Identification of OSSO as a near‐UV absorber in the Venusian atmosphere

Frandsen, Benjamin N.; Wennberg, P. O.; Kjaergaard, Henrik G.

doi:10.1002/2016gl070916

Cited by 66 publications

(102 citation statements)

References 89 publications

(156 reference statements)

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“…The identification of the UV absorber is a problem far from being solved. While this work supports the spectral similarity of the retrieved values with disulfur dioxide, it must be noted that the vertical distribution assumed here is not in complete agreement with the profiles computed by Frandsen et al (). A more recent work (Krasnopolsky, ) also shows the weaknesses of this explanation in view of state‐of‐the‐art photochemical models of Venus's atmosphere.…”

Section: Discussioncontrasting

confidence: 68%

Venus Upper Clouds and the UV Absorber From MESSENGER/MASCS Observations

et al. 2018

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One of the most intriguing, long‐standing questions regarding Venus's atmosphere is the origin and distribution of the unknown UV absorber, responsible for the absorption band detected at the near‐UV and blue range of Venus's spectrum. In this work, we use data collected by Mercury Atmospheric and Surface Composition Spectrometer (MASCS) spectrograph on board the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission during its second Venus flyby in June 2007 to address this issue. Spectra range from 0.3 μm to 1.5 μm including some gaseous H2O and CO2 bands, as well as part of the SO2 absorption band and the core of the UV absorption. We used the NEMESIS radiative transfer code and retrieval suite to investigate the vertical distribution of particles in the equatorial atmosphere and to retrieve the imaginary refractive indices of the UV absorber, assumed to be well mixed with Venus's small mode 1 particles. The results show a homogeneous equatorial atmosphere, with cloud tops (height for unity optical depth) at 75 ± 2 km above surface. The UV absorption is found to be centered at 0.34 ± 0.03 μm with a full width at half maximum of 0.14 ± 0.01 μm. Our values are compared with previous candidates for the UV aerosol absorber, among which disulfur oxide (S2O) and dioxide disulfur (S2O2) provide the best agreement with our results.

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Section: Discussioncontrasting

confidence: 68%

Venus Upper Clouds and the UV Absorber From MESSENGER/MASCS Observations

et al. 2018

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“…Several candidates could account for the core absorption around 0.35 μm, but the main problem is fitting the spectral slope at 0.4-0.5 μm. The best agreement was found for an irradiated version of S 2 O (Lo et al 2003) and S 2 O 2 or OSSO (Frandsen et al 2016) if a single absorber is assumed. Other species including iron chloride have too narrow absorption to be in agreement with the MASCS spectra.…”

Section: Sulphuric Acidmentioning

confidence: 90%

“…However, there are recent attempts to suggest gaseous species as candidates. Frandsen et al (2016) studied chemistry and optical properties of S 2 O 2 and found that this species can form in a sulphur cycle at the cloud tops and that its spectral properties match those of the unknown near-UV absorber reasonably well. The problem of this identification is that the photochemical lifetime of S 2 O 2 is very short (few seconds in sunlight) that precludes its existence on the day side of the planet.…”

Section: Sulphuric Acidmentioning

confidence: 99%

“…The problem of this identification is that the photochemical lifetime of S 2 O 2 is very short (few seconds in sunlight) that precludes its existence on the day side of the planet. Krasnopolsky (2018) included the S 2 O 2 formation rate and absorption cross sections from Frandsen et al (2016) in his photochemical model. The predicted S 2 O 2 absorption was found to be about two orders of magnitude weaker than that observed.…”

