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The thermosphere of Mars is the interface through which the planet is continuously losing its reservoir of atmospheric volatiles to space. The structure and dynamics of the thermosphere is driven by a global circulation that redistributes the incident energy from the Sun. We report mapping of the global circulation in the thermosphere of Mars with the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft. The measured neutral winds reveal circulation patterns simpler than those of Earth that persist over changing seasons. The winds exhibit pronounced correlation with the underlying topography owing to orographic gravity waves.

Interplanetary dust particles sporadically enter planetary atmospheres at orbital velocities and ablate as collisions occur with ambient gases to produce a persistent layer of metallic atoms (for example, Fe, Mg, Na) in their upper atmospheres. Such layers are well studied at Earth, but have not been directly detected elsewhere in the Solar System. Here we report the detection of a meteoric layer consisting of Mg + ions near an altitude of 90 km in the Martian atmosphere from ultraviolet remote sensing observations by NASA’s MAVEN spacecraft. We observe temporal variability in the Mg + layer over the course of a Martian year, moving up and down in altitude seasonally and in response to dust storms, and displaying diurnal fluctuations in density. We also find that most meteor showers do not significantly perturb this layer, which constrains the fluence of eleven observed Martian meteor showers to less than our estimated global dust flux. The persistence and variability of the Mg + layer are difficult to explain with existing models and reconcile with other transient layers of ions observed in the Martian ionosphere. We suggest that the transient layers are not sourced from the persistent Mg + layer and thus not derived from meteoric material, but are ambient ions produced by some unknown mechanism. Collisions of dust particles with a planet’s atmosphere lead to the accumulation of metallic atoms at high altitudes. MAVEN spacecraft observations reveal a persistent—but temporally variable—metal layer of Mg + ions in the Martian atmosphere.

Dust is common close to the martian surface, but no known process can lift appreciable concentrations of particles to altitudes above ~150 kilometers. We present observations of dust at altitudes ranging from 150 to above 1000 kilometers by the Langmuir Probe and Wave instrument on the Mars Atmosphere and Volatile Evolution spacecraft. Based on its distribution, we interpret this dust to be interplanetary in origin. A comparison with laboratory measurements indicates that the dust grain size ranges from 1 to 12 micrometers, assuming a typical grain velocity of ~18 kilometers per second. These direct observations of dust entering the martian atmosphere improve our understanding of the sources, sinks, and transport of interplanetary dust throughout the inner solar system and the associated impacts on Mars’s atmosphere.

Compositional mapping of Mars at the 100-metre scale with the Mars Odyssey Thermal Emission Imaging System (THEMIS) has revealed a wide diversity of igneous materials. Volcanic evolution produced compositions from low-silica basalts to high-silica dacite in the Syrtis Major caldera. The existence of dacite demonstrates that highly evolved lavas have been produced, at least locally, by magma evolution through fractional crystallization. Olivine basalts are observed on crater floors and in layers exposed in canyon walls up to 4.5 km beneath the surface. This vertical distribution suggests that olivine-rich lavas were emplaced at various times throughout the formation of the upper crust, with their growing inventory suggesting that such ultramafic (picritic) basalts may be relatively common. Quartz-bearing granitoid rocks have also been discovered, demonstrating that extreme differentiation has occurred. These observations show that the martian crust, while dominated by basalt, contains a diversity of igneous materials whose range in composition from picritic basalts to granitoids rivals that found on the Earth. Martian minerals mapped Infrared measurements from the orbiting Mars Odyssey probe have been used to produce the most detailed map yet of mineral distribution on the martian surface. The rocks show a surprisingly complex volcanic history. Lavas range from primitive mantle-derived basalts to silica-rich rocks that probably formed in magma chambers following the re-melting of previously erupted rocks. Also present are volcanic basalts that contain more than 20% olivine, a mineral that is quickly weathered by water. Similar olivine-rich rocks were found in eroded canyon walls and ancient crater floors that date back billions of years. This suggests that during each period of olivine layer deposition, Mars did not have extensive water on its surface.

The history of Mars’ atmosphere is important for understanding the geological evolution and potential habitability of the planet. We determine the amount of gas lost to space through time using measurements of the upper-atmospheric structure made by the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft. We derive the structure of 38Ar/36Ar between the homopause and exobase altitudes. Fractionation of argon occurs as a result of loss of gas to space by pickup-ion sputtering, which preferentially removes the lighter atom. The measurements require that 66% of the atmospheric argon has been lost to space. Thus, a large fraction of Mars’ atmospheric gas has been lost to space, contributing to the transition in climate from an early, warm, wet environment to today’s cold, dry atmosphere.

