Gregory Delory

On the origin of aurorae on Mars

] We report observations by Mars Global Surveyor(MGS) of thousands of peaked electron energy spectrasimilar to terrestrial auroral electrons. They are observed onthe Martian nightside, near strong crustal magnetic sources.The spectra have peak energies ranging from 100 eV –2.5 keV, and fluxes near the peak are 10–10000 timeshigher than typical nightside spectra. They occur onmagnetic field lines that connect the shocked solar windto crustal magnetic fields, and on adjacent closed field lines.Their detection is directly controlled by the solar wind,suggesting that magnetic reconnection is required for theirobservation. We calculate that the most energeticdistributions could produce atmospheric emission withintensity comparable to that recently reported from theMars Express (MEX) spacecraft. Half of the most energeticexamples occur during the passage of space weather eventspast Mars, suggesting that a disturbed plasma environmentis favorable for electron acceleration along magnetic fieldlines.

MAVEN observations of the response of Mars to an interplanetary coronal mass ejection

Coupling between the lower and upper atmosphere, combined with loss of gas from the upper atmosphere to space, likely contributed to the thin, cold, dry atmosphere of modern Mars. To help understand ongoing ion loss to space, the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft made comprehensive measurements of the Mars upper atmosphere, ionosphere, and interactions with the Sun and solar wind during an interplanetary coronal mass ejection impact in March 2015. Responses include changes in the bow shock and magnetosheath, formation of widespread diffuse aurora, and enhancement of pick-up ions. Observations and models both show an enhancement in escape rate of ions to space during the event. Ion loss during solar events early in Mars history may have been a major contributor to the long-term evolution of the Mars atmosphere.

Electric and magnetic signatures of dust devils from the 2000–2001 MATADOR desert tests

[1] Dust devils are significant meteorological phenomena on Mars: They are ubiquitous, continually gardening the Martian surface, and may be the primary atmospheric dustloading mechanism in nonstorm seasons. Further, dust grains in the swirling dust devils may become electrically charged via triboelectric effects. Electrical effects associated with terrestrial dust devils have been reported previously, but these were isolated measurements (electric fields only) with no corroborating measurements. To study the fluid and electrical forces associated with dust devils, NASA’s Human Exploration and Development of Space (HEDS) enterprise sponsored a set of desert field tests with a suite of mutually compatible and complementary instruments in order to determine the relationship between electric, magnetic, and fluid forces. The project (originally a selected flight project) was entitled ‘‘Martian ATmosphere And Dust in the Optical and Radio’’ (MATADOR). In this work, we present a number of interesting examples of the electromagnetic nature of the dust devil. We also describe potential hazards of the dust devil and how similar devil- and storm-related forces on Mars might affect any human occupation. INDEX TERMS: 6225 Planetology: Solar System Objects: Mars; 3304 Meteorology and Atmospheric Dynamics: Atmospheric electricity; 3379 Meteorology and Atmospheric Dynamics: Turbulence; 3394 Meteorology and Atmospheric Dynamics: Instruments and techniques; 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); KEYWORDS: triboelectricity, electric fields, dust devils, magnetic fields, atmospheric electricity

Aircraft observations conjugate to FAST: Auroral are thicknesses

Optical observations conjugate to the FAST satellite show good agreement between the widths of auroral structures observed optically and those inferred from the measured electron energy flux. The implication is that these structures are imposed by processes at or above the -4000 km altitude of FAST. A variety of widths down to about 2 km were observed, but there were no examples of finer scale structures. A pre-breakup weak discrete arc at the poleward edge of the diffuse aurora showed electron produced optical structures located on either side of upward going ion beams. The optical emission in the equatorward part of the diffuse aurora was caused almost exclusively by precipitating ions. The optical observations were made over northern Alaska between Jan 31 and Feb 16, 1997, from a jet aircraft carrying an all-sky and three narrow-field TV cameras.

