scholarly journals Interior structures and tidal heating in the TRAPPIST-1 planets

2018 ◽  
Vol 613 ◽  
pp. A37 ◽  
Author(s):  
Amy C. Barr ◽  
Vera Dobos ◽  
László L. Kiss
Keyword(s):  
Heat Fluxes ◽  
Uniform Density ◽  
Generation Model ◽  
Habitable Zone ◽  
Habitable Planet ◽  
Error Bars ◽  
Magma Oceans ◽  
Tidal Heating ◽  
M Dwarf ◽  
Rule Out

Context. With seven planets, the TRAPPIST-1 system has among the largest number of exoplanets discovered in a single system so far. The system is of astrobiological interest, because three of its planets orbit in the habitable zone of the ultracool M dwarf. Aims. We aim to determine interior structures for each planet and estimate the temperatures of their rock mantles due to a balance between tidal heating and convective heat transport to assess their habitability. We also aim to determine the precision in mass and radius necessary to determine the planets’ compositions. Methods. Assuming the planets are composed of uniform-density noncompressible materials (iron, rock, H2O), we determine possible compositional models and interior structures for each planet. We also construct a tidal heat generation model using a single uniform viscosity and rigidity based on each planet’s composition. Results. The compositions for planets b, c, d, and e remain uncertain given the error bars on mass and radius. With the exception of TRAPPIST-1c, all have densities low enough to indicate the presence of significant H2O. Planets b and c experience enough heating from planetary tides to maintain magma oceans in their rock mantles; planet c may have surface eruptions of silicate magma, potentially detectable with next-generation instrumentation. Tidal heat fluxes on planets d, e, and f are twenty times higher than Earth’s mean heat flow. Conclusions. Planets d and e are the most likely to be habitable. Planet d avoids the runaway greenhouse state if its albedo is ≳0.3. Determining the planet’s masses within ~0.1–0.5 Earth masses would confirm or rule out the presence of H2O and/or iron. Understanding the geodynamics of ice-rich planets f, g, and h requires more sophisticated modeling that can self-consistently balance heat production and transport in both rock and ice layers.

scholarly journals The DECam minute cadence survey – II. 49 variables but no planetary transits of a white dwarf

2019 ◽  
Vol 490 (1) ◽  
pp. 1066-1075 ◽  
Author(s):  
Kyra Dame ◽  
Claudia Belardi ◽  
Mukremin Kilic ◽  
Armin Rest ◽  
A Gianninas ◽  
...  
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Point Sources ◽  
Habitable Zone ◽  
Significant Evidence ◽  
Rr Lyrae ◽  
M Dwarf ◽  
Rule Out ◽  
Planetary Transits

Abstract We present minute cadence photometry of 31 732 point sources observed in one 3 $\rm deg^{2}$ DECam pointing centred at RA = 09:03:02 and Dec. = −04:35:00 over eight consecutive half-nights. We use these data to search for eclipse-like events consistent with a planetary transit of a white dwarf and other sources of stellar variability within the field. We do not find any significant evidence for minute-long transits around our targets, hence we rule out planetary transits around ∼370 white dwarfs that should be present in this field. Additionally, we identify 49 variables, including 40 new systems. These include 23 detached or contact stellar binaries, one eclipsing white dwarf + M dwarf binary, 16 δ Scuti, three RR Lyrae, and two ZZ Ceti pulsators. Results from the remaining two fields in our survey will allow us to place more stringent constraints on the frequency of planets orbiting white dwarfs in the habitable zone.

scholarly journals Tidal heating and the habitability of the TRAPPIST-1 exoplanets

2019 ◽  
Vol 624 ◽  
pp. A2 ◽  
Author(s):  
Vera Dobos ◽  
Amy C. Barr ◽  
László L. Kiss
Keyword(s):  
Liquid Water ◽  
Weighted Average ◽  
Heat Fluxes ◽  
Tidal Dissipation ◽  
Water Ice ◽  
The Earth ◽  
Tidal Heating ◽  
The Masses ◽  
Viscoelastic Rheology ◽  
M Dwarf

