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This talk will introduce the The Canary Island Long-Baseline Observatory (CILBO), a double station meteor camera setup located on the Canary Islands and operated by ESA’s Meteor Research Group since 2010. Our observations of meteors are obtained in the visual wavelength band by intensified video cameras from both stations, supplemented by an intensified video camera mounted with a spectral grating at one of the locations. The cameras observe during cloudless and precipitation-free nights and data are transferred to a main computer located at ESA/ESTEC once a day. The image frames that contain spectral information are calibrated, corrected, and finally processed into line intensity profiles. An ablation simulation, based on Bayesian statistics using a Markov-Chain Monte-Carlo method, allows to determine a parameter space, including the ablation temperatures, chemical elements and their corresponding line intensities, to fit against the line intensity profiles of the observed meteor spectra. The algorithm is presented in this talk. Several hundred spectra have been processed and will be made available through the Guest Archive Facility of the Planetary Science Archive of ESA.

The Canary Island Long-Baseline Observatory (CILBO) is a double-station meteor camera setup located on the Canary Islands operated by ESA's Meteor Research Group since 2010. Observations of meteors are obtained in the visual wavelength band by intensified video cameras from both stations, supplemented by an intensified video camera mounted with a spectral grating at one of the locations. The cameras observe during cloudless and precipitation-free nights, and data are transferred to a main computer located at ESA/ESTEC once a day. The image frames that contain spectral information are calibrated, corrected, and finally processed into line intensity profiles. An ablation simulation, based on Bayesian statistics using a Markov chain Monte Carlo method, allows determining a parameter space, including the ablation temperatures, chemical elements, and their corresponding line intensities, to fit against the line intensity profiles of the observed meteor spectra. The algorithm is presented in this paper and one example is discussed. Several hundred spectra have been processed and made available through the Guest Archive Facility of the Planetary Science Archive of ESA. The data format and metadata are explained.

Polarimetry of sunlight that is reflected by a planet or that is transmitted through its atmosphere is a powerful tool for the characterisation of the planetary atmosphere and, if present, the surface. The main reason for the power of polarimetry is that the angular distribution of the degree of linear polarisation of sunlight that has been singly scattered by particles in the atmosphere or on the surface is very sensitive to the microphysical properties of these particles (their size, shape, and composition), indeed much more sensitive than the total flux is [see 1, 2, 3]. And because multiple scattered light usually has a low degree of polarisation, it might decrease the overall degree of polarisation of the light that emerges from the planetary atmosphere, but the angular pattern, which holds the crucial information about the scatterers, will remain. A classic example of the power of polarimetry was the derivation of the size distribution, composition, and altitude of the particles constituting Venus’s main cloud deck from Earth-based, disk-integrated polarimetry across a wide phase angle range and at a few wavelengths [4]. Since then, spectrometers with some polarimetric capabilities have flown on, for example, the Pioneer Venus, Galileo, and Cassini missions. The POLDER polarimeter has flown on various Earth observing missions, and NASA’s Earth remote-sensing PACE mission with SPEXone [5] onboard is scheduled for launch in 2024. Mars, with its dust storms, its water and carbon-dioxide ice clouds, and dusty surface, appears to be an ideal target for polarimetry. The polarimetric attention for this planet has, however, been surprisingly limited. Two linear polarimeters have flown onboard the Soviet spacecraft MARS-5 and provided some information about mostly ice cloud particle shapes, sizes, and composition, even though they encountered a very clear Martian atmosphere during their short active measurement period [6, 7]. And, indeed, HST observations show linear polarisation variations that correlate with the presence of clouds and dust [8]. However, with HST orbiting the Earth, these observations were necessarily done with Mars at a small phase angle; the measured degrees of polarization are therefore very small and the angular range extremely limited. To truly enjoy the advantages of polarimetry for Mars remote-sensing, a polarimeter should either orbit the planet or be landed on the surface, because only then a range of scattering angles holding most of the information would be within reach. We will describe the case for martian spectropolarimetry from an orbiter or a lander/rover, highlighting the potential for characterisation of the atmospheric dust and clouds and of the surface, and also covering the use of circular polarimetry for identifying chiral signatures [9,10] that on Earth are typical for life. Traditionally, polarimeters have been based on polarisers in rotating filter wheels. Such designs are neither robust nor do they achieve the accuracy that fully unlocks the power of polarimetry. We will present an innovative, compact, robust (no moving parts), and accurate type of spectropolarimeter [11] whose flexible design allows incorporation on various vehicles. Finally, the analysis and interpretation of martian spectropolarimetric measurements requires radiative transfer algorithms that fully include linear (and circular) polarimetry. We will describe a few available algorithms and discuss laboratory measurements of light scattering properties of various types of atmospheric particles and surfaces that would improve the radiative transfer computations and with that the interpretation of (future) spectropolarimetry of Mars. References [1] J. E. Hansen and L. D. Travis. Light scattering in planetary atmospheres. Space Sci. Rev., 16:527–610, 1974. [2] M. I. Mishchenko and L. D. Travis. Satellite retrieval of aerosol properties over the ocean using polarization as well as intensity of reflected sunlight. J. Geophys. Res., 102:16989–17014. doi: 10.1029/96JD02425, 1997 [3] Y. Shkuratov, N. Opanasenko, E. Zubko, Y. Grynko, V. Korokhin, C. Pieters, G. Videen, U. Mall, and A. Opanasenko. Multispectral polarimetry as a tool to investigate texture and chemistry of lunar regolith particles. Icarus, 187:406–416. doi: 10.1016/j.icarus. 2006.10.012, 2007 [4] J. E. Hansen and J. W. Hovenier. Interpretation of the Polarization of Venus. J. Atmos. Sci., 31:1137–1160, 1974. [5] F. Snik, J. H. Rietjes, G. Van Harten, D. M. Stam, C. U. Keller, J. M. Smit. SPEX: the spectropolarimeter for planetary exploration. Proc. SPIE 7731:77311B. doi: 10.1117/12.857941, 2010. [6] R. Santer, M. Deschamps, L. V. Ksanfomaliti, and A. Dollfus. Photopolarimetric analysis of the Martian atmosphere by the Soviet MARS-5 orbiter. I - White clouds and dust veils. Astron. Astrophys., 150:217–228, 1985. [7] R. Santer, M. Deschamps, L. V. Ksanfomaliti, and A. Dollfus. Photopolarimetry of Martian aerosols. II - Limb and terminator measurements. Astron. Astrophys., 158:247–258, 1986. [8] Y. Shkuratov, M. Kreslavsky, V. Kaydash, G. Videen, J. Bell, M. Wolff, M. Hubbard, K. Noll, and A. Lubenow. Hubble Space Telescope imaging polarimetry of Mars during the 2003 opposition. Icarus, 176:1–11. doi: 10.1016/j.icarus.2005.01.009, 2005 [9] W. Sparks, J. H. Hough, Th. A. Germer, F. Robb, and L. Kolokolova, Remote sensing of chiral signatures on Mars, Planet. Space Sci. 72, doi: 10.1016/j.pss.2012.08.010, 2012 [10] W. Sparks, J. H. Hough, and L. E. Bergeron, The search for chiral signatures on Mars, Astrobiology, 5, doi: 10.1089/ast.2005.5.737, 2005 [11] D. M. Stam, E. Laan, F. Snik, T. Karalidi, C. Keller, R. ter Horst, R. Navarro, C. Aas, J. De Vries, G. Oomen, R. Hoogeveen, Polarimetry of Mars with SPEX, an innovative spectropolarimeter, Third International Workshop on The Mars Atmosphere: Modeling and Observations, LPI Contributions, Vol. 1447, 2008.