Free energy sources and frequency bandwidth for the auroral kilometric radiation

Electron distributions obtained in the source regions of auroral kilometric radiation (AKR) by the Fast Auroral SnapshoT (FAST) satellite have revealed several free energy sources with positive gradients with respect to v⊥ superimposed on a broad plateau with a radius close to the primary incident electron acceleration energy and covering pitch angles from near field-aligned all the way to the (upgoing) loss cone. Two-dimensional electromagnetic particle simulations are used to demonstrate that such a distribution arises as a quasi-steady feature of a process in which the increase of the perpendicular velocity of the electrons as they propagate into a region of increasing magnetic field strength is balanced by the diffusion to lower v⊥ caused by the electron-cyclotron maser instability. The maser radiation is emitted nearly perpendicular to the ambient magnetic field at frequencies between the relativistic and nonrelativistic cyclotron frequencies. In these circumstances, the entire primary auroral electron distribution can contribute to the resonant wave-particle interaction, leading to electric field intensities of the order of 500 mV/m. In contrast, a pure loss cone distribution is shown to produce much weaker electric fields, leads to emission at angles ≥ 10° away from perpendicular, and cannot produce the broad plateau observed in the electron distribution. The simulations and linear theory indicate that the maser instability in a uniform system produces an intrinsic bandwidth of the order of a few tenths of 1% of the cyclotron frequency (∼0.5-1.0 kHz in the AKR source region). Any narrower spectra would appear to require some nonuniform or time-dependent feature in the source region.

Early MAVEN Deep Dip campaign reveals thermosphere and ionosphere variability

The Mars Atmosphere and Volatile Evolution (MAVEN) mission, during the second of its Deep Dip campaigns, made comprehensive measurements of martian thermosphere and ionosphere composition, structure, and variability at altitudes down to ~130 kilometers in the subsolar region. This altitude range contains the diffusively separated upper atmosphere just above the well-mixed atmosphere, the layer of peak extreme ultraviolet heating and primary reservoir for atmospheric escape. In situ measurements of the upper atmosphere reveal previously unmeasured populations of neutral and charged particles, the homopause altitude at approximately 130 kilometers, and an unexpected level of variability both on an orbit-to-orbit basis and within individual orbits. These observations help constrain volatile escape processes controlled by thermosphere and ionosphere structure and variability.

VLF wave growth from dispersive bursts of field‐aligned electron fluxes

Large-amplitude (>200 mV/m) electrostatic whistler waves near the lower hybrid frequency (∼5 kHz to ∼20 kHz) were observed by an auroral sounding rocket during substorm breakup. The measured wavelengths (10 m to 40 m) indicate that the emissions were electrostatic and resonant with electrons that had parallel energies of a few hundred electron volts. We propose that the intense emissions drew their energy from dispersive bursts of low-energy (≲ 100 eV to ∼3 keV), field-aligned electron fluxes. The dispersive bursts are known to cause a brief (∼100 ms), but intense instability that results in large-amplitude Langmuir emissions (∼1 MHz). The high-frequency emissions can rapidly form a plateau in the one-dimensional electron distribution. We show, however, that these distributions remain unstable to electrostatic whistler waves near the lower hybrid frequency. The amplitude and wavelength of the observed emissions were sufficient to accelerate the hydrogen ions with energies between ∼50 eV and ∼200 eV.

Detections of lunar exospheric ions by the LADEE neutral mass spectrometer

The Lunar Atmosphere and Dust Environment Explorer (LADEE) Neutral Mass Spectrometer (NMS), operating in ion mode, provides sensitive detections of ions from the lunar exosphere. By analyzing ion-mode data from the entire mission, utilizing Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moons Interaction with the Sun (ARTEMIS) plasma and magnetic field measurements to organize NMS data and eliminate background sources, we identify highly significant detections of lunar ions at mass per charge of 2, 4, 12, 20, 28, 39, and 40, moderately significant detections at 14 and 23, and weak detections at 24, 25, and 36. Unlike many previous observations of Moon-derived ions, an outward pointing viewing geometry ensures that these ions originate from the exosphere, rather than directly from the surface. For species with known neutral distributions, inferred ion production rates appear consistent with expectations for both magnitude and spatial distribution, assuming photoionization as the predominant source mechanism. Unexpected signals at mass per charge 12 and 28 suggest the presence of a significant exospheric population of carbon-bearing molecules.

Solar wind plasma interaction with Gerasimovich lunar magnetic anomaly

We present the results of the first local hybrid simulations (particle ions and fluid electrons) for the solar wind plasma interaction with realistic lunar crustal fields. We use a three-dimensiona ...

The first in situ electron temperature and density measurements of the Martian nightside 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 similar to 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.