The Stratospheric Observatory for Infrared Astronomy (SOFIA) has detected the presence of atomic oxygen in the upper atmosphere of Mars. The observation is the first of its kind for 40 years, and will allow planetary scientists to refine their models of the Martian atmosphere.
SOFIA is essentially a Boeing 747SP (the SP suffix standing for "special performance" owing to the increased range over the commercial variant) modified to house a 100 inch (254 cm) diameter telescope in the side of the aircraft. The instrumentation operated with the telescope is capable of being swapped out, allowing for flexibility.
"Atomic oxygen in the Martian atmosphere is notoriously difficult to measure," states Pamela Marcum, SOFIA project scientist. "To observe the far-infrared wavelengths needed to detect atomic oxygen, researchers must be above the majority of Earth's atmosphere and use highly sensitive instruments, in this case a spectrometer. SOFIA provides both capabilities."
Atmospheric oxygen had previously been detected by the Viking landers and the Mariner orbiters as they explored the Red Planet in the 1970s. During the Mariner 6, 7 and 9 flybys of Mars between 1969 and 1971, the spacecraft deduced the atomic oxygen levels via an analysis of UV airglow. The Viking landers used instruments mounted in the air vents of their descent aeroshells known as neutral mass spectrometers to take detailed readings of the Martian atmosphere prior to touch down.
For the recent observation SOFIA was fitted with advanced infrared equipment suited to detecting and separating Mars' atmospheric atomic oxygen from its Earth-bound counterpart. To further cut down on interference, the observatory flew at an altitude of between 37,000 and 45,000 ft (11,278 – 13,716 m), high enough to cut out the majority of the disturbances created by Earth's atmosphere.
The levels of atomic oxygen detected in the Martian mesosphere were only around half of what was expected. The results of the study are significant, largely due to the fact that atomic oxygen plays an important role in, among other processes, the energy and mass flow throughout the Martian atmosphere, as well as the loss of particles to space through atmospheric erosion.
SOFIA will continue to take measurements of Mars' atomic oxygen levels going forward in an attempt to better understand the Red Planet's atmosphere.