N.I. Ignatiev

Detection of Methane in the Atmosphere of Mars

We report a detection of methane in the martian atmosphere by the Planetary Fourier Spectrometer onboard the Mars Express spacecraft. The global average methane mixing ratio is found to be 10 ± 5 parts per billion by volume (ppbv). However, the mixing ratio varies between 0 and 30 ppbv over the planet. The source of methane could be either biogenic or nonbiogenic, including past or present subsurface microorganisms, hydrothermal activity, or cometary impacts.

First detection of hydroxyl in the atmosphere of Venus

Context. Airglow emissions, such as previously observed from NO and O2(a−X )( 0−0) on Venus, provide insight into the chemical and dynamical processes that control the composition and energy balance in the upper atmospheres of planets. The OH airglow emission has been observed previously only in the Earth’s atmosphere where it has been used to infer atomic oxygen abundances. The O2(a − X )( 0−1) airglow emission also has only been observed in the Earth’s atmosphere, and neither laboratory nor theoretical studies have reached a consensus on its transition probability. Aims. We report measurements of night-side airglow emission in the atmosphere of Venus in the OH (2−0), OH (1−0), O2(a − X )( 0−1), and O2(a − X )( 0−0) bands. This is the first detection of the first three of these airglow emissions on another planet. These observations provide the most direct observational constraints to date on H, OH, and O3, key species in the chemistry of Venus’ upper atmosphere. Methods. Airglow emission detected at wavelengths of 1.40−1.49 and 2.6−3.14 µm in limb observations by the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) on the Venus Express spacecraft is attributed to the OH (2−0) and (1−0) transitions, respectively, and compared to calculations from a photochemical model. Simultaneous limb observations of airglow emission in the O2(a − X )( 0−0) and (0−1) bands at 1.27 and 1.58 µm, respectively, were used to derive the ratio of the transition probabilities for these bands. Results. The integrated emission rates for the OH (2−0) and (1−0) bands were measured to be 100 ± 40 and 880 ± 90 kR respectively, both peaking at an altitude of 96 ± 2 km near midnight local time for the considered orbit. The measured ratio of the O2(a −X )( 0−0) and (0−1) bands is 78 ± 8. Conclusions. Photochemical model calculations suggest the observed OH emission is produced primarily via the Bates-Nicolet mechanism, as on the Earth. The observed ratio of the intensities of the O2(a − X )( 0−0) and (0−1) bands implies the ratio of their transition probabilities is 63 ± 6.

Water vapour in the middle atmosphere of Venus:: An improved treatment of the Venera 15 ir spectra

In 1983, spectra of Venus in the region of 6–40 μm were measured by means of the Fourier Spectrometer aboard the Venera 15 orbiter. It covered local solar times from 4 am to 10 am and from 4 pm to 10 pm in the latitude range from 65°S up to 87°N. The results of an extended processing and analysis of these data are presented. Time and spatial variations of the water vapour were found. Most of the measurements fall in the range of 5–15 ppm, which is close to earlier results. The effective altitude of sounding is approximately equal to the altitude where the optical depth τ = 1. In the northern hemisphere, which was mainly covered by the measurements, two latitude regions can be distinguished; (A) 20° 60°, which are characterised by different altitudes of the level of τ = 1, 62 and 55 km respectively. Mean mixing ratios near this level in the two regions are almost the same, but the partial pressures and mass densities in the region (B) are 2–4 times greater than those in region (A). In region (A) a weak maximum was detected near 10 am local solar time (17 ppm at φ = 35°) and a minimum—near 10 pm (2ppm at φ = 30°). Region (B) is of inhomogeneous structure, and the retrieved mixing ratio has greater uncertainty and may probably change from the low values up to 30 ppm. In region (A) the water vapour mass density at the level of τ = 1 is 2–4 times greater than the mean density of the water contained in aerosol particles, while in region (B) this ratio may vary in the limits 0.5–5. Although the retrieval of H2O mixing ratio altitude profile from the Venera 15 data appeared to be impossible, indirect indications were found that at least in region (A) the mixing ratio decreases with altitude.

