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The transiting exoplanet community early release science program for JWST
The transiting exoplanet community early release science program for JWST
The James Webb Space Telescope (JWST) presents the opportunity to transform
our understanding of planets and the origins of life by revealing the
atmospheric compositions, structures, and dynamics of transiting exoplanets in
unprecedented detail. However, the high-precision, time-series observations
required for such investigations have unique technical challenges, and prior
experience with other facilities indicates that there will be a steep learning
curve when JWST becomes operational. In this paper we describe the science
objectives and detailed plans of the Transiting Exoplanet Community Early
Release Science (ERS) Program, which is a recently approved program for JWST
observations early in Cycle 1. The goal of this project, for which the obtained
data will have no exclusive access period, is to accelerate the acquisition and
diffusion of technical expertise for transiting exoplanet observations with
JWST, while also providing a compelling set of representative datasets that
will enable immediate scientific breakthroughs. The Transiting Exoplanet
Community ERS Program will exercise the time-series modes of all four JWST
instruments that have been identified as the consensus highest priorities,
observe the full suite of transiting planet characterization geometries
(transits, eclipses, and phase curves), and target planets with host stars that
span an illustrative range of brightnesses. The observations in this program
were defined through an inclusive and transparent process that had
participation from JWST instrument experts and international leaders in
transiting exoplanet studies. Community engagement in the project will be
centered on a two-phase Data Challenge that culminates with the delivery of
planetary spectra, time-series instrument performance reports, and open-source
data analysis toolkits in time to inform the agenda for Cycle 2 of the JWST
mission
NGTS-4b: A sub-Neptune transiting in the desert
We report the discovery of NGTS-4b, a sub-Neptune-sized planet transiting a
13th magnitude K-dwarf in a 1.34d orbit. NGTS-4b has a mass M=M_E
and radius R=R_E, which places it well within the so-called
"Neptunian Desert". The mean density of the planet (g/cm^3) is
consistent with a composition of 100% HO or a rocky core with a volatile
envelope. NGTS-4b is likely to suffer significant mass loss due to relatively
strong EUV/X-ray irradiation. Its survival in the Neptunian desert may be due
to an unusually high core mass, or it may have avoided the most intense X-ray
irradiation by migrating after the initial activity of its host star had
subsided. With a transit depth of %, NGTS-4b represents the
shallowest transiting system ever discovered from the ground, and is the
smallest planet discovered in a wide-field ground-based photometric survey
An ultrahot Neptune in the Neptune desert
About 1 out of 200 Sun-like stars has a planet with an orbital period shorter than one day: an ultrashort-period planet1,2. All of the previously known ultrashort-period planets are either hot Jupiters, with sizes above 10 Earth radii (R⊕), or apparently rocky planets smaller than 2 R⊕. Such lack of planets of intermediate size (the ‘hot Neptune desert’) has been interpreted as the inability of low-mass planets to retain any hydrogen/helium (H/He) envelope in the face of strong stellar irradiation. Here we report the discovery of an ultrashort-period planet with a radius of 4.6 R⊕ and a mass of 29 M⊕, firmly in the hot Neptune desert. Data from the Transiting Exoplanet Survey Satellite3 revealed transits of the bright Sun-like star LTT 9779 every 0.79 days. The planet’s mean density is similar to that of Neptune, and according to thermal evolution models, it has a H/He-rich envelope constituting 9.0+2.7−2.9% of the total mass. With an equilibrium temperature around 2,000 K, it is unclear how this ‘ultrahot Neptune’ managed to retain such an envelope. Follow-up observations of the planet’s atmosphere to better understand its origin and physical nature will be facilitated by the star’s brightness (Vmag = 9.8).<br
The Transiting Exoplanet Community Early Release Science Program for JWST
The James Webb Space Telescope (JWST) presents the opportunity to transform our understanding of planets and
the origins of life by revealing the atmospheric compositions, structures, and dynamics of transiting exoplanets in
unprecedented detail. However, the high-precision, timeseries observations required for such investigations have
unique technical challenges, and prior experience with Hubble, Spitzer, and other facilities indicates that there will
be a steep learning curve when JWST becomes operational. In this paper, we describe the science objectives and
detailed plans of the Transiting Exoplanet Community Early Release Science (ERS) Program, which is a recently
approved program for JWST observations early in Cycle 1. We also describe the simulations used to establish the
program. The goal of this project, for which the obtained data will have no exclusive access period, is to accelerate
the acquisition and diffusion of technical expertise for transiting exoplanet observations with JWST, while also
providing a compelling set of representative data sets that will enable immediate scientific breakthroughs. The
Transiting Exoplanet Community ERS Program will exercise the timeseries modes of all four JWST instruments
that have been identified as the consensus highest priorities, observe the full suite of transiting planet
characterization geometries (transits, eclipses, and phase curves), and target planets with host stars that span an
illustrative range of brightnesses. The observations in this program were defined through an inclusive and
transparent process that had participation from JWST instrument experts and international leaders in transiting
exoplanet studies. The targets have been vetted with previous measurements, will be observable early in the
mission, and have exceptional scientific merit. Community engagement in the project will be centered on a twophase Data Challenge that culminates with the delivery of planetary spectra, timeseries instrument performance
reports, and open-source data analysis toolkits in time to inform the agenda for Cycle 2 of the JWST mission