The mesosphere is the least-understood part of Earth’s atmosphere. It is the portion of the atmosphere from about 50 to about 90 kilometers above the earth's surface, characterized by temperatures that decrease from 10°C to -90°C with increasing altitude. The mesosphere is sensitive to external natural forcing & climate change (e.g. are noctilucent clouds possible indicators of global change and there is a need to better understand the different components of it. This is not so easy as there are limited measurements and in particular modeling for mesospheric processes is difficult as it needs to include neutral & ion chemistry and meridional circulation. The mesosphere is too high for aircraft or weather balloons to operate. In the past mainly sounding rockets have provided meteorologists and astronomers significant data about this important part of the atmosphere. This has changed with the availability of satellite measurements. Especially the atmospheric payload on the ESA satellite Envisat launched in 2002 provided height resolved measurements of the mesosphere and lower thermosphere with 3 different instruments. Whereas SCIAMACHY and GOMOS covered the mesospheric altitude range during nominal operations special modes were implemented for MIPAS operations to sound this part of the atmosphere . Based on this high quality atmospheric data archive covering a time period of more than 10 years a resurgence of mesosphere research has occurred. This has built up high impact research especially in Europe related to climate change and solar influences. Based on these data new scientific studies can be performed in order to distinguish the natural versus anthropogenic effects in the mesosphere and its possible links to climate change. In this context, MesosphEO will address the following themes:

• Retrieval of Reactive Gases and Greenhouse Gases concentrations including water vapour, methane and carbon dioxide
• Studies/Mapping on the impact of solar flares on trace gas concentrations
• Retrieval of the Sodium Layer Information
• Retrieval of Noctilucent Clouds Information
• Retrieval of Temperature information
• Retrieval of Meteroid Introduced Metals information