SOFIA ‘s First Detection of Heavy Oxygen in Earth’s Upper Atmosphere

SOFIA's First Detection of Heavy Oxygen in Earth’s Upper Atmosphere

TheStratospheric Observatory for Infra red Astronomy(SOFIA) made the first-ever measurement of heavy atomic oxygen in Earth’s upper atmosphere.

With its high spectral resolution, Sofia’s GREAT instrument measured the ratio of main to heavy oxygen in the mesosphere and lower thermosphere, making the first spectroscopic detection of heavy oxygen outside a laboratory, said NASA.

Little is known, however, about how this abundance of heavy oxygen permeates from the location of its creation near the ground into higher regions of the atmosphere.


Heavy oxygen is so called because it has 10 neutrons, rather than the normal eight of “main” oxygen, the form we breathe. Heavy oxygen is seen as a signature of biological activity, common in the lower atmosphere. Both forms are by products of photosynthesis, but main oxygen is consumed by the respiration of living things more than its heavy counterpart, leaving a larger concentration of heavy oxygen behind.


The only explanation for large concentrations of heavy oxygen in these regions is the upward and downward motion of air, which can have important implications for climate change.

“It’s tracing biological activity — that’s well-proven,” said Helmut Wiesemeyer, a scientist at the Max Planck Institute for Radio Astronomy. “So far, the altitude to which this signature extends was thought to be 60 kilometres [around 37 miles] — so, barely the lower part of the mesosphere — and the question was, does it reach higher altitudes? And if it does, because there are no living organisms up there, the only way to reach higher altitudes would be an efficient vertical mixing.”

Measuring heavy oxygen is complex because it looks so similar to main oxygen. From up in the stratosphere, SOFIA could separate the two against a lunar backdrop: the Moon’s brightness enabled the highest sensitivity to these hard-to-distinguish features.

This allowed the researchers to measure the main-to-heavy oxygen ratios up to 200 kilometres in the atmosphere. The results — published in Physical Review Research — ranged from a 382 to 468 factor difference in the two types of oxygen, similar to the ratio on the ground, NASAsaid.   

“There are processes that are altering these ratios. For Earth, this process is oxygenic life,” Wiesemeyer said — though there are other potential chemical explanations to be considered as well.

Wiesemeyer and his collaborators were very conservative in their uncertainty estimates, so they cannot completely attribute their heavy oxygen measurements to biology. Solar wind, for example, can also deliver heavy oxygen to Earth, but it is unlikely to make such a large contribution.


SOFIA was a joint project of NASA and the German Space Agency at DLR. DLR provided the telescope, scheduled aircraft maintenance, and other support for the mission. NASA’s Ames Research Centre in California’s Silicon Valley managed the SOFIA program, science, and mission operations in cooperation with the Universities Space Research Association, headquartered 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 Centre Building 703, in Palmdale, California. SOFIA achieved full operational capability in 2014 and concluded its final science flight on Sept. 29, 2022.



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