The O(1S) metastable atoms can radiatively relax by emitting airglow at 557.7 and 297.2 nm. The latter one has been observed with the Imaging Ultraviolet Spectrograph onboard the Mars Atmosphere and Volatile Evolution Mars orbiter since 2014. Limb profiles of the 297.2‐nm dayglow have been collected near periapsis with a spatial resolution of 5 km or less. They show a double‐peak structure that was previously predicted but never observed during earlier Mars missions. The production of both 297.2‐nm layers is dominated by photodissociation of CO2. Their altitude and brightness is variable with season and latitude, reflecting changes in the total column of CO2 present in the lower thermosphere. Since the lower emission peak near 85 km is solely produced by photodissociation, its peak is an indicator of the unit optical depth pressure level and the overlying CO2 column density. Its intensity is directly controlled by the Lyman‐α solar flux reaching the Martian upper atmosphere. We take advantage of the Lyman‐α flux measurements of the solar Extreme Ultraviolet Monitor instrument onboard Mars Atmosphere and Volatile Evolution to model the observed OI 297.2‐nm limb profiles. For this, we combine photodissociation sources with chemical processes and photoelectron impact excitation. To determine the relative importance of the excitation processes, we apply the model to the atmospheric structure measured by the Viking 1 lander before applying it to a model atmosphere. We find very good agreement with the lower peak structure and intensity if the CO2 density provided by the Mars Climate Database is scaled down by a factor between 0.50 and 0.66. We also determine that the previously uncertain quantum yield for production of O(1S) atoms by photodissociation of CO2 at Lyman‐α wavelength is about 8%.

We report observations of the proton aurora at Mars, obtained with the Spectroscopy for the Investigation of the Characteristics of the Atmosphere of Mars (SPICAM) ultraviolet spectrograph on board Mars Express between 2004 and 2011. This is a third type of UV aurora that is discovered on Mars, in addition to the discrete and diffuse nightside aurora. It is observed only on the dayside as it is produced by the direct interaction of solar wind protons with the upper atmosphere. The auroral signature is an enhancement of the Lyman‐α emission in the order of a few kilorayleighs. The proton aurora features peak emissions around 120 to 150 km. From the full SPICAM database, limb observations have been investigated and six clear cases have been found. We identify either coronal mass ejections and/or corotating interaction regions as triggers for each of these events.

Since 2005, Mars has progressively revealed that its atmosphere is glowing with several types of aurorae. So far, three types of aurorae have been observed in the Martian atmosphere: discrete aurorae, diffuse aurorae, and proton aurorae.Chronologically, discrete aurorae were first discovered with the Spectroscopy for the Investigation of the Characteristics of the Atmosphere of Mars (SPICAM) instrument on board European Space Agency's (ESA)

We analyze two Martian years of dayglow measurements of the CO Cameron bands and the CO2+ ultraviolet doublet (UVD) at 298–299 nm with the Imaging UltraViolet Spectrograph on board the Mars Atmosphere and Volatile EvolutioN (MAVEN) orbiter. We show that the altitude and the brightness of the two emissions peaks are strongly correlated, although data were collected over a wide range of latitudes and seasons. Averaged limb profiles are presented and compared with numerical simulations based on updated calculations of the production of the CO (a3Π) and the CO2+ (B 2Σ) states. The model simulations use the solar flux directly measured on board MAVEN with the Extreme Ultraviolet Monitor and the neutral densities provided by the Mars Climate Database version 5.3, adapted to the conditions of the observations. We show that the altitude and the shape of the sample limb profiles are well reproduced using the Mars Climate Database neutral atmosphere. The simulated peak intensities of the CO2+ UVD and Cameron bands are in good agreement considering the uncertainties on the excitation cross sections and the calibration of the Imaging Ultraviolet Spectrograph (IUVS) and Extreme Ultraviolet Monitor instruments. No significant adjustment of the electron impact cross section on CO2 to produce the a3Π state is needed. Seasonal‐latitudinal maps of the Cameron and UVD peak altitude observed during two Martian years show variations as large as 23 km. Model simulations of the amplitude of these changes are in fair agreement with the observations except during the southern summer dust period (Ls = 270–320°) when the calculated rise of the dayglow layer is underestimated.

