BULK COMPOSITION OF GJ 1214b AND OTHER SUB-NEPTUNE EXOPLANETS

Valencia, Diana; Guillot, T.; Parmentier, Vivien; Freedman, Richard

doi:10.1088/0004-637x/775/1/10

Cited by 184 publications

(203 citation statements)

References 36 publications

Supporting

Mentioning

194

Contrasting

Unclassified

Order By: Relevance

“…Kurokawa & Kaltenegger (2013) applied a heating efficiency η hν of 25% to their mass-loss study of CoRoT-7b and Kepler-10b similar to Leitzinger et al (2011). Valencia et al (2013) studied the bulk composition and thermal escape of the super-Earth GJ 1214b and other sub-Neptune-type exoplanets by assuming a lowest η hν value of 10% and a highest value of 40%. More or less similar lowest and highest η hν values of 15% and 40% have been assumed in recent works by Erkaev et al (2013), Lammer et al (2013), Erkaev et al (2014), Kislyakova et al (2013Kislyakova et al ( , 2014, and Lammer et al (2014), who studied the escape of hydrogen envelopes from early Mars and sub-Earths to super-Earths inside the habitable zone of a solar-like G-type star for XUV fluxes that are higher than several times to up to 100 times of the presentday Sun, as well as for five exoplanets between the super-Earth and mini-Neptune domain in the Kepler-11 system.…”

Section: Introductionmentioning

confidence: 99%

Heating efficiency in hydrogen-dominated upper atmospheres

Shematovich

Ionov

Lämmer

2014

A&A

121

106

View full text Add to dashboard Cite

Context. The heating efficiency η hν is defined as the ratio of the net local gas-heating rate to the rate of stellar radiative energy absorption. It plays an important role in thermal-escape processes from the upper atmospheres of planets that are exposed to stellar soft X-rays and extreme ultraviolet radiation (XUV). Aims. We model the thermal-escape-related heating efficiency η hν of the stellar XUV radiation in the hydrogen-dominated upper atmosphere of the extrasolar gas giant HD 209458b. The model result is then compared with previous thermal-hydrogen-escape studies, which assumed η hν values between 10-100%. Methods. The photolytic and electron impact processes in the thermosphere were studied by solving the kinetic Boltzmann equation and applying a Direct Simulation Monte Carlo model. We calculated the energy deposition rates of the stellar XUV flux and that of the accompanying primary photoelectrons that are caused by electron impact processes in the H 2 → H transition region in the upper atmosphere. Results. The heating by XUV radiation of hydrogen-dominated upper atmospheres does not reach higher values than 20% above the main thermosphere altitude, if the participation of photoelectron impact processes is included. Conclusions. Hydrogen-escape studies from exoplanets that assume η hν values that are ≥20% probably overestimate the thermal escape or mass-loss rates, while those who assumed values that are <20% produce more realistic atmospheric-escape rates.

show abstract

Section: Introductionmentioning

confidence: 99%

Heating efficiency in hydrogen-dominated upper atmospheres

Shematovich

Ionov

Lämmer

2014

A&A

121

106

View full text Add to dashboard Cite

show abstract

“…It is therefore more logical, from an observational point of view, to compare the evolution of two planets with the same mass and radius at a given epoch (5 Gyr in what follows). In this case, the two planets (volatile-poor and volatile-rich planet) cannot have the same gas fraction, and the difference in the evolution will be the result of both the change in volatile fraction (as demonstrated in the previous section) and of the change in gas fraction (as has been demonstrated in many papers, e.g., Nettelmann et al 2010;Valencia et al 2013;Lopez et al 2013, for planets in the mass range we consider here).…”

Section: Comparing Planets With Different Volatile Fractions and The mentioning

confidence: 79%

“…The effect of the gas fraction on the radius evolution of low-mass planets has been discussed elsewhere (see, e.g., Nettelmann et al 2010;Valencia et al 2013;Lopez et al 2013 among others). We focus in this section on the differential evolution of the two planets with the same gas fraction, but different volatile fraction.…”

