37 research outputs found
Exoplanet phase curves: observations and theory
Phase curves are the best technique to probe the three dimensional structure
of exoplanets' atmospheres. In this chapter we first review current exoplanets
phase curve observations and the particular challenges they face. We then
describe the different physical mechanisms shaping the atmospheric phase curves
of highly irradiated tidally locked exoplanets. Finally, we discuss the
potential for future missions to further advance our understanding of these new
worlds.Comment: Fig.5 has been updated. Table 1 and corresponding figures have been
updated with new values for WASP-103b and WASP-18b. Contains a table
sumarizing phase curve observation
Exoplanet Atmosphere Measurements from Transmission Spectroscopy and other Planet-Star Combined Light Observations
It is possible to learn a great deal about exoplanet atmospheres even when we
cannot spatially resolve the planets from their host stars. In this chapter, we
overview the basic techniques used to characterize transiting exoplanets -
transmission spectroscopy, emission and reflection spectroscopy, and full-orbit
phase curve observations. We discuss practical considerations, including
current and future observing facilities and best practices for measuring
precise spectra. We also highlight major observational results on the
chemistry, climate, and cloud properties of exoplanets.Comment: Accepted review chapter; Handbook of Exoplanets, eds. Hans J. Deeg
and Juan Antonio Belmonte (Springer-Verlag). 22 pages, 6 figure
TRAPPIST-1: Global results of the Spitzer Exploration Science Program Red Worlds
With more than 1000 hours of observation from Feb 2016 to Oct 2019, the
Spitzer Exploration Program Red Worlds (ID: 13067, 13175 and 14223) exclusively
targeted TRAPPIST-1, a nearby (12pc) ultracool dwarf star orbited by seven
transiting Earth-sized planets, all well-suited for a detailed atmospheric
characterization with the upcoming JWST. In this paper, we present the global
results of the project. We analyzed 88 new transits and combined them with 100
previously analyzed transits, for a total of 188 transits observed at 3.6 or
4.5 m. We also analyzed 29 occultations (secondary eclipses) of planet b
and eight occultations of planet c observed at 4.5 m to constrain the
brightness temperatures of their daysides. We identify several orphan
transit-like structures in our Spitzer photometry, but all of them are of low
significance. We do not confirm any new transiting planets. We estimate for
TRAPPIST-1 transit depth measurements mean noise floors of 35 and 25 ppm
in channels 1 and 2 of Spitzer/IRAC, respectively. most of this noise floor is
of instrumental origins and due to the large inter-pixel inhomogeneity of IRAC
InSb arrays, and that the much better interpixel homogeneity of JWST
instruments should result in noise floors as low as 10ppm, which is low enough
to enable the atmospheric characterization of the planets by transit
transmission spectroscopy. We construct updated broadband transmission spectra
for all seven planets which show consistent transit depths between the two
Spitzer channels. We identify and model five distinct high energy flares in the
whole dataset, and discuss our results in the context of habitability. Finally,
we fail to detect occultation signals of planets b and c at 4.5 m, and can
only set 3 upper limits on their dayside brightness temperatures (611K
for b 586K for c)
An eclipsing substellar binary in a young triple system discovered by SPECULOOS
Mass, radius, and age are three of the most fundamental parameters for
celestial objects, enabling studies of the evolution and internal physics of
stars, brown dwarfs, and planets. Brown dwarfs are hydrogen-rich objects that
are unable to sustain core fusion reactions but are supported from collapse by
electron degeneracy pressure. As they age, brown dwarfs cool, reducing their
radius and luminosity. Young exoplanets follow a similar behaviour. Brown dwarf
evolutionary models are relied upon to infer the masses, radii and ages of
these objects. Similar models are used to infer the mass and radius of directly
imaged exoplanets. Unfortunately, only sparse empirical mass, radius and age
measurements are currently available, and the models remain mostly unvalidated.
