Protoplanetary Disks Around Tiny Stars Are Chemically Distinct From Those Surrounding the Sun, May Influence Atmosphere of Forming Planets

The size of stars in the center of protoplanetary disks influences their components, according to a study.

Protoplanetary Disks Around Low-Mass Stars Have Distinct Chemical Makeup

Through the James Webb Space Telescope's Mid-Infrared instrument, researchers investigated ISO-ChaI 147, a young star located in the Chameleon I star-forming region of around 237 stars. They learned that planets originating around relatively low-mass stars have different atmospheres due to the chemical differences between their planetary disks and those around more massive stars, such as the Sun.

These JWST observations of ISO-ChaI 147 suggest that smaller, Earth-like planets are more likely to develop on protoplanetary disks of tiny stars than massive, Jupiter-like gas giants. Because low-mass stars are more prevalent than bigger stars in the Milky Way, our galaxy may contain more terrestrial planets than previously thought.

The results also demonstrate that, at least chemically, the planet-birthing clouds of gas and dust orbiting small stars differ from those encircling stars the size of the Sun or larger. The rocky planets of these relatively tiny stars might have significantly different atmospheres from Earth due to the varied chemical composition of their surroundings.

"This is profoundly different from the composition we see in disks around solar-type stars, where oxygen-bearing molecules such as water and carbon dioxide dominate," Inga Kamp, team member and a researcher at the University of Groningen, said in a statement.

The discovery that the protoplanetary disks orbiting very low-mass stars grow differently from those surrounding more massive stars may have ramifications for the search for rocky planets with Earth-like properties, as the surroundings in these disks shape the conditions under which new planets originate. On the other hand, planets that resemble Earth in many respects but differ greatly in others may be found orbiting small stars.

According to Thomas Henning, a researcher at the Max Planck Institute for Astronomy (MPIA) and leader of the MINDS team, many of those planets' main atmospheres will likely be dominated by hydrocarbon compounds rather than oxygen-rich gases like carbon dioxide and water. In previous work, Henning said they demonstrated that in such disks, compared to those of more massive stars, the movement of carbon-rich gas into the zone where terrestrial planets often originate occurs faster and more efficiently.

However, they do not know why the protoplanetary disks of stars with different masses have varied carbon and oxygen contents. There are various theories for this. One is that it might result from carbon enrichment or oxygen depletion in the disks surrounding smaller stars.

What Is Protoplanetary Disk?

A protoplanetary disk is an intense gas and dust disc that revolves around a young, freshly created star, also known as a Herbig Ae/Be star or a T Tauri star. Because gasses or other materials may be falling from the inner edge of the protoplanetary disk onto the star's surface, the disk may also be considered an accretion disk for the star itself.

The accretion process assumed to have built up the planets themselves should not be confused with this process. Proplyds are photo-evaporating protoplanetary disks that are lit from the outside.

Molecular clouds made mostly of hydrogen molecules produce protostars. When a section of a molecular cloud reaches a critical mass, size, or density, it starts to collapse due to its own gravity.

Random gas motions that were initially present in the collapsing cloud, known as a solar nebula, average out in favor of the direction of the nebula's net angular momentum as the cloud gets denser. As the nebula radius shrinks, the rotation increases due to the conservation of angular momentum. The cloud takes on the shape of a disk due to its rotation, flattening out like a pizza formed from dough.

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