Another reason red dwarfs might be bad for life: There are no asteroid belts

In a recent study accepted in The Astrophysical Journal Letters, a team of researchers at the University of Nevada, Las Vegas (UNLV) investigated the possibility of life on exoplanets orbiting M-dwarf stars, also known as red dwarfs , which are both smaller and cooler than our own Sun and are currently open for debate about their potential for life in orbiting planetary bodies. The study examines how the lack of an asteroid belt might indicate a lower likelihood of life on terrestrial worlds.

For the study, the researchers observed several M-dwarf systems with exoplanets inside the habitable zone (HZ) and noted the lack of giant planets outside what they refer to as the “snowline radius,” which is the distance from a star where water forms permanent ice. In our own solar system, the giant planets beyond the asteroid belt also orbit beyond the radius of our snow line. The researchers note that it is because of these giant planets that the asteroid belt exists, causing some of these asteroids to be pushed into the inner solar system and possibly carrying life with it. The findings concluded that, “None of the currently observed planets in the habitable zone around M-dwarfs have a giant planet outside the snowline radius and are therefore unlikely to have a stable asteroid belt.” Given these findings, should we therefore increase or decrease our search for life in M-dwarf systems?

“I think M dwarfs are still a great place to look for life, as these systems can provide the most detailed observations of Earth-sized planets,” said Dr. Anna Childs, who is a postdoctoral fellow at the Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) at Northwestern University, is lead author of the study and conducted the research while a doctoral student at UNLV. “Because M-dwarf stars are so small and the habitable zone is closer to the star than around larger stars, it allows us to detect smaller planets and also better characterize the atmospheres of planets that are potentially habitable. This is what the James Webb Space Telescope will do with some planetary systems around M-dwarfs like TRAPPIST-1. Having more detailed information about the atmospheres of Earth-sized planets will give us much more information about the planet’s climate, composition and formation process. There are still many uncertainties regarding these important details about exoplanets. More detailed observations of smaller planets around M-dwarfs will put better constraints on these parameters that will help us characterize these planets more comprehensively.”

As mentioned, M dwarf stars are smaller and cooler than our Sun and range in size from 0.08 to 0.6 solar masses while exhibiting luminosities of 0.0001 to 0.1 times our Sun. This means that the HZ is also much further away from the star, which could lead to some interesting star-planet interactions. So what can M-dwarf stars teach us about planet formation and evolution?

“The discovered M-dwarf systems are exciting because they are so different from the solar system,” Dr Childs said. “We find more super-Earths and fewer giant planets around low-mass stars than we do around larger stars like our Sun. For a long time, the theory of planet formation was dominated by theories that did a good job of explaining the solar system. But these M-dwarf systems suggest that either we need a more generalized theory of planet formation that is able to explain systems that form around low- and high-mass stars, or that planet formation does indeed follow different formation pathways around low- and high-mass stars. mass. New theories about the formation of planets around low-mass stars continue to be formulated, and new detailed observations of these planets offer an exciting opportunity to test these new theories.”

Our Sun is classified as a G-type star and including M dwarfs, there are seven types of stars in our universe: O, B, A, F, G, K and M ranging from largest to smallest in both size and brightness. , but they range from shortest to longest in terms of lifespan. While the lifetime of our Sun is on the order of about 10 billion years, M-type stars like the one in this study can live up to about 200 billion years, which makes them interesting for studying life beyond. from Earth. So, which star system should we most aggressively search for life beyond Earth?

“Right now, we know of only one place in the universe that has life, and that’s around our Sun,” Dr. Childs said. “While there are many practical reasons to look for life around M-dwarfs, there may come a time when we have exhausted our methods and need to change our tactics and our goals. If we fail to find life around M dwarfs, the next logical place to look would be around Sun-like stars – especially in systems that have planetary architectures similar to the Solar System.”

For now, the search for life beyond Earth continues at a fever pitch. With new instruments only the James Webb Space Telescope and more ground-based telescopes coming online in the coming years, it would be a matter of time before we find even the tiniest traces of life beyond Earth. Unless we’ve already found it and just don’t know it.

“It is possible that we have observed planets that harbor life, but we simply do not yet have the technology capable of observing any subtle traces of it,” Dr Childs said. “Life elsewhere could also be so drastically different from our current understanding of it that we cannot recognize it when we observe it. I think it’s an important philosophical and scientific question: Would we recognize life on another world if we observed it? Constantly asking this question and trying to answer it in a fundamental way will increase our chances of finding life elsewhere.”

As always, keep doing science and keep looking up!

Featured image: An artist’s rendering of a very active red dwarf star. (Credit: NASA, ESA and D. Player (STScI))