Development of the Primary Sorption Pump for the SEIS Seismometer of the InSight Mission to Mars

We report on the development of a passive sorption pump, capable of maintaining high-vacuum conditions in the InSight seismometer throughout the duration of any extended mission. The adsorber material is a novel zeolite-loaded aerogel (ZLA) composite, which consists of fine zeolite particles homogeneously dispersed throughout a porous silica network. The outgassing species within the SEIS evacuated container were analyzed and the outgassing rate was estimated by different methods. The results were used to optimize the ZLA composition to adsorb the outgassing constituents, dominated by water, while minimizing the SEIS bakeout constraints. The InSight ZLA composite additionally facilitated substantial CO₂ adsorption capabilities for risk mitigation against external leaks in Mars atmosphere. To comply with the stringent particle requirements, the ZLA getters were packaged in sealed containers, open to the SEIS interior through \(1~\upmu\mbox{m}\)-size pore filters. Results from experimental validation and verification tests of the packaged getters are presented. The pressure forecast based on these data, corroborated by rudimentary in situ pressure measurements, infer SEIS operational pressures not exceeding \(10^{-5}~\mbox{mbar}\) throughout the mission.     

Venus Atmospheric Thermal Structure and Radiative Balance

From the discovery that Venus has an atmosphere during the 1761 transit by M. Lomonosov to the current exploration of the planet by the Akatsuki orbiter, we continue to learn about the planet’s extreme climate and weather. This chapter attempts to provide a comprehensive but by no means exhaustive review of the results of the atmospheric thermal structure and radiative balance since the earlier works published in Venus and Venus II books from recent spacecraft and Earth based investigations and summarizes the gaps in our current knowledge. There have been no in-situ measurements of the deep Venus atmosphere since the flights of the two VeGa balloons and landers in 1985 (Sagdeev et al., Science 231:1411–1414, 1986). Thus, most of the new information about the atmospheric thermal structure has come from different remote sensing (Earth based and spacecraft) techniques using occultations (solar infrared, stellar ultraviolet and orbiter radio occultations), spectroscopy and microwave, short wave and thermal infrared emissions. The results are restricted to altitudes higher than about 40 km, except for one investigation of the near surface static stability inferred by Meadows and Crisp (J. Geophys. Res. 101:4595–4622, 1996) from 1 \(\upmu\)m observations from Earth. Little information about the lower atmospheric structure is possible below about 40 km altitude from radio occultations due to large bending angles. The gaps in our knowledge include spectral albedo variations over time, vertical variation of the bulk composition of the atmosphere (mean molecular weight), the identity, properties and abundances of absorbers of incident solar radiation in the clouds. The causes of opacity variations in the nightside cloud cover and vertical gradients in the deep atmosphere bulk composition and its impact on static stability are also in need of critical studies. The knowledge gaps and questions about Venus and its atmosphere provide the incentive for obtaining the necessary measurements to understand the planet, which can provide some clues to learn about terrestrial exoplanets.     

Determination of attitude motion of the <Emphasis Type="Italic">Foton M-3</Emphasis> satellite according to the data of onboard measurements of the Earth’s magnetic field

The results of reconstruction of rotational motion of the Foton M-3 satellite during its uncontrolled flight in September 2007 are presented. The reconstruction was performed by processing the data of onboard measurements of the Earth’s magnetic field obtained by the DIMAC instruments. The measurements were carried out continuously throughout the flight, but the processing technique dealt with the data portions covering time intervals of a few orbital revolutions. The data obtained on each such interval were processed jointly by the least squares method with using integration of the equations of satellite motion relative to its center of mass. When processing, the initial conditions of motion and the used mathematical model’s parameters were estimated. The results of processing 16 data sets gave us complete information about the satellite motion. This motion, which began at a low angular velocity, had gradually accelerated and in five days became close to the regular Euler precession of an axisymmetric solid body. At the end of uncontrolled flight the angular velocity of the satellite relative to its lengthwise axis was 0.5 deg/s; the angular velocity projection onto the plane perpendicular to this axis had a magnitude of about 0.18 deg/s.     

