(CN) — Exoplanets in Earth’s solar neighborhood have unique geological and mineral compositions, scientists say in a study published Tuesday that suggests greater planetary variety than previously believed.
When large stars like the Sun use up their energy, they eventually turn into small, denser stars called white dwarfs that can be surrounded by the rocky material of the exoplanets that once orbited them. In the paper published Tuesday in the journal Nature Communications, the authors analyze the atmospheres of 23 nearby white dwarfs to explore the composition of those exoplanets.
“We’ve just assumed that the planets’ [compositions] would mimic the stars that they orbit. If you had a Sun-like star and you take Earth and put it in a blender, you’d have a Sun-like composition,” Keith Putirka, a co-author of the research and professor of igneous petrology and volcanology at California State University, Fresno, said in an interview.
“When we look at these white dwarfs, we get planets that don’t look anything like a typical Sun-like star,” Putirka said. “It could be that in these extra solar systems, the ability for them to create planetary variability is much greater that we’ve thought and what we’d guess just looking at our own solar system.”
The researchers found no evidence in the white dwarf atmospheres that the exoplanets had the continental crust-type rocks that are abundant on Earth. According to Putirka, the research on the exoplanets ties back to planet Earth in big ways.
“As we look at exoplanets, it really reflects back on certain areas in which we’re relatively uncertain about Earth’s evolutionary path,” Putirka said. “How and why did plate tectonics get started here? Because that’s really the beginning of continental crust.”
Putirka said the “trajectory of biological evolution” on Earth is likely reliant on the planet’s geologic history, noting that life on Earth would be tremendously different without a continental crust. He said future scientific inquiries could examine if a planet with a similar composition, in a similar orbit or with a similar size star would look like Earth. Researchers could also examine the reasons for the differences between Earth and its neighbors Venus and Mars.
“When we look at Earth, does it look the way it does by chance or by necessity?” Putirka asked.
Siyi Xu, an observational astronomer at Gemini Observatory and co-author of the paper, said she hoped to conduct future research dealing with a greater number of white dwarfs and an expanded scope of analysis.
“I always want bigger telescopes, better data and hopefully a uniform data set,” Xu said. “The sample size is still pretty small and is rather heterogeneous. We focused on four elements, so it will be great if we can have a larger sample with a more uniform data set so we can really try to assess the diversity of the material.”
She added that the exotic rock types invited more discoveries regarding their formation and the conditions that created the exoplanets they likely came from.
“I really enjoyed this cool collaboration,” Xu said of her work with Putirka. “Now that we know of thousands of exoplanets, we’re moving to their characterization and understanding their habitability. I think it’s important to have this kind of interdisciplinary collaboration where we all learn something cool from each other and figure out a piece of the puzzle.”
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