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This work combines 17 years of Mars Express radio science (MaRS) observations with proxies for insolation and local/global atmospheric dust to investigate the combined and individual effects on the dayside ionosphere of Mars from the top down to the ionospheric base. The increase in insolation from orbital apocenter to pericenter in combination with Mars‘ dust cycle causes an average rise of the whole photochemically dominated region of the dayside ionosphere, ranging from 13 km at the ionospheric base up to 22 km above the main peak during conditions without a global dust storm. The declining phase of the 2018 global dust storm was observed by MaRS on the southern hemisphere and close to pericenter. The observed lifting effect on the whole photochemically dominated region of the ionosphere from the increased insolation and the high local and global atmospheric dust levels exceeds that seen by MaRS from similar seasons during years without a global dust storm. The average ionospheric peak altitude at the subsolar point rises for increasing levels of local atmospheric dust until a maximum elevation is reached. This maximum depends on the available insolation at the top of the planetary atmosphere. Further increases of the local atmospheric dust levels do not lead to a further rise of the average ionospheric peak altitude in the investigated data set. This indicates a limit for the warming/expansion of the lower neutral atmosphere and the consecutive lifting of the ionosphere based on the available insolation and explains why regional dust storms can cause a similar lifting of the ionospheric main peak region as global dust storms. © 2023 Elsevier Inc. All rights reserved., The Mars Express Radio Science Experiment (MaRS) was funded by BMWi Berlin via the Deutsches Zentrum für Luft- und Raumfahrt (DLR) under the Grant 50QM1802. Support for Mars Express Radio Science at Stanford University was provided by NASA through a JPL Contract. Support for the Multimission Radio Science Support Team was provided by NASA/JPL. Portions of this research were performed at the Jet Propulsion Laboratory, California Institute of Technology under contract with NASA. We thank everyone involved in the Mars Express project at ESTEC, ESOC, ESAC, JPL, and the ESTRACK and DSN ground stations for their continuous support. K. P., M. P. and S. T. acknowledge funding for this project by the Deutsche Forschungsgemeinschaft (DFG) under Grant PE 3225/2-1, PA 525/25-1 and TE 664/4-1. F.G.G. acknowledges financial support from the grant CEX2021-001131-S funded by MCIN/AEI/ 10.13039/501100011033.

Responses of solar X-ray flares were observed in a layer of the Martian ionosphere at altitudes of ~110 km from 32 electron density profiles obtained by radio science experiment onboard Mars Global Surveyor (MGS) during solar cycle 23. Of the 32 profiles recorded during flare periods, 10 were associated with X-class flares, 12 with M class and 10 with C class flares. The flare E-peak densities vary with solar X-ray flux, Solar Zenith Angle (SZA), Solar Longitude (Ls) and latitudes. Ionospheric Electron Content (IEC) and E-peak electron production rates of these flare profiles are estimated in the E region ionosphere. We found a maximum increase of ~200%, ~140% and ~90% in the time series of IEC for X, M and C class flares respectively. The dependence of flare E-peak electron production rate with Ls is fitted by a sinusoidal function. We have also calculated biological doses ~0.1–1.0 × 10−1, 1–8 × 10−3 and 1–6 × 10−4 Gy for X, M, C class flares respectively to study the human risk for exploration to Mars. Among 10 X-class flares X1 is a strong solar flare that gives highest dose, which is potentially lethal for human risk in Mars' space.

Transient eddies are important features of Mars atmosphere weather, and are linked to the genesis of dust storms. Many previous studies of transient eddies, also known as traveling waves, generally used either spacecraft observations or model simulations alone. Reanalyses, which optimally combine observations with a forecast model, provide an unprecedented opportunity to examine these traveling weather systems: their temperature, wind, pressure signatures and structure; the evolution between various wave regimes; and their seasonality and interannual variability. Using the GFDL Mars Global Climate Model (MGCM) with the Local Ensemble Transform Kalman Filter (LETKF), we have created a six year reanalysis of both Thermal Emission Spectrometer (TES) and Mars Climate Sounder (MCS) temperature retrievals, which we name the Ensemble Mars Atmosphere Reanalysis System (EMARS). We demonstrate that the transient eddies in analyses with different assumptions in the model and assimilation system, including between EMARS and the Mars Analysis Correction Data Assimilation reanalysis (MACDA), are generally robust; EMARS and MACDA eddies are more similar to each other than their respective freely running control simulations. We also reveal lower atmosphere transient eddies derived from MCS data for the first time, and compare to those derived from TES data. MCS, as a limb sounder, demonstrates some challenges in constraining the shallow eddies in EMARS compared to reanalyses using TES nadir measurements. Ensemble reanalyses are valuable in that they provide an assessment of convergence upon a unique synoptic state. We examine the six year climatology and interannual variability of transient eddies, synoptic maps, and transitions between dominant wavenumber regimes. Finally, we compare reanalysis products to other products derived from observational data, including radio science and the Viking lander surface pressure records.

