Publications by Fred Taylor

Studying the Composition and Mineralogy of the Hermean Surface with the Mercury Radiometer and Thermal Infrared Spectrometer (MERTIS) for the BepiColombo Mission: An Update

Space Science Reviews 216 (2020)

H Hiesinger, J Helbert, G Alemanno, KE Bauch, M D’Amore, A Maturilli, A Morlok, MP Reitze, C Stangarone, AN Stojic, I Varatharajan, I Weber, G Arnold, M Banaszkiewicz, K Bauch, J Benkhoff, A Bischoff, M Blecka, N Bowles, S Calcutt, L Colangeli, S Erard, S Fonti, BT Greenhagen, O Groussain, H Hirsch, J Jahn, R Killen, J Knollenberg, E Kührt, E Lorenz, I Mann, U Mall, A Maturilli, A Morlok, L Moroz, G Peter, M Rataj, M Robinson, W Skrbek, T Spohn, A Sprague, D Stöffler, A Stojic, F Taylor, I Varatharajan, H Venus, J Warrell, I Walter, I Weber, A Witzke, C Wöhler

© 2020, The Author(s). Launched onboard the BepiColombo Mercury Planetary Orbiter (MPO) in October 2018, the Mercury Radiometer and Thermal Infrared Spectrometer (MERTIS) is on its way to planet Mercury. MERTIS consists of a push-broom IR-spectrometer (TIS) and a radiometer (TIR), which operate in the wavelength regions of 7-14 μm and 7-40 μm, respectively. This wavelength region is characterized by several diagnostic spectral signatures: the Christiansen feature (CF), Reststrahlen bands (RB), and the Transparency feature (TF), which will allow us to identify and map rock-forming silicates, sulfides as well as other minerals. Thus, the instrument is particularly well-suited to study the mineralogy and composition of the hermean surface at a spatial resolution of about 500 m globally and better than 500 m for approximately 5-10% of the surface. The instrument is fully functional onboard the BepiColombo spacecraft and exceeds all requirements (e.g., mass, power, performance). To prepare for the science phase at Mercury, the team developed an innovative operations plan to maximize the scientific output while at the same time saving spacecraft resources (e.g., data downlink). The upcoming fly-bys will be excellent opportunities to further test and adapt our software and operational procedures. In summary, the team is undertaking action at multiple levels, including performing a comprehensive suite of spectroscopic measurements in our laboratories on relevant analog materials, performing extensive spectral modeling, examining space weathering effects, and modeling the thermal behavior of the hermean surface.

Diurnal variation of dust and gas production in comet 67P/Churyumov-Gerasimenko at the inbound equinox as seen by OSIRIS and VIRTIS-M on board Rosetta


C Tubiana, G Rinaldi, C Guettler, C Snodgrass, X Shi, X Hu, R Marschall, M Fulle, D Bockeele-Morvan, G Naletto, F Capaccioni, H Sierks, G Arnold, MA Barucci, J-L Bertaux, I Bertini, D Bodewits, MT Capria, M Ciarniello, G Cremonese, J Crovisier, V Da Deppo, S Debei, M De Cecco, J Deller, MC De Sanctis, B Davidsson, L Doose, S Erard, G Filacchione, U Fink, M Formisano, S Fornasier, PJ Gutierrez, W-H Ip, S Ivanovski, D Kappel, HU Keller, L Kolokolova, D Koschny, H Krueger, F La Forgia, PL Lamy, LM Lara, M Lazzarin, AC Levasseur-Regourd, Z-Y Lin, A Longobardo, JJ Lopez-Moreno, F Marzari, A Migliorini, S Mottola, R Rodrigo, F Taylor, I Toth, V Zakharov

Analysis of night-side dust activity on comet 67P observed by VIRTIS-M: A new method to constrain the thermal inertia on the surface

Astronomy and Astrophysics 630 (2019)

G Rinaldi, M Formisano, D Kappel, F Capaccioni, D Bockelée-Morvan, YC Cheng, JB Vincent, P Deshapriya, G Arnold, MT Capria, M Ciarniello, E D'Aversa, MC de Sanctis, L Doose, S Erard, C Federico, G Filacchione, U Fink, C Leyrat, A Longobardo, G Magni, A Migliorini, S Mottola, G Naletto, A Raponi, F Taylor, F Tosi, GP Tozzi, M Salatti

