A chemical survey of exoplanets with ARIEL

Abstract

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 welldefined planet sample within its 4-year mission lifetime. Transit, eclipse and phasecurve 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. H 2 O, CO 2 , CH 4 NH 3 , HCN, H 2 S through to the more exotic metallic compounds, such as TiO, VO, and condensed species. Simulations of ARIEL performance in conducting exoplanet surveys have been performedusing conservative estimates of mission performance and a

Strong biases in retrieved atmospheric composition caused by day–night chemical heterogeneities

“…We propose that 3D structural effects should already be consider when we study hot and ultra hot Jupiter to avoid erroneous conclusions. Moreover, future space missions such as JWST (Beichman et al 2014) and ARIEL (Tinetti et al 2018) will probe a very large range in wavelength (from 0.6 to 28 µm for JWST) and, then 3D effects will be even more evident in other parts of the exoplanetary spectra which has not been observed yet.…”

“…They thus offer the opportunity to study the chemistry and physics of planetary atmospheres under extreme conditions, for which we have no equivalent in the Solar System. These interesting objects will be prime targets for new generation space missions like the James-Webb Space Telescope (JWST) (Beichman et al 2014) and Atmospheric Remote-sensing Infrared Exoplanet Large-survey (ARIEL) (Tinetti et al 2018).…”

Smaller than Expected Bright-spot Offsets in Spitzer Phase Curves of the Hot Jupiter Qatar-1b

“…Overall, Qatar-1b makes an interesting target for the James Webb Space Telescope (JWST), especially as a comparison to WASP-43b, which will be observed extensively by JWST as part of Early Release Science and Guaranteed Time Observations (Bean et al 2018). The upcoming ARIEL mission will also be able to measure spectroscopic phase curves at a similar range of wavelengths as JWST (Tinetti et al 2018) and potentially probe time variability.…”

Normalized angular momentum deficit: a tool for comparing the violence of the dynamical histories of planetary systems

“…The capability of comparing the relative violence of the dynamical history of planetary systems would provide important insights into how planetary systems form and evolve and would prove critical to link the composition of planets to their formation history (e.g., Madhusudhan et al 2016;Turrini et al 2018), particularly in view of the future observations by the James Webb Space Telescope (e.g., Cowan et al 2015) and the space mission ARIEL (Atmospheric Remote-sensing Infrared Exoplanet Large-survey, Tinetti et al 2018;Turrini et al 2018) of the European Space Agency.…”