A New Window into Planet Formation and Migration: Refractory-to-Volatile Elemental Ratios in Ultra-hot Jupiters

AbstractThere are now more than 35 stars with transiting planets for which the stellar obliquity—or more precisely its sky projection—has been measured, via the eponymous effect of Rossiter and McLaughlin. The history of these measurements is intriguing. For 8 years a case was gradually building that the orbits of hot Jupiters are always well-aligned with the rotation of their parent stars. Then in a sudden reversal, many misaligned systems were found, and it now seems that even retrograde systems are not uncommon. I review the measurement technique underlying these discoveries, the patterns that have emerged from the data, and the implications for theories of planet formation and migration.

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Chemical fingerprints of hot Jupiter planet formation

Astronomy and Astrophysics ◽

10.1051/0004-6361/201732001 ◽

2018 ◽

Vol 612 ◽

pp. A93 ◽

Cited By ~ 12

Author(s):

J. Maldonado ◽

E. Villaver ◽

C. Eiroa

Keyword(s):

Planet Formation ◽

Statistical Tests ◽

Giant Planets ◽

Volatile Elements ◽

Hot Jupiters ◽

Chemical Fingerprints ◽

Gas Giant ◽

Orbital Periods ◽

And Migration

Context. The current paradigm to explain the presence of Jupiter-like planets with small orbital periods (P < 10 days; hot Jupiters), which involves their formation beyond the snow line following inward migration, has been challenged by recent works that explore the possibility of in situ formation. Aims. We aim to test whether stars harbouring hot Jupiters and stars with more distant gas-giant planets show any chemical peculiarity that could be related to different formation processes. Methods. Our methodology is based on the analysis of high-resolution échelle spectra. Stellar parameters and abundances of C, O, Na, Mg, Al, Si, S, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, and Zn for a sample of 88 planet hosts are derived. The sample is divided into stars hosting hot (a < 0.1 au) and cool (a > 0.1 au) Jupiter-like planets. The metallicity and abundance trends of the two sub-samples are compared and set in the context of current models of planet formation and migration. Results. Our results show that stars with hot Jupiters have higher metallicities than stars with cool distant gas-giant planets in the metallicity range +0.00/+0.20 dex. The data also shows a tendency of stars with cool Jupiters to show larger abundances of α elements. No abundance differences between stars with cool and hot Jupiters are found when considering iron peak, volatile elements or the C/O, and Mg/Si ratios. The corresponding p-values from the statistical tests comparing the cumulative distributions of cool and hot planet hosts are 0.20, <0.01, 0.81, and 0.16 for metallicity, α, iron-peak, and volatile elements, respectively. We confirm previous works suggesting that more distant planets show higher planetary masses as well as larger eccentricities. We note differences in age and spectral type between the hot and cool planet host samples that might affect the abundance comparison. Conclusions. The differences in the distribution of planetary mass, period, eccentricity, and stellar host metallicity suggest a different formation mechanism for hot and cool Jupiters. The slightly larger α abundances found in stars harbouring cool Jupiters might compensate their lower metallicities allowing the formation of gas-giant planets.

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Connecting planet formation and astrochemistry

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834378 ◽

2019 ◽

Vol 627 ◽

pp. A127 ◽

Cited By ~ 14

Author(s):

Alexander J. Cridland ◽

Christian Eistrup ◽

Ewine F. van Dishoeck

Keyword(s):

Solar System ◽

Planet Formation ◽

Chemical Kinetic ◽

Total Carbon ◽

Dust Grains ◽

Excess Carbon ◽

Hot Jupiters ◽

And Migration ◽

Grain Surface ◽

Carbon Excess

Combining a time-dependent astrochemical model with a model of planet formation and migration, we compute the carbon-to-oxygen ratio (C/O) of a range of planetary embryos starting their formation in the inner solar system (1–3 AU). Most of the embryos result in hot Jupiters (M ≥ MJ, orbital radius <0.1 AU) while the others result in super-Earths at wider orbital radii. The volatile and ice abundance of relevant carbon and oxygen bearing molecular species are determined through a complex chemical kinetic code that includes both gas and grain surface chemistry. This is combined with a model for the abundance of the refractory dust grains to compute the total carbon and oxygen abundance in the protoplanetary disk available for incorporation into a planetary atmosphere. We include the effects of the refractory carbon depletion that has been observed in our solar system, and posit two models that would put this missing carbon back into the gas phase. This excess gaseous carbon then becomes important in determining the final planetary C/O because the gas disk now becomes more carbon rich relative to oxygen (high gaseous C/O). One model, where the carbon excess is maintained throughout the lifetime of the disk results in hot Jupiters that have super-stellar C/O. The other model deposits the excess carbon early in the disk life and allows it to advect with the bulk gas. In this model the excess carbon disappears into the host star within 0.8 Myr, returning the gas disk to its original (substellar) C/O, so the hot Jupiters all exclusively have substellar C/O. This shows that while the solids tend to be oxygen rich, hot Jupiters can have super-stellar C/O if a carbon excess can be maintained by some chemical processing of the dust grains. The atmospheric C/O of the super-Earths at larger radii are determined by the chemical interactions between the gas and ice phases of volatile species rather than the refractory carbon model. Whether the carbon and oxygen content of the atmosphere was accreted primarily by gas or solid accretion is heavily dependent on the mass of the atmosphere and where in the disk the growing planet accreted.