The Solar Wind Ion Analyzer (SWIA) on the MAVEN mission will measure the solar wind ion flows around Mars, both in the upstream solar wind and in the magneto-sheath and tail regions inside the bow shock. The solar wind flux provides one of the key energy inputs that can drive atmospheric escape from the Martian system, as well as in part controlling the structure of the magnetosphere through which non-thermal ion escape must take place. SWIA measurements contribute to the top level MAVEN goals of characterizing the upper atmosphere and the processes that operate there, and parameterizing the escape of atmospheric gases to extrapolate the total loss to space throughout Mars’ history. To accomplish these goals, SWIA utilizes a toroidal energy analyzer with electrostatic deflectors to provide a broad 360 ∘ ×90 ∘ field of view on a 3-axis spacecraft, with a mechanical attenuator to enable a very high dynamic range. SWIA provides high cadence measurements of ion velocity distributions with high energy resolution (14.5 %) and angular resolution (3.75 ∘ ×4.5 ∘ in the sunward direction, 22.5 ∘ ×22.5 ∘ elsewhere), and a broad energy range of 5 eV to 25 keV. Onboard computation of bulk moments and energy spectra enable measurements of the basic properties of the solar wind at 0.25 Hz.

Loading of the lithosphere of Mars by the Tharsis rise explains much of the global shape and long-wavelength gravity field of the planet, including a ring of negative gravity anomalies and a topographic trough around Tharsis, as well as gravity anomaly and topographic highs centered in Arabia Terra and extending northward toward Utopia. The Tharsis-induced trough and antipodal high were largely in place by the end of the Noachian Epoch and exerted control on the location and orientation of valley networks. The release of carbon dioxide and water accompanying the emplacement of ∼ 3 × 108cubic kilometers of Tharsis magmas may have sustained a warmer climate than at present, enabling the formation of ancient valley networks and fluvial landscape denudation in and adjacent to the large-scale trough.

The MAVEN Solar Wind Electron Analyzer (SWEA) is a symmetric hemispheric electrostatic analyzer with deflectors that is designed to measure the energy and angular distributions of 3-4600-eV electrons in the Mars environment. This energy range is important for impact ionization of planetary atmospheric species, and encompasses the solar wind core and halo populations, shock-energized electrons, auroral electrons, and ionospheric primary photoelectrons. The instrument is mounted at the end of a 1.5-meter boom to provide a clear field of view that spans nearly 80 % of the sky with ∼20° resolution. With an energy resolution of 17 % ( Δ E / E ), SWEA readily distinguishes electrons of solar wind and ionospheric origin. Combined with a 2-second measurement cadence and on-board real-time pitch angle mapping, SWEA determines magnetic topology with high (∼8-km) spatial resolution, so that local measurements of the plasma and magnetic field can be placed into global context.

The Radio Occultation Science Experiment (ROSE) is part of the scientific payload of the Mars Atmosphere Volatile EvolutioN (MAVEN) spacecraft. Here we motivate the science objectives of the MAVEN ROSE investigation, which are (1) to determine the vertical structure of plasma in the ionosphere and (2) to identify the density, altitude, and width of the ionospheric density peak. MAVEN ROSE achieves these science objectives by performing two-way X-band radio occultations. Data are acquired ingress and egress opportunities using the high-gain antenna and a carrier-only signal. They are also acquired on ingress opportunities using the low-gain antenna with telemetry on the signal. Raw data are processed to yield vertical profiles of the electron density in the ionosphere of Mars with an accuracy on the order of 10 9  m − 3 , a vertical resolution on the order of 1 km, and a vertical range on the order of 100–500 km. Data products are archived at the NASA Planetary Data System. In order to ensure the reproducibility of the results of the MAVEN ROSE investigation, software programs to determine MAVEN ROSE electron density profiles from time series of frequency residuals accompany this article. Furthermore, here we examine what the MAVEN ROSE observations reveal about the behavior of the ionosphere of Mars. Peak density, peak altitude, and total electron content mostly display the expected trends with solar zenith angle. However, deviations from those trends are present. Peak density at fixed dayside solar zenith angle can vary by 30% and M1 layer density at fixed solar zenith angle can vary even more. Solar irradiance variations are the most likely cause of these variations. Peak altitude at fixed dayside solar zenith angle can vary by 20 km or more. Thermospheric responses to lower atmospheric dust events are the most likely cause of these variations. Several instances of unusual ionospheric features are present in the dayside electron density profiles. A layer with density 3 × 10 10  m − 3 that appears to occur at 60 km altitude may be a horizontally-confined region of larger density that actually occurs at higher altitudes. Significant changes in density over short vertical distances around 160 km altitude may be caused by ionospheric dynamics in the presence of strong crustal magnetic fields. Topside plasma layers around 200 km altitude may reflect sharp gradients in electron temperature.

Planetary auroras reveal the complex interplay between an atmosphere and the surrounding plasma environment. We report the discovery of low-altitude, diffuse auroras spanning much of Mars’ northern hemisphere, coincident with a solar energetic particle outburst. The Imaging Ultraviolet Spectrograph, a remote sensing instrument on the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft, detected auroral emission in virtually all nightside observations for ~5 days, spanning nearly all geographic longitudes. Emission extended down to ~60 kilometer (km) altitude (1 microbar), deeper than confirmed at any other planet. Solar energetic particles were observed up to 200 kilo­–electron volts; these particles are capable of penetrating down to the 60 km altitude. Given minimal magnetic fields over most of the planet, Mars is likely to exhibit auroras more globally than Earth.