33 research outputs found
Planetary Atmospheres: Astrobiologically Relevant Icy Worlds and Earth as a Proxy Exoplanet
No full text"How did we get here?" is a long-standing question in planetary science. Characterizing the pre-biotic atmospheric environment in which life may emerge is critical and increasingly urgent. Given the fact that the Earth provides the only ground truth of habitable worlds, most of the characterizations are based on the current Earth. However, life did not emerge on the modern Earth. It instead took place in a prebiotic environment, which includes a nitrogen-dominated, methane-abundant and oxygen-negligible reducing atmosphere. Therefore, this type of planetary atmospheres has great significance in the context of astrobiology and the search for life. Despite that real time observations can not be obtained for Early-Earth, spacecraft observations of the atmospheres of two icy worlds in the solar system, Titan and Pluto, can provide such valuable constraints. The theme of Chapter 2 and 3 of this thesis focus on this topic of investigating the atmospheres of Titan and Pluto using spectroscopic analysis. Chapter 4 studies the search for life also across the spectrum from a prospective the other way. It characterizes the Earth, the only known inhabited planet, as an exoplanet proxy, to derive observational benchmarks for habitability assessment.
Chapter 2 studies Titan. It retrieves the hydrocarbon and nitrile species in Titan’s upper atmosphere using stellar occultation observations obtained by Cassini UltraViolet Imaging Spectrograph (UVIS) during its Titan flybys. An innovative method is introduced to consider the pointing issue of the instrument, which prevents most of the previous spectral analyses. Combing an instrument simulator for handling the pointing motion and the Markov-Chain Monte Carlo (MCMC) method for parameter searching, species abundances in Titan’s atmosphere are successfully retrieved during occultations with large pointing motions. The method also obtains the altitude range where the abundance of each species could be constrained.
Chapter 3 studies Pluto. It investigates the morphology and microphysical processes of Pluto’s haze particles in the lower 50km of its atmosphere using observations obtained by multiple instruments onboard the New Horizons spacecraft during its Pluto flyby in 2015. It suggests that Pluto’s haze particles have a bimodal distribution: a large-size population of ~1μm fractal aggregates, which consists of ~20nm monomers, and a small-size one of ~80nm. This result successfully addresses the disagreement among the instruments, and provides important constraints on transport and dimensional transition of haze particles in Pluto’s atmosphere.
Chapter 4 studies exoplanets. It evaluates the observational baseline for Earth-like exoplanets using the Earth as a proxy. Observations of the Earth’s images obtained by the Deep Space Climate ObserVatoRy (DSCOVR) are integrated to one single point to generate light curves of the "proxy" planet. Using the singular value decomposition (SVD) method, we found that the surface information of the "proxy" planet is in the second principal component (PC) of its light curves, while the first PC mainly consists of that of clouds. Using the strong linear correlation between the time series of the second PC and the corresponding land fraction, we constructed the first two-dimensional surface map of the Earth seen from a hypothetical distant observer, an observer who treats the Earth as an exoplanet.</p
Respite care hotel in Amsterdam
No full textThe topic of the studio, “city hotel”, concerns sustainability and hospitality at the same time, aiming to provide a temporary living space within the doughnut model. Since the location of the project is the historical center of Amsterdam which has been largely affected by tourism and become less livable in recent years, the project aims to design for the community and especially for vulnerable groups including the elderly and children.The project is a respite care hotel locating next to Nieuwmarkt square. It weaves into the context by collaborating with its surroundings to improve the well-being of the whole community. On the one hand, the project provides short-term stays for people in need of care to release the stress of informal caregivers. On the other hand, the project benefits the community by reclaiming the existing infrastructural space as a playful urban space.Architecture, Urbanism and Building Sciences | Interiors Buildings Citie
Global Mapping of an Exo-Earth Using Sparse Modeling