It has been argued that symptom onset in neurodegeneration reflects the overload of compensatory mechanisms. The present study aimed to investigate whether neural functional compensation can be observed in the manifest neurodegenerative disease stage, by focusing on a core deficit in frontotemporal dementia, i.e. social cognition, and by combining psychophysical assessment, structural MRI and functional MRI with multidimensional neural markers that allow quantification of neural computations.Nineteen patients with clinically manifest behavioral variant frontotemporal dementia (bvFTD) and 20 controls performed facial expression recognition tasks in the MRI-scanner and offline. Group differences in grey matter volume, neural response amplitude and neural patterns were assessed via a combination of voxel-wise whole-brain, searchlight, and ROI-analyses and these measures were correlated with psychophysical measures of emotion, valence and arousal ratings.Significant group effects were observed only outside task-relevant regions, converging in the caudate nucleus. This area showed a diagnostic neural pattern as well as hyperactivation and stronger neural representation of facial expressions in the bvFTD sample. Furthermore, response amplitude was associated with behavioral arousal ratings.The combined findings reveal converging support for compensatory processes in clinically manifest neurodegeneration, complementing accounts that clinical onset synchronizes with the breakdown of compensatory processes. Furthermore, active compensation may proceed along nodes in intrinsically connected networks, rather than along the more task-specific networks. The findings underscore the potential of distributed multidimensional functional neural characteristics that may provide a novel class of biomarkers with both diagnostic and therapeutic implications, including biomarkers for clinical trials.

One of the most exciting scientific challenges is to detect Earth-like planets in the habitable zones of other stars in the galaxy and search for evidence of life. The ability to observe and characterise dozens of potentially Earth-like planets now lies within the realm of possibility due to rapid advances in key space and imaging technologies. The associated challenge of directly imaging very faint planets in orbit around nearby very bright stars is now well understood, with the key instrumentation also being perfected and developed. Such advances will allow us to develop large transformative telescopes, covering a broad UV-optical-IR spectral range, which can carry out the detailed research programmes designed to answer the questions we wish to answer: Carry out high contrast imaging surveys of nearby stars to search for planets within their habitable zones. Characterise the planets detected to determine masses and radii from photometric measurements. Through spectroscopic studies of their atmospheres and surfaces, search for habitability indicators and for signs of an environment that has been modified by the presence of life. Active studies of potential missions have been underway for a number of years. The latest of these is the Large UV Optical IR space telescope (LUVOIR), one of four flagship mission studies commissioned by NASA in support of the 2020 US Decadal Survey. LUVOIR, if selected, will be of interest to a wide scientific community and will be the only telescope capable of searching for and characterizing a sufficient number of exoEarths to provide a meaningful answer to the question - Are we alone?. This paper is a submission to the European Space Agency Voyage 2050 call for white papers outlining the case for an ESA contribution to a Large UVOIR telescope., Submission to the European Space Agency Voyage 2050 call for white papers

Snellen, I.A.G. et al., In this White Paper, which was submitted in response to the European Space Agency (ESA) Voyage 2050 Call, we recommend the ESA plays a proactive role in developing a global collaborative effort to construct a large high-contrast imaging space telescope, e.g. as currently under study by NASA. Such a mission will be needed to characterize a sizable sample of temperate Earth-like planets in the habitable zones of nearby Sun-like stars and to search for extraterrestrial biological activity. We provide an overview of relevant European expertise, and advocate ESA to start a technology development program towards detecting life outside the Solar System., I.S. acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program under grant agreement No 694513. A.L.M. acknowledges the financial support of the F.R.S.-FNRS through a postdoctoral researcher grant. MB acknowledges support from the UK Science and Technology Facilities Council (STFC) research grant ST/S000631/1. I.R. acknowledges support from the Spanish Ministry of Science and Innovation and the European Regional Development Fund through grant PGC2018-098153-B-C33, as well as the support of the Generalitat de Catalunya/CERCA programme. E.P. acknowledges support from the Spanish Ministry of Science through grant PGC2018-098153-B-C31. J.M.D. acknowledges funding from the European Research Council (ERC) under the European Unions Horizon 2020 research and innovation programme (grant agreement no. 679633; Exo-Atmos) Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. We acknowledge financial support from the ASI-INAF agreement n.2018-16-HH.0 We acknowledge financial support from Spanish MCIU SEV-2017-0709 and PID2019-110689RB-I00 awards. We acknowledge financial support from the ASI-INAF agreement n.2018-16-HH.0 AV acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 757561). KH acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 771620). NJM acknowledges funding from the Leverhulme Trust, and a Science and Technology Facilities Council Consolidated Grant (ST/R000395/1). PdV acknowledges funding from the Netherlands Organisation for Scientific Research NWO (Veni Grant No. 639.041.750). IP acknowledges financial support from the ASI-INAF agreements 2019-29-HH.06-HH.0 and 2015-019-R.1-2018. FS acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 678194; FALCONER). MJ acknowledges support from the Knut and Alice Wallenberg foundation (KAW). JLB acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program under grant agreement No 805445. T.H. acknowledges support from the European Research Council under the Horizon 2020 Framework Program via the ERC Advanced Grant Origins 83 24 28. JLG acknowledges ISSI Team 464 for useful discussion.