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Enhancements of the dayside Lyman-α emission by as much as ∼50% have been observed between 120 and 130 km in the lower Martian thermosphere from the Mars Express and MAVEN satellites, usually following solar events such as coronal mass ejections and corotating interaction regions. They have been assumed to be optical signatures of proton aurora related to an increase in the solar wind proton flux hitting Mars' bow shock. We present model simulations of the Lyman-α line profiles at different altitudes. These are partly guided by in situ measurements of the energy spectrum of protons in the magnetosheath region by the SWIA instrument on board the MAVEN spacecraft. We show that the auroral Lyman-α line profile is significantly broader than the hydrogen core of the planetary thermal H atom. Consequently, most of the auroral emission is produced outside the optically thick hydrogen core and creates the observed intensity enhancement. Simulations with incident energetic hydrogen atoms (H ENAs) produce a somewhat broader line profile. Monte Carlo calculations are made separately for incident solar wind protons and H ENAs produced by charge exchange in the hydrogen corona. Absorption by CO 2 along the line of sight significantly affects the intensity distribution in the lower thermosphere. The calculated altitude of the peak emission for both types of incident particles is consistent with the observed characteristics of the proton aurora. We show that the presence of a horizontal induced magnetic field somewhat increases the line width and decreases the altitude of the emission peak as a consequence of the magnetic barrier effect on proton precipitation. The brightness of the Lyman-α emission also drops as a result of increased magnetic shielding of the protons.

Iceland is part of the accreting plate boundary between the American and European plates. Since 1965 a number of repeated triangulation‐trilateration surveys spanning the neovolcanic zone in NE Iceland were made in order to detect crustal movements. All the measurements for a single observation epoch are separately adjusted by the method of least squares. Statistical tests are carried out to check the observations and adjustment models for outliers and model errors. To detect significant movements in repeatedly measured geodetic networks with multivariate design, a testing rule is described. After unexpected horizontal contractions of the surface of approximately 0.5 m from 1965 to 1971, enormous deformations have been found since the beginning of a major rifting episode in December 1975. During the period from 1971 to 1980 a horizontal expansion of about 7.5 m and vertical displacements of 3 m were observed across the approximately 3‐km‐wide active rifting zone of the Krafla fissure swarm. In adjacent zones, compressional strains of up to 2×10−4 occurred, rapidly decreasing to a value of 1×10−5 at a distance of 40 km from the rifting axis. After 1980 the pattern of ground deformation has altered. The east‐west shifts have decreased and are superposed by a radial component of motion around the Krafla caldera. West of the Krafla fissure swarm a shear zone is found.

We present an overview of two Martian Years (MYs) oxygen dayglow limb observations of the ultraviolet (UV) emissions at 130.4 and 135.6 nm. The data have been collected with the Imaging Ultraviolet Spectrograph (IUVS) instrument on board the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. We use solar flux measurements of EUVM on board MAVEN to remove the solar-induced variation and show the variations of the maximum limb brightness and altitude with season, solar zenith angle, and latitude, which reflects the strong variability of the Martian atmosphere. The 130.4-and 135.6-nm peak brightness and altitudes are strongly correlated and behave similarly. Both emissions are modeled for selected data using Monte Carlo codes to calculate emissions arising from electron impact on O and CO 2. Additional radiative transfer calculations are made to analyze the optically thick 130.4-nm emission. Model atmospheres from the Mars Climate Database serve as input. Both simulated limb profiles are in good agreement with the observations despite some deviations. We furthermore show that the observed 130.4-nm brightness is dominated by resonance scattering of the solar multiplet with a contribution (15-20%) by electron impact on O. Over 95% of the excitation at 135.6 nm arises from electron impact on O. Simulations indicate that the limb brightness is dependent on the oxygen and CO 2 content, while the peak emission altitude is mainly driven by the CO 2 content because of absorption processes. We deduce [O]/[CO 2 ] mixing ratios of 3.1% and 3.0% at 130 km for data sets collected at L S = 350°in Martian years 32 and 33.