199 research outputs found
A rocky planet transiting a nearby low-mass star
M-dwarf stars -- hydrogen-burning stars that are smaller than 60 per cent of
the size of the Sun -- are the most common class of star in our Galaxy and
outnumber Sun-like stars by a ratio of 12:1. Recent results have shown that M
dwarfs host Earth-sized planets in great numbers: the average number of M-dwarf
planets that are between 0.5 to 1.5 times the size of Earth is at least 1.4 per
star. The nearest such planets known to transit their star are 39 parsecs away,
too distant for detailed follow-up observations to measure the planetary masses
or to study their atmospheres. Here we report observations of GJ 1132b, a
planet with a size of 1.2 Earth radii that is transiting a small star 12
parsecs away. Our Doppler mass measurement of GJ 1132b yields a density
consistent with an Earth-like bulk composition, similar to the compositions of
the six known exoplanets with masses less than six times that of the Earth and
precisely measured densities. Receiving 19 times more stellar radiation than
the Earth, the planet is too hot to be habitable but is cool enough to support
a substantial atmosphere, one that has probably been considerably depleted of
hydrogen. Because the host star is nearby and only 21 per cent the radius of
the Sun, existing and upcoming telescopes will be able to observe the
composition and dynamics of the planetary atmosphere.Comment: Published in Nature on 12 November 2015, available at
http://dx.doi.org/10.1038/nature15762. This is the authors' version of the
manuscrip
Using Independent Component Analysis to detect exoplanet reflection spectrum from composite spectra of exoplanetary binary systems
The analysis of the wavelength-dependent albedo of exoplanets represents a
direct way to provide insight of their atmospheric composition and to constrain
theoretical planetary atmosphere modelling. Wavelength-dependent albedo can be
inferred from the exoplanet's reflected light of the host star, but this is not
a trivial task. In fact, the planetary signal may be several orders of
magnitude lower ( or below) than the flux of the host star, thus
making its extraction very challenging. Successful detection of the planetary
signature of 51~Peg\,b has been recently obtained by using cross-correlation
function (CCF) or autocorrelation function (ACF) techniques. In this paper we
present an alternative method based on the use of Independent Component
Analysis (ICA). In comparison to the above-mentioned techniques, the main
advantages of ICA are that the extraction is \textit{"blind"} i.e. it does not
require any \textit{a priori} knowledge of the underlying signals, and that our
method allows us not only to detect the planet signal but also to estimate its
wavelength dependence. To show and quantify the effectiveness of our method we
successfully applied it to both simulated data and real data of an eclipsing
binary star system. Eventually, when applied to real 51~Peg~+~51~Peg\,b data,
our method extracts the signal of 51~Peg but we could not soundly detect the
reflected spectrum of 51~Peg\,b mainly due to the insufficient of the
input composite spectra. Nevertheless, our results show that with "ad-hoc"
scheduled observations an ICA approach will be, in perspective, a very valid
tool for studying exoplanetary atmospheres.Comment: 25 pages, 12 figures. Accepted to A
Cool Gaseous Exoplanets: surveying the new frontier with Twinkle
Cool gaseous exoplanets (,
K ~K) are an as-yet understudied population, with great
potential to expand our understanding of planetary atmospheres and formation
mechanisms. In this paper, we outline the basis for a homogeneous survey of
cool gaseous planets with Twinkle, a 0.45-m diameter space telescope with
simultaneous spectral coverage from 0.5-4.5~m, set to launch in 2025. We
find that Twinkle has the potential to characterise the atmospheres of 36 known
cool gaseous exoplanets (11~sub-Neptunian, 11~Neptunian, 14~Jovian) at an SNR
5 during its 3-year primary mission, with the capability of detecting
most major molecules predicted by equilibrium chemistry to >
significance. We find that an injected mass-metallicity trend is
well-recovered, demonstrating Twinkle's ability to elucidate this fundamental
relationship into cool regime. We also find Twinkle will be able to detect
cloud layers at 3 or greater in all cool gaseous planets for clouds at
10 Pa pressure level, but will be insensitive to clouds deeper than
Pa in all cases. With these results we demonstrate the capability of the
Twinkle mission to greatly expand the current knowledge of cool gaseous
planets, enabling key insights and constraints to be obtained for this
poorly-charted region of exoplanet parameter space.Comment: 14 pages, 6 figures, 6 table
Jupiter Atmospheric Models and Outer Boundary Conditions for Giant Planet Evolutionary Calculations
We present updated atmospheric tables suitable for calculating the
post-formation evolution and cooling of Jupiter and Jupiter-like exoplanets.
