Sulfuric acid vapor and sulfur dioxide in the atmosphere of Venus as observed by the Venus Express Radio Science Experiment VeRa

<p>The main cloud deck within Venus' atmosphere, which covers the entire planet between approx. 50 and 70 km altitude, is believed to consist mostly of liquid sulfuric acid. The temperature below the main clouds is high enough to evaporate the H2SO4 droplets into gaseous sulfuric acid forming a haze layer which extends to altitudes as deep as 35 km. Gaseous sulfuric acid in Venus’ lower atmosphere is responsible for a strong absorption of radio waves as seen in Mariner, Pioneer Venus, Magellan and Venera radio science observations. Radio wave absorption measurements can be used to derive the amount of H2SO4 in Venus’ atmosphere. The radio science experiment VeRa onboard Venus Express probed the atmosphere of Venus between 2006 and 2014 with radio signals at 13 cm (S-band) and 3.6 cm (X-band) wavelengths. The orbit of the Venus Express spacecraft allowed to sound the atmosphere over a wide range of latitudes and local times providing a global picture of the sulfuric acid vapor distribution. We present the global H2SO4(g) distribution derived from the X-band radio signal attenuation for the time of the entire Venus Express mission. The observation is compared with results obtained from a 2-D transport model. The VeRa observations were additionally used to estimate the abundance of SO2 near the cloud bottom. The global distribution of SO2 at these altitudes is presented and compared with results obtained from other experiments. Eight years of VEX observation allow to study the long-term evolution of H2SO4 and SO2. The latter is presented for the northern polar region.</p>

Calibration Techniques for Studying Venus and Mars Atmospheres

The European Space Agency Venus Express mission (VEX) was sent to Venus in 2005 to unveil the unsolved mysteries regarding its atmosphere, the plasma environment and its temperatures. Radio occultation experiments performed by VeRa radio science instrument probed the planet’s atmosphere by studying the frequency shift on the radio signal sent by the spacecraft to Earth-based ground stations. This study carries out the calibration of the radio frequencies within a radio occultation experiment in order to correct the main sources of error as: thermal noise, spacecraft clock, spacecraft trajectory, and plasma noise. Any uncalibrated effects will bias the retrieval of atmospheric properties. A comparison of the occultation experiments between Venus and Mars is presented, both from the engineering and scientific point of view, through the analysis of Venus Express and Mars Global Surveyor (MGS) occultations data, highlighting stronger calibrations required for VEX, the extreme, hostile, thick Venus’ atmosphere, and a friendly, thin Mars’ atmosphere. This investigation analyzes Venus Express data recorded by the NASA Deep Space Network in 2014, and the results are compatible to previous studies of Venus atmosphere with VEX between 2006 and 2009.