Introduction: Given the extreme conditions in the lower atmosphere of Venus, various in-situ missions faced instrumental failures. As a result, the thermal structure of the deep atmosphere, particularly below 12 km is not well known. In Venus International Reference Atmosphere (VIRA), the thermal structure of the atmosphere below 12 km altitude was constructed by extrapolating the data recorded in the upper atmosphere. Only VeGa-2 lander provided the high-resolution temperature measurements below 12 km altitude. However, these measurements indicated a region of high instability below 7 km altitude. Due to a lack of physical explanation, these measurements were not included in VIRA. Methodology: In this study, we use the previous near-IR observations of Venus nightside to investigate the thermal structure of the deep atmosphere. First, a surface temperature map is generated from the near-IR observations. By correlating this map with surface topography a surface temperature vs altitude profile is generated. Assuming that the surface is in thermal equilibrium with the atmosphere [1], the surface temperature vs altitude profile then provides the thermal structure of the deep atmosphere. In the end, we compare the retrieved thermal structure with the VIRA and VeGa-2 temperature profiles. Data Processing: The near-IR observations from the VIRTIS instrument onboard the Venus Express and the IR1 imager onboard the Akatsuki orbiter are used in our study. The VIRTIS dataset has been already processed by [2] and contains the observations of the southern hemisphere having an altitude range below 4 km. The equatorial and northern highlands on Venus were observed by the IR1 imager. However, the IR1 observations are heavily contaminated by the bright straylight coming from the dayside of Venus. Also, the calibration had an uncertainty of±67%. To make use of the IR1data, we develop a correction procedure that includes (1) starylight correction, (2) limb darkening correction, and (3) cross-calibration using the VIRTIS data. Radiative Transfer: To retrieve the surface temperatures from the near-IR observations, we develop an atmospheric radiative transfer model based on the radiative transfer code from [3]. The atmosphere is constructed by using VIRA profiles. We use the cloud model from [4] and Mie scattering is treated by using the code from [5]. We model the absorption using the line-by-line code from [6] and considering eight major absorbing species. Appropriate spectral line dataset and lineshapes are used. To simulate the effect of topography on Venus, we generate the results in the form of a look-up table in which we vary the starting altitude of the atmosphere from -3 to 13 km altitude with respect to a 6051 km planetary radius. We validate our model based on the results generated by the model described in [7]. Results and Conclusion: The coverage of the VIRTIS and IR1 datasets can be observed from the maps of retrieved surface temperatures shown in Figure 1 and Figure 2. Figure 3 shows the trendlines of mean values of the deviation of surface temperature with respect to VIRA temperature profile against the altitude for both the dataset. The dotted line shows the deviation of the VeGa-2 profile. We find that the VIRTIS and IR1 temperature trendlines show a lapse rate lower than VIRA from 0 to 1.5 km altitude, as previously indicated by [8]. Above this altitude VIRTIS trendline follows the VIRA lapse rate, however, the observations are limited up to an altitude of 3.5 km. Above 2 km altitude, the IR1 temperatures fall even faster than the VeGa-2 profile and achieve a maximum deviation of∼5 K from the VIRA profile between 4-5 km and 7-8 km altitude range. This indicates that the situation could be even more complex than indicated by the VeGa-2 profile. Above 8 km altitude, the IR1 data is less reliable. The reasons behind the differences in the IR1, and VIRA profiles are not clear. Possible reasons could be surface emissivity variations, a near-surface layer of aerosols, or a composition gradient [9]. Thus, we find that both the VIRTIS and IR1 profile do not completely agree with either VIRA or VeGa-2 profile. However, observations from both VIRTIS and IR1 instruments were not ideal for the surface-emission studies. An optimized instrument could provide better coverage and quality of the data which could significantly help near-surface studies. Based on this, we highlight the need for future near-IR observations with an instrument optimized for the surface observing atmospheric windows of Venus. References: [1] Lecacheux, J., Drossart, P., Laques, P., Deladerriére, F., and Colas, F., Planetary and Space Science 41(7), 543–549 (1993). [2] Mueller, N., Helbert, J., Hashimoto, G. L., Tsang, C. C., Erard, S., Piccioni, G., and Drossart, P., Journal of GeophysicalResearch E: Planets 114(5), 1–21 (2009). [3] Wauben, W. M. F., De Haan, J., and Hovenier, J., Astronomy and Astrophysics -Berlin-282(1), 277–277 (1994). [4] Barstow, J. K., Tsang, C. C., Wilson, C. F., Irwin, P. G., Taylor, F. W., McGouldrick, K., Drossart, P., Piccioni, G., andTellmann, S., Icarus 217(2), 542–560 (2012). [5] De Rooij, W. and Stap, Van Der, C., Astronomy and astrophysics (Berlin. Print) 131(2), 237–248 (1984). [6] Stam, D. M., De Haan, J. F., Hovenier, J. W., and Stammes, P., Journal of Quantitative Spectroscopy and RadiativeTransfer 64(2), 131–149 (2000). [7] Tsang, C. C., Irwin, P. G., Taylor, F. W., and Wilson, C. F., Journal of Quantitative Spectroscopy and Radiative Transfer 109(6), 1118–1135 (2008). [8] Meadows, V. S. and Crisp, D., Journal of Geophysical Research: Planets 101(E2), 4595–4622 (1996). [9] Lebonnois, S. and Schubert, G., Nature Geoscience 10(7), 473–477 (2017).

We present a 3 Degrees of Freedom mission design and analysis for in-situ probing of Uranus' atmosphere consisting of two un-propelled gliders and one orbiting spacecraft in continuous line of sight. We focus on the study of the gliders' navigation and science modules. Because of the lack of a Global Navigation Satellite System around Uranus and the ineffective use of optical sensors due to the planet's large distance to the Sun and high atmospheric opacity, the post-processing relation between the vehicles' estimated state and measured scientific data is investigated to yield accurate state estimations. In-situ probing by the two gliders will make it possible to measure spatially variable atmospheric properties over a flight duration of up to 12 Earth days, as compared to a few hours for a conventional descent probe. Future work will include a 6 Degrees of Freedom simulation of the vehicles' flight, the chosen planet's wind model, a Flush Air Data Sensor as an additional navigation sensor, and a band-pass filter to reduce the estimated variables' noise.

Repetition suppression (RS) reflects a neural attenuation during repeated stimulation. We used fMRI and the subsequent memory paradigm to test the predictive coding hypothesis for RS during visual memory processing by investigating the interaction between RS and differences due to memory in category-selective cortex (FFA, pSTS, PPA, and RSC). Fifty-six participants encoded face and house stimuli twice, followed by an immediate and delayed (48 h) recognition memory assessment. Linear Mixed Model analyses with repetition, subsequent recognition performance, and their interaction as fixed effects revealed that absolute RS during encoding interacts with probability of future remembrance in face-selective cortex. This effect was not observed for relative RS, i.e. when controlled for adapter-response. The findings also reveal an association between adapter response and RS, both for short and long term (48h) intervals, after controlling for the mathematical dependence between both measures. These combined findings are challenging for predictive coding models of visual memory and are more compatible with adapter-related and familiarity accounts., In order to examine underlying mechanisms of repetition suppression, Stam et al conducted an fMRI study in which participants were presented with face and house stimuli followed by an immediate and 48 h-delayed memory task. Their data demonstrated that adapter-related and familiarity account modelling are more likely to be more accurate for visual memory than previous predictive coding models.

Planet-wide stationary gravity waves have been observed with the thermal camera on the Akatsuki spacecraft. These waves have been attributed to the underlying surface topography and have successfully been reproduced using the Institut Pierre Simon Laplace (IPSL) Venus Mesoscale Model (VMM). Here, we use numerical radiative transfer computations of the total and polarized fluxes of the sunlight that is reflected by Venus under the conditions of these gravity waves to show that the waves could also be observed in polarimetric observations. To model the waves, we use the density perturbations computed by the IPSL VMM. We show the computed wave signatures in the polarization for nadir-viewing geometries observed by a spacecraft in orbit around Venus and as they could be observed using an Earth-based telescope. We find that the strength of the signatures of the atmospheric density waves in the degree of polarization of the reflected sunlight depends not only on the density variations themselves, but also on the wavelength and the cloud top altitude. Observations of such wave signatures on the dayside of the planet would give insight into the occurrence of the waves and possibly into the conditions that govern their onset and development. The computed change in degree of polarization due to these atmospheric density waves is about 1000 ppm at a wavelength of 300 nm. This signal is large enough for an accurate polarimeter to detect.

