Venus has thick clouds of H2SO4 aerosol particles extending from altitudes of 40 to 60 km. The 60-100 km region (the mesosphere) is a transition region between the 4 day retrograde superrotation at the top of the thick clouds and the solar-antisolar circulation in the thermosphere (above 100 km), which has upwelling over the subsolar point and transport to the nightside. The mesosphere has a light haze of variable optical thickness, with CO, SO2, HCl, HF, H2O and HDO as the most important minor gaseous constituents, but the vertical distribution of the haze and molecules is poorly known because previous descent probes began their measurements at or below 60 km. Here we report the detection of an extensive layer of warm air at altitudes 90-120 km on the night side that we interpret as the result of adiabatic heating during air subsidence. Such a strong temperature inversion was not expected, because the night side of Venus was otherwise so cold that it was named the 'cryosphere' above 100 km. We also measured the mesospheric distributions of HF, HCl, H2O and HDO. HCl is less abundant than reported 40 years ago. HDO/H2O is enhanced by a factor of approximately 2.5 with respect to the lower atmosphere, and there is a general depletion of H2O around 80-90 km for which we have no explanation.

A new compact spaceborne high-resolution spectrometer developed for the European Space Agency's Venus Express spacecraft is described. It operates in the IR wavelength range of 2.2 to 4.3 microm and measures absorption spectra of minor constituents in the Venusian atmosphere. It uses a novel echelle grating with a groove density of 4 lines/mm in a Littrow configuration in combination with an IR acousto-optic tunable filter for order sorting and an actively cooled HgCdTe focal plane array of 256 by 320 pixels. It is designed to obtain an instrument line profile of 0.2 cm(-1). First results on optical and spectral properties are reported.

NOMAD is a spectrometer suite on board ESA's ExoMars trace gas orbiter due for launch in January 2016. NOMAD consists of two infrared channels and one ultraviolet and visible channel allowing the instrument to perform observations quasi-constantly, by taking nadir measurements at dayside and nightside, and during solar occultations. In this paper, the design, manufacturing, and testing of the two infrared channels are described. We focus upon the optical working principle in these channels, where an echelle grating, used as a diffractive element, is combined with an acousto-optical tunable filter, used as a diffraction order sorter.

[1] The SPICAM IR spectrometer on Mars Express mission (1.0-1.7 mm, spectral resolution 0.5-1.2 nm) is dedicated primarily to nadir measurements of H 2 O abundance. It is one of two channels of SPICAM UV-IR instrument. In this spectrometer we applied for the first time in planetary research the technology of an acousto-optic tunable filter (AOTF) that allowed unprecedented mass reduction for such an instrument: 0.75 kg. SPICAM IR is a point nadir-looking spectrometer with sequential scanning of the spectrum by the AOTF. Sun occultations are performed with a help of dedicated solar port. We describe instrumentation, calibrations, and the modes of operations of the device and discuss its in-flight performances. A brief overview of the scientific measurements includes water vapor measurements and the mapping of intensity of the O 2 (a 1 D g ) emission at 1.27 mm, described in detail in separate papers. Measurements in reflected solar light allow clear detection of H 2 O and CO 2 ices on the surface or in the atmosphere of Mars. We discuss solar occultation measurements by SPICAM and present resulting vertical profiles of aerosol optical depth.