HOW THERMAL EVOLUTION AND MASS-LOSS SCULPT POPULATIONS OF SUPER-EARTHS AND SUB-NEPTUNES: APPLICATION TO THE KEPLER-11 SYSTEM AND BEYOND

By E. Lopez, Jon Fortney, N. Miller. 2012

281 citations recorded by the source corpus.

We use models of thermal evolution and extreme ultraviolet (XUV) driven mass loss to explore the composition and history of low-mass, low-density transiting planets. We investigate the Kepler-11 system in detail and provide estimates of both the current and past planetary compositions. We find that an H/He envelope on Kepler-11b is highly vulnerable to mass loss. By comparing to formation models, we show that in situ formation of the system is extremely difficult. Instead we propose that it is a water-rich system of sub-Neptunes that migrated from beyond the snow line. For the broader population of observed planets, we show that there is a threshold in bulk planet density and incident flux above which no low-mass transiting planets have been observed. We suggest that this threshold is due to the instability of H/He envelopes to XUV-driven mass loss. Importantly, we find that this mass-loss threshold is well reproduced by our thermal evolution/contraction models that incorporate a standard mass-loss prescription. Treating the planets' contraction history is essential because the planets have significantly larger radii during the early era of high XUV fluxes. Over time low-mass planets with H/He envelopes can be transformed into water-dominated worlds with steam envelopes or rocky super-Earths. Finally, we use this threshold to provide likely minimum masses and radial-velocity amplitudes for the general population of Kepler candidates. Likewise, we use this threshold to provide constraints on the maximum radii of low-mass planets found by radial-velocity surveys.

Subfields: Astronomy and Astrophysics, Instrumentation, Statistical and Nonlinear Physics

View Paper: https://www.semanticscholar.org/paper/6c9c749d0d2f764708373de213fa6649ef477bc9

