Microwave emission from the moon

Measurements of the microwave emission from the moon and their interpretation in terms of the thermophysics of that body are reviewed. Variations of the brightness temperatures of the moon during a lunation and during eclipses when combined with infrared and radar measurements yield a precise set of physical parameters for the upper few meters of the lunar soil. These parameters include the density, thermal conductivity, dielectric constant, radio absorption coefficients, and the mean temperature gradiant

Microwave spectroscopy of the Mars atmosphere

A study of the use of millimeter-wavelength spectral transitions to investigate the atmosphere of Mars is presented. In the model experiments investigated it is assumed that a spectrometer in the frequency range from 100 to 260 GHz looks into a modest-sized telescope of from 30 to 50 cm aperture from a near-Mars orbit. The molecules H2O, CO, O2, O3, and H2O2 all have intense spectral lines in the Mars atmosphere in this frequency range and in addition are all very important in understanding the water cycle, the photochemistry, and the circularization in that atmosphere. It is shown that the altitude and the zonal distribution of H2O can be mapped even in atmospheric columns as dry as 0.25 precipital μm. Ozone can be mapped over the entire planet, independent of solar-lighting conditions, dust loading, or clouds in the atmosphere, because millimeter waves are insensitive to any particles that can be suspended in the Mars atmosphere. Because the signal-receiving techniques use superheterodyne devices and narrow spectral lines, zonal and meridional winds can be measured at altitudes above 10 km with a precision approaching approximately 3 m/s by the use of Doppler shifts. Temperature–pressure profiles can be measured to altitudes of 100 km by the use of CO lines in the limb-sounding mode

Analysis of Viking infrared thermal mapping data of Mars. The effects of non-ideal surfaces on the derived thermal properties of Mars

The thermal interia of the surface of Mars varies spatially by a factor of eight. This is attributable to changes in the average particle size of the fine material, the surface elevation, the atmospheric opacity due to dust, and the fraction of the surface covered by rocks and fine material. The effects of these non-ideal properties on the surface temperatures and derived thermal inertias are modeled, along with the the effects of slopes, CO2 condensed onto the surface, and layering of fine material upon solid rock. The non-ideal models are capable of producing thermal behavior similar to that observed by the Viking Infrared Thermal Mapper, including a morning delay in the post-dawn temperature rise and an enhanced cooling in the afternoon relative to any ideal, homogeneous model. The enhanced afternoon cooling observed at the Viking-1 landing site is reproduced by the non-ideal models while that atop Arsia Mons volcano is not, but may be attributed to the observing geometry

CO on Titan: More Evidence for a Well-Mixed Vertical Profile

We report new interferometric observations of the CO (2-1) rotational transition on Titan. We find that the spectrum is best fit by a uniform profile of 52 ppm, with estimated errors of 6 ppm (40 to 200 km) and 12 ppm (200 to 300 km).Comment: Submitted to as a Note to Icarus. Uses emulateapj.sty under Latex, 6 text pages, 2 figs (includes with psfig

The relationship between the system of astronomical constants and the radar determinations of the astronomical unit

Radar determinations of astronomical unit, speed of light, solar parallax, and other constant

Titan's lakes chemical composition: sources of uncertainties and variability

Between 2004 and 2007 the instruments of the CASSINI spacecraft discovered hydrocarbon lakes in the polar regions of Titan. We have developed a lake-atmosphere equilibrium model allowing the determination of the chemical composition of these liquid areas. The model is based on uncertain thermodynamic data and precipitation rates of organic species predicted to be present in the lakes and seas that are subject to spatial and temporal variations. Here we explore and discuss the influence of these uncertainties and variations. The errors and uncertainties relevant to thermodynamic data are simulated via Monte-Carlo simulations. Global Circulation Models (GCM) are also employed in order to investigate the possibility of chemical asymmetry between the south and the north poles, due to differences in precipitation rates. We find that mole fractions of compounds in the liquid phase have a high sensitivity to thermodynamic data used as inputs, in particular molar volumes and enthalpies of vaporization. When we combine all considered uncertainties, the ranges of obtained mole fractions are rather large (up to ~8500%) but the distributions of values are narrow. The relative standard deviations remain between 10% and ~300% depending on the compound considered. Compared to other sources of uncertainties and variability, deviation caused by surface pressure variations are clearly negligible, remaining of the order of a few percent up to ~20%. Moreover no significant difference is found between the composition of lakes located in north and south poles. Because the theory of regular solutions employed here is sensitive to thermodynamic data and is not suitable for polar molecules such as HCN and CH3CN, our work strongly underlines the need for experimental simulations and the improvement of Titan's atmospheric models.Comment: Accepted in Planetary and Space Scienc