On 2015 July 18, near perihelion at a heliocentric distance of 1.28 au, the Visible InfraRed Thermal Imaging Spectrometer (VIRTIS-M) on board the Rosetta spacecraft had the opportunity of observing dust activity in the inner coma with a view of the night side (shadowed side) of comet 67P/Churyumov-Gerasimenko. At the time of the measurements we present here, we observe a dust plume that originates on the far side of the nucleus. We are able to identify the approximate location of its source at the boundary between the Hapi and Anuket regions, and we find that it has been in darkness for some hours before the observation. Assuming that this time span is equal to the conductive time scale, we obtain a thermal inertia in the range 25-36 W K− m s 1/ . These thermal inertia values can be used to verify with a 3D finite-element method (FEM) numerical code whether the surface and subsurface temperatures agree with the values found in the literature. We explored three different configurations: (1) a layer of water ice mixed with dust beneath a dust mantle of 5 mm with thermal inertia of 36 J m K− s ; (2) the same structure, but with thermal inertia of 100 J m K− s ; (3) an ice-dust mixture that is directly exposed. Of these three configurations, the first seems to be the most reasonable, both for the low thermal inertia and for the agreement with the surface and subsurface temperatures that have been found for the comet 67P/Churyumov-Gerasimenko. The spectral properties of the plume show that the visible dust color ranged from 16 ± 4.8%/100 nm to 13 ± 2.6%/100 nm, indicating that this plume has no detectable color gradient. The morphology of the plume can be classified as a narrow jet that has an estimated total ejected mass of between 6 and 19 tons when we assume size distribution indices between −2.5 and −3. 1 −2 − 2 −2 1 −0.5 −2 1 −0.5

VIRTIS-H observations of the dust coma of comet 67P/Churyumov-Gerasimenko: Spectral properties and color temperature variability with phase and elevation

Astronomy and Astrophysics 630 (2019)

D Bockelée-Morvan, C Leyrat, S Erard, F Andrieu, F Capaccioni, G Filacchione, PH Hasselmann, J Crovisier, P Drossart, G Arnold, M Ciarniello, D Kappel, A Longobardo, MT Capria, MC De Sanctis, G Rinaldi, F Taylor

We analyze 2-5 μm spectroscopic observations of the dust coma of comet 67P/Churyumov-Gerasimenko obtained with the Visible InfraRed Thermal Imaging Spectrometer (VIRTIS-H) instrument on board Rosetta from 3 June to 29 October 2015 at heliocentric distances rh = 1.24-1.55 AU. The 2-2.5 μm color, bolometric albedo, and color temperature were measured using spectral fitting. Data obtained at α = 90° solar phase angle show an increase in bolometric albedo (0.05-0.14) with increasing altitude (0.5-8 km), accompanied by a possible marginal decrease in color and color temperature. Possible explanations include dark particles on ballistic trajectories in the inner coma and radial changes in particle composition. In the phase angle range 50°-120°, phase reddening is significant (0.031%/100 nm deg-1) for a mean color of 2%/100 nm at α = 90°, which might be related to the roughness of the dust particles. Moreover, a decrease in color temperature with decreasing phase angle is also observed at a rate of ~0.3 K deg-1, consistent with the presence of large porous particles, with low thermal inertia, and showing a significant day-to-night temperature contrast. Comparing data acquired at fixed phase angle (α = 90°), a 20% increase in bolometric albedo is observed near perihelion. Heliocentric variations in dust color are not significant in the time period we analyzed. The measured color temperatures vary from 260 to 320 K, and follow a rh-0.6 variation in the rh = 1.24-1.5 AU range, which is close to the expected rh-0.5 value.

