Bio-signatures of Planet Earth from Spectropolarimetry

AbstractPolarimetry is routinely used to characterise the surfaces of bodies in our solar system. In the near future, polarisation measurements of the starlight reflected by exoplanets will become a common and powerful tool to constrain the atmospheres and the surface properties of other worlds.If extra-terrestial life has similar signatures as the life we know, then astronomical observations of planet Earth represent a benchmark to eventually probe bio-signatures also on other planets. In fact, linear polarisation spectra of Earthshine (the sunlight that has been first reflected by Earth and then reflected back to Earth by the Moon), allow us to detect the presence of oxygen, ozone, and water in the atmosphere of our planet. Surface properties such as fractional contributions of clouds and ocean, as well as vegetation can be inferred. Ultimately, Earthshine observations provide strong observational constraints on model predictions for Earth-like exoplanets.In this contribution, we review the most recent observations of Earthshine by polarimetry. We highlight some advances in the interpretation and modelling of whole Earth polarisation, which will be of paramount importance to interpret possible bio-signatures of Earth-like planets in the habitable zone of nearby stars in the future.

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How surfaces shape the climate of habitable exoplanets

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa387 ◽

2020 ◽

Vol 495 (1) ◽

pp. 1-11 ◽

Cited By ~ 4

Author(s):

Jack Madden ◽

Lisa Kaltenegger

Keyword(s):

Surface Albedo ◽

Atmospheric Composition ◽

Habitable Zone ◽

Planetary Surfaces ◽

Earth Like Planets ◽

Planetary Environment ◽

Near Future ◽

Host Stars

ABSTRACT Large ground- and space-based telescopes will be able to observe Earth-like planets in the near future. We explore how different planetary surfaces can strongly influence the climate, atmospheric composition, and remotely detectable spectra of terrestrial rocky exoplanets in the habitable zone depending on the host star’s incident irradiation spectrum for a range of Sun-like host stars from F0V to K7V. We update a well-tested 1D climate-photochemistry model to explore the changes of a planetary environment for different surfaces for different host stars. Our results show that using a wavelength-dependent surface albedo is critical for modelling potentially habitable rocky exoplanets.

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Bayesian constraints on the origin and geology of exo-planetary material using a population of externally polluted white dwarfs

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab736 ◽

2021 ◽

Author(s):

John H D Harrison ◽

Amy Bonsor ◽

Mihkel Kama ◽

Andrew M Buchan ◽

Simon Blouin ◽

...

Keyword(s):

Solar System ◽

White Dwarf ◽

Bayesian Model ◽

Total Mass ◽

White Dwarfs ◽

Bulk Composition ◽

Planetary Systems ◽

The Moon ◽

Planetary Bodies ◽

Nearby Stars

Abstract White dwarfs that have accreted planetary bodies are a powerful probe of the bulk composition of exoplanetary material. In this paper, we present a Bayesian model to explain the abundances observed in the atmospheres of 202 DZ white dwarfs by considering the heating, geochemical differentiation, and collisional processes experienced by the planetary bodies accreted, as well as gravitational sinking. The majority (>60%) of systems are consistent with the accretion of primitive material. We attribute the small spread in refractory abundances observed to a similar spread in the initial planet-forming material, as seen in the compositions of nearby stars. A range in Na abundances in the pollutant material is attributed to a range in formation temperatures from below 1,000 K to higher than 1,400 K, suggesting that pollutant material arrives in white dwarf atmospheres from a variety of radial locations. We also find that Solar System-like differentiation is common place in exo-planetary systems. Extreme siderophile (Fe, Ni or Cr) abundances in 8 systems require the accretion of a core-rich fragment of a larger differentiated body to at least a 3σ significance, whilst one system shows evidence that it accreted a crust-rich fragment. In systems where the abundances suggest that accretion has finished (13/202), the total mass accreted can be calculated. The 13 systems are estimated to have accreted masses ranging from the mass of the Moon to half that of Vesta. Our analysis suggests that accretion continues for 11Myrs on average.

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Carbonate-silicate cycle predictions of Earth-like planetary climates and testing the habitable zone concept

Nature Communications ◽

10.1038/s41467-020-19896-2 ◽

2020 ◽

Vol 11 (1) ◽

Author(s):

Owen R. Lehmer ◽

David C. Catling ◽

Joshua Krissansen-Totton

Keyword(s):

Liquid Water ◽

Physicochemical Parameters ◽

Silicate Weathering ◽

Habitable Zone ◽

Two Dimensional ◽

Land Area ◽

Incident Flux ◽

Earth Like Planets ◽

Surface Liquid ◽

Log Linear

AbstractIn the conventional habitable zone (HZ) concept, a CO2-H2O greenhouse maintains surface liquid water. Through the water-mediated carbonate-silicate weathering cycle, atmospheric CO2 partial pressure (pCO2) responds to changes in surface temperature, stabilizing the climate over geologic timescales. We show that this weathering feedback ought to produce a log-linear relationship between pCO2 and incident flux on Earth-like planets in the HZ. However, this trend has scatter because geophysical and physicochemical parameters can vary, such as land area for weathering and CO2 outgassing fluxes. Using a coupled climate and carbonate-silicate weathering model, we quantify the likely scatter in pCO2 with orbital distance throughout the HZ. From this dispersion, we predict a two-dimensional relationship between incident flux and pCO2 in the HZ and show that it could be detected from at least 83 (2σ) Earth-like exoplanet observations. If fewer Earth-like exoplanets are observed, testing the HZ hypothesis from this relationship could be difficult.