These tables are generated using a 1D radiative transfer modeling code that
incorporates the latest opacities and realistic prescriptions for stellar
irradiation and ammonia clouds. To ensure the accuracy of our model parameters,
we calibrate them against the measured temperature structure and geometric
albedo spectrum of Jupiter, its effective temperature, and its inferred
internal temperature. As a test case, we calculate the cooling history of
Jupiter using an adiabatic and homogeneous interior and compare with extant
models now used to evolve Jupiter and the giant planets. We find that our model
reasonably matches Jupiter after evolving a hot-start initial condition to the
present age of the solar system, with a discrepancy in brightness
temperature/radius within two per cent. Our algorithm allows us to customize
for different cloud, irradiation, and metallicity parameters. This class of
boundary conditions can be used to study the evolution of solar-system giant
planets and exoplanets with more complicated interior structures and
non-adiabatic, inhomogeneous internal profiles.Comment: 11 pages, 5 figures. Accepted to 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 Transit Spectra of Earth and Jupiter
In recent years, a number of observations have been made of the transits of
'Hot Jupiters', such as HD 189733b, which have been modelled to derive
atmospheric structure and composition. As measurement techniques improve, the
transit spectra of 'Super-Earths' such as GJ 1214b are becoming better
constrained, allowing model atmospheres to be fitted for this class of planet
also. While it is not yet possible to constrain the atmospheric states of small
planets such as the Earth or cold planets like Jupiter, this may become
practical in the coming decades and if so, it is of interest to determine what
we might infer from such measurements. Here we have constructed atmospheric
models of the Solar System planets from 0.4 - 15.5 microns that are consistent
with ground-based and satellite observations and from these calculate the
primary transit and secondary eclipse spectra (with respect to the Sun and
typical M-dwarfs) that would be observed by a 'remote observer', many light
years away. From these spectra we test what current retrieval models might
infer about their atmospheres and compare these with the 'ground truths' in
order to assess: a) the inherent uncertainties in transit spectra observations;
b) the relative merits of primary transit and secondary eclipse spectra; and c)
the advantages of directly imaged spectra. We find that secondary eclipses
would not give sufficient information, but that primary transits give much
better determination. We find that a single transit of Jupiter in front of the
Sun could potentially be used to determine temperature and stratospheric
composition, but for the Earth the mean atmospheric composition could only be
determined if it were orbiting an M-dwarf. For both planets we note that direct
imaging with sufficient nulling of the light from the parent star provides the
best method of determining the atmospheric properties of such planets
Dynamic mineral clouds on HD 189733b. II. Monte Carlo radiative transfer for 3D cloudy exoplanet atmospheres : combining scattering and emission spectra
G.L. and Ch.H. highlight the financial support of the European community under the FP7 ERC starting grant 257431.Context. As the 3D spatial properties of exoplanet atmospheres are being observed in increasing detail by current and new generations of telescopes, the modelling of the 3D scattering effects of cloud forming atmospheres with inhomogeneous opacity structures becomes increasingly important to interpret observational data. Aims. We model the scattering and emission properties of a simulated cloud forming, inhomogeneous opacity, hot Jupiter atmosphere of HD 189733b. We compare our results to available Hubble Space Telescope (HST) and Spitzer data and quantify the effects of 3D multiple scattering on observable properties of the atmosphere. We discuss potential observational properties of HD 189733b for the upcoming Transiting Exoplanet Survey Satellite (TESS) and CHaracterising ExOPlanet Satellite (CHEOPS) missions. Methods. We developed a Monte Carlo radiative transfer code and applied it to post-process output of our 3D radiative-hydrodynamic, cloud formation simulation of HD 189733b. We employed three variance reduction techniques, i.e. next event estimation, survival biasing, and composite emission biasing, to improve signal to noise of the output. For cloud particle scattering events, we constructed a log-normal area distribution from the 3D cloud formation radiative-hydrodynamic results, which is stochastically sampled in order to model the Rayleigh and Mie scattering behaviour of a mixture of grain sizes. Results. Stellar photon packets incident on the eastern dayside hemisphere show predominantly Rayleigh, single-scattering behaviour, while multiple scattering occurs on the western hemisphere. Combined scattered and thermal emitted light predictions are consistent with published HST and Spitzer secondary transit observations. Our model predictions are also consistent with geometric albedo constraints from optical wavelength ground-based polarimetry and HST B band measurements. We predict an apparent geometric albedo for HD 189733b of 0.205 and 0.229, in the TESS and CHEOPS photometric bands respectively. Conclusions. Modelling the 3D geometric scattering effects of clouds on observables of exoplanet atmospheres provides an important contribution to the attempt to determine the cloud properties of these objects. Comparisons between TESS and CHEOPS photometry may provide qualitative information on the cloud properties of nearby hot Jupiter exoplanets.Publisher PDFPeer reviewe
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