Diffuse reflectance of altered olivine grains: Remote sensing detection and implications for Mars studies

The study of Mars linked to its climatic history, the presence of water and possible forms of life on the planet, are becoming more and more important in recent years. In this paper we present laboratory reflection measurements on olivine samples which are believed to be the product of alteration induced by their coexistence with water. The reflection spectra have been obtained in the wavelength range from 0.2 to and for different grain sizes; they exhibit, among various bands, some of which due to H₂O and OH^-, a characteristic absorption feature at about , whose emission wings at 0.56 and near have relative strengths which are size dependent and well correlated. The identification of such feature in the observed spectra of Mars would provide useful information about the grain size of the Martian regolith and, in association with other bands, also about the possible presence of olivine altered by water in the past.     

A global solution for the Mars static and seasonal gravity, Mars orientation, Phobos and Deimos masses, and Mars ephemeris

With the collection of six years of MGS tracking data and three years of Mars Odyssey tracking data, there has been a continual improvement in the JPL Mars gravity field determination. This includes the measurement of the seasonal changes in the gravity coefficients (e.g., , , , , , ) caused by the mass exchange between the polar ice caps and atmosphere. This paper describes the latest gravity field MGS95J to degree and order 95. The improvement comes from additional tracking data and the adoption of a more complete Mars orientation model with nutation, instead of the IAU 2000 model. Free wobble of the Mars' spin axis, i.e. polar motion, has been constrained to be less than 10 mas by looking at the temporal history of and . A strong annual signature is observed in , and this is a mixture of polar motion and ice mass redistribution. The Love number solution with a subset of Odyssey tracking data is consistent with the previous liquid outer core determination from MGS tracking data [Yoder et al., 2003. Science 300, 299-303], giving a combined solution of k₂=0.152±0.009 using MGS and Odyssey tracking data. The solutions for the masses of the Mars' moons show consistency between MGS, Odyssey, and Viking data sets; Phobos GM=(7.16±0.005)×¹⁰⁻⁴ km³/s² and Deimos GM=(0.98±0.07)×¹⁰⁻⁴ km³/s². Average MGS orbit errors, determined from differences in the overlaps of orbit solutions, have been reduced to 10-cm in the radial direction and 1.5 m along the spacecraft velocity and normal to the orbit plane. Hence, the ranging to the MGS and Odyssey spacecraft has resulted in position measurements of the Mars system center-of-mass relative to the Earth to an accuracy of one meter, greatly reducing the Mars ephemeris errors by several orders of magnitude, and providing mass estimates for Asteroids 1 Ceres, 2 Pallas, 3 Juno, 4 Vesta, and 324 Bamberga.     

Near infrared imaging spectroscopy of Venus with the Anglo-Australian Telescope

We have obtained full-disk spatially resolved spectra of the Venus nightside at near-infrared wavelengths during July 2007 using the Anglo-Australian Telescope and Infrared Imager and Spectrograph 2 (IRIS2). The data have been used to map the intensity and rotational temperature of the O₂(a¹Δ_g) airglow band at . The temperatures agree with those obtained in earlier IRIS2 observations and are significantly higher than expected from the Venus International Reference Atmosphere (VIRA) profile. We also report the detection of the corresponding ν=0-1O₂ airglow band at with a similar spatial distribution to the ν=0-0 band. Observations in the thermal window have been used to image surface topography using two different methods of cloud correction. We have also obtained images that can be used to study cloud motion.     

Environmental predictions for the Beagle 2 lander, based on GCM climate simulations

The Mars climate database (MCD) is a database of statistics based on output from physically consistent numerical model simulations which describe the climate and surface environment of Mars. It is used here to predict the meteorological environment of the Beagle 2 lander site. The database was constructed directly on the basis of output from multiannual integrations of two general circulation models, developed jointly at Laboratoire de Météorologie Dynamique du Centre National de la Recherche Scientifique, France, and the University of Oxford, UK. In an atmosphere with dust opacities similar to that observed by Mars Global Surveyor, the predicted surface temperature at the time of landing (L_s=322°, 13:00 local time), is , and varying between ∼186 and over the Martian day. The predicted air temperature at above the surface, the height of the fully extended Beagle 2 robot arm, is at the time of landing. The expected mean wind near the surface on landing is north-westerly in direction, becoming more southerly over the mission. An increase in mean surface pressure is expected during the mission. Heavy global dust storm predictions are discussed; conditions which may only occur in the extreme as the expected time of landing is around the end of the main dust storm period. Past observations show approximately a one in five chance of a large-scale dust storm in a whole Mars year over the landing region, Isidis Planitia. This statistic results from observations of global, encircling, regional and local dust storms but does not include any small-scale dust “events” such as dust devils.     

