIA and found that the upper atmosphere has an 18O fraction close to that of the lower atmosphere.
Image: © Compilation: Helmut Wiesemeyer, created from: photo of atmospheric layers (NASA), SOFIA model (Stéphane Guisard & NIESYTO design), atomic nuclei (Robert Simmon, NASA GSFC); The higher layers of the Earth’s atmosphere. SOFIA observations were performed in the stratosphere at 13 to 14 km above the surface. The spectrum shows the column densities of oxygen lines of 16O and the heavier isotope 18O which were detected in absorption against the moon in the upper mesosphere and lower thermosphere.