Context. New estimates of the masses and radii of the seven planets orbiting the ultracool M-dwarf TRAPPIST-1 star permit improved modelling of their compositions, heating by tidal dissipation, and removal of tidal heat by solid-state convection. Aims. Here we compute the heat flux due to insolation and tidal heating for the inner four planets. Methods. We apply a Maxwell viscoelastic rheology to compute the tidal response of the planets using the volume-weighted average of the viscosities and rigidities of the metal, rock, high-pressure ice, and liquid water/ice I layers. Results. We show that TRAPPIST-1d and e can avoid entering a runaway greenhouse state. Planet e is the most likely to support a habitable environment, with Earth-like surface temperatures and possibly liquid water oceans. Planet d also avoids a runaway greenhouse, if its surface reflectance is at least as high as that of the Earth. Planets b and c, closer to the star, have heat fluxes high enough to trigger a runaway greenhouse and to support volcanism on the surfaces of their rock layers, rendering them too warm for life. Planets f, g, and h are too far from the star to experience significant tidal heating, and likely have solid ice surfaces with possible subsurface liquid water oceans.

scholarly journals An Astrobiological Experiment to Explore the Habitability of Tidally Locked M-Dwarf Planets

2012 ◽  
Vol 8 (S293) ◽  
pp. 192-196
Author(s):  
Daniel Angerhausen ◽  
Haley Sapers ◽  
Eugenio Simoncini ◽  
Stefanie Lutz ◽  
Marcelo da Rosa Alexandre ◽  
...  
Keyword(s):  
Academic Research ◽  
Environmental Parameters ◽  
Climate Simulation ◽  
Habitable Zone ◽  
Dwarf Stars ◽  
Dwarf Planets ◽  
Late Type Star ◽  
M Dwarf Stars ◽  
M Dwarf ◽  
Simulation Chamber

AbstractWe present a summary of a three-year academic research proposal drafted during the Sao Paulo Advanced School of Astrobiology (SPASA) to prepare for upcoming observations of tidally locked planets orbiting M-dwarf stars. The primary experimental goal of the suggested research is to expose extremophiles from analogue environments to a modified space simulation chamber reproducing the environmental parameters of a tidally locked planet in the habitable zone of a late-type star. Here we focus on a description of the astronomical analysis used to define the parameters for this climate simulation.

scholarly journals The habitability of stagnant-lid Earths around dwarf stars

2019 ◽  
Vol 625 ◽  
pp. A12 ◽  
Author(s):  
Mareike Godolt ◽  
Nicola Tosi ◽  
Barbara Stracke ◽  
John Lee Grenfell ◽  
Thomas Ruedas ◽  
...  
Keyword(s):  
Water Loss ◽  
Main Sequence ◽  
Extrasolar Planets ◽  
Water Reservoir ◽  
Habitable Zone ◽  
High Luminosity ◽  
Dwarf Stars ◽  
Surface Conditions ◽  
M Dwarf Stars ◽  
M Dwarf

Context. The habitability of a planet depends on various factors, such as the delivery of water during its formation, the co-evolution of the interior and the atmosphere, and the stellar irradiation which changes in time. Aims. Since an unknown number of rocky extrasolar planets may operate in a one-plate convective regime, i.e. without plate tectonics, our aim is to understand the conditions under which planets in such a stagnant-lid regime may support habitable surface conditions. Understanding the interaction of the planetary interior and outgassing of volatiles in combination with the evolution of the host star is crucial to determining the potential habitability. M-dwarf stars in particular possess a high-luminosity pre-main sequence phase that endangers the habitability of planets around them via water loss. We therefore explore the potential of secondary outgassing from the planetary interior to rebuild a water reservoir allowing for habitability at a later stage. Methods. We compute the boundaries of the habitable zone around M-, K-, G-, and F-dwarf stars using a 1D cloud-free radiative-convective climate model accounting for the outgassing history of CO2 and H2O from an interior evolution and outgassing model for different interior compositions and stellar luminosity evolutions. Results. The outer edge of the habitable zone strongly depends on the amount of CO2 outgassed from the interior, while the inner edge is mainly determined via the stellar irradiation, as soon as a sufficiently large water reservoir has been outgassed. A build-up of a secondary surface and atmospheric water reservoir for planets around M-dwarf stars is possible even after severe water loss during the high-luminosity pre-main sequence phase as long as some water has been retained within the mantle. For small mantle water reservoirs, between 62 and 125 ppm, a time delay in outgassing from the interior permits such a secondary water reservoir build-up especially for early and mid-M dwarfs because their pre-main sequence lifetimes are shorter than the outgassing timescale. Conclusions. We show that Earth-like stagnant-lid planets allow for habitable surface conditions within a continuous habitable zone that is dependent on interior composition. Secondary outgassing from the interior may allow for habitability of planets around M-dwarf stars after severe water loss during the high-luminosity pre-main sequence phase by rebuilding a surface water reservoir.

