Internal Structure of Giant and Icy Planets: Importance of Heavy Elements and Mixing

Helled, Ravit; Guillot, T.

doi:10.1007/978-3-319-30648-3_44-1

Cited by 15 publications

(12 citation statements)

References 72 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The available measurements of the fundamental physical properties of Uranus and Neptune such as mass, radius, 1-bar temperature, and gravitational field can be used to constrain their interiors. However, there are still substantial uncertainties regarding their bulk compositions and internal structures, since the planets' interiors are complex and at the same time the available data are somewhat limited (e.g., 1995, Guillot, 2005, Podolak & Helled, 2012, Fortney & Nettelmann, 2010, Nettelmann et al, 2013, Helled & Guillot, 2018. In addition, the formation process of these planets remains a great challenge for planet formation theories, as well as their subsequent evolution.…”

Section: Introductionmentioning

confidence: 99%

Uranus and Neptune: Origin, Evolution and Internal Structure

2020

Self Cite

View full text Add to dashboard Cite

There are still many open questions regarding the nature of Uranus and Neptune, the outermost planets in the Solar System. In this review we summarize the current-knowledge about Uranus and Neptune with a focus on their composition and internal structure, formation including potential subsequent giant impacts, and thermal evolution. We present key open questions and discuss the uncertainty in the internal structures of the planets due to the possibility of non-adiabatic and inhomogeneous interiors. We also provide the reasoning for improved observational constraints on their fundamental physical parameters such as their gravitational and magnetic fields, rotation rates, and deep atmospheric composition and temperature. Only this way will we be able to improve our understating of these planetary objects, and the many similar-sized objects orbiting other stars.

show abstract

Section: Introductionmentioning

confidence: 99%

Uranus and Neptune: Origin, Evolution and Internal Structure

2020

Self Cite

View full text Add to dashboard Cite

show abstract

“…Uranus and Neptune, the solar system ice giants, are often considered as twin planets, mainly due to similar measurements of mass, radius, magnetic field, and atmospheric metallicity (Guillot & Gautier 2014;Helled & Guillot 2018). One fundamental difference between the planets is their luminosity: while Neptune's luminosity seems to be consistent with an adiabatic structure, Uranus' luminosity is significantly lower, indicating very low to zero intrinsic flux (Hubbard et al 1995;Fortney et al 2011;Nettelmann et al 2013).…”

Section: Introductionmentioning

confidence: 99%

Explaining the low luminosity of Uranus: a self-consistent thermal and structural evolution

Vazan

Helled

2020

A&A

Self Cite

View full text Add to dashboard Cite

The low luminosity of Uranus is a longstanding challenge in planetary science. Simple adiabatic models are inconsistent with the measured luminosity, which indicates that Uranus is non-adiabatic due to the existence of thermal boundary layers and/or conductive regions. A gradual composition distribution acts as a thermal boundary to suppress convection and slow down the internal cooling.Here we investigate whether composition gradients in Uranus' deep interior can explain its low luminosity, what composition gradient is required, and whether it is stable for convective-mixing for a timescale of billion of years. We vary the primordial composition distribution and the planet initial energy budget, and opt the models that fit Uranus measured properties (radius, luminosity, and moment of inertia) at present time. We present several alternative non-adiabatic internal structures that fit Uranus measurements. It is found that convection-mixing is limited in Uranus interior and a composition gradient is stable and sufficient to explain its current luminosity. As a result, Uranus' interior could still be very hot, in spite of its low luminosity. The stable composition gradient also indicates that Uranus' current-state internal structure is not very different from its primordial one. Moreover, initial energy content of Uranus cannot be greater than 20% of its formation (accretion) energy. We also find that an interior with ice+rock mixture, rather than separated ice and rock shells, is consistent with measurements, suggesting that Uranus might not be "differentiated". Our models can explain Uranus' luminosity and are also consistent with its metal-rich atmosphere, and the predictions for the location where its magnetic field is generated.In previous works we developed a detailed non-adiabatic structure evolution model for gas giants (Vazan et al. 2015(Vazan et al. , 2016. This model also includes the change in the interior structure in time by convective-mixing. The evolution of ice giants may be different than that of the gas giants. The more metalrich interior, lower mass, and high atmospheric metallicity affect the thermodynamic properties and the heat transport mechanism in the interior. Therefore, we expand our model by using the evolution features of metal-rich planets (Vazan et al. 2018b,c). We then apply our method to Uranus, and investigate whether a composition gradient is consistent with the low luminosity and the other measurements. Since we follow the entire evolution of Uranus interior in detail, the initial properties can be derived by its current-state.This paper is structured as follows, in Section 2 we describe the model initial composition and properties (Sec. 2.1, 2.2), the thermal and structural evolution methods (2.3), the nature of non-adiabatic structure evolution (2.4), and the parameters we fit (2.5). In Section 3 we present several examples of Uranus valid models (3.1), emphasis the importance of the non-adiabatic evolution (3.2), and summaries the properties of all valid models in our study (3....

show abstract

“…This is particularly true for Uranus whose internal heat source is close to zero. More details on non-adiabaticity of the outer planets can be found in Helled and Guillot (2017).…”

Section: Introductionmentioning

confidence: 99%

Effect of non-adiabatic thermal profiles on the inferred compositions of Uranus and Neptune

Podolak

Helled

Schubert

2019

Monthly Notices of the Royal Astronomical Society

Self Cite

View full text Add to dashboard Cite

It has been a common assumption of interior models that the outer planets of our solar system are convective, and that the internal temperature distributions are therefore adiabatic. This assumption is also often applied to exoplanets.However, if a large portion of the thermal flux can be transferred by conduction, or if convection is inhibited, the thermal profile could be substantially different and would therefore affect the inferred planetary composition. Here we investigate how the assumption of non-adiabatic temperature profiles in Uranus and Neptune affects their internal structures and compositions. We use a set of plausible temperature profiles together with density profiles that match the measured gravitational fields to derive the planets' compositions. We find that the inferred compositions of both Uranus and Neptune are quite sensitive to the assumed thermal profile in the outer layers, but relatively insensitive to the thermal profile in the central, high pressure region. The overall value of the heavy element mass fraction, Z, for these planets is between 0.8 and 0.9. Finally, we suggest that large parts of Uranus' interior might be conductive, a conclusion that is consistent with Uranus dynamo models and a hot central inner region. thermal profile. For planets in our solar system, where the mass, radius, and gravitational field are well characterized, the thermal profile remains ambiguous. For Jupiter it was long thought that this problem is not very acute and simple arguments could be made to strongly constrain the thermal profile and general composition. Jupiter's low density requires that a large fraction of its mass be composed of hydrogen and helium, while its high thermal flux requires that much of its volume be convective (Hubbard 1968), and this implies that much of the interior follows an adiabatic temperature profile. However, more recent work questions this view. The latest measurements of Jupiter's gravity field by the

show abstract

Internal Structure of Giant and Icy Planets: Importance of Heavy Elements and Mixing

Cited by 15 publications

References 72 publications

Uranus and Neptune: Origin, Evolution and Internal Structure

Uranus and Neptune: Origin, Evolution and Internal Structure

Explaining the low luminosity of Uranus: a self-consistent thermal and structural evolution

Effect of non-adiabatic thermal profiles on the inferred compositions of Uranus and Neptune

Contact Info

Product

Resources

About