Extend the search for habitable planets to the soot line

2023-05-26 11:03:39

Artist’s impression of a young planet formation disk illustrating the respective locations of the soot and water-ice lines. – ARI GEA/SAYOSTUDIO.

MADRID, 26 May. (EUROPA PRESS) –

The search for habitable planets must extend to the area between the star and what is called the soot line in the planet-forming disks, suggests new research.

The worlds that form in this region, a disk of dust that revolves around a central star from which planets can be built, could have surfaces rich in volatile carbon compounds very different from those of Earth. These planets would also be rich in organic carbon but poor in water, according to Ted Bergin, an astronomer at the University of Michigan who led the study with a team of geochemists, planetary scientists, astrochemists and exoplanet experts.

When we search for planets similar to Earth, we are particularly interested not only in bodies that resemble our own, but also in those that are formed by processes similar to ours. Current models of rocky exoplanets are built using Earth-like atmospheric conditions and a bulk composition, including the essential molecules for life that are formed from carbon and water based building blocks.

These models also focus on zones within planet-forming disks called ice lines, regions far enough from the disk’s central star that they mark where water or other key molecules make the transition from gas to solid phase.

Terrestrial worlds, like our planet, were formed from solids. It has long been thought that the Earth, which contains only about 0.1% water by mass, it must have formed inside the water ice line.

But that kind of model may be too limited, Bergin said. To expand the search for habitable planets, Bergin and his research team suggest a new model that considers the soot line, a closer boundary to the star of the solar system. Between this boundary and the star, the organic compounds in the solids sublime from the solid into a gas. Taking into account that this region would also encompass rocky planets that may have more carbon than Earth, it raises questions about what that means for habitability on these kinds of planets.

The findings of the interdisciplinary research team are published in The Astrophysical Journal Letters.

“It adds a new dimension in our search for habitability. It can be a negative dimension or it can be a positive dimension,” Bergin said. “It’s exciting because it leads to all kinds of infinite possibilities.”

Just as the Earth is poor in water, it is also poor in carbon, Bergin said. When it formed, it probably received only 1 carbon atom for every 100 available in planet-forming materials. Astronomers believe that the soot line explains why Earth has so little carbon. If Earth’s building blocks formed within the soot line, temperature and solar radiation destroyed the materials that would form the young planet, turning carbon-rich compounds into gas and limiting the carbon in the solids that are supplied to the forming Earth.

The team’s model theorizes the formation of other planets born between the soot line and water ice lines.

Such a world does not appear to exist in our solar system, but our solar system is not representative of most known planetary systems around other stars, Bergin said. These other planetary systems look completely different. Its planets are closer to the sun and much larger, ranging in size from what are called super-Earths to mini-Neptunes, he said. it’s a statement.

“These are big rocks or small gas giants, that’s the most common type of planetary system. So perhaps, within all those other solar systems in the Milky Way galaxy, there is a population of bodies that we haven’t recognized before. They have a lot more carbon in their interiors, what are the consequences of that, Bergin said. “What this means for habitability needs to be explored.”

In their study, the team models what happens when a silicate-rich world with 0.1% and 1% carbon by mass and variable water content forms in the soot line region. They found that such a planet would develop a methane-rich atmosphere through a process called outgassing. In this circumstance, organic compounds on a silicate-rich planet produce a methane-rich atmosphere.

The presence of methane provides a fertile environment for haze generation through interactions with stellar photons. This is analogous to the generation of methane mists on Titan in our own solar system.

“Planets born within this region, which exists in every planet-forming disk system, will release more volatile carbon from their mantles.” Bergin said. “This could easily lead to the natural production of hazes. Such hazes have been observed in the atmospheres of exoplanets and have the potential to change the reckoning of what we consider to be habitable worlds.”

The haze around a planet could be a sign that the planet has volatile carbon in its mantle. And more carbon, the backbone of life, in a planet’s mantle means the planet has a chance of being considered habitable, or at least worth a second look, Bergin said.

“If this is true, then there could be a common class of hazy planets with abundant volatile carbonand what that means for habitability needs to be explored,” he said.