Double-line eclipsing binaries provide the most direct route for the absolute
determination of the masses and radii of stars. Here, we report the SPECULOOS
discovery of 2M1510A, a nearby, eclipsing, double-line brown dwarf binary, with
a widely-separated tertiary brown dwarf companion. We also find that the system
is a member of the Myr-old moving group, Argus. The system's age
matches those of currently known directly-imaged exoplanets. 2M1510A provides
an opportunity to benchmark evolutionary models of brown dwarfs and young
planets. We find that widely-used evolutionary models do reproduce the mass,
radius and age of the binary components remarkably well, but overestimate the
luminosity by up to 0.65 magnitudes, which could result in underestimated
photometric masses for directly-imaged exoplanets and young field brown dwarfs
by 20 to 35%
Development of the SPECULOOS exoplanet search project
SPECULOOS (Search for habitable Planets EClipsing ULtra-cOOl Stars) aims to
perform a transit search on the nearest (pc) ultracool (K) dwarf
stars. The project's main motivation is to discover potentially habitable
planets well-suited for detailed atmospheric characterisation with upcoming
giant telescopes, like the James Webb Space Telescope (JWST) and European Large
Telescope (ELT). The project is based on a network of 1m robotic telescopes,
namely the four ones of the SPECULOOS-Southern Observatory (SSO) in Cerro
Paranal, Chile, one telescope of the SPECULOOS-Northern Observatory (SNO) in
Tenerife, and the SAINT-Ex telescope in San Pedro M\'artir, Mexico. The
prototype survey of the SPECULOOS project on the 60~cm TRAPPIST telescope
(Chile) discovered the TRAPPIST-1 system, composed of seven temperate
Earth-sized planets orbiting a nearby (12~pc) Jupiter-sized star. In this
paper, we review the current status of SPECULOOS, its first results, the plans
for its development, and its connection to the Transiting Exoplanet Survey
Satellite (TESS) and JWST
Mapping Exoplanets
The varied surfaces and atmospheres of planets make them interesting places
to live, explore, and study from afar. Unfortunately, the great distance to
exoplanets makes it impossible to resolve their disk with current or near-term
technology. It is still possible, however, to deduce spatial inhomogeneities in
exoplanets provided that different regions are visible at different
times---this can be due to rotation, orbital motion, and occultations by a
star, planet, or moon. Astronomers have so far constructed maps of thermal
emission and albedo for short period giant planets. These maps constrain
atmospheric dynamics and cloud patterns in exotic atmospheres. In the future,
exo-cartography could yield surface maps of terrestrial planets, hinting at the
geophysical and geochemical processes that shape them.Comment: Updated chapter for Handbook of Exoplanets, eds. Deeg & Belmonte. 17
pages, including 6 figures and 4 pages of reference
Refining the transit-timing and photometric analysis of TRAPPIST-1: Masses, Radii, densities, dynamics, and ephemerides
We have collected transit times for the TRAPPIST-1 system with the Spitzer
Space Telescope over four years. We add to these ground-based, HST and K2
transit time measurements, and revisit an N-body dynamical analysis of the
seven-planet system using our complete set of times from which we refine the
mass ratios of the planets to the star. We next carry out a photodynamical
analysis of the Spitzer light curves to derive the density of the host star and
the planet densities. We find that all seven planets' densities may be
described with a single rocky mass-radius relation which is depleted in iron
relative to Earth, with Fe 21 wt% versus 32 wt% for Earth, and otherwise
Earth-like in composition. Alternatively, the planets may have an Earth-like
composition, but enhanced in light elements, such as a surface water layer or a
core-free structure with oxidized iron in the mantle. We measure planet masses
to a precision of 3-5%, equivalent to a radial-velocity (RV) precision of 2.5
cm/sec, or two orders of magnitude more precise than current RV capabilities.
We find the eccentricities of the planets are very small; the orbits are
extremely coplanar; and the system is stable on 10 Myr timescales. We find
evidence of infrequent timing outliers which we cannot explain with an eighth
planet; we instead account for the outliers using a robust likelihood function.