The primary gravity science objective of NASA's Clipper mission to Europa is to confirm the presence or absence of a global subsurface ocean beneath Europa's Icy crust. Gravity field measurements obtained with a radio science investigation can reveal much about Europa's interior structure. Here, we conduct extensive simulations of the radio science measurements with the anticipated spacecraft trajectory and attitude (17F12v2) and assets on the spacecraft and the ground, including antenna orientations and beam patterns, transmitter characteristics, and receiver noise figures. In addition to two-way Doppler measurements, we also include radar altimeter crossover range measurements. We concentrate on +/-2 hour intervals centered on the closest approach of each of the 46 flybys. Our covariance analyses reveal the precision with which the tidal Love number k2, second-degree gravity coefficients C20 and C22, and higher-order gravity coefficients can be determined. The results depend on the Deep Space Network (DSN) assets that are deployed to track the spacecraft. We find that some DSN allocations are sufficient to conclusively confirm the presence or absence of a global ocean. Given adequate crossover range performance, it is also possible to evaluate whether the ice shell is hydrostatic., Accepted for publication in Icarus

The radio thermal emission from Pluto was observed from the New Horizons spacecraft at a wavelength of 4.2 cm along two scans across the planetary disk shortly after closest approach to Pluto on 14 July 2015. The measurements were performed as part of the New Horizons Radio Science Experiment (REX) using the 2.1 m High Gain Antenna (HGA) and the spacecraft's X-Band receiver. The HGA boresight first scanned along a diametric chord across the Pluto disk and then reversed direction to traverse a chord that crossed close to Pluto's winter pole. The diametric scan reveals a “hot spot” on the Pluto nightside associated with an optically bright region centered roughly at the planetocentric coordinates 280° E, 55° S, imaged in 2002–03 with the Hubble Space Telescope. The nightside was also found to be warmer than the dayside during the polar scan. The highest emission was not observed at the maximum southern latitude, however, but rather near the outbound Pluto limb at lower latitude. The REX emission profile from the polar scan is qualitatively consistent with a bright U-shaped polar cap observed on Pluto's Charon-facing hemisphere during the recurring Pluto/Charon mutual events in the late 1980's. The REX radiometer measurements show distinct variations in microwave brightness that constrain volatile transport models and provide unique information on the thermal structure and composition on the regions in winter night during the New Horizons encounter at Pluto.

The Venus Express (VEX) Radio Science experiment VeRa utilizes radio occultation techniques to investigate the Venus atmosphere over a wide range of latitudes. Radio attenuation measurements with the VEX 3.6 cm (X-band) signal provide information on the absorptivity distribution within the Venus cloud deck. The combined results from 6 years of occultation measurements reveal a distinct latitudinal variation in absorptivity in the altitude range from 50 to 55 km. Enhanced absorptivity is observed at equatorial and mid-latitudes (0–50°S), exceeding 0.008 dB/km on the dayside and 0.01 dB/km on the nightside of the southern hemisphere. Poleward of 50°S latitude a decrease in the absorptivity is observed, reaching minimal values at polar latitudes (>70°S), where the absorptivity did not exceed 0.005 dB/km on the dayside and 0.004 dB/km on the nightside. The main absorber of radio waves in the Venus atmosphere, gaseous sulfuric acid, can serve as a tracer for atmospheric motions. The inferred absorptivity was used to determine the abundance of gaseous sulfuric acid. Abundances of about 1–2 ppm are found between 0°S and 70°S latitude in the altitude range from 50 to about 52 km, sometimes increasing to values of about 3 ppm on the dayside and 5 ppm on the nightside near 50 km. The abundance at polar latitudes (>70°S) did not exceed 1 ppm within the considered altitude range. The absorptivity and gaseous sulfuric acid height profiles are compared with previous measurements.

Gravity results are available from radio Doppler data acquired by the Deep Space Network during the encounter of the Cassini spacecraft with Enceladus in February 2005. We report the mass of Enceladus to be ( 1.0798 ± 0.0016 ) × 10 20 kg , which implies a density of 1608.9 ± 4 kg m −3 . For a core made of hydrated silicates with a density of 2500 kg m−3 the core radius is ∼ 190 km and the quadrupole moment C 22 ∼ 1.4 × 10 −3 . If Enceladus is in hydrostatic equilibrium, the larger than previously anticipated density implies that the recently proposed secondary spin–orbit resonance cannot be present. Therefore, the source of endogenic activity of Enceladus remains unexplained.

