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Low-mass stars are currently the most promising targets when searching for potentially habitable planets, but new research has revealed that some of these stars produce significant amounts of ultraviolet (UV) radiation throughout their lifetimes. Such radiation could hinder the development of life on any orbiting planets.

M-dwarfs are stars that are cooler and less massive than stars like our Sun, and are the most common type of star in the Galaxy, meaning that it is vital that we better understand them and the influence they have on their planets.

Detecting terrestrial planets in the habitable zone – the region where liquid water can exist on a planet’s surface – when they pass in front of, or transit, Sun-like stars is difficult. This is partly because we only see a small dip in the light as the planet crosses the star, and also partly because their orbits are long enough that we have to wait several years to observe multiple transits. However, because M-dwarfs are smaller and cooler, the planets in their habitable zone are much closer to their star, resulting in larger and more frequent drops in light, making them easier to detect.

This makes M-dwarfs ideal candidates when searching for potentially habitable planets, which has led to habitable zone terrestrial planets being discovered around M-dwarfs including Proxima Centauri, TRAPPIST-1and Ross 128.

 Ultraviolet levels over time

A paper by astrophysicists Adam Schneider and Evgenya Shkolnik from Arizona State University, recently published in The Astronomical Journal,has revealed that the hottest and most massive M-dwarfs, referred to as ‘early type’, emit different amounts of UV radiation over their lifetime compared to the less massive and cooler ‘mid-’ and ‘late-type’ M-dwarfs. The paper used observations from NASA’s Galaxy Evolution Explorer (GALEX) spacecraft to study several populations of M-dwarfs in ultraviolet light.

M-dwarfs are known to emit higher levels of potentially harmful UV radiation than stars like our Sun. UV radiation can erode planetary atmospheres and have a detrimental effect on biology. It can also affect the abundances of molecules in planetary atmospheres, including carbon dioxide, oxygen and ozone……….

Harmful to life

The results suggest that lower-mass M-dwarfs have persistent UV radiation, which could rule out the possibility of life on any orbiting planets, including those around TRAPPIST-1 and Proxima Centauri………https://www.astrobio.net/alien-life/ultraviolet-radiation-from-low-mass-stars-could-render-planets-uninhabitable/