The data assimilation technique adopted by the science team will allow them to model the atmospheric circulation. Mapping of the deuterium/hydrogen ratio (D/H) will also be performed, to provide new information on water reservoirs and atmospheric escape.ДЄ third goal is characterising the state of the atmosphere, in particular temperatures, aerosols, water vapour, and ozone. The first scientific goal will be to detect a broad suite of atmospheric trace gases, and key isotopologues (molecules that have at least one atom with a different number of neutrons than the parent molecules), to establish the atmospheric inventory.ДЇollowing a positive detection of key species, geographical (location and altitude) and seasonal mapping will be carried out. This includes mapping the distribution of trace gases, identifying their sources and sinks, and studying geographical and temporal variability. The Orbiter is used to investigate trace gases with the following scientific objectives:Дeliver a detailed characterisation of the Martian atmosphere's composition. It is also providingВ new data for the study of the temporal and spatial evolution of trace gases in the Martian atmosphere, and for the location of their source regions.ДЄrtist's impression of the Trace Gas Orbiter showing where the science instruments are located. The Trace Gas Orbiter carries scientific instruments for the detection of trace gases with an improved accuracy - 1000 times better - compared to previous measurements from orbit and ground-based measurements. There is particular focus on hydrocarbons or sulphur species which could be signatures of active biological or geological processes, at present or in the past. It is investigatingВ trace gases вЂ“ gases which are present in small concentrations in the atmosphere, making up less than 1 per cent of it. The ExoMars Trace Gas Orbiter is an ESA and Roscosmos mission to Mars. ExoMars Trace Gas Orbiter Instruments Investigating the Martian atmosphere

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