Over the past few decades, humans have discovered thousands of exoplanets, which are worlds orbiting other stars. New observatories, such as the James Webb Space Telescope, are now working to resolve key features of these distant planets, including whether they might have the right conditions to support life.
One of the biggest open questions in this effort is whether extraterrestrials might exist on planets that orbit red dwarfs, also known as M dwarfs, a class of very small, dim stars that are extremely common in the Milky Way.
Now, Rafael Luque, postdoctoral researcher and astronomer at the University of Chicago, and Enric Pallé, astronomer at the Institute of Astrophysics of the Canary Islands and the University of La Laguna, present tantalizing new evidence that these systems contain d waterlogged. worlds, as well as rocky, gas-rich planets, which “could potentially be habitable if the right conditions are met,” according to a study published Thursday in Science.
The team reached this conclusion by compiling newly available mass and radius estimates of small worlds that orbit red dwarfs, in a unique approach. For years, scientists have been able to estimate the size of these exoplanets by watching them pass in front of their stars from our vantage point on Earth, but it wasn’t until recently that it became possible to estimate the mass of these worlds. .
With these two parameters, Luque and Pallé were able to analyze exoplanet densities in red dwarf systems, a value that can shed light on planetary composition where size alone is insufficient. For example, two planets can both be similar in size to Earth, but if one is made up of heavier rocky materials and the other is largely made up of much lighter ingredients, such as water, they will have very different masses.
The new study is the first to provide a population-level look at small exoplanets in red dwarf systems, with a sample of 43 such worlds, instead of the kinds of individual case-by-case studies that have been published. so far.
“We were building a large enough sample, for these types of stars only, to do a demographic study for the first time,” Luque said on a joint call with Pallé.
“No one had collected all the public data,” Pallé added. “Once you have mass and once you have radius, you can get densities, which is a much more physical property and more informative about the makeup of these planets, than just radius.”
As the researchers compiled the data, they were surprised to identify a strange type of exoplanet that appeared lighter in mass than previous estimates based solely on radius measurements. While planets like Earth are mostly made of rock, these worlds appear to contain up to 50% water by mass.
“Right after doing the analysis, we suddenly saw a lineup that was really striking,” Luque said. “We didn’t expect this line-up at all, because we never saw it. It was just a consequence of sample refinement, and that sample increased.
“I don’t think anyone in the field thought in the last five years that these aquatic worlds could exist and be as common as they are,” he added.
Since water is the key ingredient for life on Earth, this seems like good news in the search for extraterrestrial life. But while it might be exciting to imagine huge oceans filled with alien whales and squid, that’s not what these water-rich worlds look like, according to the models.
These exoplanets are likely more like big, dirty snowballs, Pallé said, merging into the icy confines of red dwarf systems and migrating closer to their stars over time. As a result, any molten water they harbor is buried in underground pockets, possibly mixed with magma, which may not be suitable environments for life. Some worlds, like Jupiter’s moon Europa, are known to contain subterranean oceans that could be habitable, but water-rich worlds orbiting red dwarfs are completely different because water, rock, and other materials are likely to be much more mixed within them. .
“Their true nature, we don’t know,” Pallé said. “It’s something new.”
While the researchers stressed that their study makes no direct statements about the habitability of these worlds, they said the findings have implications for future work that could address the chances of life around red dwarfs. For example, the study found an abundance of rocky worlds that appear similar in density and composition to Earth, suggesting that analogues of our planet may be common in red dwarf systems. The team also identified a third type of gas-rich exoplanet, known as sub-Neptunes, which may contain habitable regions with water.
Red dwarf systems provide “low-hanging fruits of possible habitable environments,” Pallé said, because it’s easier to spot potential signs of life, known as biomarkers, on their exoplanets. Planets orbiting red dwarfs can block more of the light from their stars as they pass in front of them, compared to planets orbiting larger stars, producing a better contrast ratio for disentangling their characteristics.
“The sample of M dwarfs from minor planets is important because it is the one that will be accessible for studies of atmospheres and the search for biomarkers in the near future – the next two or three decades – because minor planets are easy to detect. .and easy to characterize if the star is that small,” Pallé noted.
Luque also plans to conduct more population-level studies of exoplanets among larger classes of stars, to see if strange water-rich worlds are common beyond red dwarf systems.
To extend our sample to different types of stars is something very immediate and a logical consequence, and also to study these planets with the [James Webb Space Telescope]”, Luque said.
This is something the community will be happy to test – what are the properties of these water worlds, the smaller ones and also these sub-Neptunes? he concluded. “How much water do they have?” What are the properties of their atmospheres, if any? These are questions that I would say that in the next few years the field will try to answer.