We describe the sensors, the sensor biasing and control, the signal-processing unit, and the operation of the Langmuir Probe and Waves (LPW) instrument on the Mars Atmosphere and Volatile EvolutioN ...(MAVEN) mission. The LPW instrument is designed to measure the electron density and temperature in the ionosphere of Mars and to measure spectral power density of waves (DC-2 MHz) in Mars’ ionosphere, including one component of the electric field. Low-frequency plasma waves can heat ions resulting in atmospheric loss. Higher-frequency waves are used to calibrate the density measurement and to study strong plasma processes. The LPW is part of the Particle and Fields (PF) suite on the MAVEN spacecraft. The LPW instrument utilizes two, 40 cm long by 0.635 cm diameter cylindrical sensors with preamplifiers, which can be configured to measure either plasma currents or plasma waves. The sensors are mounted on a pair of
∼
7
meter long stacer booms. The sensors and nearby surfaces are controlled by a Boom Electronics Board (BEB). The Digital Fields Board (DFB) conditions the analog signals, converts the analog signals to digital, processes the digital signals including spectral analysis, and packetizes the data for transmission. The BEB and DFB are located inside of the Particle and Fields Digital Processing Unit (PFDPU).
We present Mars' electron temperature (Te) and density (ne) altitude profiles derived from the MAVEN (Mars Atmosphere and Volatile EvolutioN) mission deep dip orbits in April 2015, as measured by the ...Langmuir probe instrument. These orbits had periapsides below 130 km in altitude at low solar zenith angles. The periapsides were above the peak in ne during this period. Using a Chapman function fit, we find that scale height and projected altitude of the ne peak are consistent with models and previous measurements. The peak electron density is slightly higher than earlier works. For the first time, we present in situ measurements of Te altitude profiles in Mars' dayside in the altitude range from ~130 km to 500 km and provide a functional fit. Importantly, Te rises rapidly with altitude from ~180 km to ~300 km. These results and functional fit are important for modeling Mars' ionosphere and understanding atmospheric escape.
Key Points
First in situ measurements of the electron temperature at Mars
Electron density and temperature profiles at Mars
The Neutral Mass Spectrometer (NMS) onboard the Lunar Atmosphere and Dust Environment Explorer (LADEE) provided the first global characterization of He and Ar along with the discovery of Ne in the ...lunar exosphere. The mapping of the equatorial distribution of these noble gases revealed new selenographic and temporal variations. Helium was found to be controlled by the supply of solar wind alpha particles and by the presence of an endogenous source that supplies the exosphere at a rate of 1.9 × 1023 atoms s−1. Neon was detected over the nightside at levels comparable to He and was found to exhibit the spatial distribution of a surface accommodated noncondensable gas. The global measurements of NMS revealed the presence of a localized Ar enhancement that has never been identified before at the western maria. The variability resulting from this local enhancement is coupled to a more global but transient source.
Key Points
Exospheric He is controlled by solar wind and by an endogenous radiogenic source
Neon is present on the nightside at levels comparable to He
Localized Ar enhancement is present at the western maria
The design, performance, and on-orbit operation of the three-axis electric field instrument (EFI) for the NASA THEMIS mission is described. The 20 radial wire boom and 10 axial stacer boom antenna ...systems making up the EFI sensors on the five THEMIS spacecraft, along with their supporting electronics have been deployed and are operating successfully on-orbit without any mechanical or electrical failures since early 2007. The EFI provides for waveform and spectral three-axis measurements of the ambient electric field from DC up to 8 kHz, with a single, integral broadband channel extending up to 400 kHz. Individual sensor potentials are also measured, providing for on-board and ground-based estimation of spacecraft floating potential and high-resolution plasma density measurements. Individual antenna baselines are 50- and 40-m in the spin plane, and 6.9-m along the spin axis.
The EFI has provided for critical observations supporting a clear and definitive understanding of the electrodynamics of both the boundaries of the terrestrial magnetosphere, as well as internal processes, such as relativistic particle acceleration and substorm dynamics. Such multi-point electric field observations are key for pushing forward the understanding of electrodynamics in space, in that without high-quality estimates of the electric field, the underlying electromagnetic processes involved in current sheets, reconnection, and wave-particle interactions may only be inferred, rather than measured, quantified, and used to discriminate between competing hypotheses regarding those processes.
On the origin of aurorae on Mars Brain, D. A.; Halekas, J. S.; Peticolas, L. M. ...
Geophysical research letters,
16 January 2006, Letnik:
33, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We report observations by Mars Global Surveyor (MGS) of thousands of peaked electron energy spectra similar to terrestrial auroral electrons. They are observed on the 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 times higher than typical nightside spectra. They occur on magnetic field lines that connect the shocked solar wind to 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 their observation. We calculate that the most energetic distributions could produce atmospheric emission with intensity comparable to that recently reported from the Mars Express (MEX) spacecraft. Half of the most energetic examples occur during the passage of space weather events past Mars, suggesting that a disturbed plasma environment is favorable for electron acceleration along magnetic field lines.