Preliminary room-temperature measurements of the microwave opacity of phosphine (Hoffman and Steffes 1999). Icarus 140 , 235–238, suggested that phosphine (PH 3 ) may contribute significantly to the microwave emission spectrum of Neptune, and to the centimeter-wavelength opacity measured by the Voyager 2 spacecraft at Neptune and Saturn. As a result, new laboratory measurements of the microwave opacity of PH 3 in an H 2 /He atmosphere have been conducted at frequencies (wavelengths) of 1.5 GHz (20 cm), 2.2 GHz (13.3 cm) 8.3 GHz (3.6 cm), 13.3, GHz (2.3 cm), 21.6 GHz (1.4 cm), and 27 GHz (1.1 cm) over a range of temperatures (175–298 K) and pressures (1–6 bars). A measurement-based centimeter-wavelength opacity formalism for phosphine has been developed and provides an order of magnitude improvement over previous models. The resulting model is applied to results from the Voyager 2 radio science experiments at Saturn and Neptune and to disk-averaged, centimeter-wavelength observations of Neptune and Saturn. Future uses will include application to spatially resolved microwave images of the outer planets from radio telescopes and spacecraft radiometry and to future radio occultation measurements, including Cassini–Saturn.

It has been suggested that phosphine (PH3) may contribute significantly to the microwave emission spectrum of Neptune, and to the centimeter-wavelength opacity measured by the Voyager 2 spacecraft at Neptune (D. R. DeBoer and P. G. Steffes 1996a, Icarus123, 324–335). As a result, laboratory measurements of the microwave opacity and refractivity of PH3 in an H2/He atmosphere have been conducted at 1.5 GHz (20 cm), 2.2 GHz (13.3 cm), 8.3 GHz (3.6 cm), 13.3 GHz (2.3 cm), and 21.6 GHz (1.4 cm) at pressures of 1, 3, and 5 bars at room temperature. Results indicate that current theories significantly understate the centimeter-wavelength opacity of PH3. This higher-than-expected opacity is likely due to a molecular inversion spectrum, of which no measurements have been reported. These results will elucidate the interpretation of centimeter-wavelength microwave observations from radio telescopes and spacecraft radio occultation measurements of the atmospheres of all four jovian planets.

Six previously unseen Pan wakes are found interior and exterior to the Encke gap in Saturn's A ring, one in the Voyager 2 photopolarimeter (PPS) stellar occultation data and five in the Voyager 1 radio science (RSS) Earth occultation data. Pan orbits at the center of the Encke gap and maintains it...The detection of Pan wakes at longitudes greater than 360(deg) demonstrates that wakes persist for much longer than originally hypothesized and may interact with one another.

The shapes and kinematics of the two major eccentric ringlets in Saturn's C ring are studied in data acquired by four Voyager experiments: imaging science (ISS), radio science (RSS), ultraviolet spectrometer (UVS), and photopolarimeter (PPS). It is found that the ringlets have mean widths of ∼25 km (Titan, 1.29 R_s) and ∼64 km (Maxwell, 1.45R_s), eccentricities of order 10^(−4), sharp edges on a scale of ∼1 km, normal optical depths τ ∼ 1−2, and are embedded in essentially empty gaps (τ < 0.05). In addition, they exhibit positive linear width-radius relations, suggesting that differential precession across the ringlets is being prevented by the self-gravity of the ring particles. The kinematics of the Maxwell ringlet are determined solely by Saturn's nonspherical gravity field; the kinematics of the Titan ringlet are apparently determined by its interaction with Titan. Masses, mean surface mass densities, and mass extinction coefficients have been calculated. The comparatively large optical depths and mass extinction coefficients in these features suggest an environment and particle size distribution different from the remainder of the C ring and presumably caused by the mechanism responsible for ring confinement.

The objective of the radio science investigations is to extract the maximum scientific information from the data provided by the radio and radar systems on the Viking Orbiters and Landers. Unique features of the Viking missions include tracking of the landers on the surface of Mars, dual-frequency S- and X-band tracking data from the orbiters, lander-to-orbiter communications system data, and lander radar data, all of which provide sources of information for a number of scientific investigations. Post-flight analyses will provide both new and improved scientific information on physical and surface properties of Mars, on atmospheric and ionospheric properties of Mars, and on solar system properties.