Structure of the venus middle atmosphere: Venera 15 fourier spectrometry data revisited

Abstract The data obtained by Infrared Fourier Spectrometer on board Venera 15 Orbiter are revisited. The new database of temperature and aerosol profiles is created for the altitude range 55–100 km. The main improvements concern the involving of the whole spectral range free from absorption by any gases but CO 2 into the temperature retrieval procedure. Besides the CO 2 15 μm fundamental band, this range also includes the weak hot and isotopic CO 2 bands. HITRAN-96 spectral database was used for calculation of the gaseous absorption coefficients. The diurnal variations at the isobaric levels are investigated. At low latitudes at the altitude h > 85 km a minimal temperature is observed in the afternoon, and a maximal one is on the morning day side. The temperature differences reach 20 K near 0.1 mb level. The temperature difference changes its sign below 1 mb level: in the afternoon it is warmer by more than 10 K than in the morning. The density of the clouds at all latitudes is found to be higher in the afternoon than in the morning. In the coldest parts of the ‘cold collar’ the clouds are found to be composed of the mode 3 particles. The thermal zonal wind field reveals the presence of the midlatitude jet, connected with the ‘cold collar’. The low latitude jet near 85 km, connected with the temperature inversion above this level, is observed. It is also possible that another low latitude jet exists near the cloud tops at low latitudes.

The Venus nighttime atmosphere as observed by the VIRTIS‐M instrument. Average fields from the complete infrared data set

We present and discuss here the average fields of the Venus atmosphere derived from the nighttime observations in the 1960–2350 cm−1 spectral range by the VIRTIS-M instrument on board the Venus Express satellite. These fields include: (a) the air temperatures in the 1–100 mbar pressure range (~85–65 km above the surface), (b) the altitude of the clouds top, and (c) the average CO mixing ratio. A new retrieval code based on the Bayesian formalism has been developed and validated on simulated observations, to statistically assess the retrieval capabilities of the scheme once applied to the VIRTIS data. The same code has then been used to process the entire VIRTIS-M data set. Resulting individual retrievals have been binned on the basis of local time and latitude, to create average fields. Air temperature fields confirm the general trends previously reported in Grassi et al. (2010), using a simplified retrieval scheme and a more limited data set. At the lowest altitudes probed by VIRTIS (~65 km), air temperatures are strongly asymmetric around midnight, with a pronounced minima at 3LT, 70°S. Moving to higher levels, the air temperatures first become more uniform in local time (~75 km), then display a colder region on the evening side at the upper boundary of VIRTIS sensitivity range (~80 km). As already shown by Ignatiev et al. (2008) for the dayside, the cloud effective altitude increases monotonically from the south pole to the equator. However, the variations observed in night data are consistent with an overall variation of just 1 km, much smaller than the 4 km reported for the dayside. The cloud altitudes appear slightly higher on the evening side. Both observations are consistent with a less vigorous meridional circulation on the nightside of the planet. Carbon monoxide is not strongly constrained by the VIRTIS-M data. However, average fields present a clear maximum of 80 ppm around 60°S, well above the retrieval uncertainty. Once the intrinsic low sensitivity of VIRTIS data in the region of cold collar is kept in mind, this datum is consistent with a [CO] enrichment toward the poles driven by meridional circulation.

A mapping of martian water sublimation during early northern summer using OMEGA/Mars Express

The OMEGA imaging spectrometer aboard Mars Express has been used to map the water vapor abundance over the martian surface, from the analysis of the 2.6 μm band of H 2 O. As a preliminary result of this study, we present water vapor maps in the northern hemisphere at the time of the northern polar cap sublimation (Ls = 94-112 deg). The maps show a mean H 2 O mixing ratio of about 2-3 x 10 -4 at a latitude of 40N, and in the range of 5 x 10 -4 -10 -3 at 60N-80N latitudes. The corresponding mean H 2 O column densities are about 25 pr-μm at 40N and between 40 and 60 pr-μm at 60N-80N, with uncertainties of about 30 percent. Our results are in agreement with previous results by MAWD/Viking and TES/MGS for latitudes up to 60N, but seem to indicate lower values at high latitude. However they are still globally consistent in view of our error bars.