The Lunar Atmosphere and Dust Environment Explorer (LADEE) mission was designed to address long-standing scientific questions about the Moon’s environment, including the assessment of the composition ...of the lunar atmosphere, and characterization of the lunar dust environment at low orbital altitudes. LADEE was derived from the Modular Common Spacecraft Bus design that was developed at NASA Ames Research Center; it used modularized subassemblies and existing commercial spaceflight hardware to reduce cost. LADEE was launched on the very first Minotaur V, and was also the first deep space mission launched from Wallops Flight Facility in Virginia. LADEE was equipped with two in situ instruments and a remote sensing instrument to address the atmosphere and dust measurement requirements. LADEE also carried the first deep-space optical communications demonstration, the Lunar Laser Communications Demonstration. LADEE was launched in early September, 2013, took science data for over 140 days in low lunar orbit, and impacted the surface on April 18, 2014.
We present two Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) observations of diamagnetic fields in the lunar wake at strengths exceeding ...twice the ambient magnetic field during high plasma beta conditions. The first observation was 350 km from the lunar surface while the Moon was located in the terrestrial magnetosheath with elevated particle temperatures. The second observation was in the solar wind ranging from 500 to 2000 km downstream, with a relatively low magnetic field strength of approximately 1.6 nT. In both cases, the plasma beta exceeded 10. We discuss the observations and compare the data to hybrid plasma simulations in order to validate the model under such extreme conditions and to elucidate the global structure of the lunar wake during these observations. The extreme nature of the diamagnetic field in the lunar wake provides an important end‐member test case for theoretical and modeling studies of the various plasma processes operating in the lunar wake.
Key Points
Present ARTEMIS observations of extreme diamagnetic fields in the lunar wake
Extreme diamagnetic fields are a result of high ambient plasma beta (>10)
Successfully compare to a hybrid plasma model of the lunar wake for high beta
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 Moon's 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.
Key Points
The LADEE neutral mass spectrometer detected exospheric ions at the Moon
NMS detected H2+, He+, C+, Ne+, Na+, K+, Ar+, and an ambiguous 28 amu ion
Simultaneous plasma data are critical for interpreting NMS ion measurements
ARTEMIS observes pickup ions around the Moon, at distances of up to 20,000 km from the surface. The observed ions form a plume with a narrow spatial and angular extent, generally seen in a single ...energy/angle bin of the ESA instrument. Though ARTEMIS has no mass resolution capability, we can utilize the analytically describable characteristics of pickup ion trajectories to constrain the possible ion masses that can reach the spacecraft at the observation location in the correct energy/angle bin. We find that most of the observations are consistent with a mass range of ∼20–45 amu, with a smaller fraction consistent with higher masses, and very few consistent with masses below ∼15 amu. With the assumption that the highest fluxes of pickup ions come from near the surface, the observations favor mass ranges of ∼20–24 and ∼36–40 amu. Although many of the observations have properties consistent with a surface or near‐surface release of ions, some do not, suggesting that at least some of the observed ions have an exospheric source. Of all the proposed sources for ions and neutrals about the Moon, the pickup ion flux measured by ARTEMIS correlates best with the solar wind proton flux, indicating that sputtering plays a key role in either directly producing ions from the surface, or producing neutrals that subsequently become ionized.
Key Points
ARTEMIS observes pickup ions from the lunar exosphere and/or surface
Using ion trajectory information, we can constrain the mass of lunar ions
Lunar pickup ion flux correlates with solar wind flux
We report observations by the twin‐probe mission ARTEMIS of pick‐up ions of lunar origin obtained during times when the Moon was within the terrestrial magnetotail lobes. These ions were detected as ...two separate focused beams above the dayside lunar surface. Analysis of these beams has shown that they possess both field‐aligned and field‐perpendicular velocities, implying the presence of electric fields both parallel and perpendicular to the magnetotail lobe magnetic field. We suggest that the sources of these two electric fields are (a) the near‐surface electric field due to the lunar photoelectron sheath and (b) the electric field generated by the magnetotail lobe convection velocity. We use the energy and pitch angle spectra to constrain the source locations and compositions of these ions, and conclude that exospheric ionization of the neutral exosphere is the dominant lunar pick‐up ion production mechanism in the tail lobes.
Key Points
ARTEMIS observes pickup ions in the terrestrial magnetotail lobes
Photoelectric and convection electric fields affect these ions
These ions originate from the neutral exosphere and possibly a geologic vent
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