Energy optimization in extrasolar planetary systems: the transition from peas-in-a-pod to runaway growth

Adams, Fred C.; Batygin, Konstantin; Bloch, Anthony M.; Laughlin, Gregory

doi:10.1093/mnras/staa624

Cited by 35 publications

(36 citation statements)

References 46 publications

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“…Common sizing of multiplanet systems has previously been found for Kepler systems (e.g., Millholland et al 2017;Wang 2017;Weiss et al 2018;Gilbert & Fabrycky 2020). From a planet formation standpoint, Adams et al (2020) found that energy optimization occurs when planets are nearly equal in mass for low-mass (super-Earth/sub-Neptune) planet systems, which is consistent with what we see with K2-138. Though, we note that the outer planets of K2-138 have larger radii than the inner planets, a trend consistent with the findings of Ciardi et al (2013), Millholland et al (2017, Kipping (2018), and Weiss et al (2018), possibly the result of enhanced photoevaporation closer to the star.…”

Section: G CMsupporting

confidence: 90%

K2-138 g: Spitzer Spots a Sixth Planet for the Citizen Science System

Hardegree-Ullman

Christiansen

Ciardi

et al. 2021

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K2 greatly extended Kepler's ability to find new planets, but it was typically limited to identifying transiting planets with orbital periods below 40 days. While analyzing K2 data through the Exoplanet Explorers project, citizen scientists helped discover one super-Earth and four sub-Neptune sized planets in the relatively bright (V = 12.21, K = 10.3) K2-138 system, all which orbit near 3:2 mean-motion resonances. The K2 light curve showed two additional transit events consistent with a sixth planet. Using Spitzer photometry, we validate the sixth planet's orbital period of 41.966 ± 0.006 days and measure a radius of, solidifying K2-138 as the K2 system with the most currently known planets. There is a sizeable gap between the outer two planets, since the fifth planet in the system, K2-138 f, orbits at 12.76 days. We explore the possibility of additional nontransiting planets in the gap between f and g. Due to the relative brightness of the K2-138 host star, and the near resonance of the inner planets, K2-138 could be a key benchmark system for both radial velocity and transit-timing variation mass measurements, and indeed radial velocity masses for the inner four planets have already been obtained. With its five sub-Neptunes and one super-Earth, the K2-138 system provides a unique test bed for comparative atmospheric studies of warm to temperate planets of similar size, dynamical studies of near-resonant planets, and models of planet formation and migration.

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Section: G CMsupporting

confidence: 90%

K2-138 g: Spitzer Spots a Sixth Planet for the Citizen Science System

Hardegree-Ullman

Christiansen

Ciardi

et al. 2021

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“…The longest contact phases, naturally found for our least massive systems (with a total system mass of 20 M ), lasts for about 10 Myr, and occur in systems with initial mass ratios near one. The majority of our contact binary models have the tendency to evolve towards equal component masses, corresponding to the lowest energy state of binary systems (Adams et al 2020). We find that the longer a system spends time in contact, the higher the likelihood that it attains a mass ratio of unity before merging on the main sequence.…”

Section: Discussionmentioning

confidence: 82%

Detailed evolutionary models of massive contact binaries – I. Model grids and synthetic populations for the Magellanic Clouds

Menon

Langer

Mink

et al. 2021

Monthly Notices of the Royal Astronomical Society

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The majority of close massive binary stars with initial periods of a few days experience a contact phase, in which both stars overflow their Roche lobes simultaneously. We perform the first dedicated study of the evolution of massive contact binaries and provide a comprehensive prediction of their observed properties. We compute 2790 detailed binary models for the Large and Small Magellanic Clouds each, assuming mass transfer to be conservative. The initial parameter space for both grids span total masses from 20 to 80 M⊙ , orbital periods of 0.6 to 2 days and mass ratios of 0.6 to 1.0. We find that models that remain in contact over nuclear timescales evolve towards equal masses, echoing the mass ratios of their observed counterparts. Ultimately, the fate of our nuclear-timescale models is to merge on the main sequence. Our predicted period-mass ratio distributions of O-type contact binaries are similar for both galaxies, and we expect 10 such systems together in both Magellanic Clouds. While we can largely reproduce the observed distribution, we over-estimate the population of equal-mass contact binaries. This situation is somewhat remedied if we also account for binaries that are nearly in contact. Our theoretical distributions work particularly well for contact binaries with periods <2 days and total masses ⪅45 M⊙ . We expect stellar winds, non-conservative mass transfer and envelope inflation to have played a role in the formation of the more massive and longer-period contact binaries.

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“…The discovery that more than half of all Sun‐like stars host close‐in planets intermediate in size between the Earth and Neptune (“sub‐Neptune size planets”) is perhaps the most profound discovery from NASA's Kepler mission—see Figure 1 (Fressin et al., 2013; Howard et al., 2012). The existence of these planets in large numbers wasn't predicted by planet formation theories (Ida & Lin, 2004; Mordasini et al., 2009), and their provenance remains hotly debated (e.g., F. C. Adams et al., 2020; Chiang & Laughlin, 2013; Ginzburg et al., 2016; Hansen & Murray, 2013; Izidoro et al., 2017; Lee & Chiang, 2016; Lee et al., 2014; Raymond & Cossou, 2014; Raymond et al., 2008; Raymond, Boulet, et al., 2018; L. A. Rogers et al., 2011; Schlichting, 2014).…”

Section: Introductionmentioning

confidence: 99%

The Nature and Origins of Sub‐Neptune Size Planets

2021

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Planets intermediate in size between the Earth and Neptune, and orbiting closer to their host stars than Mercury does the Sun, are the most common type of planet revealed by exoplanet surveys over the last quarter century. Results from NASA's Kepler mission have revealed a bimodality in the radius distribution of these objects, with a relative underabundance of planets between 1.5 and 2.0 R⊕. This bimodality suggests that sub‐Neptunes are mostly rocky planets that were born with primary atmospheres a few percent by mass accreted from the protoplanetary nebula. Planets above the radius gap were able to retain their atmospheres (“gas‐rich super‐Earths”), while planets below the radius gap lost their atmospheres and are stripped cores (“true super‐Earths”). The mechanism that drives atmospheric loss for these planets remains an outstanding question, with photoevaporation and core‐powered mass loss being the prime candidates. As with the mass‐loss mechanism, there are two contenders for the origins of the solids in sub‐Neptune planets: the migration model involves the growth and migration of embryos from beyond the ice line, while the drift model involves inward‐drifting pebbles that coagulate to form planets close‐in. Atmospheric studies have the potential to break degeneracies in interior structure models and place additional constraints on the origins of these planets. However, most atmospheric characterization efforts have been confounded by aerosols. Observations with upcoming facilities are expected to finally reveal the atmospheric compositions of these worlds, which are arguably the first fundamentally new type of planetary object identified from the study of exoplanets.

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Energy optimization in extrasolar planetary systems: the transition from peas-in-a-pod to runaway growth

Cited by 35 publications

References 46 publications

K2-138 g: Spitzer Spots a Sixth Planet for the Citizen Science System

K2-138 g: Spitzer Spots a Sixth Planet for the Citizen Science System

Detailed evolutionary models of massive contact binaries – I. Model grids and synthetic populations for the Magellanic Clouds

The Nature and Origins of Sub‐Neptune Size Planets

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