Context. Homochirality is a generic and unique property of life on Earth and is considered a universal and agnostic biosignature. Homochirality induces fractional circular polarization in the incident light that it reflects. Because this circularly polarized light can be sensed remotely, it can be one of the most compelling candidate biosignatures in life detection missions. While there are also other sources of circular polarization, these result in spectrally flat signals with lower magnitude. Additionally, circular polarization can be a valuable tool in Earth remote sensing because the circular polarization signal directly relates to vegetation physiology. Aims. While high-quality circular polarization measurements can be obtained in the laboratory and under semi-static conditions in the field, there has been a significant gap to more realistic remote sensing conditions. Methods. In this study, we present sensitive circular spectropolarimetric measurements of various landscape elements taken from a fast-moving helicopter. Results. We demonstrate that during flight, within mere seconds of measurements, we can differentiate (S/N>5) between grass fields, forests, and abiotic urban areas. Importantly, we show that with only nonzero circular polarization as a discriminant, photosynthetic organisms can even be measured in lakes. Conclusions. Circular spectropolarimetry can be a powerful technique to detect life beyond Earth, and we emphasize the potential of utilizing circular spectropolarimetry as a remote sensing tool to characterize and monitor in detail the vegetation physiology and terrain features of Earth itself., 7 pages, 6 figures

LOUPE, the Lunar Observatory for Unresolved Polarimetry of the Earth, is a small, robust spectro-polarimeter with a mission to observe the Earth as an exoplanet. Detecting Earth-like planets in stellar habitable zones is one of the key challenges of modern exoplanetary science. Characterising such planets and searching for traces of life requires the direct detection of their signals. LOUPE provides unique spectral flux and polarisation data of sunlight reflected by the Earth, the only planet known to harbor life. This data will be used to test numerical codes to predict signals of Earth-like exoplanets, to test algorithms that retrieve planet properties, and to fine-tune the design and observational strategies of future space observatories. From the Moon, LOUPE will continuously see the entire Earth, enabling it to monitor the signal changes due to the planet's daily rotation, weather patterns, and seasons, across all phase angles. Here, we present both the science case and the technology behind LOUPE's instrumental and mission design., 13 pages, 5 figures. Accepted for publication in Royal Society Philosophical Transactions A. Corrected typos in v2

Importance During a time with the potential for novel treatment strategies, early detection of disease manifestations at an individual level in presymptomatic carriers of a hexanucleotide repeat expansion in the C9orf72 gene (preSxC9) is becoming increasingly relevant. Objectives To evaluate changes in glucose metabolism before symptom onset of amyotrophic lateral sclerosis or frontotemporal dementia in preSxC9 using simultaneous fluorine 18–labeled fluorodeoxyglucose ([18F]FDG positron emission tomographic (PET) and magnetic resonance imaging as well as the mutation’s association with clinical and fluid biomarkers. Design, Setting, and Participants A prospective, case-control study enrolled 46 participants from November 30, 2015, until December 11, 2018. The study was conducted at the neuromuscular reference center of the University Hospitals Leuven, Leuven, Belgium. Main Outcomes and Measures Neuroimaging data were spatially normalized and analyzed at the voxel level at a height threshold of P

Retrievals of Venus cloud top altitudes have primarily been performed using measurements of the total flux of sunlight that is reflected by the planet across CO2 absorption bands. Linearly polarize...

Many biologically produced chiral molecules such as amino acids and sugars show a preference for left or right handedness (homochirality). Light reflected by biological materials such as algae and leaves therefore exhibits a small amount of circular polarization that strongly depends on wavelength. Our Life Signature Detection polarimeter (LSDpol) is optimized to measure these signatures of life. LSDpol is a compact spectropolarimeter concept with no moving parts that instantaneously measures linear and circular polarization averaged over the field of view with a sensitivity of better than 1e-4. We expect to launch the instrument into orbit after validating its performance on the ground and from aircraft. LSDpol is based on a spatially varying quarter-wave retarder that is implemented with a patterned liquid-crystal. It is the first optical element to maximize the polarimetric sensitivity. Since this pattern as well as the entrance slit of the spectrograph have to be imaged onto the detector, the slit serves as the aperture, and an internal field stop limits the field of view. The retarder's fast axis angle varies linearly along one spatial dimension. A fixed quarter-wave retarder combined with a polarization grating act as the disperser and the polarizing beam-splitter. Circular and linear polarization are thereby encoded at incompatible modulation frequencies across the spectrum, which minimizes the potential cross-talk from linear into circular polarization., Comment: 10 pages, 10 figures, SPIE Proceedings 11443-167

Context. Circumstellar disks and self-luminous giant exoplanets or companion brown dwarfs can be characterized through direct-imaging polarimetry at near-infrared wavelengths. SPHERE/IRDIS at the Very Large Telescope has the capabilities to perform such measurements, but uncalibrated instrumental polarization effects limit the attainable polarimetric accuracy. Aims. We aim to characterize and correct the instrumental polarization effects of the complete optical system, i.e. the telescope and SPHERE/IRDIS. Methods. We create a detailed Mueller matrix model in the broadband filters Y-, J-, H- and Ks, and calibrate it using measurements with SPHERE's internal light source and observations of two unpolarized stars. We develop a data-reduction method that uses the model to correct for the instrumental polarization effects, and apply it to observations of the circumstellar disk of T Cha. Results. The instrumental polarization is almost exclusively produced by the telescope and SPHERE's first mirror and varies with telescope altitude angle. The crosstalk primarily originates from the image derotator (K-mirror). At some orientations, the derotator causes severe loss of signal (>90% loss in H- and Ks-band) and strongly offsets the angle of linear polarization. With our correction method we reach in all filters a total polarimetric accuracy of, 28 pages, 25 figures

Understanding the total flux and polarization signals of Earth-like planets and their spectral and temporal variability is essential for the future characterization of such exoplanets. We provide computed total (F) and linearly (Q and U) and circularly (V) polarized fluxes, and the degree of polarization P of sunlight that is reflected by a model Earth, to be used for instrument designs, optimizing observational strategies, and/or developing retrieval algorithms. We modeled a realistic Earth-like planet using one year of daily Earth-observation data: cloud parameters (distribution, optical thickness, top pressure, and particle effective radius), and surface parameters (distribution, surface type, and albedo). The Stokes vector of the disk-averaged reflected sunlight was computed for phase angles alpha from 0 to 180 degrees, and for wavelengths lambda from 350 to 865 nm. The total flux F is one order of magnitude higher than the polarized flux Q, and Q is two and four orders of magnitude higher than U and V, respectively. Without clouds, the peak-to-peak daily variations due to the planetary rotation increase with increasing lambda for F, Q, and P, while they decrease for U and V. Clouds modify but do not completely suppress the variations that are due to rotating surface features. With clouds, the variation in F increases with increasing lambda, while in Q, it decreases with increasing lambda, except at the largest phase angles. In earlier work, it was shown that with oceans, Q changes color from blue through white to red. The alpha where the color changes increases with increasing cloud coverage. Here, we show that this unique color change in Q also occurs when the oceans are partly replaced by continents, with or without clouds. The degree of polarization P shows a similar color change. Our computed fluxes and degree of polarization will be made publicly available., Accepted for publication in Astronomy & Astrophysics