Estimations of the Seismic Pressure Noise on Mars Determined from Large Eddy Simulations and Demonstration of Pressure Decorrelation Techniques for the Insight Mission

The atmospheric pressure fluctuations on Mars induce an elastic response in the ground that creates a ground tilt, detectable as a seismic signal on the InSight seismometer SEIS. The seismic pressure noise is modeled using Large Eddy Simulations (LES) of the wind and surface pressure at the InSight landing site and a Green’s function ground deformation approach that is subsequently validated via a detailed comparison with two other methods: a spectral approach, and an approach based on Sorrells’ theory (Sorrells, Geophys. J. Int. 26:71–82, 1971; Sorrells et al., Nat. Phys. Sci. 229:14–16, 1971). The horizontal accelerations as a result of the ground tilt due to the LES turbulence-induced pressure fluctuations are found to be typically \(\sim 2 \mbox{--} 40~\mbox{nm}/\mbox{s}^{2}\) in amplitude, whereas the direct horizontal acceleration is two orders of magnitude smaller and is thus negligible in comparison. The vertical accelerations are found to be \(\sim 0.1\mbox{--}6~\mbox{nm}/\mbox{s}^{2}\) in amplitude. These are expected to be worst-case estimates for the seismic noise as we use a half-space approximation; the presence at some (shallow) depth of a harder layer would significantly reduce quasi-static displacement and tilt effects.We show that under calm conditions, a single-pressure measurement is representative of the large-scale pressure field (to a distance of several kilometers), particularly in the prevailing wind direction. However, during windy conditions, small-scale turbulence results in a reduced correlation between the pressure signals, and the single-pressure measurement becomes less representative of the pressure field. The correlation between the seismic signal and the pressure signal is found to be higher for the windiest period because the seismic pressure noise reflects the atmospheric structure close to the seismometer.In the same way that we reduce the atmospheric seismic signal by making use of a pressure sensor that is part of the InSight Auxiliary Payload Sensor Suite, we also the use the synthetic noise data obtained from the LES pressure field to demonstrate a decorrelation strategy. We show that our decorrelation approach is efficient, resulting in a reduction by a factor of \(\sim 5\) in the observed horizontal tilt noise (in the wind direction) and the vertical noise. This technique can, therefore, be used to remove the pressure signal from the seismic data obtained on Mars during the InSight mission.     

The Juno Gravity Science Instrument

The Juno mission’s primary science objectives include the investigation of Jupiter interior structure via the determination of its gravitational field. Juno will provide more accurate determination of Jupiter’s gravity harmonics that will provide new constraints on interior structure models. Juno will also measure the gravitational response from tides raised on Jupiter by Galilean satellites. This is accomplished by utilizing Gravity Science instrumentation to support measurements of the Doppler shift of the Juno radio signal by NASA’s Deep Space Network at two radio frequencies. The Doppler data measure the changes in the spacecraft velocity in the direction to Earth caused by the Jupiter gravity field. Doppler measurements at X-band (\(\sim 8\) GHz) are supported by the spacecraft telecommunications subsystem for command and telemetry and are used for spacecraft navigation as well as Gravity Science. The spacecraft also includes a Ka-band (\(\sim 32\) GHz) translator and amplifier specifically for the Gravity Science investigation contributed by the Italian Space Agency. The use of two radio frequencies allows for improved accuracy by removal of noise due to charged particles along the radio signal path.     

