Astrophysicists unlock the mysterious secrets of strange volcanic worlds

The study reveals how magma oceans can influence the evolution of hot exoplanets.

Massive exoplanets, home to lava worlds, glowing skies, and volcanic oceans called magma oceans, are unlike the planets in our solar system.

To date, approximately 50% of all rocky exoplanets discovered so far have been found to be capable of maintaining magma on their surfaces, as these planets are so close to their host stars that they orbit within 10 days. Being so close causes the planet to be bombarded with extreme weather conditions and to drop surface temperatures to extremes that make it completely inhospitable to life as we know it today.

Impact of melted oceans

Now, in a new study, scientists have shown that these swept-up molten oceans have a large influence on observed properties of hot rocky super-Earths, such as their size and evolutionary trajectory.

Their study, published recently The Astrophysical JournalDue to the highly compressible nature of lava, oceans of magma can make volcanic planets without atmospheres moderately denser than similar-sized solid planets, and can affect the structure of their mantles, the dense inner layer surrounding a planet’s core.

Even so, because these objects are notoriously understudied, characterizing the fundamental functions of volcanic planets is a difficult task, Kiersten Bohle said. She is the study’s lead author and a graduate student in astronomy at The Ohio State University.

Detection and understanding

„Lava worlds are very different, very interesting things, and because of finding exoplanets, we’re more biased toward finding them,” said Boley, whose research revolves around understanding what makes exoplanets unique and what changes those elements. As for volcanic worlds, their temperatures change them completely.

One of the most well-known of these mysterious burning worlds is 55 Cancri e, an extraterrestrial About 41 light-years away, scientists describe it as home to both twinkling skies and seas of lava.

When there are objects in our solar system, such as ThursdayThe Moon is, alas, so volcanically active that there are no true volcanic planets in space that scientists can get up close and personal with. However, studying how the composition of magma oceans contributes to the evolution of other planets, how long they stay molten and for what reasons they eventually cool, Boley said, can provide clues about Earth’s own fiery history.

„Early on when planets form, especially rocky terrestrial planets, they go through a magma ocean phase as they cool,” Boley said. „So lava worlds can give us some insight into what might have happened in the evolution of almost any terrestrial planet.”

Research techniques and findings

Using Exoplanet Interior Modeler software Exoplex And using data collected from previous studies to create a module that includes information on different types of magma compositions, the researchers simulated several evolutionary scenarios of an Earth-like planet with surface temperatures between 2600 and 3860 degrees. Fahrenheit – The melting point at which a planet’s solid mantle becomes liquid.

From the models they created, the team was able to learn that the mantles of magma ocean planets can take one of three forms: the first is where the entire mantle is completely melted, the second is a magma ocean on the surface, and a third sandwich-esque model is a magma ocean on the surface, with a layer of solid rock in the middle. and consists of another layer of molten magma closest to the planet’s core.

The results suggest that the second and third forms are slightly more abundant than completely molten planets. Depending on the composition of the magma oceans, some atmosphere-free exoplanets are better than others at trapping volatile elements — compounds like oxygen and carbon needed to form early atmospheres — for billions of years.

For example, the study notes that a basal magma-glass planet 4 times the size of Earth would trap 130 times more water than is in Earth’s oceans today and 1,000 times the amount of carbon currently present on the planet’s surface. and crust.

„When we’re talking about the evolution of a planet, and when you’re talking about the possibility of having different elements that you need to support life, trapping a lot of volatile elements into their crusts has more implications for life,” Boley said.

Habitat and implications for future research

Volcanic planets are far from becoming habitable enough to support life, but understanding the processes that help these worlds get there is important. Still, the study makes clear that measuring their density relative to solid exoplanets as magma oceans isn’t the best way to classify these worlds, Boley said, adding that the planet’s density doesn’t significantly increase or decrease.

Instead, their research reveals that scientists should focus on other topographic parameters, such as fluctuations in a planet’s surface gravity, especially if future researchers plan to use their data to aid larger planetary studies to test their theories about how hot volcanic worlds behave.

„This work, a combination of Earth science and astronomy, opens up exciting new questions about lava worlds,” Boley said.

Reference: “Fizzy Super-Earths: Impacts of Magma Composition on the Bulk Density and Structure of Lava Worlds” by Kiersten M. Boley, Wendy R. Panero, Cayman T. Unterborn, Joseph G. Schulze, Romy Rodríguez Martínez and Ji Wang, 7 September 2023, The Astrophysical Journal.
DOI: 10.3847/1538-4357/acea85

This study was supported by the National Science Foundation. Other co-authors are Wendy Panero, Joseph Schulz, Romy Martinez and Ji Wang of Ohio State and Camon Underborn of Southwestern Research Institute.