Summer outbursts in the coma of comet 67P/Churyumov-Gerasimenko as observed by Rosetta-VIRTIS

Monthly Notices of the Royal Astronomical Society 481 (2018) 1235-1250

G Rinaldi, D Bockelée-Morvan, M Ciarniello, GP Tozzi, F Capaccioni, SL Ivanovski, G Filacchione, U Fink, L Doose, F Taylor, D Kappel, S Erard, C Leyrat, A Raponi, E D'Aversa, MT Capria, A Longobardo, E Palomba, F Tosi, A Migliorini, A Rotundi, V Della Corte, M Salatti

We present an analysis of transient events observed by the Visible InfraRed Thermal Imaging Spectrometer, instrument aboard Rosetta, for the dates of 2015 August 10, September 13 and 14, during the two months surrounding the comet perihelion passage of the Rosetta spacecraft. We detected and characterized events with life-times ranging from 26 min down to 6 min. The temporal evolution of the outburst shows a sudden increase of radiance from quiescent coma to the maximum in a few minutes. This rapid onset is correlated with a change of the visible dust colour from red, 15-18± 3 per cent/100 nm, to bluer with values of 7-10± 0.3 per cent/100 nm. The dust morphology of these outbursts can be classified into two main types: narrow and collimated plumes (August 10, September 13) and broad blobs (September 14). The observations suggest that there are localized regions on the surface that are more prone to outbursts than the rest of the nucleus. The projected dust velocity during the outburst events ranges between 22.2 ± 2.2 m s and 64.9 ± 10.6 m s . The total ejected mass during an outburst event is estimated to be between 10 and 500 tons for a duration of 6-26 min assuming size distribution indices between -2.5 and -3. -1 -1

Venus: The Atmosphere, Climate, Surface, Interior and Near-Space Environment of an Earth-Like Planet


FW Taylor, H Svedhem, HJW III

Cometary coma dust size distribution from in situ IR spectra

Monthly Notices of the Royal Astronomical Society 469 (2017) S598-S605

G Rinaldi, V Della Corte, M Fulle, F Capaccioni, A Rotundi, SL Ivanovski, D Bockelée-Morvan, G Filacchione, E D’Aversa, MT Capria, GP Tozzi, S Erard, C Leyrat, E Palomba, A Longobardo, M Ciarniello, F Taylor, S Mottola, M Salatti

Dust is the most abundant component in cometary comae. Here, we investigate the dust size distribution in 67P/Churyumov-Gerasimenko (67P/CG) using data from the Rosetta spacecraft that was in close proximity to the comet from 2014 August to 2016 September. The Visual, Infrared and Thermal Imaging Spectrometer (VIRTIS-M), spectral range of 0.25–5 μm, and the Grain Impact Analyser and Dust Accumulator (GIADA), both part of the Rosetta payload, together provide a powerful means to characterize the dust coma properties. On March 28, Rosetta performed a flyby close to the nucleus that allowed GIADA to detect a large amount of dust particles used to constraint the differential size distribution power-law index of −2.2 ± 0.3. In April 2015, VIRTIS-M observed the spectral radiance in the wavelength range of 1–5 μm. A simple radiative transfer model has been applied to simulate the VIRTIS-M radiances, thus allowing to infer the dust properties. We assumed an optically thin dust coma and spherical amorphous carbon particles in the size range between 0.1 to 1000 μm. We obtained the infrared data best fit with a differential dust size distribution power-law index of −3.1 . This index matches the one determined using GIADA March 2015 data indicating that, before perihelion, the inner coma radiance is dominated by particles larger than 10 μm; and the dust coma did not change its properties during most of the 67P/CG inbound orbit. + 3 − 0.1

Seasonal exposure of carbon dioxide ice on the nucleus of comet 67P/Churyumov-Gerasimenko.

Science American Association for the Advancement of Science 354 (2016) 1563-1566

G Filacchione, A Raponi, F Capaccioni, M Ciarniello, F Tosi, MT Capria, MC De Sanctis, A Migliorini, G Piccioni, P Cerroni, MA Barucci, S Fornasier, B Schmitt, E Quirico, S Erard, D Bockelee-Morvan, C Leyrat, G Arnold, V Mennella, E Ammannito, G Bellucci, J Benkhoff, JP Bibring, A Blanco, MI Blecka

Carbon dioxide is one of the most abundant species in cometary nuclei, but due to its high volatility CO2 ice is generally only found beneath the surface. We report the infrared spectroscopic identification of a CO2 ice-rich surface area, located in the Anhur region of comet 67P/Churyumov-Gerasimenko. Spectral modeling shows that about 0.1% of the 80×60 m area is CO2 ice. This exposed ice was observed a short time after exiting from local winter; following the increased illumination, the CO2 ice completely disappeared over about three weeks. We estimate the mass of the sublimated CO2 ice and the depth of the surface eroded layer. The presence of CO2 ice is interpreted as the result of the extreme seasonal changes induced by the rotation and orbit of the comet.