IRIS Mariner 9 data revisited: water and dust daily cycles

Abstract IRIS Mariner 9 data have been studied, after correction for an instrumental effect, as a function of season and local time, searching for a relation between water content of the atmosphere and dust. After averaging data for different local time bins, the vertical temperature profile and atmospheric dust content were retrieved. The temperature profile was then used for evaluation of water mixing ratio. This last procedure was without ambiguity only when no thermal inversion was found in the vertical profile. This fact limits our basic results only on the day side. Our results indicate that the ground temperature and the atmospheric temperature (mainly in the low altitudes) show a strong modulation during the day, with a peak temperature around 12–14 local time. Together with the temperature, the atmospheric water content shows a strong modulation: the peak of the water content, around 140 ppm , is observed with the peak of the temperature. The integrated atmospheric dust opacity computed at 1000 cm −1 shows an anti-correlated behavior: peaks are observed at early morning and late evening, while a local minimum is observed around noon. Our observations, with the integrated dust opacity decreasing around noon, are consistent with a model in which a large part of atmospheric water vapor is adsorbed by dust and soil, and is released as water vapor during the hot hours. In the afternoon, water is adsorbed quickly again as new dust is added by dust devils. The vertical temperature profile does not allow, during the entire day, ice condensation around dust. The water lines and the continuum around 200– 400 cm −1 give spectral evidence of frost on soil only very early in the morning or very late in the evening. The 200– 400 cm −1 region is a very good indicator of the presence of frost.

Atmospheric photochemistry above possible martian hot spots

Abstract Considering the possibility of outgassing from some localized sources on Mars, we have developed a one-dimensional photochemical model that includes methane (CH4), sulfur dioxide (SO2) and hydrogen sulfide (H2S). Halogens were considered but were found to have no significant impact on the martian atmospheric chemistry. We find that the introduction of methane into the martian atmosphere results in the formation of mainly formaldehyde (CH2O), methyl alcohol (CH3OH) and ethane (C2H6), whereas the introduction of the sulfur species produces mainly sulfur monoxide (SO) and sulfuric acid (H2SO4). Depending upon the flux of the outgassed molecules from possible hot spots, some of these species and the resulting new molecules may be detectable locally, either by remote sensing (e.g., with the Planetary Fourier Spectrometer on Mars Express) or in situ measurements.

AOST: Fourier spectrometer for studying mars and phobos

An AOST Fourier spectrometer of the Phobos-Soil project is intended for studying Mars and Phobos by means of measurements of IR radiation spectra of the Martian surface and atmosphere, the Phobos surface, and the spectrum of solar radiation passing through the Martian atmosphere on its limb. The main scientific problems to be solved with the spectrometer on Mars are measurements of methane content, search for minor constituents, and study of diurnal variations in the temperature and atmospheric aerosol. The spectrometer will also study the Martian and Phobos surface both remotely and after landing. The spectral range of the instrument is 2.5–25 μm, the best spectral resolution (without apodization) is 0.6 cm−1, and the instantaneous field of view is 2.5°. The recording time of one spectrum is equal to 5 s in solar observations and 50 s in observations of Mars and Phobos. The instrument has self-thermal stabilization and two-axis pointing systems, as well as a built-in radiation source for flight calibration. The spectrometer mass is 4 kg, and power consumption is up to 13 W. Scientific problems, measurement modes, and, briefly, engineering implementation of the experiment are discussed in this work.

ACS experiment for atmospheric studies on “ExoMars-2016” Orbiter

ACS is a set of spectrometers for atmospheric studies (Atmospheric Chemistry Suite). It is one of the Russian instruments for the Trace Gas Orbiter (TGO) of the Russian-European “ExoMars” program. The purpose of the experiment is to study the Martian atmosphere by means of two observations regimes: sensitive trace gases measurements in solar occultations and by monitoring the atmospheric state during nadir observations. The experiment will allow us to approach global problems of Mars research such as current volcanism, and the modern climate status and its evolution. Also, the experiment is intended to solve the mystery of methane presence in the Martian atmosphere. Spectrometers of the ACS set cover the spectral range from the near IR-range (0.7 μm) to the thermal IR-range (17 μm) with spectral resolution λ/Δλ reaching 50000. The ACS instrument consists of three independent IR spectrometers and an electronics module, all integrated in a single unit with common mechanical, electrical and thermal interfaces. The article gives an overview of scientific tasks and presents the concept of the experiment.