A University of Michigan astronomer and his team propose a new way to broaden the search for habitable worlds by considering a previously unaccounted for area: the space between a star and the so-called “soot line” in the dust disks where planets form.
The worlds forming in this region, a ring of dust spinning around a central star where planets could form, would likely have surfaces rich in volatile carbon compounds very different from those we see on Earth find, say .
These planets would also be rich in organic carbon but poor in water, says Ted Bergin, who led the research, which included geochemists, planetary scientists, astrochemists and exoplanet experts.
According to the team of scientists, when astronomers look for planets similar to our own, they are not only interested in celestial bodies that look like Earth, but also formed in much the same way. Current models of exoplanets are developed using Earth’s atmospheric conditions and composition, including the vital molecules formed from carbon-based components and water.
These models also focus on areas within planet-forming disks called ice lines, regions far enough from the host star where water or other essential molecules transition from the gaseous phase to the solid phase.
Earth worlds, like our planet, were formed from solid bodies. Researchers have long assumed that the earth must have formed in this ice region, and that the water makes up only about 0.1% of its mass.
Look closer to the stars
But this type of model is too limited, judges Mr. Bergin. To expand the possibilities for finding habitable planets, the researcher and his team propose a new model that takes into account the soot line, a boundary closer to a star in a solar system.
Between this boundary and the star, the organic components contained in the solids sublimate and become gases. Taking into account that there are also telluric (rocky) planets in this region that have more carbon than Earth, this raises questions about the habitability of these types of worlds, the researchers conclude.
The conclusions of the work will be published in The Astrophysical Journal Letters.
“It adds an extra dimension to our search for habitable planets. It could be both negative and positive,” says Mr. Bergin.
“It’s exciting because it opens the door to endless possibilities. »
Just as the earth is poor in water, it is also poor in carbon, Mr. Bergin recalls. When the planet formed, it probably received only one carbon atom for every 100 available atoms. Astronomers say the soot line explains why the Earth is so low in carbon.
As our planet’s “bricks” formed within the soot line, high temperature and solar radiation bombarded the materials that would form the new planet, converting carbon-rich components to gases and limiting the amount of carbon present in the solid materials were then used to build our world.
The model developed by the research team theorizes the formation of additional planets between the soot and ice lines.
Such a world does not appear to exist in our solar system, but it is not representative of known solar systems around other stars, Bergin said.
These other solar systems appear to be completely different: their planets are closer to their star and larger, ranging from the so-called “super-Earth” to “mini-Neptune,” the researcher notes.
“They’re either big rocks or small gas giants — that’s the most common type of planetary system.” So maybe in every other solar system in the galaxy there’s a group of celestial bodies that we haven’t recognized yet that have a lot more carbon have under their crust. What are the consequences? asks Herr Bergin.
“We still have to explore what this means for the habitability of the planets. »
“If you have an Earth-sized planet that contains more carbon than our world, what does that mean for the question of habitability? We don’t know, and that’s the exciting part! concludes the researcher.