We forecast JWST timing observations, and speculate on possible implications of
the planet densities for the formation, migration and evolution of the planet
system
Stellar Coronal and Wind Models: Impact on Exoplanets
Surface magnetism is believed to be the main driver of coronal heating and
stellar wind acceleration. Coronae are believed to be formed by plasma confined
in closed magnetic coronal loops of the stars, with winds mainly originating in
open magnetic field line regions. In this Chapter, we review some basic
properties of stellar coronae and winds and present some existing models. In
the last part of this Chapter, we discuss the effects of coronal winds on
exoplanets.Comment: Chapter published in the "Handbook of Exoplanets", Editors in Chief:
Juan Antonio Belmonte and Hans Deeg, Section Editor: Nuccio Lanza. Springer
Reference Work
A chemical survey of exoplanets with ARIEL
Thousands of exoplanets have now been discovered with a huge range of masses, sizes and orbits: from rocky Earth-like planets to large gas giants grazing the surface of their host star. However, the essential nature of these exoplanets remains largely mysterious: there is no known, discernible pattern linking the presence, size, or orbital parameters of a planet to the nature of its parent star. We have little idea whether the chemistry of a planet is linked to its formation environment, or whether the type of host star drives the physics and chemistry of the planet’s birth, and evolution. ARIEL was conceived to observe a large number (~1000) of transiting planets for statistical understanding, including gas giants, Neptunes, super-Earths and Earth-size planets around a range of host star types using transit spectroscopy in the 1.25–7.8 μm spectral range and multiple narrow-band photometry in the optical. ARIEL will focus on warm and hot planets to take advantage of their well-mixed atmospheres which should show minimal condensation and sequestration of high-Z materials compared to their colder Solar System siblings. Said warm and hot atmospheres are expected to be more representative of the planetary bulk composition. Observations of these warm/hot exoplanets, and in particular of their elemental composition (especially C, O, N, S, Si), will allow the understanding of the early stages of planetary and atmospheric formation during the nebular phase and the following few million years. ARIEL will thus provide a representative picture of the chemical nature of the exoplanets and relate this directly to the type and chemical environment of the host star. ARIEL is designed as a dedicated survey mission for combined-light spectroscopy, capable of observing a large and well-defined planet sample within its 4-year mission lifetime. Transit, eclipse and phase-curve spectroscopy methods, whereby the signal from the star and planet are differentiated using knowledge of the planetary ephemerides, allow us to measure atmospheric signals from the planet at levels of 10–100 part per million (ppm) relative to the star and, given the bright nature of targets, also allows more sophisticated techniques, such as eclipse mapping, to give a deeper insight into the nature of the atmosphere. These types of observations require a stable payload and satellite platform with broad, instantaneous wavelength coverage to detect many molecular species, probe the thermal structure, identify clouds and monitor the stellar activity. The wavelength range proposed covers all the expected major atmospheric gases from e.g. H2O, CO2, CH4 NH3, HCN, H2S through to the more exotic metallic compounds, such as TiO, VO, and condensed species. Simulations of ARIEL performance in conducting exoplanet surveys have been performed – using conservative estimates of mission performance and a full model of all significant noise sources in the measurement – using a list of potential ARIEL targets that incorporates the latest available exoplanet statistics. The conclusion at the end of the Phase A study, is that ARIEL – in line with the stated mission objectives – will be able to observe about 1000 exoplanets depending on the details of the adopted survey strategy, thus confirming the feasibility of the main science objectives.Peer reviewedFinal Published versio
The 0.8-4.5 μm Broadband Transmission Spectra of TRAPPIST-1 Planets
The TRAPPIST-1 planetary system represents an exceptional opportunity for the
atmospheric characterization of temperate terrestrial exoplanets with the
upcoming James Webb Space Telescope (JWST). Assessing the potential impact of
stellar contamination on the planets' transit transmission spectra is an
essential precursor step to this characterization. Planetary transits
themselves can be used to scan the stellar photosphere and to constrain its
heterogeneity through transit depth variations in time and wavelength. In this
context, we present our analysis of 169 transits observed in the optical from
space with K2 and from the ground with the SPECULOOS and Liverpool telescopes.
Combining our measured transit depths with literature results gathered in the
mid/near-IR with Spitzer/IRAC and HST/WFC3, we construct the broadband
transmission spectra of the TRAPPIST-1 planets over the 0.8-4.5 m spectral
range. While planets b, d, and f spectra show some structures at the 200-300ppm
level, the four others are globally flat. Even if we cannot discard their
instrumental origins, two scenarios seem to be favored by the data: a stellar
photosphere dominated by a few high-latitude giant (cold) spots, or,
alternatively, by a few small and hot (3500-4000K) faculae. In both cases, the
stellar contamination of the transit transmission spectra is expected to be
less dramatic than predicted in recent papers. Nevertheless, based on our
results, stellar contamination can still be of comparable or greater order than
planetary atmospheric signals at certain wavelengths. Understanding and
correcting the effects of stellar heterogeneity therefore appears essential to
prepare the exploration of TRAPPIST-1's with JWST