More Earth-Like Planets May Be Habitable Than Previously Thought If We Consider Airborne Dust

Simulations of exoplanets with airborne dust (color scale) and wind (arrows) around an M-dwarf host star (in the background), has effectively widened the habitable zones of stars. Denis Sergeev/ University of Exeter

Katy Pallister 10 Jun 2020, 17:02

When you picture a distant planet, your mind may jump to an image of a barren landscape with swirling clouds of dust (like in the sci-fi film Dune). Astronomers now believe that Earth-like planets that possess significant amounts of airborne dust could sustain life even if they orbit outside of a star’s habitable zone. Researchers from the UK used a series of simulations to highlight three areas in which our understanding of potentially habitable worlds can be enhanced by exploring the impact of dusty atmospheres.

The team first focused on planets outside of our Solar System that orbit smaller and cooler stars than our Sun (so-called M-dwarfs) at close distances, which are not thought to allow liquid water to exist. However, these planets are likely tidally locked (or have a “synchronized orbit”), meaning they have a permanent day and night side. If their atmospheres were also saturated with dust, their warmer day side cools and the cooler night side warms up, making for a much more moderate climate that could support life.

“On Earth and Mars, dust storms have both cooling and warming effects on the surface, with the cooling effect typically winning out,” lead author Dr Ian Boutle, from the Met Office and the University of Exeter, said in a statement. “But these ‘synchronized orbit’ planets are very different. Here, the dark sides of these planets are in perpetual night, and the warming effect wins out, whereas on the dayside, the cooling effect wins out. The effect is to moderate the temperature extremes, thus making the planet more habitable.”

Boutle and his team’s second point relates to planets sitting on the inner edge of a star’s habitable zone. Here, planets that may have surface water could lose it due to the heat from its host star. As the authors explain in their study published in Nature Communications, shrinking oceans can increase the amount of atmospheric dust, which in turn cools down the planet and postpones further water loss. This negative climate feedback could extend the habitability of a planet.

But the importance of dust doesn’t stop there. These naturally occurring particles were found by the researchers to obscure markers for life (biomarkers), such as methane, from scientists' observations. They warn that worlds should not be classified as habitable before the effects of dust are accounted for.

“Airborne dust is something that might keep planets habitable, but also obscures our ability to find signs of life on these planets,” Professor Manoj Joshi, co-author from the University of East Anglia, said in a statement. “These effects need to be considered in future research.”

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