The near-infrared nitric oxide nightglow in the upper atmosphere of Venus

Abstract

The v ‫؍‬ 0 progressions of the C 3 X and A 3 X band systems of nitric oxide dominate the middle-UV spectrum of the night-time upper atmospheres of the Earth, Mars, and Venus. The C(0) 3 A(0)؉h radiative transition at 1.224 m, the only channel effectively populating the A(0) level, must therefore occur also. There have been, however, no reported detections of the C(0) 3 A(0) band in the atmospheres of these or any other planets. We analyzed all available near-infrared limb observations of the darkside atmosphere of Venus by the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) instrument on the Venus Express spacecraft and found 2 unambiguous detections of this band at equatorial latitudes that seem to be associated with episodic events of highly enhanced nightglow emission. The discovery of the C(0) 3 A(0) band means observations in the 1.2-1.3 m region, which also contains the a(0) 3 X(0) emission band of molecular oxygen, can provide a wealth of information on the high-altitude chemistry and dynamics of the Venusian atmosphere.T he luminescence that results from exothermic chemical reactions between the constituents of a planetary atmosphere is customarily termed the night airglow or, simply, the nightglow (1). Although possibly present all day long, it appears most distinctly at night when the other processes of atomic and molecular excitation that depend directly on the action of the Sun are not at play and the diffuse radiation of solar light is at its minimum. The nightglow may originate from various, possibly minor, atmospheric constituents and provides insight into the chemistry, composition, temperature and energy balance of the atmosphere of a planet.The C 2 ⌸ 3 X 2 ⌸ and A 2 ⌺ ϩ 3 X 2 ⌸ band systems of nitric oxide (often referred to as the ␦ and ␥ bands, respectively) have long been known in the upper-atmospheric nightglow of the Earth (2, 3) and Venus (4, 5). More recently, they have also been reported in the atmosphere of Mars (6). A common structure, caused by the vЈ ϭ 0 progression of the aforementioned systems, characterizes the night-time middle-UV spectrum of all 3 planets. Separately and in combination with other nightglow emissions, observations of the nitric oxide nightglow have been used to infer details of the odd-nitrogen chemistry and dynamics in the emitting atmospheres.In the dayglow, resonance scattering of solar photons from ground-state nitric oxide gives rise to additional A 3 X (vЈ Ն 0) bands that have been observed on the sunlit side of the Earth (7) but that remain undetected in the atmospheres of Mars and Venus. On Mars, and expectedly also on Venus, the emission of the a 3 ⌸ 3 X 1 ⌺ system of carbon monoxide is likely to mask the nitric oxide A 3 X dayglow (8). The fluorescence efficiency of the C state is low for v ϭ 0 and negligible for vϾ0, presumably due to rapid predissociation (9-12). Day-time observations of the terrestrial atmosphere have found weak C 3 X (vЈ ϭ 0) bands, which have been attributed to resonance scattering (13-15), although there are significa...

Concurrent observations of the ultraviolet nitric oxide and infrared O2 nightglow emissions with Venus Express

“…Emission from the C 2 P (v = 0) ! A 2 S (v = 0) transition at 1.224 mm was recently observed with the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) -M in the Venus nightglow [García Muñoz et al, 2009]. The N and O atoms are mainly produced by dissociation of N 2 and CO 2 on the dayside by extreme ultraviolet (EUV) photons and photoelectrons.…”

“…The emission is produced by radiative recombination through inverse predissociation of nitrogen N( 4 S) and oxygen O( 3 P) atoms and dominates the middle ultraviolet nightglow spectrum. In this process, excited NO molecules radiate the ultraviolet δ and γ bands between 180 and 310 nm: giving rise to Emission from the C 2 Π (v = 0) → A 2 Σ (v = 0) transition at 1.224 μ m was recently observed with the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) ‐M in the Venus nightglow [ García Muñoz et al , 2009]. The N and O atoms are mainly produced by dissociation of N 2 and CO 2 on the dayside by extreme ultraviolet (EUV) photons and photoelectrons.…”

Limb imaging of the Venus O2 visible nightglow with the Venus Monitoring Camera

“…Some of the occurring reactions are exothermic and lead to excited state products that radiate in the form of nightglow. The list of gases contributing to the Venus nightglow includes O, O 2 , NO, and OH, which produce emission features throughout the ultraviolet, visible, and near-infrared spectrum [Connes et al, 1979;Feldman et al, 1979;García Muñoz et al, 2009a;Krasnopolsky et al, 1977;Piccioni et al, 2008;Slanger et al, 2001].…”

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

“…Near‐infrared spectra collected with the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) on Venus Express have been found to contain the 0–0 and 0–1 bands of O 2 a – X , the 1–0, 2–1, 2–0 and 3–2 bands of OH X – X and the 0–0 band of NO C – A , all of them except the O 2 band at 1.27 μ m seen for the first time in the atmosphere of Venus [ Piccioni et al , 2008; García Muñoz et al , 2009]. In the present work, we extend the investigation of Venus' nightglow with VIRTIS to the visible wavelengths, where the O 2 c (0)– X ( v ″) progression appears as a prominent emission.…”