No full textWe develop a new retrieval scheme for obtaining two-dimensional surface maps of exoplanets from scattered light curves. In our scheme, the combination of the L1-norm and total squared variation, which is one of the techniques used in sparse modeling, is adopted to find the optimal map. We apply the new method to simulated scattered light curves of the Earth, and find that the new method provides a better spatial resolution of the reconstructed map than those using Tikhonov regularization. We also apply the new method to observed scattered light curves of the Earth obtained during the two-year Deep Space Climate Observatory/Earth Polychromatic Imaging Camera observations presented by Fan et al. The method with Tikhonov regularization enables us to resolve North America, Africa, Eurasia, and Antarctica. In addition to that, the sparse modeling identifies South America and Australia, although it fails to find Antarctica, maybe due to low observational weights on the poles. Besides, the proposed method is capable of retrieving maps from noise-injected light curves of a hypothetical Earthlike exoplanet at 5 pc with a noise level expected from coronagraphic images from a 8 m space telescope. We find that the sparse modeling resolves Australia, Afro-Eurasia, North America, and South America using 2 yr observation with a time interval of one month. Our study shows that the combination of sparse modeling and multiepoch observation with 1 day or 5 days per month can be used to identify main features of an Earth analog in future direct-imaging missions such as the Large UV/Optical/IR Surveyor
Simulations of the Solar System's Early Dynamical Evolution with a Self-gravitating Planetesimal Disk
No full textSimulations of the Solar System's Early Dynamical Evolution with a Self-gravitating Planetesimal Disk
No full textOver the course of the last decade, the Nice model has dramatically changed our view of the solar system's formation and early evolution. Within the context of this model, a transient period of planet–planet scattering is triggered by gravitational interactions between the giant planets and a massive primordial planetesimal disk, leading to a successful reproduction of the solar system's present-day architecture. In typical realizations of the Nice model, self-gravity of the planetesimal disk is routinely neglected, as it poses a computational bottleneck to the calculations. Recent analyses have shown, however, that a self-gravitating disk can exhibit behavior that is dynamically distinct, and this disparity may have significant implications for the solar system's evolutionary path. In this work, we explore this discrepancy utilizing a large suite of Nice model simulations with and without a self-gravitating planetesimal disk, taking advantage of the inherently parallel nature of graphic processing units. Our simulations demonstrate that self-consistent modeling of particle interactions does not lead to significantly different final planetary orbits from those obtained within conventional simulations. Moreover, self-gravitating calculations show similar planetesimal evolution to non-self-gravitating numerical experiments after dynamical instability is triggered, suggesting that the orbital clustering observed in the distant Kuiper Belt is unlikely to have a self-gravitational origin
Surface Mapping of Earth-like Exoplanets using Single Point Light Curves
No full textSpatially resolving exoplanet features from single-point observations is essential for evaluating the potential habitability of exoplanets. The ultimate goal of this protocol is to determine whether these planetary worlds harbor geological features and/or climate systems. We present a method of extracting information from multi-wavelength single-point light curves and retrieving surface maps. It uses singular value decomposition (SVD) to separate sources that contribute to light curve variations and infer the existence of partially cloudy climate systems. Through analysis of the time series obtained from SVD, physical attributions of principal components (PCs) could be inferred without assumptions of any spectral properties. Combining with viewing geometry, it is feasible to reconstruct surface maps if one of the PCs are found to contain surface information. Degeneracy originated from convolution of the pixel geometry and spectrum information determines the quality of reconstructed surface maps, which requires the introduction of regularization. For the purpose of demonstrating the protocol, multi-wavelength light curves of Earth, which serves as a proxy exoplanet, are analyzed. Comparison between the results and the ground truth is presented to show the performance and limitation of the protocol. This work provides a benchmark for future generalization of exoplanet applications
Chemical species in Titan's upper atmosphere observed by Cassini/UVIS stellar occultations
No full textThe archive files contain the line-of-sight abundances and local densities of CH4, C2H2, C2H4, C2H6, C4H2, C6H6, HCN, HC3N, and haze particles in Titan's upper atmosphere retrieved using Cassini/UVIS stellar occultation observations during 18 Titan flybys. These results are shown in Figures 5-10 of the manuscript listed below.
