Visible and near‐infrared nightglow of molecular oxygen in the atmosphere of Venus

Abstract

[1] The Herzberg II system of O 2 has been a known feature of Venus' nightglow since the Venera 9 and 10 orbiters detected its c(0)-X(v 00 ) progression more than 3 decades ago. We search for its emission at 400 nm-700 nm in spectra obtained with the VIRTIS instrument on Venus Express. Despite the weakness of the signal, integration over a few hours of limb observations of the planet's upper atmosphere reveals the unambiguous pattern of the progression. The selected data sample mainly the northern latitudes within a few hours of local midnight. The emission is ubiquitous on the nightside of Venus and can be discerned at tangent altitudes from 80 km to 110 km. The average emission vertical profiles of the c(0)-X(v 00 ) progression and the O 2 a(0)-X(0) band, the latter from simultaneous near-infrared spectra, are quite similar, with their respective peaks occurring within ±1 km of each other. We conclude that the net yield for production of the c(0) state is low, $1%-2% of the oxygen recombination rate, and that O( 3 P) and CO 2 are the two likely quenchers of the Herzberg II nightglow, although CO cannot be ruled out. We also derive a value of 2.45 Â 10 À16 cm 3 s À1 for the rate constant at which CO 2 collisionally quenches the c(0) state. Our VIRTIS spectra show hints of O 2 A 0 (0)-a(v 00 ) emission but no traces of the O ( 1 S-1 D) green line at 557.7 nm.

Six years of Venus winds at the upper cloud level from UV, visible and near infrared observations from VIRTIS on Venus Express

“…These ranges were loosely defined after examination of the calibrated Instrument Transfer Function that show similar instrument behavior for wavelengths in each of these ranges (see Fig. 1 in García-Muñoz et al, 2009). After the contrast enhancement implied by the convolution kernel the images were mapped into cylindrical or polar projections depending on the geometry of the observation.…”

“…Because of the observing geometry many orbits were affected by stray light in the instrument caused by direct sunlight close to, but outside the VIRTIS-M field of view entering the instrument (Arnold et al, 2008) and by contamination of short-wavelength images by long-wavelength light (García-Muñoz et al, 2009), both effects reducing image contrast. Additionally, all images were subject to a substantial difference of responsivity between adjacent pixels in the detector and in the spectral direction, an odd-even defect (Cardesin, 2010) that translated into a high-frequency noise when sharpening individual images.…”

Collisional relaxation of O2($X^3\Sigma _g^ -$X3Σg−, υ = 1) and O2(a1Δg, υ = 1) by atmospherically relevant species

“…In the case of Venus, relatively slow removal by CO 2 is compensated by the high density of CO 2 in the emitting layer: for a density on the order of 10 15 cm −3 at a ∼100 km altitude, 69,70 the collisional removal rate is on the order of 10 s −1 , more than 4 orders of magnitude higher than the radiative rate. Given that the O 2 (a 1 g , υ = 1) + CO 2 rate coefficient seems to have a significant temperature dependence, here we estimate its value at the relevant temperatures of ∼160-170 K (Ref.…”

Prediction of blue, red and green aurorae at Mars

“…As part of the scientific payload of Mars Express, the OMEGA instrument should also be able to observe auroral-like structures (Bertaux et al, 2012); comparisons in the IR have successfully been performed between SPICAM and OMEGA (Fedorova et al, 2012). A similar instrument onboard Venus Express (Migliorini et al, 2011) has observed the visible Venusian O 2 nightglow bands (García Muñoz et al, 2009), but the atomic oxygen green line OI at 557.7 nm has so far eluded direct space-born observations.…”

“…García Muñoz et al (2009) tried to observe the Venusian nightglow in the 400-700 nm range using limb observations. To reach the signalto-noise ratio necessary to observe it, they had to integrate hours of limb observations over the local midnight, for tangent altitude between 80 km and 110 km.…”