Investigation into the disparate origin of CO2 and H2O outgassing for Comet 67/P

ICARUS 277 (2016) 78-97

U Fink, L Doose, G Rinaldi, A Bieler, F Capaccioni, D Bockelee-Morvan, G Filacchione, S Erard, C Leyrat, M Blecka, MT Capria, M Combi, J Crovisier, MC De Sanctis, N Fougere, F Taylor, A Migliorini, G Piccioni

Refractory and semi-volatile organics at the surface of comet 67P/Churyumov-Gerasimenko: Insights from the VIRTIS/Rosetta imaging spectrometer

ICARUS 272 (2016) 32-47

E Quirico, LV Moroz, B Schmitt, G Arnold, M Faure, P Beck, L Bonal, M Ciarniello, F Capaccioni, G Filacchione, S Erard, C Leyrat, D Bockelee-Morvan, A Zinzi, E Palomba, P Drossart, F Tosi, MT Capria, MC De Sanctis, A Raponi, S Fonti, F Mancarella, V Orofino, A Barucci, MI Blecka, R Carlson, D Despan, A Faure, S Fornasier, MS Gudipati, A Longobardo, K Markus, V Mennella, F Merlin, G Piccioni, B Rousseau, F Taylor, RVIRTIS Team

Water and carbon dioxide distribution in the 67P/Churyumov-Gerasimenko coma from VIRTIS-M infrared observations


A Migliorini, G Piccioni, F Capaccioni, G Filacchione, D Bockelee-Morvan, S Erard, C Leyrat, MR Combi, N Fougere, J Crovisier, FW Taylor, MC De Sanctis, MT Capria, D Grassi, G Rinaldi, GP Tozzi, U Fink

Exposed water ice on the nucleus of comet 67P/Churyumov-Gerasimenko.

Nature 529 (2016) 368-372

G Filacchione, MC De Sanctis, F Capaccioni, A Raponi, F Tosi, M Ciarniello, P Cerroni, G Piccioni, MT Capria, E Palomba, G Bellucci, S Erard, D Bockelee-Morvan, C Leyrat, G Arnold, MA Barucci, M Fulchignoni, B Schmitt, E Quirico, R Jaumann, K Stephan, A Longobardo, V Mennella, A Migliorini, E Ammannito, J Benkhoff, JP Bibring, A Blanco, MI Blecka, R Carlson, U Carsenty, L Colangeli, M Combes, M Combi, J Crovisier, P Drossart, T Encrenaz, C Federico, U Fink, S Fonti, WH Ip, P Irwin, E Kuehrt, Y Langevin, G Magni, T McCord, L Moroz, S Mottola, V Orofino, U Schade, F Taylor, D Tiphene, GP Tozzi, P Beck, N Biver, L Bonal, J-P Combe, D Despan, E Flamini, M Formisano, S Fornasier, A Frigeri, D Grassi, MS Gudipati, D Kappel, F Mancarella, K Markus, F Merlin, R Orosei, G Rinaldi, M Cartacci, A Cicchetti, S Giuppi, Y Hello, F Henry, S Jacquinod, JM Reess, R Noschese, R Politi, G Peter