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Searching for 3D effects in the optical, high spectral resolution emission spectrum of KELT-9b

10.5194/epsc2021-308 ◽

2021 ◽

Author(s):

Lorenzo Pino ◽

Matteo Brogi ◽

Jean-Michel Désert ◽

Emily Rauscher

Keyword(s):

Emission Spectrum ◽

Spectral Resolution ◽

Planet Formation ◽

Emission Spectra ◽

Optical Emission ◽

High Spectral Resolution ◽

Optical Emission Spectrum ◽

Hot Jupiters ◽

Atmospheric Structure ◽

3D Effects

Ultra-hot Jupiters (UHJs; Teq &#8805; 2500 K) are the hottest gaseous giants known. They emerged as ideal laboratories to test theories of atmospheric structure and its link to planet formation. Indeed, because of their high temperatures, (1) they likely host atmospheres in chemical equilibrium and (2) clouds do not form in their day-side. Their continuum, which can be measured with space-facilities, can be mostly attributed to H- opacity, an indicator of metallicity. From the ground, the high spectral resolution emission spectra of UHJs contains thousands of lines of refractory (Fe, Ti, TiO, &#8230;) and volatile species (OH, CO, &#8230;), whose combined atmospheric abundances could track planet formation history in a unique way. In this talk, we take a deeper look to the optical emission spectrum of KELT-9b covering planetary phases 0.25 - 0.75 (i.e. between secondary eclipse and quadrature), and search for the effect of atmospheric dynamics and three-dimensionality of the planet atmosphere on the resolved line profiles, in the context of a consolidated statistical framework. We discuss the suitability of the traditionally adopted 1D models to interprete phase-resolved observations of ultra-hot Jupiters, and the potential of this kind of observations to probe their 3D atmospheric structure and dynamics. Ultimately, understanding which factors affect the line-shape in UHJs will also lead to more accurate and more precise abundance measurements, opening a new window on exoplanet formation and evolution.

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Giant Planet Formation and Migration

Space Science Reviews ◽

10.1007/s11214-018-0472-y ◽

2018 ◽

Vol 214 (1) ◽

Cited By ~ 5

Author(s):

Sijme-Jan Paardekooper ◽

Anders Johansen

Keyword(s):

Planet Formation ◽

Giant Planet ◽

And Migration

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Protoplanetary disc evolution in magnetically layered disc models

Symposium - International Astronomical Union ◽

10.1017/s0074180900218123 ◽

2004 ◽

Vol 202 ◽

pp. 319-321

Author(s):

Philip J. Armitage

Keyword(s):

Angular Momentum ◽

Planet Formation ◽

Momentum Transport ◽

Magnetohydrodynamic Turbulence ◽

Angular Momentum Transport ◽

And Migration ◽

Self Gravity

I discuss protoplanetary disc evolution under the assumption that magnetohydrodynamic turbulence and self-gravity are the sole sources of angular momentum transport. This assumption implies a magnetically layered disc structure which leads to unsteady accretion, and larger disc masses at late epochs. The resulting environment for planet formation and migration differs qualitatively from the highly simplified – almost toy – models often adopted.

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Connecting planet formation and astrochemistry

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936105 ◽

2019 ◽

Vol 632 ◽

pp. A63 ◽

Cited By ~ 12

Author(s):

Alex J. Cridland ◽

Ewine F. van Dishoeck ◽

Matthew Alessi ◽

Ralph E. Pudritz

Keyword(s):

