TOWARD CHEMICAL CONSTRAINTS ON HOT JUPITER MIGRATION

By N. Madhusudhan, M. Amin, G. Kennedy. 2014

149 citations recorded by the source corpus.

The origin of hot Jupiters—gas giant exoplanets orbiting very close to their host stars—is a long-standing puzzle. Planet formation theories suggest that such planets are unlikely to have formed in situ but instead may have formed at large orbital separations beyond the snow line and migrated inward to their present orbits. Two competing hypotheses suggest that the planets migrated either through interaction with the protoplanetary disk during their formation, or by disk-free mechanisms such as gravitational interactions with a third body. Observations of eccentricities and spin–orbit misalignments of hot Jupiter systems have been unable to differentiate between the two hypotheses. In the present work, we suggest that chemical depletions in hot Jupiter atmospheres might be able to constrain their migration mechanisms. We find that sub-solar carbon and oxygen abundances in Jovian-mass hot Jupiters around Sun-like stars are hard to explain by disk migration. Instead, such abundances are more readily explained by giant planets forming at large orbital separations, either by core accretion or gravitational instability, and migrating to close-in orbits via disk-free mechanisms involving dynamical encounters. Such planets also contain solar or super-solar C/O ratios. On the contrary, hot Jupiters with super-solar O and C abundances can be explained by a variety of formation–migration pathways which, however, lead to solar or sub-solar C/O ratios. Current estimates of low oxygen abundances in hot Jupiter atmospheres may be indicative of disk-free migration mechanisms. We discuss open questions in this area which future studies will need to investigate.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/c3177480e7b09ded10d2bf14477a3991c510afbf

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In Astronomy and Astrophysics

1. N. Madhusudhan
2. Jon Fortney
3. M. Line
4. A. Showman
5. Laura Kreidberg
6. J. D'esert
7. R. MacDonald
8. C. Mordasini

In Instrumentation

1. N. Madhusudhan
2. Jon Fortney
3. M. Line
4. Laura Kreidberg
5. A. Showman
6. J. D'esert
7. J. Bean
8. R. MacDonald

Citations in the corpus

• A DETECTION OF WATER IN THE TRANSMISSION SPECTRUM OF THE HOT JUPITER WASP-12b AND IMPLICATIONS FOR ITS ATMOSPHERIC COMPOSITION (2015, background): “…formation site, the relative accretion rates of gas and solids, and possible migration pathways (e.g. Atreya et al. 1999; Owen et al. 1999; Gautier et al. 2001; Atreya et al. 2003; Hersant et al. 2004; Lodders 2004; DodsonRobinson et al. 2009; Öberg et al. 2011; Madhusudhan et al. 2011a, 2014a).”
• HD 209458b in new light: evidence of nitrogen chemistry, patchy clouds and sub-solar water (2017, methodology): “…2013), temperature profiles (Haynes et al. 2015; Line et al. 2016), circulation patterns (Stevenson et al. 2014), clouds/hazes (Sing et al. 2016), and escape processes (Ehrenreich et al. 2015); for recent reviews see e.g. Madhusudhan et al. (2014a); Crossfield (2015); Madhusudhan et al. (2016c).”
• THE IMPRINT OF EXOPLANET FORMATION HISTORY ON OBSERVABLE PRESENT-DAY SPECTRA OF HOT JUPITERS (2016, methodology): “Madhusudhan et al. (2014) consider two different compositional models for the volatiles and refractory disk, one including carbon grains based on protoplanetary disk observations and one without 5 The solar C/O ratio is ∼ 0.56 (Asplund et al. 2009). carbon grains.”
• Chemical enrichment of giant planets and discs due to pebble drift (2017, methodology): “Similar abundance patterns were found in previous models that neglected radial drift (e.g. Madhusudhan et al. 2014a, 2016).”
• Retrieving scattering clouds and disequilibrium chemistry in the atmosphere of HR 8799e (2020, methodology): “Measuring a planet’s C/O has been suggested as a powerful tool to trace where in the protoplanetary disk a planet may have formed (e.g., Öberg et al. 2011; Madhusudhan et al. 2014b; Mordasini et al. 2016; Cridland et al. 2016).”
• Observing transiting planets with JWST. Prime targets and their synthetic spectral observations (2016, background): “While it was theorized that muted water features could also be caused by depletion of water (Madhusudhan et al. 2014b), or a general depletion of metals in the atmospheres, evidence nowadays seems to point to the presence of clouds (Sing et al. 2015a; Iyer et al. 2016) or a combination of clouds…”
• Mass–Metallicity Trends in Transiting Exoplanets from Atmospheric Abundances of H2O, Na, and K (2019, background): “An atmosphere depleted up to 100× in O/H while being enriched in other elements is unlikely (Madhusudhan et al. 2014a).”
• H2O abundances and cloud properties in ten hot giant exoplanets (2018, methodology): “Hot Jupiter atmospheres are expected to possess super-stellar oxygen abundances if they are formed through core-accretion followed by migration within the disk (Madhusudhan et al. 2014b; Mordasini MNRAS 000, 1–15 (2018)”
• Exoplanetary Atmospheres: Key Insights, Challenges, and Prospects (2019, methodology): “In previous studies, the treatment of chemistry in the disk was simplistic based on fixed condensation fronts depending on the mid plane temperature (197, 164).”