Fan, S., Zhao, D., Li, C., Shemansky, D. E., Liang, M. -C., and Yung, Y. L. (2022) Seasonal Variations of Chemical Species in Titan’s Upper Atmosphere. The Planetary Science Journal
Forecasting the progression of human civilization on the Kardashev Scale through 2060 with a machine learning approach
No full textInternational audienceEnergy has been propelling the development of human civilization for millennia. Humanity presently stands at Type 0.7276 on the Kardashev Scale, which was proposed to quantify the relationship between energy consumption and the development of civilizations. However, current predictions of human civilization remain underdeveloped and energy consumption models are oversimplified. In order to improve the precision of the prediction, we use machine learning models random forest and autoregressive integrated moving average to simulate and predict energy consumption on a global scale and the position of humanity on the Kardashev Scale through 2060. The result suggests that global energy consumption is expected to reach ~ 887 EJ in 2060, and humanity will become a Type 0.7449 civilization. Additionally, the potential energy segmentation changes before 2060 and the influence of the advent of nuclear fusion are discussed. We conclude that if energy strategies and technologies remain in the present course, it may take human civilization millennia to become a Type 1 civilization. The machine learning tool we develop significantly improves the previous projection of the Kardashev Scale, which is critical in the context of civilization development
Retrieval of Chemical Abundances in Titan's Upper Atmosphere from Cassini UVIS Observations with Pointing Motion
No full textCassini/UVIS FUV observations of stellar occultations at Titan are well suited for probing its atmospheric composition and structure. However, due to instrument pointing motion, only five out of tens of observations have been analyzed. We present an innovative retrieval method that corrects for the effect of pointing motion by forward modeling the Cassini/UVIS instrument response function with the pointing motion value obtained from the SPICE C‐kernel along the spectral dimension. To illustrate the methodology, an occultation observation made during flyby T52 is analyzed, when the Cassini spacecraft had insufficient attitude control. A high‐resolution stellar model and an instrument response simulator that includes the position of the point source on the detector are used for the analysis of the pointing motion. The Markov Chain Monte‐Carlo method is used to retrieve the line‐of‐sight abundance profiles of eleven species (CH_4, C_2H_2, C_2H_4, C_2H_6, C_4H_2, C_6H_6, HCN, C_2N_2, HC_3N, C_6N_2 and haze particles) in the spectral vector fitting process. We obtain tight constraints on all of the species aside from C_2H_6, C_2N_2 and C_6N_2, for which we only retrieved upper limits. This is the first time that the T52 occultation was used to derive abundances of major hydrocarbon and nitrile species in Titan's upper and middle atmosphere, as pointing motion prohibited prior analysis. With this new method, nearly all of the occultations obtained over the entire Cassini mission could yield reliable profiles of atmospheric composition, allowing exploration of Titan's upper atmosphere over seasons, latitudes, and longitudes
Impacts of Organic Ice Condensation on the Optical Properties of Haze on Pluto
No full textInternational audienceThe flyby of the New Horizons spacecraft in 2015 July revealed an unexpected cold atmosphere of Pluto and confirmed the existence of its atmospheric haze. The observed and simulated vertical profiles of chemical species and microphysical processes suggest that the haze particles in Pluto's middle and lower atmosphere may contain organic ice condensation. Such organic ice components can potentially affect Pluto's haze chemistry and optical properties, as well as its energy budget. This study investigates the influence of the ice components on the scattering properties of Pluto's haze by comparing New Horizons observations and simulated particle scattering properties. Comprehensive tests are performed for various haze particle parameters, including their size, chemical component, ice content, and morphology. Scattering properties of these ice-bearing haze particles are calculated by a discrete dipole approximation method and compared to multispectral observations obtained by four New Horizons instruments in spectral regions ranging from the ultraviolet to the near-infrared. The results indicate that the inclusion of the organic ice component leads to higher ratios of backscattering in the visible to extinction in the ultraviolet and provides better agreement with observations compared to monodispersed homogeneous aggregates. But it alone is not sufficient to explain the observed forward scattering values in the visible and near-infrared. Therefore, other scattering sources and/or mechanisms are still required to explain the full set of scattering observations. Further observations, as well as laboratory measurements and numerical tests, are anticipated to improve our understanding of the morphology and ice content of Pluto's haze