Although water vapour is the main species observed in the coma of comet 67P/Churyumov-Gerasimenko and water is the major constituent of cometary nuclei, limited evidence for exposed water-ice regions on the surface of the nucleus has been found so far. The absence of large regions of exposed water ice seems a common finding on the surfaces of many of the comets observed so far. The nucleus of 67P/Churyumov-Gerasimenko appears to be fairly uniformly coated with dark, dehydrated, refractory and organic-rich material. Here we report the identification at infrared wavelengths of water ice on two debris falls in the Imhotep region of the nucleus. The ice has been exposed on the walls of elevated structures and at the base of the walls. A quantitative derivation of the abundance of ice in these regions indicates the presence of millimetre-sized pure water-ice grains, considerably larger than in all previous observations. Although micrometre-sized water-ice grains are the usual result of vapour recondensation in ice-free layers, the occurrence of millimetre-sized grains of pure ice as observed in the Imhotep debris falls is best explained by grain growth by vapour diffusion in ice-rich layers, or by sintering. As a consequence of these processes, the nucleus can develop an extended and complex coating in which the outer dehydrated crust is superimposed on layers enriched in water ice. The stratigraphy observed on 67P/Churyumov-Gerasimenko is therefore the result of evolutionary processes affecting the uppermost metres of the nucleus and does not necessarily require a global layering to have occurred at the time of the comet's formation.

Properties of the dust in the coma of 67P/Churyumov-Gerasimenko observed with VIRTIS- M

Monthly Notices of the Royal Astronomical Society 462 (2016) S547-S561

G Rinaldi, U Fink, L Doose, GP Tozzi, F Capaccioni, G Filacchione, D Bockelée-Morvan, C Leyrat, G Piccioni, S Erard, A Bieler, M Błecka, M Ciarniello, M Combi, N Fougere, A Migliorini, E Palomba, A Raponi, F Taylor

An investigation is presented of the dust scattering in the coma of 67P/Churyumov- Gerasimenko for the dates of 2015 February 28, March 15 and April 27. A comparison of the morphology of dust continuum maps at 1.1 μm and gas emission shows that for the above dates the spatial distribution of the dust is strongly correlated with H O but not with CO emission. For April 27, the radial profile on the illuminated side of the nucleus in the inner coma agrees well with the direct simulation Monte Carlo (DSMC) calculations as the dust is accelerating and flows outwards but follows a 1/ρ distribution at distances larger than 4 km from the nucleus. The azimuthal distribution of the dust is narrower than the broader emission of the gas. Afρ values are 1.13 m for 2015 February 28, 2.02 m for April 27, while local values for March 15 are 2.3-5.3 m, depending on the nucleus illumination. In the inner coma, the spectral reflectivity from 0.35 to 3.5 μm displays a red slope with a change at around 1 μm. From 0.35 to 0.8 μm, the values range from 9 to 12 ± 1 per cent per 100 nm both on the sunlit side and on the dark side. From 1 to 2.5 μm, the values are 1.7 ± 0.2 per cent per 100 nm on the sunlit side and 3 ± 1 per cent per 100 nm on the dark side. For the August 26 jet, no significant increase of the colour gradient with distance from the nucleus could be observed, nor any significant difference detected between the jet and the background coma. 2 2

First observations of H2O and CO2 vapor in comet 67P/Churyumov-Gerasimenko made by VIRTIS onboard Rosetta


D Bockelee-Morvan, V Debout, S Erard, C Leyrat, F Capaccioni, G Filacchione, N Fougere, P Drossart, G Arnold, M Combi, B Schmitt, J Crovisier, M-C de Sanctis, T Encrenaz, E Kuehrt, E Palomba, FW Taylor, F Tosi, G Piccioni, U Fink, G Tozzi, A Barucci, N Biver, M-T Capria, M Combes, W Ip, M Blecka, F Henry, S Jacquinod, J-M Reess, A Semery, D Tiphene

Cometary science. The organic-rich surface of comet 67P/Churyumov-Gerasimenko as seen by VIRTIS/Rosetta.

Science (New York, N.Y.) 347 (2015) aaa0628-

F Capaccioni, A Coradini, G Filacchione, S Erard, G Arnold, P Drossart, MC De Sanctis, D Bockelee-Morvan, MT Capria, F Tosi, C Leyrat, B Schmitt, E Quirico, P Cerroni, V Mennella, A Raponi, M Ciarniello, T McCord, L Moroz, E Palomba, E Ammannito, MA Barucci, G Bellucci, J Benkhoff, JP Bibring, A Blanco, M Blecka, R Carlson, U Carsenty, L Colangeli, M Combes, M Combi, J Crovisier, T Encrenaz, C Federico, U Fink, S Fonti, WH Ip, P Irwin, R Jaumann, E Kuehrt, Y Langevin, G Magni, S Mottola, V Orofino, P Palumbo, G Piccioni, U Schade, F Taylor, D Tiphene, GP Tozzi, P Beck, N Biver, L Bonal, J-P Combe, D Despan, E Flamini, S Fornasier, A Frigeri, D Grassi, M Gudipati, A Longobardo, K Markus, F Merlin, R Orosei, G Rinaldi, K Stephan, M Cartacci, A Cicchetti, S Giuppi, Y Hello, F Henry, S Jacquinod, R Noschese, G Peter, R Politi, JM Reess, A Semery

