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Encrenaz Thérèse, Greathouse Thomas K., Roe Henry, Richter Matthew J., Lacy John H., Bézard Bruno, Fouchet Thierry, Widemann Thomas

HDO and SO2 thermal mapping on Venus: evidence for strong SO2 variability

Astronomy and Astrophysics, 2012, vol. 543, pp. 153

Référence DOI : 10.1051/0004-6361/201219419
Référence ADS : 2012A&A...543A.153E

Résumé :

We have been using the TEXES high-resolution imaging spectrometer at the NASA Infrared Telescope Facility to map sulfur dioxide and deuterated water over the disk of Venus. Observations took place on January 10-12, 2012. The diameter of Venus was 13 arcsec, with an illumination factor of 80%. Data were recorded in the 1344-1370 cm<SUP>-1</SUP> range (around 7.35 mum) with a spectral resolving power of 80 000 and a spatial resolution of about 1.5 arcsec. In this spectral range, the emission of Venus comes from above the cloud top (z = 60-80 km). Four HDO lines and tens of SO<SUB>2</SUB> lines have been identified in our spectra. Mixing ratios have been estimated from HDO/CO<SUB>2</SUB> and SO<SUB>2</SUB>/CO<SUB>2</SUB> line depth ratios, using weak neighboring transitions of comparable depths. The HDO maps, recorded on Jan. 10 and Jan. 12, are globally uniform with no significant variation between the two dates. A slight enhancement of the HDO mixing ratio toward the limb might be interpreted as a possible increase of the D/H ratio with height above the cloud level. The mean H<SUB>2</SUB>O mixing ratio is found to be 1.5 +/-0.75 ppm, assuming a D/H ratio of 0.0312 (i.e. 200 times the terrestrial value) over the cloud deck. The SO<SUB>2</SUB> maps, recorded each night from Jan. 10 to Jan. 12, show strong variations over the disk of Venus, by a factor as high as 5 to 10. In addition, the position of the maximum SO<SUB>2</SUB> mixing ratio strongly varies on a timescale of 24 h. The maximum SO<SUB>2</SUB> mixing ratio ranges between 75 +/-25 ppb and 125 +/-50 ppb between Jan. 10 and Jan. 12. The high variability of sulfur dioxide is probably a consequence of its very short photochemical lifetime.

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