An exoplanet's habitability will depend strongly on the presence of liquid water. Flux and/or polarization measurements of starlight that is reflected by exoplanets could help to identify exo-oceans. We investigate which broadband spectral features in flux and polarization phase functions of reflected starlight uniquely identify exo-oceans. We compute total fluxes F and polarized fluxes Q of starlight reflected by cloud-free and (partly) cloudy exoplanets, for wavelengths from 350 to 865 nm. The ocean surface has waves composed of Fresnel reflecting wave facets and whitecaps, and scattering within the water body is included. Total flux F, polarized flux Q, and degree of polarization P of ocean planets change color from blue, through white, to red at phase angles alpha ranging from 134-108 deg for F, and from 123-157 deg for Q, with cloud coverage fraction fc increasing from 0.0 to 1.0 for F, and to 0.98 for Q. The color change in P only occurs for fc ranging from 0.03-0.98, with the color crossing angle alpha ranging from 88-161 deg. The total flux F of a cloudy, zero surface albedo planet can also change color, and for fc=0.0, an ocean planet's F will not change color for surface pressures ps > 8 bars. Polarized flux Q of a zero surface albedo planet does not change color for any fc. The color change of P of starlight reflected by an exoplanet, from blue, through white, to red with increasing alpha above 88 deg, appears to identify a (partly) cloudy exo-ocean. The color change of polarized flux Q with increasing alpha above 123 deg appears to uniquely identify an exo-ocean, independent of surface pressure or cloud fraction. At the color changing phase angle, the angular distance between a star and its planet is much larger than at the phase angle where the glint appears in reflected light. The color change in polarization thus offers better prospects for detecting exo-oceans., Accepted for publication in Astron. Astrophys; multicolumn version

Theory of mind (ToM) refers to the ability to attribute mental states to others. Behavioral variant frontotemporal dementia (bvFTD) is a neurodegenerative disorder characterized by profound deficits in social cognition, including ToM. We investigate whether bvFTD affects intention attribution tendency while viewing abstract animations and whether this might represent a primary deficit. A sample of 15 bvFTD patients and 19 matched controls were assessed on cognition and performed an implicit ToM task. They were instructed to describe what they observed in movement patterns displayed by geometrical shapes (triangles). These movement patterns either represented animacy, goal-directed actions or manipulation of mental state (ToM). The responses were scored for both accuracy and intentionality attribution. Using Voxel-Based Morphometry, we investigated the structural neuroanatomy associated with intention attribution tendency. The behavioral results revealed deficits in the bvFTD group on intentionality attribution that were specific for the ToM condition after controlling for global cognitive functioning (MMSE-score), visual attention (TMT B-score), fluid intelligence (RCPMT-score) and confrontation naming (BNT-score). In the bvFTD sample, the intention attribution tendency on the ToM-condition was associated with grey matter volume of a cluster in the cerebellum, spanning the right Crus I, Crus II, VIIIb, IX, left VIIb, IX and vermal IX and X. The results reveal a specific, primary, implicit domain-general ToM deficit in bvFTD that cannot be explained by cognitive dysfunction. Furthermore, the findings point to a contribution of the cerebellum in the social-cognitive phenotype of bvFTD., Highlights • We show a reduction in intention attribution tendency to abstract shapes in bvFTD. • Cognitive or subordinate processes did not explain the reduction. • The reduction was associated with structural integrity of a cerebellar cluster.

Context: Detecting moons around exoplanets is a major goal of current and future observatories. Moons are suspected to influence rocky exoplanet habitability, and gaseous exoplanets in stellar habitable zones could harbour abundant and diverse moons to target in the search for extraterrestrial habitats. Exomoons will contribute to exoplanetary signals but are virtually undetectable with current methods. Aims: We identify and analyse traces of exomoons in the temporal variation of total and polarised fluxes of starlight reflected by an Earth-like exoplanet and its spatially unresolved moon across all phase angles, with both orbits viewed in an edge-on geometry. Methods: We compute the total and linearly polarised fluxes, and the degree of linear polarization P of starlight that is reflected by the exoplanet with its moon along their orbits, accounting for the temporal variation of the visibility of the planetary and lunar disks, and including effects of mutual transits and mutual eclipses. Our computations pertain to a wavelength of 450 nm. Results: Total flux F shows regular dips due to planetary and lunar transits and eclipses. Polarization P shows regular peaks due to planetary transits and lunar eclipses, and P can increase and/or slightly decrease during lunar transits and planetary eclipses. Changes in F and P will depend on the radii of the planet and moon, on their reflective properties, and their orbits, and are about one magnitude smaller than the smooth background signals. The typical duration of a transit or an eclipse is a few hours. Conclusions: Traces of an exomoon due to planetary and lunar transits and eclipses show up in F and P of sunlight reflected by planet-moon systems and could be searched for in exoplanet flux and/or polarisation phase functions., Accepted for publication in Astronomy & Astrophysics

PyMieDAP (the Python Mie Doubling-Adding Programme) is a Python--based tool for computing the total, linearly, and circularly polarized fluxes of incident unpolarized sun- or starlight that is reflected by, respectively, Solar System planets or moons, or exoplanets at a range of wavelengths. The radiative transfer computations are based on an adding--doubling Fortran algorithm and fully include polarization for all orders of scattering. The model (exo)planets are described by a model atmosphere composed of a stack of homogeneous layers containing gas and/or aerosol and/or cloud particles bounded below by an isotropically, depolarizing surface (that is optionally black). The reflected light can be computed spatially--resolved and/or disk--integrated. Spatially--resolved signals are mostly representative for observations of Solar System planets (or moons), while disk--integrated signals are mostly representative for exoplanet observations. PyMieDAP is modular and flexible, and allows users to adapt and optimize the code according to their needs. PyMieDAP keeps options open for connections with external programs and for future additions and extensions. In this paper, we describe the radiative transfer algorithm that PyMieDAP is based on and the code's principal functionalities. And we provide benchmark results of PyMieDAP that can be used for testing its installation and for comparison with other codes. PyMieDAP is available online under the GNU GPL license at http://gitlab.com/loic.cg.rossi/pymiedap, 15 pages, 7 figures, 4 tables. Accepted for publication in Astronomy and Astrophysics

The circular polarization of light that planets reflect is often neglected because it is very small compared to the linear polarization. It could, however, provide information on a planet's atmosphere and surface, and on the presence of life, because homochiral molecules that are the building blocks of life on Earth are known to reflect circularly polarized light. We compute $P_c$, the degree of circular polarization, for light that is reflected by rocky (exo)planets with liquid water or sulfuric acid solution clouds, both spatially resolved across the planetary disk and, for planets with patchy clouds, integrated across the planetary disk, for various planetary phase angles $\alpha$. The optical thickness and vertical distribution of the atmospheric gas and clouds, the size parameter and refractive index of the cloud particles, and $\alpha$ all influence $P_c$. Spatially resolved, $P_c$ varies between $\pm 0.20\%$ (the sign indicates the polarization direction). Only for small gas optical thicknesses above the clouds do significant sign changes (related to cloud particle properties) across the planets' hemispheres occur. For patchy clouds, the disk--integrated $P_c$ is typically smaller than $\pm 0.025\%$, with maximums for $\alpha$ between $40^\circ$ and $70^\circ$, and $120^\circ$ to $140^\circ$. As expected, the disk--integrated $P_c$ is virtually zero at $\alpha=0^\circ$ and 180$^\circ$. The disk--integrated $P_c$ is also very small at $\alpha \approx 100^\circ$. Measuring circular polarization signals appears to be challenging with current technology. The small atmospheric circular polarization signal could, however, allow the detection of circular polarization due to homochiral molecules. Confirmation of the detectability of such signals requires better knowledge of the strength of circular polarization signals of biological sources., Comment: 15 pages, 11 figures, Accepted for publication in Astronomy and Astrophysics

Aerosols affect Earth’s energy level by scattering and absorbing radiation and by changing the properties of clouds. Such effects influence the precipitation patterns and lead to modifications of the global circulation systems that constitute Earth’s climate. The aerosol effects on our climate cannot be at full scale estimated due to the insufficient knowledge of their properties at a global scale. Achieving global measurement coverage requires an instrument with a large instantaneous field of view that can perform polarization measurements with high accuracy, typically better than 0.1%. Developing such an instrument can be considered as the most important challenge in polarimetric aerosol remote sensing. Using a novel technique to measure polarization, we have designed an instrument for a low-Earth orbit, e.g. International Space Station, that can simultaneously characterize the intensity and state of linear polarization of scattered sunlight, from 400 to 800 nm and 1200 to 1600 nm, for 30 viewing directions, each with a 30° viewing angle. In this article we present the instrument’s optical design concept.

