Edge of Space: The Science of NASA’s AIM Spacecraft
Science & Technology

Edge of Space: The Science of NASA’s AIM Spacecraft

Artist’s rendition of the AIM spacecraft in orbit above Earth with the solar breaking over the globe’s horizon. Credit score: Emily Hill

Launched in 2007, the Aeronomy of Ice within the Mesosphere, or AIM, mission is the primary detailed exploration of Earth’s distinctive and elusive clouds which are actually on the “edge of area.” Different space-based and ground-based measurements have probed some features of this uncommon phenomenon in Earth’s mesosphere (the area simply above the stratosphere), however little or no is understood about how these clouds kind over the poles, why they’re being seen at decrease latitudes than ever earlier than, or why they’ve been rising brighter and extra frequent. Some scientists have advised that these polar mesospheric clouds stands out as the direct end result of human-induced local weather change.

Over the course of its mission, AIM has helped reply these questions by documenting for the primary time your complete complicated life cycle of these clouds. With this data, scientists are working to resolve many of the mysteries about how these clouds kind and to raised predict how they may change sooner or later.

Some key scientific discoveries from AIM, embody: 

AIM’s measurements have additionally helped scientists observe how air within the environment strikes vertically, in addition to between the hemispheres.

The formation of polar mesospheric clouds at such excessive altitudes doesn’t comply with typical meteorological ideas of how clouds kind decrease within the environment. Earlier than AIM’s launch, one principle was that the cloud particles develop on “seeds” of volcanic or meteoric mud — and AIM helped present that the particles do, certainly, kind round meteroic mud. These clouds look like a comparatively current phenomenon, being first reported within the late nineteenth century shortly after the volcanic eruption at Krakatoa. The brightest clouds are actually identified to be primarily composed of water ice, and their seasonal lifecycle is managed by complicated interactions between temperature, water vapor, photo voltaic exercise, atmospheric chemistry and small particles on which the cloud crystals kind.

AIM has additionally made simultaneous measurements of the primary elements wanted to unravel the function of pure components such because the photo voltaic cycle and meteorology within the formation of these clouds from the attainable function of anthropogenic components similar to carbon dioxide, which causes a warming within the decrease environment however a cooling on this area of the environment. This analysis may help present information wanted to find out the function of polar mesospheric clouds as an indicator of our planet’s altering local weather.

Photo voltaic Cycle

Polar mesospheric clouds happen within the area the place the Solar first interacts with Earth’s environment, inflicting chemical and thermal modifications. Photo voltaic radiation at this altitude can break aside water vapor molecules, thus decreasing the quantity of water ice out there to kind ice crystals within the clouds. The photo voltaic ultraviolet radiation at work on this course of is understood to fluctuate with the 11-year photo voltaic cycle.

Satellite tv for pc observations have proven a sample of rising photo voltaic ultraviolet radiation adopted by declining brightness and frequency of these clouds over two photo voltaic cycles. However the change in photo voltaic exercise happens practically a 12 months earlier than modifications are seen within the clouds, indicating that the connection is just not a easy matter of direct trigger and impact.

Water Vapor and Temperature

Three issues are wanted to ensure that these high-altitude clouds to kind: chilly temperatures, water vapor and small particles that present surfaces for water to condense. Two of the main suspects behind the current modifications in polar mesospheric clouds are a rise of water vapor within the area and colder temperatures. Local weather fashions predict that the end result of rising greenhouse gases within the environment could be hotter temperatures within the decrease environment, the place emitted radiation is “trapped” by the air above, however colder temperatures within the mesosphere the place the radiation is misplaced to area. Colder temperatures would permit extra icy cloud particles to kind. Alternately, a buildup of water vapor within the higher environment may trigger the identical enhance in polar mesospheric clouds. By measuring water vapor, temperature and the presence of clouds on the identical time, AIM will permit scientists to isolate which of these components is the important thing driver of cloud formation.

Understanding the processes that management water vapor in the summertime polar mesosphere will present a foundation for understanding the formation and evolution of these clouds. Water vapor is transported upward into the polar summer time mesosphere from the decrease environment. It’s also produced by the photochemical destruction of methane within the stratosphere and mesosphere.

There are few direct measurements of water abundance together with polar mesospheric cloud properties within the area the place these clouds kind. AIM will measure a complete information set of water vapor and key chemical substances that result in water formation and that can be utilized as tracers of the final atmospheric movement. These mixed observations will yield an in depth view of the motion and formation of water vapor on this area of the environment.

One uncommon supply of mesospheric water vapor — exhaust from rocket engines — was lately proven to be the trigger of a rise in Arctic polar mesospheric clouds (Geophysical Analysis Letters, M. H. Stevens et al., July 6, 2005). The exhaust plume from an August 1997 area shuttle launch moved northward to kind a burst of clouds every week after launch. Water vapor from rockets, nevertheless, is just not considered a significant contributor to the long-term enhance in these clouds.

AIM additionally examines the relative contributions of photo voltaic and human-induced results that trigger change within the higher environment. Scientists have identified a attainable reference to international change as a result of the clouds have gotten brighter and occurring extra incessantly with time and they’re being noticed at decrease latitudes than ever earlier than. One believable clarification is that temperatures the place the clouds kind have change into colder with time because of the construct up within the decrease environment of greenhouse gases from human actions. Excessive within the environment, the greenhouse-gas buildup ends in cooling.

AIM checks this speculation by serving to to offer a clearer understanding of why polar mesospheric clouds kind and the way they reply to short-term environmental modifications. The complete information from the mission permits scientists to construct pc simulations that reproduce the noticed modifications in these clouds. With these instruments in hand, scientists can enhance their skill to foretell future modifications within the clouds and see to what extent they’re an indicator of international local weather change.


“Are noctilucent clouds harbingers of international change within the center environment?” by Gary E. Thomas, 11 February 2004, Advances in House Analysis.

“1 / 4-century of satellite tv for pc polar mesospheric cloud observations” by Matthew T. DeLand, Eric P. Shettle, Gary E. Thomas and John J. Olivero, 5 October 2005, Journal of Atmospheric and Photo voltaic-Terrestrial Physics.

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