The Stratospheric Observatory for Infrared Astronomy (SOFIA) has made the first measurement of heavy atomic oxygen in Earth’s upper atmosphere. Heavy oxygen is so named because it has 10 neutrons instead of the usual eight of “elementary” oxygen, the form we breathe. Heavy oxygen is seen as a sign of biological activity prevalent in the lower atmosphere. Both forms are byproducts of photosynthesis, but essential oxygen, which is consumed more than heavy oxygen during the respiration of living things, leaves a higher concentration of heavy oxygen.

However, little is known about how this extra-heavy oxygen penetrates the upper atmosphere from its near-earth formation. Thanks to its high spectral resolution, SOFIA GREAT device made the first spectroscopic detection of heavy oxygen outside the laboratory by measuring the ratio of basic oxygen to heavy oxygen in the mesosphere and lower thermosphere.

“This monitoring of biological activity has been proven,” said Helmut Wiesemeyer, a researcher at the Max Planck Institute for Radio Astronomy. “Until now, the altitude at which this feature extends was thought to be 60 kilometers. [приблизно 37 миль] – therefore, only the lower part of the mesosphere – and the question was: does it reach higher? And if so, since there are no living organisms, the only way to reach higher altitudes is through efficient vertical mixing.”

In other words, the only explanation for the high heavy oxygen concentrations in these regions is up and down air movement, which could have significant implications for climate change.

Heavy oxygen is difficult to measure because it is very similar to basic oxygen. SOFIA could set them apart against the Moon’s background from above in the stratosphere: the Moon’s brightness provided the highest sensitivity for these elusive features. This allowed the researchers to measure the ratio of basic and heavy oxygen up to 200 kilometers in the atmosphere. The results, published in Physical Review Research, ranged from a factor of 382 to 468 across the two types of oxygen, similar to the rate on Earth.

“There are processes that change these rates. For Earth, that process is oxygen life,” Wiesemeyer said, but there are other potential chemical explanations to consider.

Wiesemeyer and his colleagues have been very conservative in their uncertainty estimates, so they can’t link large oxygen measurements exactly to biology. The solar wind, for example, may also provide heavy oxygen to Earth, but it is unlikely to contribute that much.

This pilot study measuring the balance between two forms of oxygen proves a technique that atmospheric scientists can use to study vertical mixing. The results of the study may also help to better define the biologically relevant boundaries of the Earth’s atmosphere.

More assertively, future instruments that could be sensitive to different oxygen signatures could potentially use similar techniques to measure oxygen ratios on exoplanets. Combining the high oxygen content with the understanding of vertical mixing in these exoplanets could point to biological activity, although the team cautions that such a study would require enormous precision not found in current technology.

“The idea is to understand what’s going on at your own doorstep before delving deeper elsewhere,” Wiesemeyer says. Said.

These observations are too low, even for low-orbit satellites, but too sensitive to be made from the ground. Observations based on stratospheric balloons may offer potential for further research in the future.

SOFIA was a joint project between NASA and the German space agency DLR. DLR provided the telescope, routine aircraft maintenance, and other support for the mission. He led the SOFIA program, science and mission operations in collaboration with NASA’s Ames Research Center in California’s Silicon Valley, the Association of Universities for Space Research based in Columbia, Maryland, and the German SOFIA Institute at the University of Stuttgart. The aircraft was maintained and operated by NASA’s Armstrong Flight Research Center, Building 703, Palmdale, California. SOFIA reached full operational capacity in 2014 and completed its last science flight on 29 September 2022.