Section: Physical Origin Of the Differential Radius Evolutionmentioning

confidence: 98%

Constraining the volatile fraction of planets from transit observations

Alibert

2016

A&A

View full text Add to dashboard Cite

Context. The determination of the abundance of volatiles in extrasolar planets is very important as it can provide constraints on transport in protoplanetary disks and on the formation location of planets. However, constraining the internal structure of low-mass planets from transit measurements is known to be a degenerate problem. Aims. Using planetary structure and evolution models, we show how observations of transiting planets can be used to constrain their internal composition, in particular the amount of volatiles in the planetary interior, and consequently the amount of gas (defined in this paper to be only H and He) that the planet harbors. We first explore planets that are located close enough to their star to have lost their gas envelope. We then concentrate on planets at larger distances and show that the observation of transiting planets at different evolutionary ages can provide statistical information on their internal composition, in particular on their volatile fraction. Methods. We computed the evolution of low-mass planets (super-Earths to Neptune-like) for different fractions of volatiles and gas. We used a four-layer model (core, silicate mantle, icy mantle, and gas envelope) and computed the internal structure of planets for different luminosities. With this internal structure model, we computed the internal and gravitational energy of planets, which was then used to derive the time evolution of the planet. Since the total energy of a planet depends on its heat capacity and density distribution and therefore on its composition, planets with different ice fractions have different evolution tracks. Results. We show for low-mass gas-poor planets that are located close to their central star that assuming evaporation has efficiently removed the entire gas envelope, it is possible to constrain the volatile fraction of close-in transiting planets. We illustrate this method on the example of 55 Cnc e and show that under the assumption of the absence of gas, the measured mass and radius imply at least 20% of volatiles in the interior. For planets at larger distances, we show that the observation of transiting planets at different evolutionary ages can be used to set statistical constraints on the volatile content of planets. Conclusions. These results can be used in the context of future missions like PLATO to better understand the internal composition of planets, and based on this, their formation process and potential habitability.

show abstract

“…between 2 and 3 Å R and likely has a massive heavy-element core. The compositions of planets in this region of the massradius diagram are not uniquely determined and could be a range of different admixtures of various chemical species, including iron, rock, water, and H/He (Rogers & Seager 2010;Valencia et al 2013). To assess possible compositions, we considered a couple of different two-layer planet models, and in each case we constrained the mass fraction of each layer.…”

Section: K2-66mentioning

confidence: 99%

K2-66b and K2-106b: Two Extremely Hot Sub-Neptune-size Planets with High Densities

Sinukoff

Howard

Petigura

et al. 2017

View full text Add to dashboard Cite

We report precise mass and density measurements of two extremely hot sub-Neptune-size planets from the K2 mission using radial velocities, K2 photometry, and adaptive optics imaging. K2-66 harbors a close-in subNeptune-sized ( -+ 2.49 0.24 0.34 Å R ) planet (K2-66b) with a mass of  21.3 3.6 Å M . Because the star is evolving up the subgiant branch, K2-66b receives a high level of irradiation, roughly twice the main-sequence value. K2-66b may reside within the so-called "photoevaporation desert," a domain of planet size and incident flux that is almost completely devoid of planets. Its mass and radius imply that K2-66b has, at most, a meager envelope fraction (<5%) and perhaps no envelope at all, making it one of the largest planets without a significant envelope. K2-106 hosts an ultra-short-period planet (P=13.7 hr) that is one of the hottest sub-Neptune-size planets discovered to date. Its radius ( -+ 1.82 0.14 0.20 Å R ) and mass (  9.0 1.6 Å M ) are consistent with a rocky composition, as are all other small ultra-short-period planets with well-measured masses. K2-106 also hosts a larger, longer-period planet (R p = -+ 2.77 0.23 0.37 Å R , P=13.3 days) with a mass less than 24.4 Å M at 99.7% confidence. K2-66b and K2-106b probe planetary physics in extreme radiation environments. Their high densities reflect the challenge of retaining a substantial gas envelope in such extreme environments.

show abstract

BULK COMPOSITION OF GJ 1214b AND OTHER SUB-NEPTUNE EXOPLANETS

Cited by 184 publications

References 36 publications

Heating efficiency in hydrogen-dominated upper atmospheres

Heating efficiency in hydrogen-dominated upper atmospheres

Constraining the volatile fraction of planets from transit observations

K2-66b and K2-106b: Two Extremely Hot Sub-Neptune-size Planets with High Densities

Contact Info

Product

Resources

About