First results from the Neutral Gas and Ion Mass Spectrometer instrument on the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft reveal density profiles of protonated species that are mostly ...in good qualitative agreement with recent models of the Martian thermosphere/ionosphere. We present here the first photochemical model in which the density profiles of water and water ions in the ionosphere/thermosphere are predicted. We find that the computed peak densities of OH+, H2O+, and H3O+ are in fairly good agreement with the measured values. The computed column density of water is predicted to be about 1010 cm−2, and the mixing ratio at 80 km is 0.4 ppb. The actual water densities must be small enough so that HCO+ is not destroyed by proton transfer to water during the daytime and large enough so that H3O+ dominates the ionosphere at low altitudes just beyond the terminator. The calculations also show that the mass‐2 ion is almost certainly H
2+.
Key Points
We preset the first model of water in the Martian thermosphere
The predicted density profiles of H2O, H2O+, and H3O+ are presented
We predict that H
2+ is the mass‐2 ion rather than D+
The Martian plasma environment contains a complex magnetic topology, with contributions from the interplanetary magnetic field (IMF) and crustal magnetic fields. The topology can control how plasma ...is exchanged between the solar wind and the Martian ionosphere. Here we use 7 years of suprathermal electron pitch angle distributions recorded by the Mars Global Surveyor (MGS) spacecraft to determine the topology at 2 am and 400 km on the Martian nightside as a function of geographic location and external drivers. Observations show that topology statistically varies with IMF direction, solar wind pressure, solar extreme ultraviolet (EUV) flux, and season. Changes in topology with IMF direction and season are consistent with changes in the likelihood of magnetic reconnection between individual crustal fields and the draped IMF. Changes in topology at a given location with solar wind pressure and solar EUV flux are consistent with reconfiguration of topological structures in the plasma environment.
Key Points
Magnetic topology on the nightside of Mars responds in systematic ways to external drivers
Changes in interplanetary magnetic field direction or in season are consistent with changes in topology via magnetic reconnection
Changes in solar wind ram pressure or in solar EUV flux are consistent with changes in the measured topology via reconfiguration
We report the first in situ detection of metal ions in the upper atmosphere of Mars resulting from the ablation of dust particles from comet Siding Spring. This detection was carried out by the ...Neutral Gas and Ion Mass Spectrometer on board the Mars Atmosphere and Volatile Evolution Mission. Metal ions of Na, Mg, Al, K, Ti, Cr, Mn, Fe, Co, Ni, Cu, and Zn, and possibly of Si, and Ca, were identified in the ion spectra collected at altitudes of ~185 km. The measurements revealed that Na+ was the most abundant species, and that the remaining metals were depleted with respect to the CI (type 1 carbonaceous Chondrites) abundance of Na+. The temporal profile and abundance ratios of these metal ions suggest that the combined effects of dust composition, partial ablation, differential upward transport, and differences in the rates of formation and removal of these metal ions are responsible for the observed depletion.
Key Points
Metal ions were identified for the first time in the upper atmosphere of Mars
Metal ions result from cometary dust ablation in the atmosphere of Mars
Metal ions were depleted with respect to the CI abundance of Na+
Abstract Interplanetary dust particles have long been expected to produce permanent ionospheric metal ion layers at Mars, as on Earth, but the two environments are so different that uncertainty ...existed as to whether terrestrial-established understanding would apply to Mars. The Mars Atmosphere and Volatile EvolutioN (MAVEN) mission made the first in situ detection of the continuous presence of Na+, Mg+, and Fe+ at Mars and indeed revealed non-Earthlike features/processes. There is no separation of the light Mg+ and the heavy Fe+ with increasing altitude as expected for gravity control. The metal ions are well-mixed with the neutral atmosphere at altitudes where no mixing process is expected. Isolated metal ion layers mimicking Earths sporadic E layers occur despite the lack of a strong magnetic field as required at Earth. Further, the metal ion distributions are coherent enough to always show atmospheric gravity wave signatures. All features and processes are unique to Mars.