Introduction Behavioral variant frontotemporal dementia (bvFTD) is associated with abnormal emotion recognition and moral processing. Methods We assessed emotion detection, discrimination, matching, selection, and categorization as well as judgments of nonmoral, moral impersonal, moral personal low- and high-conflict scenarios. Results bvFTD patients gave more utilitarian responses on low-conflict personal moral dilemmas. There was a significant correlation between a facial emotion processing measure derived through principal component analysis and utilitarian responses on low-conflict personal scenarios in the bvFTD group (controlling for MMSE-score and syntactic abilities). Voxel-based morphometric multiple regression analysis in the bvFTD group revealed a significant association between the proportion of utilitarian responses on personal low-conflict dilemmas and gray matter volume in ventromedial prefrontal areas (pheight < .0001). In addition, there was a correlation between utilitarian responses on low-conflict personal scenarios in the bvFTD group and resting-state fractional Amplitude of Low Frequency Fluctuations (fALFF) in the anterior insula (pheight < .005). Conclusions The results underscore the importance of emotions in moral cognition and suggest a common basis for deficits in both abilities, possibly related to reduced experience of emotional sensations. At the neural level abnormal moral cognition in bvFTD is related to structural integrity of the medial prefrontal cortex and functional characteristics of the anterior insula. The present findings provide a common basis for emotion recognition and moral reasoning and link them with areas in the default mode and salience network., Brain and Behavior, 7 (12), ISSN:2162-3279

Earth-like, potentially habitable exoplanets are prime targets in the search for extraterrestrial life. Information about their atmosphere and surface can be derived by analyzing light of the parent star reflected by the planet. We investigate the influence of the surface albedo $A_{\rm s}$, the optical thickness $b_{\rm cloud}$ and altitude of water clouds, and the mixing ratio $\eta$ of biosignature O$_2$ on the strength of the O$_2$ A-band (around 760 nm) in flux and polarization spectra of starlight reflected by Earth-like exoplanets. Our computations for horizontally homogeneous planets show that small mixing ratios ($\eta$ < 0.4) will yield moderately deep bands in flux and moderate to small band strengths in polarization, and that clouds will usually decrease the band depth in flux and the band strength in polarization. However, cloud influence will be strongly dependent on their properties such as optical thickness, top altitude, particle phase, coverage fraction, horizontal distribution. Depending on the surface albedo, and cloud properties, different O$_2$ mixing ratios $\eta$ can give similar absorption band depths in flux and band strengths in polarization, in particular if the clouds have moderate to high optical thicknesses. Measuring both the flux and the polarization is essential to reduce the degeneracies, although it will not solve them, in particular not for horizontally inhomogeneous planets. Observations at a wide range of phase angles and with a high temporal resolution could help to derive cloud properties and, once those are known, the mixing ratio of O$_2$ or any other absorbing gas., Comment: 21 pages, 20 figures, accepted for publication in ApJ

Context. Polarimetry is a powerful remote sensing tool to characterise solar system planets and, potentially, to detect and characterise exoplanets. The linear polarisation of a planet as a function of wavelength and phase angle is sensitive to the cloud and haze particle properties in planetary atmospheres, as well as to their altitudes and optical thicknesses. Aims: We present for the first time polarimetric signals of Jupiter mapped over the entire disk, showing features such as contrasts between the belts and zones, the polar regions, and the Great Red Spot. We investigate the use of these maps for atmospheric characterisation and discuss the potential application of polarimetry to the study of the atmospheres of exoplanets. Methods: We have obtained polarimetric images of Jupiter, in the B, V, and R filters, over a phase angle range of α = 4°-10.5°. In addition, we have obtained two spectropolarimetric datasets, over the wavelength range 500-850 nm. An atmospheric model was sought for all of the datasets, which was consistent with the observed behaviour over the wavelength and phase angle range. Results: The polarimetric maps show clear latitudinal structure, with increasing polarisation towards the polar regions, in all filters. The spectropolarimetric datasets show a decrease in polarisation as a function of wavelength along with changes in the polarisation in methane absorption bands. A model fit was achieved by varying the cloud height and haze optical thickness; this can roughly produce the variation across latitude for the V and R filters, but not for the B filter data. The same model particles are also able to produce a close fit to the spectropolarimetric data. The atmosphere of Jupiter is known to be complex in structure, and data taken at intermediate phase angles (unreachable for Earth-based telescopes) seems essential for a complete characterisation of the atmospheric constituents. Because exoplanets orbit other stars, they are observable at intermediate phase angles and thus promise to be better targets for Earth-based polarimetry. Based on data obtained with ToPol at the one-metre "Omicron" (West) telescope of the C2PU (Centre Pédagogique Planète et Univers) facility (Calern plateau, Observatoire de la Côte d'Azur, France), and FoReRo2, at the two-metre RCC telescope of the Rozhen National Astronomical Observatory, Bulgaria.

Young giant exoplanets emit infrared radiation that can be linearly polarized up to several percent. This linear polarization can trace: 1) the presence of atmospheric cloud and haze layers, 2) spatial structure, e.g. cloud bands and rotational flattening, 3) the spin axis orientation and 4) particle sizes and cloud top pressure. We introduce a novel high-contrast imaging scheme that combines angular differential imaging (ADI) and accurate near-infrared polarimetry to characterize self-luminous giant exoplanets. We implemented this technique at VLT/SPHERE-IRDIS and developed the corresponding observing strategies, the polarization calibration and the data-reduction approaches. By combining ADI and polarimetry we can characterize planets that can be directly imaged with a very high signal-to-noise ratio. We use the IRDIS pupil-tracking mode and combine ADI and principal component analysis to reduce speckle noise. We take advantage of IRDIS' dual-beam polarimetric mode to eliminate differential effects that severely limit the polarimetric sensitivity (flat-fielding errors, differential aberrations and seeing), and thus further suppress speckle noise. To correct for instrumental polarization effects, we apply a detailed Mueller matrix model that describes the telescope and instrument and that has an absolute polarimetric accuracy $\leq0.1\%$. Using this technique we have observed the planets of HR 8799 and the (sub-stellar) companion PZ Tel B. Unfortunately, we do not detect a polarization signal in a first analysis. We estimate preliminary $1\sigma$ upper limits on the degree of linear polarization of $\sim1\%$ and $\sim0.1\%$ for the planets of HR 8799 and PZ Tel B, respectively. The achieved sub-percent sensitivity and accuracy show that our technique has great promise for characterizing exoplanets through direct-imaging polarimetry., Comment: 16 pages, 8 figures, 2 tables; v2: added acknowledgement and corrected two typos

To assess the impact of atmospheric aerosols on health, climate, and air traffic, aerosol properties must be measured with fine spatial and temporal sampling. This can be achieved by actively involving citizens and the technology they own to form an atmospheric measurement network. We establish this new measurement strategy by developing and deploying iSPEX, a low-cost, mass-producible optical add-on for smartphones with a corresponding app. The aerosol optical thickness (AOT) maps derived from iSPEX spectropolarimetric measurements of the daytime cloud-free sky by thousands of citizen scientists throughout the Netherlands are in good agreement with the spatial AOT structure derived from satellite imagery and temporal AOT variations derived from ground-based precision photometry. These maps show structures at scales of kilometers that are typical for urban air pollution, indicating the potential of iSPEX to provide information about aerosol properties at locations and at times that are not covered by current monitoring efforts.