Rayleigh Wave Ellipticity Modeling and Inversion for Shallow Structure at the Proposed InSight Landing Site in Elysium Planitia,Mars

The SEIS (Seismic Experiment for Interior Structure) instrument onboard the InSight mission will be the first seismometer directly deployed on the surface of Mars. From studies on the Earth and the Moon, it is well known that site amplification in low-velocity sediments on top of more competent rocks has a strong influence on seismic signals, but can also be used to constrain the subsurface structure. Here we simulate ambient vibration wavefields in a model of the shallow sub-surface at the InSight landing site in Elysium Planitia and demonstrate how the high-frequency Rayleigh wave ellipticity can be extracted from these data and inverted for shallow structure. We find that, depending on model parameters, higher mode ellipticity information can be extracted from single-station data, which significantly reduces uncertainties in inversion. Though the data are most sensitive to properties of the upper-most layer and show a strong trade-off between layer depth and velocity, it is possible to estimate the velocity and thickness of the sub-regolith layer by using reasonable constraints on regolith properties. Model parameters are best constrained if either higher mode data can be used or additional constraints on regolith properties from seismic analysis of the hammer strokes of InSight’s heat flow probe HP³ are available. In addition, the Rayleigh wave ellipticity can distinguish between models with a constant regolith velocity and models with a velocity increase in the regolith, information which is difficult to obtain otherwise.     

Ion Composition of the Earth’s Radiation Belts in the Range from 100 keV to $100mbox{ MeV}/mbox{nucleon}$: Fifty Years of Research

Spatial, energy and angular distributions of ion fluxes in the Earth’s radiation belts (ERB) near the equatorial plane, at middle geomagnetic latitudes and at low altitudes are systematically reviewed herein. Distributions of all main ion components, from protons to Fe (including hydrogen and helium isotopes), and their variations under the action of solar and geomagnetic activity are considered. For ions with (Zgeq 2) and especially for ions with (Z geq 9), these variations are much more than for protons, and these have no direct connection with the intensity of magnetic storms ((Z) is the charge of the atomic nucleus with respect to the charge of the proton). The main physical mechanisms for the generation of ion fluxes in the ERB and the losses of these ions are considered. Solar wind, Solar Cosmic Rays (SCR), Galactic Cosmic Rays (GCR), and Anomalous component of Cosmic Rays (ACR) as sources of ions in the ERB are considered.     

The Modern Near-Surface Martian Climate: A Review of In-situ Meteorological Data from Viking to Curiosity

We analyze the complete set of in-situ meteorological data obtained from the Viking landers in the 1970s to today’s Curiosity rover to review our understanding of the modern near-surface climate of Mars, with focus on the dust, CO₂ and H₂O cycles and their impact on the radiative and thermodynamic conditions near the surface. In particular, we provide values of the highest confidence possible for atmospheric opacity, atmospheric pressure, near-surface air temperature, ground temperature, near-surface wind speed and direction, and near-surface air relative humidity and water vapor content. Then, we study the diurnal, seasonal and interannual variability of these quantities over a span of more than twenty Martian years. Finally, we propose measurements to improve our understanding of the Martian dust and H₂O cycles, and discuss the potential for liquid water formation under Mars’ present day conditions and its implications for future Mars missions. Understanding the modern Martian climate is important to determine if Mars could have the conditions to support life and to prepare for future human exploration.     

The VIR Spectrometer

The Dawn spectrometer (VIR) is a hyperspectral spectrometer with imaging capability. The design fully accomplishes Dawn’s scientific and measurement objectives. Determination of the mineral composition of surface materials in their geologic context is a primary Dawn objective. The nature of the solid compounds of the asteroid (silicates, oxides, salts, organics and ices) can be identified by visual and infrared spectroscopy using high spatial resolution imaging to map the heterogeneity of asteroid surfaces and high spectral resolution spectroscopy to determine the composition unambiguously. The VIR Spectrometer—covering the range from the near UV (0.25 μm) to the near IR (5.0 μm) and having moderate to high spectral resolution and imaging capabilities—is the appropriate instrument for the determination of the asteroid global and local properties. VIR combines two data channels in one compact instrument. The visible channel covers 0.25–1.05 μm and the infrared channel covers 1–5.0 μm. VIR is inherited from the VIRTIS mapping spectrometer (Coradini et al. in Planet. Space Sci. 46:1291–1304, 1998; Reininger et al. in Proc. SPIE 2819:66–77, 1996) on board the ESA Rosetta mission. It will be operated for more than 2 years and spend more than 10 years in space.