The observations made by the Mars Atmosphere and Volatile EvolutioN spacecraft in the topside (≥200 km) ionosphere of Mars show that this region is very responsive to the variations of the external ...(solar extreme ultraviolet flux, solar wind, and interplanetary magnetic field IMF) and internal (the crustal magnetic field) drivers. With the growth of the solar irradiance the ionosphere broadens while with increase of the solar wind dynamic pressure it shrinks. As a result, the upper ionospheric boundary at solar zenith angles of 60–70° can move from ∼400 to ∼1,200 km. Similar trends are observed at the nightside ionosphere. At Pdyn ≥ 1–2 nPa the nightside ionosphere becomes very fragmented and depleted. On the other hand, the ion density in the nightside ionosphere significantly (up to a factor of 10) increases with the rise of the solar extreme ultraviolet flux. Large‐amplitude motions of the topside ionosphere also occur with variations of the value of the cross‐flow component of the IMF. The upper dayside ionosphere at altitudes of more than 300–400 km is sensitive also to the direction of the cross‐flow component of the IMF or, correspondingly, to the direction of the motional electric field in the solar wind. The ionosphere becomes very asymmetrical with respect to the Vsw×BIMF direction and the asymmetry strongly enhances at the nightside. The topside ionosphere above the areas with strong crustal magnetic field in the dayside southern hemisphere is significantly denser and expands to higher altitudes as compared to the ionosphere above the northern nonmagnetized lowlands. The crustal magnetic field also protects the nightside ionosphere from being filled by plasma transported from the dayside. The draping IMF penetrates deeply into the ionosphere and actively influences its structure. Weak fields and, correspondingly, weak magnetic field forces only slightly affect the ionosphere. With increase of the induced magnetic field strength the transport motions driven by the magnetic field pressure and field tensions seem to be intensified and we observe that the local ion densities at the dayside considerably decrease. A different trend is observed at the nightside. The ion density in the nightside ionosphere above the northern lowlands is higher than in the southern hemisphere indicating that plasma transport from the dayside is the main source of the nightside ionosphere. Nonstop variations in the solar wind, the IMF and the solar irradiance together with planetary rotation of the crustal magnetic field sources lead to a continuous expansion/shrinking and reconfiguration of the topside ionosphere of Mars.
Key Points
Upper ionosphere of Mars is very sensitive to the solar wind variations
Upper ionosphere of Mars is very sensitive to the variations of the interplanetary magnetic field
Upper ionosphere of Mars is very sensitive to the planetary crustal field
The MAVEN Solar Wind Electron Analyzer Mitchell, D. L.; Mazelle, C.; Sauvaud, J.-A. ...
Space science reviews,
04/2016, Letnik:
200, Številka:
1-4
Journal Article
Recenzirano
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.
We report observations of Martian mesospheric ice clouds and thermospheric scale heights by the Imaging Ultraviolet Spectrograph on NASA's Mars Atmosphere and Volatile Evolution mission. The clouds ...are observed between 6 A.M. and 8 A.M. local time using mid‐UV limb observations between 60 and 80 km tangent altitude where ice particles that scatter sunlight can appear as detached layers near the equator. The equatorial longitudinal distribution shows populations of clouds near −110°E and −10°E as well as a population near 90°E, which does not have a clear precedent. The cloud populations indicate a wave 3 pattern near 70 km, which is confirmed by independent mesospheric temperature observations. Scale heights 100 km above the clouds derived from concurrent Imaging Ultraviolet Spectrograph (IUVS) observations also reveal a wave 3 longitudinal structure, suggesting that the temperature oscillations enabling the formation of mesospheric clouds couple to the upper atmosphere.