We present a comprehensive set of spectropolarimetric observations of Earthshine as obtained by FORS2 at the VLT for phase angles from 50degree to 135degree (Sun-Earth-Moon angle), covering a spectral range from 430nm to 920nm. The degree of polarization in BVRI passbands, the differential polarization vegetation index, and the equivalent width of the O2A polarization band around 760nm are determined with absolute errors around 0.1 percent in the degree of polarization. Earthshine polarization spectra are corrected for the effect of depolarization introduced by backscattering on the lunar surface, introducing systematic errors of the order of 1 percent in the degree of polarization. Distinct viewing sceneries such as observing the Atlantic or Pacific side in Earthshine yield statistically different phase curves. The equivalent width defined for the O2A band polarization is found to vary from -5nm to +2nm. A differential polarized vegetation index is introduced and reveals a larger vegetation signal for those viewing sceneries that contain larger fractions of vegetated surface areas. We corroborate the observed correlations with theoretical models from the literature, and conclude that the Vegetation Red Edge(VRE) is a robust and sensitive signature in polarization spectra of planet Earth. The overall behaviour of polarization of planet Earth in the continuum and in the O2A band can be explained by existing models. Biosignatures such as the O2A band and the VRE are detectable in Earthshine polarization with a high degree of significance and sensitivity. An in-depth understanding of Earthshines temporal and spectral variability requires improved models of Earths biosphere, as a prerequisite to interpret possible detections of polarised biosignatures in earthlike exoplanets in the future., 19 pages, 14 figures, 3 tables

EnVision is an ambitious but low-risk response to ESA's call for a medium-size mission opportunity for a launch in 2022. Venus is the planet most similar to Earth in mass, bulk properties and orbital distance, but has evolved to become extremely hostile to life. EnVision's 5-year mission objectives are to determine the nature of and rate of change caused by geological and atmospheric processes, to distinguish between competing theories about its evolution and to help predict the habitability of extrasolar planets. Three instrument suites will address specific surface, atmosphere and ionosphere science goals. The Surface Science Suite consists of a 2.2 m 2 radar antenna with Interferometer, Radiometer and Altimeter operating modes, supported by a complementary IR surface emissivity mapper and an advanced accelerometer for orbit control and gravity mapping. This suite will determine topographic changes caused by volcanic, tectonic and atmospheric processes at rates as low as 1 mm a -1. The Atmosphere Science Suite consists of a Doppler LIDAR for cloud top altitude, wind speed and mesospheric structure mapping, complemented by IR and UV spectrometers and a spectrophotopolarimeter, all designed to map the dynamic features and compositions of the clouds and middle atmosphere to identify the effects of volcanic and solar processes. The Ionosphere Science Suite uses a double Langmiur probe and vector magnetometer to understand the behaviour and long-term evolution of the ionosphere and induced magnetosphere. The suite also includes an interplanetary particle analyser to determine the delivery rate of water and other components to the atmosphere. © 2011 Springer Science+Business Media B.V.

The Hera Saturn entry probe mission is proposed as an M--class mission led by ESA with a contribution from NASA. It consists of one atmospheric probe to be sent into the atmosphere of Saturn, and a Carrier-Relay spacecraft. In this concept, the Hera probe is composed of ESA and NASA elements, and the Carrier-Relay Spacecraft is delivered by ESA. The probe is powered by batteries, and the Carrier-Relay Spacecraft is powered by solar panels and batteries. We anticipate two major subsystems to be supplied by the United States, either by direct procurement by ESA or by contribution from NASA: the solar electric power system (including solar arrays and the power management and distribution system), and the probe entry system (including the thermal protection shield and aeroshell). Hera is designed to perform in situ measurements of the chemical and isotopic compositions as well as the dynamics of Saturn's atmosphere using a single probe, with the goal of improving our understanding of the origin, formation, and evolution of Saturn, the giant planets and their satellite systems, with extrapolation to extrasolar planets. Hera's aim is to probe well into the cloud-forming region of the troposphere, below the region accessible to remote sensing, to the locations where certain cosmogenically abundant species are expected to be well mixed. By leading to an improved understanding of the processes by which giant planets formed, including the composition and properties of the local solar nebula at the time and location of giant planet formation, Hera will extend the legacy of the Galileo and Cassini missions by further addressing the creation, formation, and chemical, dynamical, and thermal evolution of the giant planets, the entire solar system including Earth and the other terrestrial planets, and formation of other planetary systems., Comment: Accepted for publication in Planetary and Space Science

We provide a proof of the technical feasibility of LOUPE, the first integral-field snapshot spectropolarimeter, designed to monitor the reflected flux and polarization spectrum of Earth. These are to be used as benchmark data for the retrieval of biomarkers and atmospheric and surface characteristics from future direct observations of exoplanets. We perform a design tradeoff for an implementation in which LOUPE performs snapshot integral-field spectropolarimetry at visible wavelengths. We used off-the-shelf optics to construct a polarization modulator, in which polarization information is encoded into the spectrum as a wavelength-dependent modulation, while spatial resolution is maintained using a micro-lens array. The performance of this design concept is validated in a laboratory setup. Our proof-of-concept is capable of measuring a grid of 50 x 50 polarization spectra between 610 and 780 nm of a mock target planet - proving the merit of this design. The measurements are affected by systematic noise on the percent level, and we discuss how to mitigate this in future iterations. We conclude that LOUPE can be small and robust while meeting the science goals of this particular space application, and note the many potential applications that may benefit from our concept for doing snapshot integral-field spectropolarimetry.

SPICES (Spectro-Polarimetric Imaging and Characterization of Exoplanetary Systems) is a five-year M-class mission proposed to ESA Cosmic Vision. Its purpose is to image and characterize long-period extrasolar planets and circumstellar disks in the visible (450 - 900 nm) at a spectral resolution of about 40 using both spectroscopy and polarimetry. By 2020/22, present and near-term instruments will have found several tens of planets that SPICES will be able to observe and study in detail. Equipped with a 1.5 m telescope, SPICES can preferentially access exoplanets located at several AUs (0.5-10 AU) from nearby stars ($