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The habitable zone of Earth-mass planets around 47 UMa: results for land and water worlds

International Journal of Astrobiology ◽

10.1017/s1473550403001368 ◽

2003 ◽

Vol 2 (1) ◽

pp. 35-39 ◽

Cited By ~ 20

Author(s):

S. Franck ◽

M. Cuntz ◽

W. von Bloh ◽

C. Bounama

Keyword(s):

Surface Water ◽

System Approach ◽

Distinct Type ◽

Integrated System ◽

Habitable Zone ◽

Stable Orbit ◽

The Earth ◽

Earth Like Planets ◽

Very High

In a previous paper, we showed that Earth-type habitable planets around 47 UMa are in principle possible if a distinct set of conditions is warranted. These conditions include that the Earth-type planets have successfully formed and are orbitally stable and, in addition, that the 47 UMa star–planet system is relatively young ([lsim ]6 Gyr). We now extend this study by considering Earth-like planets with different land/ocean coverages. This study is again based on the so-called integrated system approach, which describes the photosynthetic biomass production taking into account a variety of climatological, biogeochemical and geodynamical processes. This approach implies a special characterization of the habitable zone defined for a distinct type of planet. We show that the likelihood of finding a habitable Earth-like planet on a stable orbit around 47 UMa critically depends on the percentage of the planetary land/ocean coverage. The likelihood is significantly increased for planets with a very high percentage of ocean surface (‘water worlds’).

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Relativistic aspects of rotational motion of celestial bodies

Proceedings of the International Astronomical Union ◽

10.1017/s174392130999024x ◽

2009 ◽

Vol 5 (S261) ◽

pp. 112-123 ◽

Cited By ~ 2

Author(s):

S. A. Klioner ◽

E. Gerlach ◽

M. H. Soffel

Keyword(s):

High Precision ◽

Rotational Motion ◽

Earth Rotation ◽

Theoretical Framework ◽

Reference Systems ◽

The Moon ◽

Newtonian Theory ◽

Recent Developments ◽

Celestial Bodies ◽

Near Future

AbstractRelativistic modelling of rotational motion of extended bodies represents one of the most complicated problems of Applied Relativity. The relativistic reference systems of IAU (2000) give a suitable theoretical framework for such a modelling. Recent developments in the post-Newtonian theory of Earth rotation in the limit of rigidly rotating multipoles are reported below. All components of the theory are summarized and the results are demonstrated. The experience with the relativistic Earth rotation theory can be directly applied to model the rotational motion of other celestial bodies. The high-precision theories of rotation of the Moon, Mars and Mercury can be expected to be of interest in the near future.

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Longevity of moons around habitable planets

International Journal of Astrobiology ◽

10.1017/s1473550414000184 ◽

2014 ◽

Vol 13 (4) ◽

pp. 324-336 ◽

Cited By ~ 22

Author(s):

Takashi Sasaki ◽

Jason W. Barnes

Keyword(s):

Orbital Period ◽

Extrasolar Planets ◽

The Sun ◽

Habitable Zone ◽

Evolution Theory ◽

Earth System ◽

The Moon ◽

Tidal Dissipation ◽

Habitable Planets ◽

Rocky Planets

AbstractWe consider tidal decay lifetimes for moons orbiting habitable extrasolar planets using the constant Q approach for tidal evolution theory. Large moons stabilize planetary obliquity in some cases, and it has been suggested that large moons are necessary for the evolution of complex life. We find that the Moon in the Sun–Earth system must have had an initial orbital period of not slower than 20 h rev−1 for the moon's lifetime to exceed a 5 Gyr lifetime. We assume that 5 Gyr is long enough for life on planets to evolve complex life. We show that moons of habitable planets cannot survive for more than 5 Gyr if the stellar mass is less than 0.55 and 0.42 M⊙ for Qp=10 and 100, respectively, where Qp is the planetary tidal dissipation quality factor. Kepler-62e and f are of particular interest because they are two actually known rocky planets in the habitable zone. Kepler-62e would need to be made of iron and have Qp=100 for its hypothetical moon to live for longer than 5 Gyr. A hypothetical moon of Kepler-62f, by contrast, may have a lifetime greater than 5 Gyr under several scenarios, and particularly for Qp=100.

