183 research outputs found
Spectral Evolution of an Earth-Like Planet
We have developed a characterization of the geological evolution of the
Earths atmosphere and surface in order to model the observable spectra of an
Earth-like planet through its geological history. These calculations are
designed to guide the interpretation of an observed spectrum of such a planet
by future instruments that will characterize exoplanets. Our models focus on
spectral features that either imply habitability or are required for
habitability. These features are generated by H2O, CO2, CH4, O2, O3, N2O, and
vegetation-like surface albedos. We chose six geological epochs to
characterize. These epochs exhibit a wide range in abundance for these
molecules, ranging from a CO2 rich early atmosphere, to a CO2/CH4-rich
atmosphere around 2 billion years ago to a present-day atmosphere. We analyzed
the spectra to quantify the strength of each important spectral feature in both
the visible and thermal infrared spectral regions, and the resolutions required
to unambiguously observe the features for each epoch. We find a wide range of
spectral resolutions required for observing the different features. For
example, H2O and O3 can be observed with relatively low resolution, while O2
and N2O require higher resolution. We also find that the inclusion of clouds in
our models significantly affects both the strengths and resolutions required to
observe all spectral features.Comment: 34 pages, 24 fig, pdf, ApJ, TB
Habitability of Earth-type Planets and Moons in the Kepler-16 System
We demonstrate that habitable Earth-mass planets and moons can exist in the
Kepler-16 system, known to host a Saturn-mass planet around a stellar binary,
by investigating their orbital stability in the standard and extended habitable
zone (HZ). We find that Earth-mass planets in satellite-like (S-type)orbits are
possible within the standard HZ in direct vicinity of Kepler-16b, thus
constituting habitable exomoons. However, Earth-mass planets cannot exist in
planetary-like (P-type) orbits around the two stellar components within the
standard HZ. Yet, P-type Earth-mass planets can exist superior to the Saturnian
planet in the extended HZ pertaining to considerably enhanced back-warming in
the planetary atmosphere if facilitated. We briefly discuss the potential
detectability of such habitable Earth-mass moons and planets positioned in
satellite and planetary orbits, respectively. The range of inferior and
superior P-type orbits in the HZ is between 0.657 to 0.71 AU and 0.95 to 1.02
AU, respectively.Comment: 14 pages, 3 figures, 1 table; Astrophysical Journal (in press
A scene model of exosolar systems for use in planetary detection and characterisation simulations
Instrumental projects that will improve the direct optical finding and
characterisation of exoplanets have advanced sufficiently to trigger organized
investigation and development of corresponding signal processing algorithms.
The first step is the availability of field-of-view (FOV) models. These can
then be submitted to various instrumental models, which in turn produce
simulated data, enabling the testing of processing algorithms. We aim to set
the specifications of a physical model for typical FOVs of these instruments.
The dynamic in resolution and flux between the various sources present in
such a FOV imposes a multiscale, independent layer approach. From review of
current literature and through extrapolations from currently available data and
models, we derive the features of each source-type in the field of view likely
to pass the instrumental filter at exo-Earth level.
Stellar limb darkening is shown to cause bias in leakage calibration if
unaccounted for. Occurrence of perturbing background stars or galaxies in the
typical FOV is unlikely. We extract galactic interstellar medium background
emissions for current target lists. Galactic background can be considered
uniform over the FOV, and it should show no significant drift with parallax.
Our model specifications have been embedded into a Java simulator, soon to be
made open-source. We have also designed an associated FITS input/output format
standard that we present here.Comment: 9 pages (+5 of appendices), 7 figures, accepted for publication in
Astronomy & Astrophysic
Earthshine observations of an inhabited planet
Earthshine is sunlight that has been reflected from the dayside Earth onto
the dark side of the Moon and back again to Earth. In recent times, there has
been renewed interest in ground-based visible and near-infrared measurements of
earthshine as a proxy for exoplanet observations. Observations of earthshine
allow us to explore and characterize the globally integrated photometric,
spectral and polarimetric features of the Earth, and to extract precise
information on the distinctive characteristics of our planet, and life in
particular. They also allow us to quantify how this feature changes with time
and orbital configuration. Here we present a brief review of the main
earthshine observations and results.Comment: To appear in the proceedings of the Les Houches Winter School
"Physics and Astrophysics of Planetary Systems",(EDP Sciences: EAS
Publications Series
Signals of exomoons in averaged light curves of exoplanets
The increasing number of transiting exoplanets sparked a significant interest
in discovering their moons. Most of the methods in the literature utilize
timing analysis of the raw light curves. Here we propose a new approach for the
direct detection of a moon in the transit light curves via the so called
Scatter Peak. The essence of the method is the valuation of the local scatter
in the folded light curves of many transits. We test the ability of this method
with different simulations: Kepler "short cadence", Kepler "long cadence",
ground-based millimagnitude photometry with 3-min cadence, and the expected
data quality of the planned ESA mission of PLATO. The method requires ~100
transit observations, therefore applicable for moons of 10-20 day period
planets, assuming 3-4-5 year long observing campaigns with space observatories.