[Abridged] The transmission of light through a planetary atmosphere can be studied as a function of altitude and wavelength using stellar or solar occultations, giving often unique constraints on the atmospheric composition. For exoplanets, a transit yields a limb-integrated, wavelength-dependent transmission spectrum of an atmosphere. When scattering haze and/or cloud particles are present in the planetary atmosphere, the amount of transmitted flux not only depends on the total optical thickness of the slant light path that is probed, but also on the amount of forward-scattering by the scattering particles. Here, we present results of calculations with a three-dimensional Monte Carlo code that simulates the transmitted flux during occultations or transits. For isotropically scattering particles, like gas molecules, the transmitted flux appears to be well-described by the total atmospheric optical thickness. Strongly forward-scattering particles, however, such as commonly found in atmospheres of Solar System planets, can increase the transmitted flux significantly. For exoplanets, such added flux can decrease the apparent radius of the planet by several scale heights, which is comparable to predicted and measured features in exoplanet transit spectra. We performed detailed calculations for Titan's atmosphere between 2.0 and 2.8 micron and show that haze and gas abundances will be underestimated by about 8% if forward-scattering is ignored in the retrievals. At shorter wavelengths, errors in the gas and haze abundances and in the spectral slope of the haze particles can be several tens of percent, also for other Solar System planetary atmospheres. We also find that the contribution of forward-scattering can be fairly well described by modelling the atmosphere as a plane-parallel slab., Icarus, accepted for publication

We present a Monte Carlo model of the uranian rings, and compare this model to images of the system obtained with the Keck adaptive optics system in July 2004, at a wavelength of 2.2 μm (from de Pater et al. (de Pater, I., Gibbard, S.G., Hammel, H.B. [2006a]. Icarus 180, 186–200)). We confirm the presence of the ζ ring, but show that this ring must extend inwards much further than previously thought, although with an optical depth much lower than that in the main ζ ring component. We further confirm dust rings between rings α–4 and β–α, as well as near the λ ring. In addition, we show that a broad sheet of faint material (τ0 ∼ 10−3) must be present through most of the ring region, from the α ring through the λ ring.

We discuss how to read a planet's spectrum to assess its habitability and search for the signatures of a biosphere.\ud After a decade rich in giant exoplanet detections, observation techniques have advanced to a level where we now have the capability to find planets of less than 10 Earth masses (MEarth) (so-called "super Earths"), which may be habitable. How can we characterize those planets and assess whether they are habitable? This new field of exoplanet search has shown an extraordinary capacity to combine research in astrophysics, chemistry, biology, and geophysics into a new and exciting interdisciplinary approach to understanding our place in the\ud Universe. The results of a first-generation mission will most likely generate an amazing scope of diverse planets\ud that will set planet formation, evolution, and our planet into an overall context.

International audience; To estimate the occurrence of terrestrial exoplanets and maximize the chance of finding them, it is crucial to understand the formation of planetary systems in general and that of terrestrial planets in particular. We show that a reliable formation theory should not only explain the formation of the Solar System, with small terrestrial planets within a few AU and gas giants farther out, but also the newly discovered exoplanetary systems with close-in giant planets. Regarding the presently known exoplanets, we stress that our current knowledge is strongly biased by the sensitivity limits of current detection techniques (mainly the radial velocity method). With time and improved detection methods, the diversity of planets and orbits in exoplanetary systems will definitely increase and help to constrain the formation theory further. In this work, we review the latest state of planetary formation in relation to the origin and evolution of habitable terrestrial planets.

The European Space Agency and other space agencies such as NASA recognize that the question with regard to\ud life beyond Earth in general, and the associated issue of the existence and study of exoplanets in particular, is of\ud paramount importance for the 21st century. The new Cosmic Vision science plan, Cosmic Vision 2015–2025, which is built around four major themes, has as its first theme: \ud "What are the conditions for planet formation and the emergence of life?" This main theme is addressed through further questions:\ud \ud (1) How do gas and dust give rise to stars and planets?\ud \ud (2) How will the search for and study of exoplanets eventually lead to the detection of life outside Earth (biomarkers*)?\ud \ud (3) How did life in the Solar System arise and evolve?\ud \ud Although ESA has busied itself with these issues since the beginning of the Darwin study in 1996, it has\ud become abundantly clear that, as these topics have evolved, only a very large effort, addressed from the ground\ud and from space with the utilization of different instruments and space missions, can provide the empirical results required for a complete understanding. The good news is that the problems can be addressed and solved within\ud a not-too-distant future. In this short essay, we present the present status of a roadmap related to projects that are related to the key long-term goal of understanding and characterizing exoplanets, in particular Earthlike\ud planets.

Context. Clouds have already been detected in exoplanetary atmospheres. They play crucial roles in a planet's atmosphere and climate and can also create ambiguities in the determination of atmospheric parameters such as trace gas mixing ratios. Knowledge of cloud properties is required when assessing the habitability of a planet. Aims. We aim to show that various types of cloud cover such as polar cusps, subsolar clouds, and patchy clouds on Earth-like exoplanets can be distinguished from each other using the polarization and flux of light that is reflected by the planet. Methods. We have computed the flux and polarization of reflected starlight for different types of (liquid water) cloud covers on Earth-like model planets using the adding-doubling method, that fully includes multiple scattering and polarization. Variations in cloud-top altitudes and planet-wide cloud cover percentages were taken into account. Results. We find that the different types of cloud cover (polar cusps, subsolar clouds, and patchy clouds) can be distinguished from each other and that the percentage of cloud cover can be estimated within 10%. Conclusions. Using our proposed observational strategy, one should be able to determine basic orbital parameters of a planet such as orbital inclination and estimate cloud coverage with reduced ambiguities from the planet's polarization signals along its orbit., Comment: 14 pages, 18 figures. Accepted for publication in Astronomy and Astrophysics

著者人数：156名, Accepted: 2008-05-27, 資料番号: SA1000998000

We present measurements of ratios of elements of the scattering matrix of Martian analogue palagonite particles for scattering angles ranging from 3 to 174 degrees and a wavelength of 632.8 nm. To facilitate the use of these measurements in radiative transfer calculations we have devised a method that enables us to obtain, from these measurements, a normalized synthetic scattering matrix covering the complete scattering angle range from 0 to 180 degrees. Our method is based on employing the coefficients of the expansions of scattering matrix elements into generalized spherical functions. The synthetic scattering matrix elements and/or the expansion coefficients obtained in this way, can be used to include multiple scattering by these irregularly shaped particles in (polarized) radiative transfer calculations, such as calculations of sunlight that is scattered in the dusty Martian atmosphere., Comment: 34 pages 7 figures 1 table

The atmospheres of (exo) planets and moons, as well as reflection nebulae, contain in general independently scattering particles in random orientation and are often supposed to be plane-parallel. Relations are presented for the (bidirectional) reflection function and several related functions of such a medium in case the directions of incidence and reflection both tend to horizontal directions. The results are quite general. The medium may be semi-infinite or finite, with or without a reflecting surface underneath, and vertically homogeneous or inhomogeneous. Some approximative formulae for the reflection function of a plane-parallel medium with independently scattering particles in random orientation, including Lambert's law, may be very inaccurate if the directions of incidence and reflection are both nearly horizontal.

We show that the intensity vector of light reflected by a plane-parallel atmosphere is discontinuous if the directions of incidence and reflection are both horizontal. An exact expression describing the discontinuity is presented. This expression shows that the discontinuity is only due to first order scattering at the top of the atmosphere and occurs for all four Stokes parameters, as well as for the polarized intensity. No discontinuity exists, however, for the degrees of linear and circular polarization. The exact expression may be applied, for example, to clarify the results of photo-polarimetric observations of regions near the intensity poles of a planet. Another application concerns the possibility of obtaining values for the albedo of single scattering and scattering matrix elements as functions of the scattering angle at the top of a cloud deck or aerosol layer from observations for nearly horizontal directions of incidence and reflection.