The Pioneer Anomaly

Radio-metric Doppler tracking data received from the Pioneer 10 and 11 spacecraft from heliocentric distances of 20-70 AU has consistently indicated the presence of a small, anomalous, blue-shifted frequency drift uniformly changing with a rate of ~6 x 10^{-9} Hz/s. Ultimately, the drift was interpreted as a constant sunward deceleration of each particular spacecraft at the level of a_P = (8.74 +/- 1.33) x 10^{-10} m/s^2. This apparent violation of the Newton's gravitational inverse-square law has become known as the Pioneer anomaly; the nature of this anomaly remains unexplained. In this review, we summarize the current knowledge of the physical properties of the anomaly and the conditions that led to its detection and characterization. We review various mechanisms proposed to explain the anomaly and discuss the current state of efforts to determine its nature. A comprehensive new investigation of the anomalous behavior of the two Pioneers has begun recently. The new efforts rely on the much-extended set of radio-metric Doppler data for both spacecraft in conjunction with the newly available complete record of their telemetry files and a large archive of original project documentation. As the new study is yet to report its findings, this review provides the necessary background for the new results to appear in the near future. In particular, we provide a significant amount of information on the design, operations and behavior of the two Pioneers during their entire missions, including descriptions of various data formats and techniques used for their navigation and radio-science data analysis. As most of this information was recovered relatively recently, it was not used in the previous studies of the Pioneer anomaly, but it is critical for the new investigation.Comment: 165 pages, 40 figures, 16 tables; accepted for publication in Living Reviews in Relativit

Titan's diverse landscapes as evidenced by Cassini RADAR's third and fourth looks at Titan

International audienceCassini's third and fourth radar flybys, T7 and T8, covered diverse terrains in the high southern and equatorial latitudes, respectively. The T7 synthetic aperture radar (SAR) swath is somewhat more straightforward to understand in terms of a progressive poleward descent from a high, dissected, and partly hilly terrain down to a low flat plain with embayments and deposits suggestive of the past or even current presence of hydrocarbon liquids. The T8 swath is dominated by dunes likely made of organic solids, but also contain somewhat enigmatic, probably tectonic, features that may be partly buried or degraded by erosion or relaxation in a thin crust. The dark areas in T7 show no dune morphology, unlike the dark areas in T8, but are radiometrically warm like the dunes. The Huygens landing site lies on the edge of the T8 swath; correlation of the radar and Huygens DISR images allows accurate determination of its coordinates, and indicates that to the north of the landing site sit two large longitudinal dunes. Indeed, had the Huygens probe trajectory been just 10 km north of where it actually was, images of large sand dunes would have been returned in place of the fluvially dissected terrain actually seen?illustrating the strong diversity of Titan's landscapes even at local scales

Multi-frequency imaging of the galaxy cluster Abell 2163 using the Sunyaev-Zel'dovich effect

Context. Observations of the Sunyaev-Zel'dovich effect (SZE) from galaxy clusters are emerging as a powerful tool in cosmology. Besides large cluster surveys, resolved SZE images of individual clusters can shed light on the physics of the intra-cluster medium (ICM) and allow accurate measurements of the cluster gas and total masses. Aims. We used the APEX-SZ and LABOCA bolometer cameras on the APEX telescope to map both the decrement of the SZE at 150 GHz and the increment at 345 GHz toward the rich and X-ray luminous galaxy cluster Abell 2163 at redshift 0.203. The SZE images were used, in conjunction with archival XMM-Newton X-ray data, to model the radial density and temperature distribution of the ICM, as well as to derive the gas mass fraction in the cluster under the assumption of hydrostatic equilibrium. Methods. We describe the data analysis techniques developed to extract the faint and extended SZE signal. We used the isothermal model to fit the SZE decrement/increment radial profiles. We performed a simple, non-parametric de-projection of the radial density and temperature profiles, in conjunction with X-ray data, under the simplifying assumption of spherical symmetry. We combined the peak SZE signals derived in this paper with published SZE measurements of this cluster to derive the cluster line-of-sight bulk velocity and the central Comptonization, using priors on the ICM temperature. Results. We find that the best-fit isothermal model to the SZE data is consistent with the ICM properties implied by the X-ray data, particularly inside the central 1 Mpc radius. Inside a radius of ~1500 kpc from the cluster center, the mean gas temperature derived from our SZE/X-ray joint analysis is 10.4 1.4 keV. The error budget for the derived temperature profile is dominated by statistical errors in the 150 GHz SZE image. From the isothermal analysis combined with previously published data, we find a line-of-sight peculiar velocity consistent with zero; vr = -140 460 km s-1, and a central Comptonization y0 = 3.42 0.32 10-4 for Abell 2163. Conclusions. Although the assumptions of hydrostatic equilibrium and spherical symmetry may not be optimal for this complex system, the results obtained under these assumptions are consistent with X-ray and weak-lensing measurements. This shows the applicability of the simple joint SZE and X-ray de-projection technique described in this paper for clusters with a wide range of dynamical states