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Citations in the corpus

The California-Kepler Survey. V. Peas in a Pod: Planets in a Kepler Multi-planet System Are Similar in Size and Regularly Spaced (2017, background): “Photo-evaporation (e.g., Lopez et al. 2012; Owen & Wu 2013; Zahnle & Catling 2017) could produce such an effect, since the expectation from photo-evaporation is that inner planets should be smaller than outer planets (assuming identical core masses), and that this effect should be more pronounced…”
HOW ROCKY ARE THEY? THE COMPOSITION DISTRIBUTION OF KEPLER’S SUB-NEPTUNE PLANET CANDIDATES WITHIN 0.15 AU (2014, background): “That said, the photoevaporation of subNeptunes is an active area of theoretical research (e.g. Owen & Jackson 2012; Lopez et al. 2012; Lammer et al. 2013), and so we err on the side of a simple yet theoretically motivated prescription to arrive at a realistic result.”
ALL SIX PLANETS KNOWN TO ORBIT KEPLER-11 HAVE LOW DENSITIES (2013, methodology): “The existence of such a mass-loss threshold is a robust predication of planet evolution models that include photoevaporation (Owen & Jackson 2012; Lopez et al. 2012).”
SUPER-EARTH ATMOSPHERES: SELF-CONSISTENT GAS ACCRETION AND RETENTION (2015, methodology): “In addition to this spontaneous mass shedding, gas envelopes are also vulnerable to evaporation by high-energy stellar photons (see, e.g. Lopez et al. 2012; Owen & Wu 2013).”
DENSITY AND ECCENTRICITY OF KEPLER PLANETS (2012, background): “7), and naturally produces planets with comparable core/envelope masses (also see discussions in Lopez et al. 2012).”
THE MASS OF KOI-94d AND A RELATION FOR PLANET RADIUS, MASS, AND INCIDENT FLUX (2013, background): “The current population of observed planets can be sculpted to some degree by evaporative mass loss (Baraffe et al. 2004, 2006; Hubbard et al. 2007; Lopez et al. 2012).”
KEPLER PLANETS: A TALE OF EVAPORATION (2013, methodology): “Low-mass planets Unlike the Jupiter-type planets discussed above, several authors have suggested that the effects of evaporation will be more prominent around lower mass planets (e.g. Hubbard et al. 2007a; Baraffe et al. 2008; Jackson et al. 2012; Owen & Jackson 2012; Lopez et al. 2012).”
BULK COMPOSITION OF GJ 1214b AND OTHER SUB-NEPTUNE EXOPLANETS (2013, background): “This stands in contrast to the findings by Nettelmann et al. (2011) and (Lopez et al. 2012).”
A FRAMEWORK FOR CHARACTERIZING THE ATMOSPHERES OF LOW-MASS LOW-DENSITY TRANSITING PLANETS (2013, background): “A more subtle but emerging trend is the incident flux versus planet density plane, which shows a lack of LMLD planets at high incident fluxes (Lopez et al. 2012; Lopez & Fortney 2013).”
Revised Radii of Kepler Stars and Planets Using Gaia Data Release 2 (2018, background): “Both results have been tied to processes such as photoevaporation (Lopez et al. 2012; Owen & Wu 2017), but are limited subsamples consisting of less than half of planet candidates.”
THE MASS OF Kepler-93b AND THE COMPOSITION OF TERRESTRIAL PLANETS (2014, background): “…predict that planets intermediate in size between Earth and Neptune could be gaseous “mini-Neptunes,” water worlds, or rocky “Super-Earths” (Kuchner 2003; Léger et al. 2004; Valencia et al. 2006; Seager et al. 2007; Fortney et al. 2007; Rogers et al. 2011; Lopez et al. 2012; Zeng & Sasselov 2013).”
Atmospheric Escape and the Evolution of Close-In Exoplanets (2018, background): “A key insight of this early work is that because low-mass planets have significantly large radii at young ages (in some cases up to 10 R⊕, Lopez et al. 2012; Lopez & Fortney 2013) and the received high energy fluxes were much higher as well, the majority of the mass-loss typically occurred in the…”
THE RADIUS DISTRIBUTION OF PLANETS AROUND COOL STARS (2013, background): “…systems have been measured from the effects of mutual gravitational interactions (e.g. Cochran et al. 2011, Lithwick et al. 2012, Nesvorny et al. 2013) providing insight into the composition and atmospheric evolution of these planets (Wu & Lithwick 2013; Owen & Wu 2013; Lopez et al. 2012).”
A REVISED ESTIMATE OF THE OCCURRENCE RATE OF TERRESTRIAL PLANETS IN THE HABITABLE ZONES AROUND KEPLER M-DWARFS (2013, background): “Planets with radius > 1.4 R⊕ are thought to have either homogeneous composition of water ice, silicate or iron or some differential composition of these compounds (Seager et al. 2007; Rogers et al. 2011; Lopez et al. 2012).”
The Evaporation Valley in the Kepler Planets (2017, unknown): “E P] 4 O ct 2 01 7 at large separations (e.g. Lopez et al. 2012; Owen & Wu 2013; Lopez & Fortney 2013; Jin et al. 2014; Howe & Burrows 2015).”
AN ANCIENT EXTRASOLAR SYSTEM WITH FIVE SUB-EARTH-SIZE PLANETS (2015, methodology): “Because the planetary masses are unknown (regardless of which star they orbit), we estimated their masses for an exhaustive range of compositional schemes using mass-radius relations derived from theoretical thermal evolution models (Fortney et al. 2007; Lopez et al. 2012).”
UNDERSTANDING THE MASS–RADIUS RELATION FOR SUB-NEPTUNES: RADIUS AS A PROXY FOR COMPOSITION (2013, methodology): “…mass is critical for understanding how volatile rich planets accrete their initial H/He envelope (Bodenheimer et al. 2000; Ikoma & Hori 2012) and whether they can retain it against X-ray and EUV driven photo-evaporation (Lopez et al. 2012; Lopez & Fortney 2013; Owen & Jackson 2012; Owen & Wu 2013).”