Plain Language Summary
The manuscript describes the observation of Martian mesospheric clouds between 60 and 80 km altitude by the Imaging Ultraviolet Spectrograph (IUVS) on NASA's MAVEN spacecraft. The cloud observations are uniquely obtained at early morning local times, which complement previous observations obtained primarily later in the diurnal cycle. Differences in the geographic distribution of the clouds from IUVS observations indicate that the local time is crucial for the interpretation of mesospheric cloud formation. We also report concurrent observations of upper atmospheric scale heights near 170 km altitude, which are diagnostic of temperature. These observations suggest that the dynamics enabling the formation of mesospheric clouds propagate all the way to the upper atmosphere.
Key Points
Martian mesospheric clouds are observed by solar scattering of midultraviolet sunlight from a fully illuminated atmosphere
The early morning mesospheric cloud observations are complementary to previous observations, which are primarily made in the afternoon
The data suggest that the geographic distribution of clouds is controlled by tides that propagate all the way to the upper atmosphere
The identification of magnetic reconnection on the dayside of Mars has been elusive owing to the lack of comprehensive plasma and field measurements. Here we present direct measurements of dayside in ...situ reconnection signatures by the comprehensive particles and fields package on board the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft over strong crustal magnetic fields in the southern hemisphere of Mars. During a crossing of a bifurcated current sheet consisting of northward and southward magnetic fields, MAVEN recorded (i) ionospheric photoelectrons trapped on closed magneticfield lines, (ii) Hall magnetic fields and a nonzero normal field with polarity consistent with a crossing northward of the X line, and (iii) northward Alfvenic ion jets. Dayside magnetic reconnection on crustal magnetic fields could control the global configuration and topology of the Martian magnetosphere and alter the ion escape pattern from the dayside ionosphere.
The first in situ nightside electron density and temperature profiles at Mars are presented as functions of altitude and local time (LT) from the Langmuir Probe and Waves (LPW) instrument on board ...the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission spacecraft. LPW is able to measure densities as low as ∼100
cm−3, a factor of up to 10 or greater improvement over previous measurements. Above 200 km, near‐vertical density profiles of a few hundred cubic centimeters were observed for almost all nightside LT, with the lowest densities and highest temperatures observed postmidnight. Density peaks of a few thousand cubic centimeters were observed below 200 km at all nightside LT. The lowest temperatures were observed below 180 km and approach the neutral atmospheric temperature. One‐dimensional modeling demonstrates that precipitating electrons were able to sustain the observed nightside ionospheric densities below 200 km.
Key Points
First in situ nightside electron density and temperature profiles on the nightside of Mars
Electron temperatures approach neutral atmospheric temperatures below 200 km
Electron densities below 200 km require additional ionization source
Neutral density response to solar flares at Mars Thiemann, E. M. B.; Eparvier, F. G.; Andersson, L. A. ...
Geophysical research letters,
16 November 2015, Letnik:
42, Številka:
21
Journal Article
Recenzirano
Odprti dostop
First direct observations of heating of the Mars neutral atmosphere by solar flares are presented in this study. Solar flares were detected using the Extreme Ultraviolet Monitor on board the Mars ...Atmosphere and Volatile EvolutioN (MAVEN) spacecraft, and upper atmospheric temperature enhancements were determined by changes in the density scale height of Argon (Ar) made by the Neutral Gas and Ion Mass Spectrometer also on board MAVEN. We analyzed 14 M‐class or greater flares that occurred during the early part of the MAVEN mission in addition to a 30 day period of high flare activity during May 2015. We report that the Mars dayside upper atmosphere shows significant heating near the flare soft X‐ray peak; and it responds and recovers rapidly to heating from M‐class or larger flares. In addition, we present atmospheric density versus altitude profiles that were taken near the soft X‐ray peak of two flares.
Key Points
First observations of neutral heating at Mars due to solar flares are reported
The upper atmosphere shows significant heating near the flare soft X‐ray peak
The Mars atmosphere responds and recovers rapidly to heating from M‐class flares
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