39 research outputs found
Viscoelastic Models of Tidally Heated Exomoons
Tidal heating of exomoons may play a key role in their habitability, since
the elevated temperature can melt the ice on the body even without significant
solar radiation. The possibility of life is intensely studied on Solar System
moons such as Europa or Enceladus, where the surface ice layer covers tidally
heated water ocean. Tidal forces may be even stronger in extrasolar systems,
depending on the properties of the moon and its orbit. For studying the tidally
heated surface temperature of exomoons, we used a viscoelastic model for the
first time. This model is more realistic than the widely used, so-called fixed
Q models, because it takes into account the temperature dependency of the tidal
heat flux, and the melting of the inner material. With the use of this model we
introduced the circumplanetary Tidal Temperate Zone (TTZ), that strongly
depends on the orbital period of the moon, and less on its radius. We compared
the results with the fixed Q model and investigated the statistical volume of
the TTZ using both models. We have found that the viscoelastic model predicts
2.8 times more exomoons in the TTZ with orbital periods between 0.1 and 3.5
days than the fixed Q model for plausible distributions of physical and orbital
parameters. The viscoelastic model gives more promising results in terms of
habitability, because the inner melting of the body moderates the surface
temperature, acting like a thermostat.Comment: accepted for publication in Ap
Habitability of Exoplanetary Systems
The aim of my dissertation is to investigate habitability in extra-Solar
Systems. Most of the time, only planets are considered as possible places where
extraterrestrial life can emerge and evolve, however, their moons could be
inhabited, too. I present a comprehensive study, which considers habitability
not only on planets, but on satellites, as well. My research focuses on three
closely related topics. The first one is the circumstellar habitable zone,
which is usually used as a first proxy for determining the habitability of a
planet around the host star. The word habitability is used in the sense that
liquid water, which is essential for life as we know it, may be present on the
planetary surface. Whether the planet is habitable or not, its moon might have
a suitable surface temperature for holding water reservoirs, providing that
tidal heating is in action. Tidal heating is generated inside the satellite and
its source is the strong gravitational force of the nearby planet. The second
topic of my research explores tidal heating and the habitability of extra-solar
moons with and without stellar radiation and other related energy sources. Life
is possible to form even on icy planetary bodies, inside tidally heated
subsurface oceans. The third topic probes the possibility of identifying an
ice-covered satellite from photometric observations. A strong indication of
surface ice is the high reflectance of the body, which may be measured when the
moon disappears behind the host star, so its reflected light is blocked out by
the star.Comment: PhD Dissertation, E\"otv\"os Lor\'and University, 91 page
The Effect of Multiple Heat Sources on Exomoon Habitable Zones
With dozens of Jovian and super-Jovian exoplanets known to orbit their host
stars in or near the stellar habitable zones, it has recently been suggested
that moons the size of Mars could offer abundant surface habitats beyond the
solar system. Several searches for such exomoons are now underway, and the
exquisite astronomical data quality of upcoming space missions and ground-based
extremely large telescopes could make the detection and characterization of
exomoons possible in the near future. Here we explore the effects of tidal
heating on the potential of Mars- to Earth-sized satellites to host liquid
surface water, and we compare the tidal heating rates predicted by tidal
equilibrium model and a viscoelastic model. In addition to tidal heating, we
consider stellar radiation, planetary illumination and thermal heat from the
planet. However, the effects of a possible moon atmosphere are neglected. We
map the circumplanetary habitable zone for different stellar distances in
specific star-planet-satellite configurations, and determine those regions
where tidal heating dominates over stellar radiation. We find that the
`thermostat effect' of the viscoelastic model is significant not just at large
distances from the star, but also in the stellar habitable zone, where stellar
radiation is prevalent. We also find that tidal heating of Mars-sized moons
with eccentricities between 0.001 and 0.01 is the dominant energy source beyond
3--5 AU from a Sun-like star and beyond 0.4--0.6 AU from an M3 dwarf star. The
latter would be easier to detect (if they exist), but their orbital stability
might be under jeopardy due to the gravitational perturbations from the star.Comment: accepted for publication in A&A, 8 pages, 4 figure
Interior Structures and Tidal Heating in the TRAPPIST-1 Planets
With seven planets, the TRAPPIST-1 system has 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. Assuming the planets are composed of
non-compressible iron, rock, and HO, we determine possible interior
structures for each planet. To determine how much tidal heat may be dissipated
within each planet, we construct a tidal heat generation model using a single
uniform viscosity and rigidity for each planet based on the planet's
composition. With the exception of TRAPPIST-1c, all seven of the planets have
densities low enough to indicate the presence of significant HO in some
form. Planets b and c experience enough heating from planetary tides to
maintain magma oceans in their rock mantles; planet c may have eruptions of
silicate magma on its surface, which may be detectable with next-generation
instrumentation. Tidal heat fluxes on planets d, e, and f are lower, but are
still twenty times higher than Earth's mean heat flow. 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
to 0.5 Earth masses would confirm or rule out the presence of HO and/or
iron in each planet, and permit detailed models of heat production and
transport in each planet. 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.Comment: 34 pages, 3 tables, 4 figures. Accepted for publication in Astronomy
& Astrophysics -- final version including corrections made in proof stag
Possibility for albedo estimation of exomoons: Why should we care about M dwarfs?
