Strange lava worlds: Magma oceans affect the evolution of hot planets

Lava planets, characterized by their gleaming skies and turbulent seas of molten volcanic material, starkly differ from the celestial bodies within our solar system. 

Remarkably, around half of all identified rocky exoplanets demonstrate the ability to sustain surface magma, a phenomenon attributed to their proximity to host stars, resulting in orbits completed in less than 10 days. 

Such closeness subjects these planets to severe weather conditions and elevates surface temperatures, rendering them largely unsuitable for known life forms.

Hot Super-Earths

Now, a team of scientists led by Ohio State University (OSU) has highlighted the significant role of these vast molten oceans in determining the characteristics and evolutionary trajectory of hot rocky Super-Earths. 

The study, recently published in The Astrophysical Journal, discovered that the highly compressible nature of lava leads to magma-abundant planets without atmospheres being slightly denser than their solid counterparts, thus affecting the structure of their mantles, which encompass the core of the planet.

Complex nature

However, the complex nature of these celestial bodies makes understanding the basic principles governing lava planets challenging, according to Kiersten Boley, the study’s main author and an astronomy graduate student at OSU.

“Lava worlds are very odd, very interesting things and because of the way we detect exoplanets, we’re more biased to finding them,” said Boley, whose research focuses on understanding what crucial ingredients makes exoplanets unique and how tweaking these ingredients – or in the case of lava worlds, their temperatures – can fundamentally change them.

55 Cancri e, an exoplanet located approximately 41 light-years away and hosting both sparkling skies and roiling lava seas, stands as one of the most notable examples of these enigmatic burning worlds.

Insights into Earth’s past

While our solar system does contain highly volcanic entities like Jupiter’s moon Io, it lacks genuine lava planets for close study. 

However, according to Boley, exploring how the makeup of magma oceans influences the development of other celestial bodies can provides insights into Earth’s volcanic past.

“When planets initially form, particularly for rocky terrestrial planets, they go through a magma ocean stage as they’re cooling down,” she explained. “So lava worlds can give us some insight into what may have happened in the evolution of nearly any terrestrial planet.”

How the research was conducted 

Employing the exoplanet interior modeler software Exoplex and data from earlier studies, the researchers modeled several evolutionary scenarios for an Earth-like planet with surface temperatures ranging from 2,600 to 3,860 degrees Fahrenheit – temperatures at which the solid mantle would liquify.

What the researchers discovered 

The constructed models revealed three potential forms for magma ocean planets’ mantles: one entirely molten, another featuring a surface magma ocean, and a third exhibiting a layered structure with magma oceans at the surface and near the core, separated by a solid rock layer.

Interestingly, the study revealed that the second and third mantle structures appear slightly more frequently than entirely molten forms. 

The composition of the magma oceans on these planets impacts their ability to retain volatile elements crucial for early atmospheric formation for extended periods.

Study implications 

As Boley stresses, the capacity to trap significant amounts of volatile elements within their mantles has broader implications for planets habitability potential. 

“When we’re talking about the evolution of a planet and its potential to have different elements that you would need to support life, being able to trap a lot of volatile elements within their mantles could have greater implications for habitability,” she explained.

Although lava planets are far from hosting life, understanding the mechanisms that might lead them there is crucial. 

However, assessing their density is not the most accurate method for characterizing these planets compared to solid exoplanets, as the presence of a magma ocean doesn’t markedly alter a planet’s density.

Broader planetary studies 

The study suggests that focusing on different terrestrial aspects, such as variations in surface gravity, will yield more insights into the functioning of hot lava planets, which will be beneficial for future broader planetary studies.

“This work, which is a combination of earth sciences and astronomy, basically opens up exciting new questions about lava worlds,” Boley concluded.

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