The VIRTIS (Visible, Infrared and Thermal Imaging Spectrometer) instrument on board the Rosetta spacecraft has provided evidence of carbon-bearing compounds on the nucleus of the comet 67P/Churyumov-Gerasimenko. The very low reflectance of the nucleus (normal albedo of 0.060 ± 0.003 at 0.55 micrometers), the spectral slopes in visible and infrared ranges (5 to 25 and 1.5 to 5% kÅ(-1)), and the broad absorption feature in the 2.9-to-3.6-micrometer range present across the entire illuminated surface are compatible with opaque minerals associated with nonvolatile organic macromolecular materials: a complex mixture of various types of carbon-hydrogen and/or oxygen-hydrogen chemical groups, with little contribution of nitrogen-hydrogen groups. In active areas, the changes in spectral slope and absorption feature width may suggest small amounts of water-ice. However, no ice-rich patches are observed, indicating a generally dehydrated nature for the surface currently illuminated by the Sun.

Radiation in the Atmosphere of Venus

in Exploring Venus as a Terrestrial Planet, (2013) 121-138

DV Titov, MA Bullock, D Crisp, NO Renno, FW Taylor, LV Zasova

This chapter reviews the observations of the radiative fluxes inside and outside the Venusian atmosphere, along with the available data about the planetary energy balance and the distribution of sources and sinks of radiative energy. We also briefly address the role of the heat budget on the atmospheric temperature structure, global circulation, thermodynamics, climate and evolution. We compare the main features of radiative balance on the terrestrial planets, and provide a general description of the radiative-convective equilibrium models used to study their atmospheres. We describe the physics of the greenhouse effect as it applies to the evolution of the Venusian climate, concluding with a summary of outstanding open issues.

Venus Express and Terrestrial Planet Climatology

in Exploring Venus as a Terrestrial Planet, (2013) 157-170

FW Taylor, H Svedhem, DM Titov

After a delay of more than a decade, the exploration of Venus has resumed through the European Venus Express mission, now in orbit around the planet. The mission payload, its implementation in an elliptical polar orbit, and the science operations planned, all focus on outstanding problems associated with the atmosphere and climate of Venus. Many of these problems, such as understanding the extreme surface warming produced by the carbon dioxide-driven greenhouse effect, and the role of sulfate aerosols in the atmosphere, have resonances with climate-change issues on the Earth and Mars. As data on all three terrestrial planets accumulates, and models of the energy balance and general circulation of their atmospheres improve, it becomes increasingly possible to define and elucidate their behavior in a common, comparative framework. Venus Express seeks to contribute to progress in this area.

Models of the global cloud structure on Venus derived from Venus Express observations

Icarus 217 (2012) 542-560

JK Barstow, CCC Tsang, CF Wilson, PGJ Irwin, FW Taylor, K McGouldrick, P Drossart, G Piccioni, S Tellmann