Tvashtar awakening detected in April 2006 with OSIRIS at the W.M. Keck Observatory

We detected a volcanic outburst in Io's northern hemisphere on 17 April 2006 with the OSIRIS imaging spectrometer at Keck, and confirmed it was still erupting on 2 June 2006. The eruption, which we name 060417A, was located in Tvashtar Paterae, ∼100 km southeast of the February 2000 eruption. The observed temperature was , over a surface area of , providing a total thermal output of .     

CCD photometry of 23 minor planets

We present CCD photometric observations of 23 main-belt asteroids, of which 8 have never been observed before; thus, the data of these objects are the first in the literature. The majority showed well-detectable light variations, exceeding 0^m1. We have determined synodic periods for 756 Lilliana (936), 1270 Datura (34), 1400 Tirela (1336), 1503 Kuopio (998), 3682 Welther (359), 7505 Furushu (414) and 11436 1969 QR (123), while uncertain period estimates were possible for 469 Argentina (123), 546 Herodias (104) and 1026 Ingrid (53). The shape of the lightcurves of 3682 Welther changed on a short time-scale and showed dimmings that might be attributed to eclipses in a binary system. For the remaining objects, only lower limits of the periods and amplitudes were concluded.     

On the mean oxygen isotope composition of the Solar System

Since the first discovery of extraordinary oxygen isotope compositions in carbonaceous meteorites by Clayton et al. [Clayton, R.N., Grossman, L., Mayeda, T.K., 1973. Science 182, 485-488], numerous studies have been done to explain the unusual mass-independent isotope fractionation, but the problem is still unresolved to this day. Clayton's latest interpretation [Clayton, R.N., 2002. Nature 415, 860-861] sheds new light on the problem, and possible hypotheses now seem to be fairly well defined. A key issue is to resolve whether the oxygen isotopes in the Solar System represented by the Sun (solar oxygen) are the same as oxygen isotopes in planetary objects such as bulk meteorites, Mars, Earth, and Moon, or whether the solar oxygen is more similar to the lightest oxygen isotopes observed in CAIs (Calcium Aluminum-rich Inclusions) in primitive meteorites. Here, we examined the problem using oxygen isotope analytical data of about 400 bulk meteorite samples of various classes or types (data compiled by K. Lodders). We used in our discussion exclusively the parameter , a direct measure of the degree of mass-independent isotope fractionation of oxygen isotopes. When is arranged according to a characteristic size of their host planetary object, it shows a systematic trend: (1) values scatter around zero; (2) the scatter from the mean () decreases with increasing representative size of the respective host planetary object. This systematic trend is easily understood on the basis of a hierarchical scenario of planetary formation, that is, larger planetary objects have formed by progressive accretion of planetesimals by random sampling over a wide spectrum of proto-solar materials. If this progressive random sampling of planetesimals were the essential process of planetary formation, the isotopic composition of planetary oxygen should approach that of the solar oxygen. To test this random sampling hypothesis, we applied a multiscale, multistep bootstrap statistical method [Shimodaira, H., 2004. Ann. Statist. 32, 2616-2641] to the meteorite oxygen isotope data, and deduced a σ-N relation, where σ is the standard deviation of , and N is the representative size of a host planetary object. If we assign 200 and 500 km as a representative sizes of the chondrite and achondrite parent bodies, the observed σ of agree well with the values predicted by the σ-N relation. A common mean value of for all planetary objects also agrees with the progressive random sampling process. Therefore, we conclude that the solar oxygen is the same as planetary oxygen, but differs from CAI oxygen. The conclusion implies that a massive enrichment in ¹⁷O and ¹⁸O resulting from CO self-shielding, a current influential interpretation of CAI-O, did not occur.     