The biological impact of superflares on planets in the Habitable Zone

2018 ◽  
Vol 14 (S345) ◽  
pp. 176-180
Author(s):  
Adriana Valio ◽  
Raissa Estrela ◽  
Luisa Cabral ◽  
Abel Grangeiro
Keyword(s):  
Survival Rates ◽  
Shallow Waters ◽  
The Sun ◽  
Habitable Zone ◽  
Biological Impact ◽  
Solar Type ◽  
Living Organisms ◽  
Multicellular Organisms ◽  
The Impact ◽  
M Dwarf

AbstractYounger and fully convective stars are much more active than our Sun, producing many superflares. Here we estimate the impact of the superflares UV radiation on living organisms on the surface of orbiting planets in the habitable zone of the star. For this we study two active stars, Kepler-96 (solar type) and TRAPPIST-1 (M dwarf). Kepler-96, with an age of 2.4 Gyr, is at the same stage of the Sun when the first multicellular organisms appeared on Earth. The biological impact of super flares are studied on a hypothetical Earth at 1AU of Kepler-96 and on planets TRAPPIST-1e, f, and g for three atmospheres scenarios: an Archean and Present-day atmospheres with and without ozone. We estimated the survival rates of two bacteria and concluded that life would only survive on the surface of these planets if their atmosphere had an ozone layer, or in shallow waters of an ocean.

scholarly journals Polarimetry as a tool to find and characterise habitable planets orbiting white dwarfs

2014 ◽  
Vol 10 (S305) ◽  
pp. 325-332 ◽  
Author(s):  
Luca Fossati ◽  
Stefano Bagnulo ◽  
Carole A. Haswell ◽  
Manish R. Patel ◽  
Richard Busuttil ◽  
...  
Keyword(s):  
Radiation Dose ◽  
Uv Radiation ◽  
Uv Irradiation ◽  
White Dwarf ◽  
White Dwarfs ◽  
Terrestrial Planet ◽  
Habitable Zone ◽  
Habitable Planets ◽  
Earth Like Planets ◽  
M Dwarf

AbstractThere are several ways planets can survive the giant phase of the host star, hence one can consider the case of Earth-like planets orbiting white dwarfs. As a white dwarf cools from 6000 K to 4000 K, a planet orbiting at 0.01 AU from the star would remain in the continuous habitable zone (CHZ) for about 8 Gyr. Polarisation due to a terrestrial planet in the CHZ of a cool white dwarf (CWD) is 102 (104) times larger than it would be in the habitable zone of a typical M-dwarf (Sun-like star). Polarimetry is thus a powerful tool to detect close-in planets around white dwarfs. Multi-band polarimetry would also allow one to reveal the presence of a planet atmosphere, even providing a first characterisation. With current facilities a super-Earth-sized atmosphereless planet is detectable with polarimetry around the brightest known CWD. Planned future facilities render smaller planets detectable, in particular by increasing the instrumental sensitivity in the blue. Preliminary habitability study show also that photosynthetic processes can be sustained on Earth-like planets orbiting CWDs and that the DNA-weighted UV radiation dose for an Earth-like planet in the CHZ is less than the maxima encountered on Earth, hence white dwarfs are compatible with the persistence of complex life from the perspective of UV irradiation.

scholarly journals The subsurface habitability of small, icy exomoons

2020 ◽  
Vol 636 ◽  
pp. A50
Author(s):  
J. N. K. Y. Tjoa ◽  
M. Mueller ◽  
F. F. S. van der Tak
Keyword(s):  
Solar System ◽  
Liquid Water ◽  
Internal Heat ◽  
Phenomenological Approach ◽  
Habitable Zone ◽  
Melting Depth ◽  
Icy Moons ◽  
Subsurface Ocean ◽  
Tidal Heating ◽  
Ice Shell