Solar System ◽

Planet Formation ◽

Water Ice ◽

Hot Jupiters ◽

Formation History ◽

General Mass ◽

Exoplanetary Atmospheres ◽

Molecular Abundances ◽

Gas Accretion ◽

Oxygen Ratio

To understand the role that planet formation history has on the observable atmospheric carbon-to-oxygen ratio (C/O) we have produced a population of astrochemically evolving protoplanetary disks. Based on the parameters used in a pre-computed population of growing planets, their combination allows us to trace the molecular abundances of the gas that is being collected into planetary atmospheres. We include atmospheric pollution of incoming (icy) planetesimals as well as the effect of refractory carbon erosion noted to exist in our own solar system. We find that the carbon and oxygen content of Neptune-mass planets are determined primarily through solid accretion and result in more oxygen-rich (by roughly two orders of magnitude) atmospheres than hot Jupiters, whose C/O are primarily determined by gas accretion. Generally we find a “main sequence” between the fraction of planetary mass accreted through solid accretion and the resulting atmospheric C/O; planets of higher solid accretion fraction have lower C/O. Hot Jupiters whose atmospheres have been chemically characterized agree well with our population of planets, and our results suggest that hot-Jupiter formation typically begins near the water ice line. Lower mass hot Neptunes are observed to be much more carbon rich (with 0.33 ≲ C/O ≲ 1) than is found in our models (C/O ~ 10−2), and suggest that some form of chemical processing may affect their observed C/O over the few billion years between formation and observation. Our population reproduces the general mass-metallicity trend of the solar system and qualitatively reproduces the C/O metallicity anti-correlation that has been inferred for the population of characterized exoplanetary atmospheres.

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Planet formation in evolving protoplanetary discs

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313008296 ◽

2013 ◽

Vol 8 (S299) ◽

pp. 179-189 ◽

Cited By ~ 1

Author(s):

Richard Alexander

Keyword(s):

Planet Formation ◽

And Migration ◽

Protoplanetary Discs

AbstractI attempt to summarize our knowledge of planet formation in evolving protoplanetary discs. I first review the physics of disc evolution and dispersal. For most of the disc lifetime evolution is driven by accretion and photoevaporation, and I discuss how the interplay between these processes shapes protoplanetary discs. I also discuss the observations that we use to test these models, and the major uncertainties that remain. I will then move on to consider planet formation and migration in evolving discs, and discuss how observations of both discs and planets can be used to inform our understanding of protoplanetary disc evolution.

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Metals in the day-side of ultra-hot Jupiter atmospheres: a key test for planetary formation

10.5194/epsc2020-812 ◽

2020 ◽

Author(s):

Lorenzo Pino ◽

Jean-Michel Désert ◽

Matteo Brogi ◽

Valerio Nascimbeni ◽

Aldo Stefano Bonomo ◽

...

Keyword(s):

Emission Spectrum ◽

Planet Formation ◽

High Spectral Resolution ◽

Optical Data ◽

Thermal Inversion ◽

Hot Jupiters ◽

Refractory Elements ◽

Metal Abundances ◽

A New Technique ◽

Side Emission

Ultra-hot Jupiters (Teq &#8805;&#160;2,500 K) are the hottest gaseous giants known. They emerged as ideal laboratories to test theories of atmospheric structure and its link to planet formation. Indeed, because of their high temperatures, (1) they likely host atmospheres in chemical equilibrium and (2) clouds do not form in their day-side. Thousands of lines of refractory elements such as iron, normally inaccessible in planets, can be studied through high spectral resolution emission spectroscopy, providing a first look into the chemistry of refractory elements in exoplanets. In this talk we report the detection of neutral iron in the day-side emission spectrum of KELT-9b (Tday ~ 4,000&#160; K), the first detection of an atomic species in the emission spectrum of an exoplanet, obtained with HARPS-N optical data gathered in the framework of the GAPS collaboration. Our detection unambiguously indicates the presence of a thermal inversion in the atmosphere of the planet. We also present a new technique to extract planetary parameters from the cross-correlation function in a statistically sound framework, which makes possible the combination with information from the planetary continuum that can be obtained with complementary space facilities.&#160;This is a crucial step towards the measurement of metal abundances in exoplanets, a quantity that can be compared to predictions of planet formation theories. In the near future, our technique will be extended to cooler exoplanets. In the era of EELTs and JWST, this kind of measurements could ultimately open a new window on exoplanet formation and evolution.

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Radio Interferometry Observations of the Hallmarks of Planet Formation

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313007977 ◽

2013 ◽

Vol 8 (S299) ◽

pp. 80-89

Author(s):

Sean M. Andrews

Keyword(s):

Planet Formation ◽

Angular Resolution ◽

Planetary System ◽

Planetary Systems ◽

Protoplanetary Disks ◽

Circumstellar Disks ◽

High Angular Resolution ◽

Radio Interferometry ◽

New Directions ◽

And Migration

AbstractSome of the fundamental processes involved in the evolution of circumstellar disks and the assembly of planetary systems are just now becoming accessible to astronomical observations. The new promise of observational work in the field of planet formation makes for a very dynamic research scenario, which is certain to be amplified in the coming years as the revolutionary Atacama Large Millimeter/submillimeter Array (ALMA) facility ramps up to full operations. To highlight the new directions being explored in these fields, this brief review will describe how high angular resolution measurements at millimeter/radio wavelengths are being used to study several crucial aspects of the formation and early evolution of planetary systems, including: the gas and dust structures of protoplanetary disks, the growth and migration of disk solids, and the interactions between a young planetary system and its natal, gas-rich disk.

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