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The Potential for Archaeology Within and Beyond the Habitable Zones (HZ) of the Milky Way

Symposium - International Astronomical Union ◽

10.1017/s0074180900193799 ◽

2004 ◽

Vol 213 ◽

pp. 505-510

Author(s):

John B. Campbell

Keyword(s):

Remote Sensing ◽

Solar System ◽

Milky Way ◽

Extrasolar Planets ◽

Habitable Zone ◽

The Moon ◽

Habitable Zones ◽

Remote Sensing Techniques ◽

Main Region

As archaeology is established on Earth and we are actively exploring the Solar System and beyond, there is the potential to develop a number of forms of exo-archaeology. The archaeology of the things intelligent species do in theory could be practised anywhere, provided one can detect the evidence. Sites are being created by us elsewhere within our star's habitable zone (HZ), namely on the Moon and Mars, and at least molecular traces of human-created probes are being left beyond the HZ (Venus, Jupiter etc.). The successful detection of extrasolar planets and the possible identification of HZs round other stars raise the possibility for the development of extrasolar archaeology, at least initially by remote sensing techniques. Within the Milky Way the main region to investigate is the galactic habitable zone (GHZ), though there could be archaeological traces of technological behaviours beyond it.

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Resilient habitability of nearby exoplanet systems

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz3408 ◽

2019 ◽

Vol 492 (1) ◽

pp. 352-368 ◽

Cited By ~ 2

Author(s):

Giorgi Kokaia ◽

Melvyn B Davies ◽

Alexander J Mustill

Keyword(s):

Giant Planet ◽

Planetary Systems ◽

Observational Constraints ◽

Habitable Zone ◽

Habitable Zones ◽

Test Particles ◽

Planetary Orbits ◽

Two Systems ◽

Earth Like Planets ◽

Exoplanet Systems

ABSTRACT We investigate the possibility of finding Earth-like planets in the habitable zone of 34 nearby FGK-dwarfs, each known to host one giant planet exterior to their habitable zone detected by RV. First we simulate the dynamics of the planetary systems in their present day configurations and determine the fraction of stable planetary orbits within their habitable zones. Then, we postulate that the eccentricity of the giant planet is a result of an instability in their past during which one or more other planets were ejected from the system. We simulate these scenarios and investigate whether planets orbiting in the habitable zone survive the instability. Explicitly we determine the fraction of test particles, originally found in the habitable zone, which remain in the habitable zone today. We label this fraction the resilient habitability of a system. We find that for most systems the probability of planets existing [or surviving] on stable orbits in the habitable zone becomes significantly smaller when we include a phase of instability in their history. We present a list of candidate systems with high resilient habitability for future observations. These are: HD 95872, HD 154345, HD 102843, HD 25015, GJ 328, HD 6718, and HD 150706. The known planets in the last two systems have large observational uncertainties on their eccentricities, which propagate into large uncertainties on their resilient habitability. Further observational constraints of these two eccentricities will allow us to better constrain the survivability of Earth-like planets in these systems.

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Dust size and spatial distributions in debris discs: predictions for exozodiacal dust dragged in from an exo-Kuiper belt

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2029 ◽

2020 ◽

Vol 497 (1) ◽

pp. 1143-1165 ◽

Cited By ~ 1

Author(s):

Jessica K Rigley ◽

Mark C Wyatt

Keyword(s):

Kuiper Belt ◽

Spectral Energy ◽

Habitable Zone ◽

Energy Distributions ◽

Mid Infrared ◽

Nearby Stars ◽

Computationally Expensive ◽

Free Parameters ◽

Grain Properties ◽

Size Distribution Of Particles

ABSTRACT The spectral energy distributions of some nearby stars show mid-infrared (IR) excesses from warm habitable zone dust, known as exozodiacal dust. This dust may originate in collisions in a planetesimal belt before being dragged inwards. This paper presents an analytical model for the size distribution of particles at different radial locations in such a scenario, considering evolution due to destructive collisions and Poynting–Robertson (P–R) drag. Results from more accurate but computationally expensive numerical simulations of this process are used to validate the model and fit its free parameters. The model predicts 11 μm excesses (R11) for discs with a range of dust masses and planetesimal belt radii using realistic grain properties. We show that P–R drag should produce exozodiacal dust levels detectable with the Large Binocular Telescope Interferometer (LBTI) ($R_{11} \gt 0.1{{\ \rm per\ cent}}$) in systems with known outer belts; non-detection may indicate dust depletion, e.g. by an intervening planet. We also find that LBTI could detect exozodiacal dust dragged in from a belt too faint to detect at far-IR wavelengths, with fractional luminosity f ∼ 10−7 and radius ∼10–80 au. Application to systems observed with LBTI shows that P–R drag can likely explain most (5/9) of the exozodiacal dust detections in systems with known outer belts; two systems (β Uma and η Corvi) with bright exozodi may be due to exocomets. We suggest that the three systems with exozodiacal dust detections but no known belt may have cold planetesimal belts too faint to be detectable in the far-IR. Even systems without outer belt detections could have exozodiacal dust levels $R_{11} \gt 0.04{{\ \rm per\ cent}}$ which are problematic for exo-Earth imaging.

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