Context. Assuming our Solar System as typical, exomoons may outnumber exoplanets. If their habitability fraction is similar, they would thus constitute the largest portion of habitable real estate in the Universe. Icy moons in our Solar System, such as Europa and Enceladus, have already been shown to possess liquid water, a prerequisite for life on Earth. Aims. We intend to investigate under what thermal and orbital circumstances small, icy moons may sustain subsurface oceans and thus be “subsurface habitable”. We pay specific attention to tidal heating, which may keep a moon liquid far beyond the conservative habitable zone. Methods. We made use of a phenomenological approach to tidal heating. We computed the orbit averaged flux from both stellar and planetary (both thermal and reflected stellar) illumination. We then calculated subsurface temperatures depending on illumination and thermal conduction to the surface through the ice shell and an insulating layer of regolith. We adopted a conduction only model, ignoring volcanism and ice shell convection as an outlet for internal heat. In doing so, we determined at which depth, if any, ice melts and a subsurface ocean forms. Results. We find an analytical expression between the moon’s physical and orbital characteristics and the melting depth. Since this expression directly relates icy moon observables to the melting depth, it allows us to swiftly put an upper limit on the melting depth for any given moon. We reproduce the existence of Enceladus’ subsurface ocean; we also find that the two largest moons of Uranus (Titania and Oberon) could well sustain them. Our model predicts that Rhea does not have liquid water. Conclusions. Habitable exomoon environments may be found across an exoplanetary system, largely irrespective of the distance to the host star. Small, icy subsurface habitable moons may exist anywhere beyond the snow line. This may, in future observations, expand the search area for extraterrestrial habitable environments beyond the circumstellar habitable zone.

scholarly journals Evidence for He i 10830 Å Absorption during the Transit of a Warm Neptune around the M-dwarf GJ 3470 with the Habitable-zone Planet Finder

2020 ◽  
Vol 894 (2) ◽  
pp. 97 ◽  
Author(s):  
Joe P. Ninan ◽  
Gudmundur Stefansson ◽  
Suvrath Mahadevan ◽  
Chad Bender ◽  
Paul Robertson ◽  
...  
Keyword(s):  
Habitable Zone ◽  
M Dwarf

scholarly journals Constraints on the Habitability of Extrasolar Moons

2012 ◽  
Vol 8 (S293) ◽  
pp. 159-164 ◽  
Author(s):  
René Heller ◽  
Rory Barnes
Keyword(s):  
Habitable Zone ◽  
Space Telescope ◽  
Future Technology ◽  
Tidal Heating ◽  
Near Future

AbstractDetections of massive extrasolar moons are shown feasible with the Kepler space telescope. Kepler's findings of about 50 exoplanets in the stellar habitable zone naturally make us wonder about the habitability of their hypothetical moons. Illumination from the planet, eclipses, tidal heating, and tidal locking distinguish remote characterization of exomoons from that of exoplanets. We show how evaluation of an exomoon's habitability is possible based on the parameters accessible by current and near-future technology.

scholarly journals Flares from ultracool L dwarfs with Kepler

2015 ◽  
Vol 11 (S320) ◽  
pp. 153-154
Author(s):  
John E. Gizis ◽  
Rishi Paudel ◽  
Peter K. G. Williams ◽  
Adam J. Burgasser ◽  
Sarah J. Schmidt
Keyword(s):  
White Light ◽  
Habitable Zone ◽  
Dwarf Stars ◽  
Kepler Mission ◽  
L Dwarfs ◽  
M Dwarf

AbstractWe report on our search for L dwarf flares using NASA's Kepler mission. Spectroscopically confirmedflares were detected with the original Kepler mission from an L1 dwarf stars. We discuss the physicalcharacteristics of these white light flares and compare them to M dwarf flares. For “habitable zone” planets, the apparent flare brightnesses would be comparable to the most powerful M dwarf flares. Weare monitoring more L dwarfs with the Kepler K2 mission. We discussthe prospect for more detections during the remainder of the K2 mission.

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