Section: Sulphuric Acidmentioning

confidence: 99%

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Clouds and Hazes of Venus

et al. 2018

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More than three decades have passed since the publication of the last review of the Venus clouds and hazes. The paper published in 1983 in the Venus book summarized the discoveries and findings of the US Pioneer Venus and a series of Soviet Venera spacecraft (Esposito et al. in Venus, p. 484, 1983). Due to the emphasis on in-situ investigations from descent probes, those missions established the basic features of the Venus cloud system, its vertical structure, composition and microphysical properties. Since then, significant progress in understanding of the Venus clouds has been achieved due to exploitation of new observation techniques onboard Galileo and Messenger flyby spacecraft and Venus Express and Akatsuki orbiters. They included detailed investigation of the mesospheric hazes in solar and stellar occultation geometry applied in the broad spectral range from UV to thermal IR. Imaging spectroscopy in the near-IR transparency "windows" on the night side opened a new and very effective way of sounding the deep atmosphere. This technique together with near-simultaneous UV imaging enabled comprehensive study of the cloud morphology from the cloud top to its deep layers. Venus Express operated from April 2006 until December 2014 and provided a continuous data set characterizing Venus clouds and hazes over a time span of almost 14 Venus years thus enabling a detailed study of temporal and spatial variability. The polar orbit of Venus Express allowed complete latitudinal coverage. These studies are being complemented by JAXA Akatsuki orbiter that began observations in May 2016. This paper reviews the current status of our knowledge of the Venus cloud system focusing mainly on the results acquired after the Venera, Pioneer Venus and Vega missions.

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“…According to data from descent probes the unknown absorber may be located in the upper clouds (Tomasko et al 1980;Esposito 1980), and absorbs about half of the solar radiance deposited at the cloud top level, accounting for ∼3 K/Earth day of the global mean solar heating around 65 km altitude, when the total global mean solar heating is ∼6 K/day (Crisp 1986). Many candidates have been proposed for the unknown absorber, including OSSO, S 2 O, S x , FeCl 3 , and iron-bearing microorganism (Mills et al 2007;Frandsen et al 2016;Krasnopolsky 2017;Pérez-Hoyos et al 2018;Limaye et al 2018). However, none of these species satisfy both the spectral features produced by the unknown absorber, and the lifetime and simulated vertical profile required to fit the observations (Krasnopolsky 2018;Pérez-Hoyos et al 2018).…”

Section: Introductionmentioning

confidence: 99%

Long-term Variations of Venus’s 365 nm Albedo Observed by Venus Express, Akatsuki, MESSENGER, and the Hubble Space Telescope

Lee

Jessup

Pérez‐Hoyos

et al. 2019

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An unknown absorber near the cloud top level of Venus generates a broad absorption feature from the ultraviolet (UV) to visible, peaking around 360 nm, and therefore plays a critical role in the solar energy absorption. We present a quantitative study on the variability of the cloud albedo at 365 nm and its impact on Venus solar heating rates based on an analysis of Venus Express and Akatsuki's UV images, and Hubble Space Telescope and MESSENGER's UV spectral data; in this analysis the calibration correction factor of the UV images of Venus Express (VMC) is updated relative to the Hubble and MESSENGER albedo measurements. Our results indicate that the 365-nm albedo varied by a factor of 2 from 2006 to 2017 over the entire planet, producing a 25-40% change in the low latitude solar heating rate according to our radiative transfer calculations. Thus, the cloud top level atmosphere should have experienced considerable solar heating variations over this period. Our global circulation model calculations show that this variable solar heating rate may explain the observed variations of zonal wind from 2006 to 2017. Overlaps in the timescale of the long-term UV albedo and the solar activity variations make it plausible that solar extreme UV intensity and cosmic-ray variations influenced the observed albedo trends. The albedo variations might also be linked with temporal variations of the upper cloud SO 2 gas abundance, which affects the H 2 SO 4 -H 2 O aerosol formation.

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Identification of OSSO as a near‐UV absorber in the Venusian atmosphere

Cited by 66 publications

References 89 publications

Venus Upper Clouds and the UV Absorber From MESSENGER/MASCS Observations

Venus Upper Clouds and the UV Absorber From MESSENGER/MASCS Observations

Clouds and Hazes of Venus

Long-term Variations of Venus’s 365 nm Albedo Observed by Venus Express, Akatsuki, MESSENGER, and the Hubble Space Telescope

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