arXiv subjects

Anthony Del Genio

Publications and source records attributed to Anthony Del Genio.

7 recordsLinked to original sources

arXiv2020

Climates of Warm Earth-like Planets II: Rotational 'Goldilocks' Zones for Fractional Habitability and Silicate Weathering

Planetary rotation rate has a significant effect on atmospheric circulation, where the strength of the Coriolis effect in part determines the efficiency of latitudinal heat transport, altering cloud distributions, surface temperatures, and precipitation patterns. In this study we use the ROCKE-3D dynamic-ocean general circulation model to study the effects of slow rotations and increased insolations on the 'fractional habitability' and silicate weathering rate of an Earth-like world. Defining the fractional habitability f_h to be the percentage of a planet's surface which falls in the 0 <= T <= 100 C temperature regime, we find a moderate increase in f_h with a 10% and 20% increase in insolation and a possible maximum in f_h at sidereal day-lengths between 8 and 32 times that of the modern Earth. By tracking precipitation and run-off we further determine that there is a rotational regime centered on a 4-day period in which the silicate weathering rate is maximized and is particularly strongly peaked at higher overall insolations. Because of weathering's integral role in the long-term carbonate-silicate cycle, we suggest that climate stability may be strongly affected by the anticipated rotational evolution of temperate terrestrial-type worlds, and should be considered a major factor in their study. In light of our results we argue that planetary rotation period is an important factor to consider when determining the habitability of terrestrial worlds.

astro-ph.EP↗

arXiv2019

The Importance of 3D General Circulation Models for Characterizing the Climate and Habitability of Terrestrial Extrasolar Planets

While recently discovered exotic new planet-types have both challenged our imaginations and broadened our knowledge of planetary system workings, perhaps the most compelling objective of exoplanet science is to detect and characterize habitable and possibly inhabited worlds orbiting in other star systems. For the foreseeable future, characterizations of extrasolar planets will be made via remote sensing of planetary spectroscopic and temporal signals, along with careful fitting of this data to advanced models of planets and their atmospheres. Terrestrial planets are small and significantly more challenging to observe compared to their larger gaseous brethren; however observatories coming on-line in the coming decade will begin to allow their characterization. Still, it is not enough to invest only in observational endeavors. Comprehensive modeling of planetary atmospheres is required in order to fully understand what it is that our grand telescopes see in the night-sky. In our quest to characterize habitable, and possibly inhabited worlds, 3D general circulation models (GCMs) should be used to evaluate potential climate states and their associated temporal and spatial dependent observable signals. 3D models allow for coupled, self-consistent, multi-dimensional simulations, which can realistically simulate the climates of terrestrial extrasolar planets. A complete theoretical understanding of terrestrial exoplanetary atmospheres, gained through comprehensive 3D modeling, is critical for interpreting spectra of exoplanets taken from current and planned instruments, and is critical for designing future missions that aim to measure spectra of potentially habitable exoplanets as one of their key science goals. We recommend continued institutional support for 3D GCM modeling teams that focus on planetary and exoplanetary applications.

astro-ph.EP↗

arXiv2018

Exoplanet Biosignatures: A Framework for Their Assessment

Finding life on exoplanets from telescopic observations is an ultimate goal of exoplanet science. Life produces gases and other substances, such as pigments, which can have distinct spectral or photometric signatures. Whether or not life is found with future data must be expressed with probabilities, requiring a framework of biosignature assessment. We present a framework in which we advocate using biogeochemical "Exo-Earth System" models to simulate potential biosignatures in spectra or photometry. Given actual observations, simulations are used to find the Bayesian likelihoods of those data occurring for scenarios with and without life. The latter includes "false positives" where abiotic sources mimic biosignatures. Prior knowledge of factors influencing planetary inhabitation, including previous observations, is combined with the likelihoods to give the Bayesian posterior probability of life existing on a given exoplanet. Four components of observation and analysis are necessary. 1) Characterization of stellar (e.g., age and spectrum) and exoplanetary system properties, including "external" exoplanet parameters (e.g., mass and radius) to determine an exoplanet's suitability for life. 2) Characterization of "internal" exoplanet parameters (e.g., climate) to evaluate habitability. 3) Assessment of potential biosignatures within the environmental context (components 1-2) and any corroborating evidence. 4) Exclusion of false positives. The resulting posterior Bayesian probabilities of life's existence map to five confidence levels, ranging from "very likely" (90-100%) to "very unlikely" ($\le$10%) inhabited.

astro-ph.EP↗

arXiv2018

Modeling Venus-Like Worlds Through Time

We explore the atmospheric and surface history of a hypothetical paleo-Venus climate using a 3-D General Circulation Model. We constrain our model with the in-situ and remote sensing Venus data available today. Given that Venus and Earth are believed to be similar geochemically some aspects of Earth's history are also utilized. We demonstrate that it is possible for ancient Venus and Venus-like exoplanetary worlds to exist within the liquid water habitable zone with insolations up to nearly 2 times that of modern Earth.

astro-ph.EP↗

arXiv2018

Life Beyond the Solar System: Observation and Modeling of Exoplanet Environments

The search for life on planets outside our solar system has largely been the province of the astrophysics community until recently. A major development since the NASA Astrobiology Strategy 2015 document (AS15) has been the integration of other NASA science disciplines (planetary science, heliophysics, Earth science) with ongoing exoplanet research in astrophysics. The NASA Nexus for Exoplanet System Science (NExSS) provides a forum for scientists to collaborate across disciplines to accelerate progress in the search for life elsewhere. Here we describe recent developments in these other disciplines, with a focus on exoplanet properties and environments, and the prospects for future progress that will be achieved by integrating emerging knowledge from astrophysics with insights from these fields.

astro-ph.EP↗

arXiv2018

Life Beyond the Solar System: Remotely Detectable Biosignatures

For the first time in human history, we will soon be able to apply the scientific method to the question "Are We Alone?" The rapid advance of exoplanet discovery, planetary systems science, and telescope technology will soon allow scientists to search for life beyond our Solar System through direct observation of extrasolar planets. This endeavor will occur alongside searches for habitable environments and signs of life within our Solar System. While the searches are thematically related and will inform each other, they will require separate observational techniques. The search for life on exoplanets holds potential through the great diversity of worlds to be explored beyond our Solar System. However, there are also unique challenges related to the relatively limited data this search will obtain on any individual world. This white paper reviews the scientific community's ability to use data from future telescopes to search for life on exoplanets. This material summarizes products from the Exoplanet Biosignatures Workshop Without Walls (EBWWW). The EBWWW was constituted by a series of online and in person activities, with participation from the international exoplanet and astrobiology communities, to assess state of the science and future research needs for the remote detection of life on planets outside our Solar System.

astro-ph.EP↗

arXiv2009

New Worlds: Evaluating terrestrial planets as astrophysical objects

Terrestrial exoplanets are on the verge of joining the ranks of astronomically accessible objects. Interpreting their observable characteristics, and informing decisions on instrument design and use, will hinge on the ability to model these planets successfully across a vast range of configurations and climate forcings. A hierarchical approach that addresses fundamental behaviors as well as more complex, specific, situations is crucial to this endeavor and is presented here. Incorporating Earth-centric knowledge, and continued cross-disciplinary work will be critical, but ultimately the astrophysical study of terrestrial exoplanets must be encouraged to develop as its own field.

astro-ph.EP↗