Spatially-resolved near-infrared spectra from the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) on Venus Express have been used to derive improved models of the vertical structure and global distribution of cloud properties in the southern hemisphere of Venus. VIRTIS achieved the first systematic, global mapping of Venus at wavelengths within transparency windows in the 1.6-2.6. μm range, which are sensitive on the nightside to absorption by the lower and middle cloud layers of thermally-emitted radiation from the hot lower atmosphere (Taylor, F.W., Crisp, D., Bézard, B. [1997]. Venus II: Geology, Geophysics, Atmosphere, and Solar Wind Environment, pp. 325-351). The cloud model used to interpret the spectra is based on previous work by Pollack et al. (Pollack, J., Dalton, J., Grinspoon, D., Wattson, R., Freedman, R., Crisp, D., Allen, D., Bézard, B., de Bergh, C., Giver, L. [1993]. Icarus 103, 1-42), Grinspoon et al. (Grinspoon, D.H., Pollack, J.B., Sitton, B.R., Carlson, R.W., Kamp, L.W., Baines, K.H., Encrenaz, T., Taylor, F.W. [1993]. Planet. Space Sci. 41, 515-542) and Crisp (Crisp, D. [1986]. Icarus 67, 484-514), and assumes a composition for the cloud particles of sulfuric acid and water, with acid concentration as a free parameter to be determined. Other retrieved parameters are the average size of the particles and the altitude of the cloud base in the model. Latitudinal variation in the atmospheric temperature structure was incorporated using data from the Venus Radio Science experiment (VeRa). Values are estimated initially using wavelength pairs selected for their unique sensitivity to each parameter, and then validated by comparing measured to calculated spectra over the entire wavelength range, the latter generated using the NEMESIS radiative transfer and retrieval code (Irwin, P.G.J., Teanby, N.A., de Kok, R., Fletcher, L.N., Howett, C.J.A., Tsang, C.C.C., Wilson, C.F., Calcutt, S.B., Nixon, C.A., Parrish, P.D. [2008]. J. Quant. Spectrosc. Radiat. Trans. 109, 1136-1150). The sulfuric acid concentration in the cloud particles is found to be higher in regions of optically thick cloud. The cloud base altitude shows a dependence on latitude, reaching a maximum height near -50°. The increased average particle size near the pole found by Wilson et al. (Wilson, C.F., Guerlet, S., Irwin, P.G.J., Tsang, C.C.C., Taylor, F.W., Carlson, R.W., Drossart, P., Piccioni, G. [2008]. J. Geophys. Res. (Planets) 113, E12) and the finding of spatially variable water vapor abundance at35-40. km altitude first reported by Tsang et al. (Tsang, C.C.C., Wilson, C.F., Barstow, J.K., Irwin, P.G.J., Taylor, F.W., McGouldrick, K., Piccioni, G., Drossart, P., Svedhem, H. [2010]. Geophys. Res. Lett. 37, L02202) are both confirmed. The implications of these improved descriptions of cloud structure and variability for the chemistry, meteorology, and radiative energy balance on Venus are briefly discussed. © 2011 Elsevier Inc.

The surface composition and temperature of asteroid 21 Lutetia as observed by Rosetta/VIRTIS.

Science (New York, N.Y.) 334 (2011) 492-494

A Coradini, F Capaccioni, S Erard, G Arnold, MC De Sanctis, G Filacchione, F Tosi, MA Barucci, MT Capria, E Ammannito, D Grassi, G Piccioni, S Giuppi, G Bellucci, J Benkhoff, JP Bibring, A Blanco, M Blecka, D Bockelee-Morvan, F Carraro, R Carlson, U Carsenty, P Cerroni, L Colangeli, M Combes, M Combi, J Crovisier, P Drossart, ET Encrenaz, C Federico, U Fink, S Fonti, L Giacomini, WH Ip, R Jaumann, E Kuehrt, Y Langevin, G Magni, T McCord, V Mennella, S Mottola, G Neukum, V Orofino, P Palumbo, U Schade, B Schmitt, F Taylor, D Tiphene, G Tozzi

The Visible, InfraRed, and Thermal Imaging Spectrometer (VIRTIS) on Rosetta obtained hyperspectral images, spectral reflectance maps, and temperature maps of the asteroid 21 Lutetia. No absorption features, of either silicates or hydrated minerals, have been detected across the observed area in the spectral range from 0.4 to 3.5 micrometers. The surface temperature reaches a maximum value of 245 kelvin and correlates well with topographic features. The thermal inertia is in the range from 20 to 30 joules meter(-2) kelvin(-1) second(-0.5), comparable to a lunarlike powdery regolith. Spectral signatures of surface alteration, resulting from space weathering, seem to be missing. Lutetia is likely a remnant of the primordial planetesimal population, unaltered by differentiation processes and composed of chondritic materials of enstatitic or carbonaceous origin, dominated by iron-poor minerals that have not suffered aqueous alteration.

Comparative planetology, climatology and biology of Venus, Earth and Mars


FW Taylor