The success rate for finding a 1 R_Earth moon around a 1 R_Jupiter exoplanet
turned out to be quite promising even for the simulated ground-based
observations, while the detection limit of the expected PLATO data is around
0.4 R_Earth. We give practical suggestions for observations and data reduction
to improve the chance of such a detection: (i) transit observations must
include out-of-transit phases before and after a transit, spanning at least the
same duration as the transit itself; (ii) any trend filtering must be done in
such a way that the preceding and following out-of-transit phases remain
unaffected.Comment: 9 pages, 5 figures, accepted for publication in MNRAS. Typos
correcte
Searching for transits in the Wide Field Camera Transit Survey with difference-imaging light curves
The Wide Field Camera Transit Survey is a pioneer program aiming at for searching extra-solar planets in the near-infrared. The images from the survey are processed by a data reduction pipeline, which uses aperture photometry to construct the light curves. We produce an alternative set of light curves using the difference-imaging method for the most complete field in the survey and carry out a quantitative comparison between the photometric precision achieved with both methods. The results show that differencephotometry light curves present an important improvement for stars with J > 16. We report an implementation on the box-fitting transit detection algorithm, which performs a trapezoid-fit to the folded light curve, providing more accurate results than the boxfitting model. We describe and optimize a set of selection criteria to search for transit candidates, including the V-shape parameter calculated by our detection algorithm. The optimized selection criteria are applied to the aperture photometry and difference-imaging light curves, resulting in the automatic detection of the best 200 transit candidates from a sample of ~475 000 sources. We carry out a detailed analysis in the 18 best detections and classify them as transiting planet and eclipsing binary candidates. We present one planet candidate orbiting a late G-type star. No planet candidate around M-stars has been found, confirming the null detection hypothesis and upper limits on the occurrence rate of short-period giant planets around M-dwarfs presented in a prior study. We extend the search for transiting planets to stars with J ≤ 18, which enables us to set a stricter upper limit of 1.1%. Furthermore, we present the detection of five faint extremely-short period eclipsing binaries and three M-dwarf/M-dwarf binary candidates. The detections demonstrate the benefits of using the difference-imaging light curves, especially when going to fainter magnitudes.Peer reviewe
SPECULOOS exoplanet search and its prototype on TRAPPIST
One of the most significant goals of modern science is establishing whether
life exists around other suns. The most direct path towards its achievement is
the detection and atmospheric characterization of terrestrial exoplanets with
potentially habitable surface conditions. The nearest ultracool dwarfs (UCDs),
i.e. very-low-mass stars and brown dwarfs with effective temperatures lower
than 2700 K, represent a unique opportunity to reach this goal within the next
decade. The potential of the transit method for detecting potentially habitable
Earth-sized planets around these objects is drastically increased compared to
Earth-Sun analogs. Furthermore, only a terrestrial planet transiting a nearby
UCD would be amenable for a thorough atmospheric characterization, including
the search for possible biosignatures, with near-future facilities such as the
James Webb Space Telescope. In this chapter, we first describe the physical
properties of UCDs as well as the unique potential they offer for the detection
of potentially habitable Earth-sized planets suitable for atmospheric
characterization. Then, we present the SPECULOOS ground-based transit survey,
that will search for Earth-sized planets transiting the nearest UCDs, as well
as its prototype survey on the TRAPPIST telescopes. We conclude by discussing
the prospects offered by the recent detection by this prototype survey of a
system of seven temperate Earth-sized planets transiting a nearby UCD,
TRAPPIST-1.Comment: Submitted as a chapter in the "Handbook of Exoplanets" (editors: H.
Deeg & J.A. Belmonte; Section Editor: N. Narita). 16 pages, 4 figure
SPICES: Spectro-Polarimetric Imaging and Characterization of Exoplanetary Systems
SPICES (Spectro-Polarimetric Imaging and Characterization of Exoplanetary
Systems) is a five-year M-class mission proposed to ESA Cosmic Vision. Its
purpose is to image and characterize long-period extrasolar planets and
circumstellar disks in the visible (450 - 900 nm) at a spectral resolution of
about 40 using both spectroscopy and polarimetry. By 2020/22, present and
near-term instruments will have found several tens of planets that SPICES will
be able to observe and study in detail. Equipped with a 1.5 m telescope, SPICES
can preferentially access exoplanets located at several AUs (0.5-10 AU) from
nearby stars (25 pc) with masses ranging from a few Jupiter masses to Super
Earths (2 Earth radii, 10 M) as well as circumstellar
disks as faint as a few times the zodiacal light in the Solar System
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