The Planetary Fourier Spectrometer (PFS) onboard the European Mars Express mission

The Planetary Fourier Spectrometer (PFS) for the Mars Express mission is an infrared spectrometer optimised for atmospheric studies. This instrument has a short wave (SW) channel that covers the spectral range from 1700 to (1.2-) and a long-wave (LW) channel that covers 250- (5.5-). Both channels have a uniform spectral resolution of . The instrument field of view FOV is about 1.6^° (FWHM) for the Short Wavelength channel (SW) and 2.8^° (FWHM) for the Long Wavelength channel (LW) which corresponds to a spatial resolution of 7 and 12 km when Mars is observed from an height of 250  km. PFS can provide unique data necessary to improve our knowledge not only of the atmosphere properties but also about mineralogical composition of the surface and the surface-atmosphere interaction.The SW channel uses a PbSe detector cooled to 200-220 K while the LW channel is based on a pyroelectric (L_iT_aO₃) detector working at room temperature. The intensity of the interferogram is measured every 150 nm of physical mirrors displacement, corresponding to 600 nm optical path difference, by using a laser diode monochromatic light interferogram (a sine wave), whose zero crossings control the double pendulum motion. PFS works primarily around the pericentre of the orbit, only occasionally observing Mars from large distances. Each measurements take 4 s, with a repetition time of 8.5 s. By working roughly 0.6 h around pericentre, a total of 330 measurements per orbit will be acquired 270 looking at Mars and 60 for calibrations. PFS is able to take measurements at all local times, facilitating the retrieval of surface temperatures and atmospheric vertical temperature profiles on both the day and the night side.     

Coring experiments with cryogenic water and carbon dioxide ices—toward planetary surface operations

As a prelude to the design of sampling devices able to extract materials from the icy surfaces of comets, outer-planet satellites, and the martian poles, it is necessary to understand some of the physical properties of these ices. To this end we have investigated the mechanical resistance displayed by two ices subjected to coring operations at low temperatures and under vacuum. The ices used in this study were water ice, frozen from liquid water, and carbon dioxide ice grown from its vapour. The coring tool employed had dimensions and required power levels that were comparable to a sample extraction system designed for a present-day spacecraft lander. The specific cutting strength, a parameter that measures the toughness of the material, has been measured while coring these two ices. For water ice this property rose from at an ice temperature of , to at . At the lower temperature of , pore-free carbon dioxide ice has also been measured to have a specific cutting strength approximately half that of water ice at the same temperature. These laboratory-based measurements may be used as guides for the power levels needed to core solid water and CO₂ ices at certain rates.     

Experimental study of the sublimation of ice through an unconsolidated clay layer: Implications for the stability of ice on Mars and the possible diurnal variations in atmospheric water

We have studied the sublimation of ice and water vapor transport through various thicknesses of clay (<63 μm grain size). We experimentally demonstrate that both adsorption and diffusion strongly affect the transport of water, and that the processes of diffusion and adsorption can be separately quantified once the system comes to a steady state. At shallow depths of clay, water vapor transport is determined by diffusion through both the atmosphere and the clay layer, whereas at greater depth the rate of sublimation of the ice is governed only by diffusion through the clay. Using two different models, we determine the diffusion coefficient for water vapor through unconsolidated clay layer to be 1.08±0.04×¹⁰⁻⁴ and . We also determined the adsorption isotherms for the clay layer, which follow the Langmuir theory at low water vapor pressure (<100 Pa, where a monolayer of water molecules forms on the surface of the clay) and the BET theory at higher pressure (where multiple water layers form). From our analysis of both types of isotherms we determined the adsorption constants to be and c=30±10, respectively, and specific surface areas of 1.10±0.2×¹⁰⁵ and , respectively. Finally, we report a theoretical kinetic model for the simultaneous diffusion and adsorption from which we determine adsorption kinetic constants according to the Langmuir theory of and . If the martian regolith possesses diffusive properties similar to those of the unconsolidated montmorillonite soil we investigated here, it would not represent a significant barrier to the sublimation of subsurface ice. However, at the low subsurface temperatures of high latitude (180 K on average), ice could survive from the last glaciation period (about 300 to 400,000 years ago). Higher subsurface temperatures in the equatorial regions would prevent long-timescale survival of ice in the shallow subsurface. In agreement with previous work, we show that adsorption of water by a clay regolith could provide a significant reservoir of subsurface water and it might account for the purported diurnal cycle in the water content of the atmosphere.