Occultation light curves of exomoons may give information on their albedo and
hence indicate the presence of ice cover on the surface. Icy moons might have
subsurface oceans thus these may potentially be habitable. The objective of our
paper is to determine whether next generation telescopes will be capable of
albedo estimations for icy exomoons using their occultation light curves. The
success of the measurements depends on the depth of the moon's occultation in
the light curve and on the sensitivity of the used instruments. We applied
simple calculations for different stellar masses in the V and J photometric
bands, and compared the flux drop caused by the moon's occultation and the
estimated photon noise of next generation missions with 5 confidence.
We found that albedo estimation by this method is not feasible for moons of
solar-like stars, but small M dwarfs are better candidates for such
measurements. Our calculations in the J photometric band show that E-ELT
MICADO's photon noise is just about 4 ppm greater than the flux difference
caused by a 2 Earth-radii icy satellite in a circular orbit at the snowline of
an 0.1 stellar mass star. However, considering only photon noise underestimates
the real expected noise, because other noise sources, such as CCD read-out and
dark signal become significant in the near infrared measurements. Hence we
conclude that occultation measurements with next generation missions are far
too challenging, even in the case of large, icy moons at the snowline of small
M dwarfs. We also discuss the role of the parameters that were neglected in the
calculations, e.g. inclination, eccentricity, orbiting direction of the moon.
We predict that the first albedo estimations of exomoons will probably be made
for large icy moons around the snowline of M4 -- M9 type main sequence stars.Comment: 13 pages, 6 figures, accepted for publication in A&
Stable and habitable systems with two giant planets
We have studied planetary systems which are similar to the Solar System and
built up from three inner rocky planets (Venus, Earth, Mars) and two outer gas
giants. The stability of the orbits of the inner planets is discussed in the
cases of different masses of the gas planets. To demonstrate the results
stability maps were made and it was found that Jupiter could be four times and
Saturn could be three times more massive while the orbits of the inner planets
stay stable. Similar calculations were made by changing the mass of the Sun. In
this case the position of the rocky planets and the extension of the liquid
water habitable and the UV habitable zones were studied for different masses of
the Sun. It was found that the orbits of the planets were stable for values
greater than 0.33 M_Sun where M_Sun is the mass of the Sun and at lower masses
of the Sun (at about 0.8 M_Sun) only Venus, but for higher mass values (at
about 1.2 M_Sun) Earth and also Mars are located in both habitable zones.Comment: 8 page
A target list for searching for habitable exomoons
We investigate the habitability of hypothetical moons orbiting known exoplanets. This study focuses on big, rocky exomoons that are capable of maintaining a significant atmosphere. To determine their habitability, we calculate the incident stellar radiation and the tidal heating flux arising in the moons as the two main contributors to the energy budget. We use the runaway greenhouse and the maximum greenhouse flux limits as a definition of habitability. For each exoplanet, we run our calculations for plausible ranges of physical and orbital parameters for the moons and the planet using a Monte Carlo approach. We calculate the moon habitability probability for each planet, which is the fraction of the investigated cases that lead to habitable conditions. Based on our results, we provide a target list for observations of known exoplanets of which the top 10 planets have more than 50 per cent chance for hosting habitable moons on stable orbits. Two especially promising candidates are Kepler-62 f and Kepler-16 b, both of them with known masses and radii. Our target list can help to detect the first habitable exomoon.Peer reviewe
Tidal heating and the habitability of the TRAPPIST-1 exoplanets
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 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
a multicentre prevalence study
Objectives: The aim of this study was to measure the prevalence of skin
diseases in aged nursing home residents and to explore possible associations
with demographic and medical characteristics. Design: Descriptive multicentre
prevalence study. Setting and participants: The study was conducted in a
random sample of ten institutional long-term care facilities in the federal
state of Berlin, Germany. In total, n=223 residents were included. Results: In
total, 60 dermatological diseases were diagnosed. The most frequently
diagnosed skin disease was xerosis cutis (99.1%, 95% CI 97.7% to 100.0%)
followed by tinea ungium (62.3%, 95% CI 56.0% to 69.1%) and seborrheic
keratosis (56.5%, 95% CI 50.2% to 63.0%). Only few bivariate associations have
been detected between skin diseases and demographic and medical
characteristics. Conclusion: Study results indicate that almost every resident
living in residential care has at least one dermatological diagnosis.
Dermatological findings range from highly prevalent xerosis and cutaneous
infection up to skin cancer. Not all conditions require immediate
dermatological treatment and can be managed by targeted skin care
interventions. Caregivers need knowledge and diagnostic skills to make
appropriate clinical decisions. It is unlikely that specialised dermatological
care will be delivered widely in the growing long-term care sector. Trial
registration number: This study is registered at
https://clinicaltrials.gov/ct2/show/NCT02216526