Dust Could Guide Humanity to Habitable Planets

(CN) — New evidence released Tuesday suggests that the presence of airborne dust in the atmosphere of planets orbiting distant stars could be the key component to understanding potentially habitable planets.

According to a study published in the journal Nature Communications, planets with significant presence of airborne dust are increasingly capable of sustaining life, similar to the classic sci-fi movie "Dune." Planets that meet this criteria have an increasing window of habitability over various ranges of distance from their parent star.

In this study, a team of scientists from the University of Exeter, the Met Office and the University of East Anglia identified three main impacts of this airborne dust, all of which contribute to a more life-supporting environment.

Firstly, the researchers found that in planets orbiting close to M-dwarf stars, or stars cooler and smaller than the sun, there exist permanent day and night sides due to a synchronized rotation state.

In these planets, the dust widens the zones considered habitable, meaning that can support surface water, by cooling down the day side and warming the night side. So far, these types of planets are the most effective for detection and characterization of potentially habitable worlds.

“On Earth and Mars, dust storms have both cooling and warming effects on the surface, with the cooling effect typically winning out. But these 'synchronised 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,” said Ian Boutle, lead author of the study and jointly from the Met Office and the University of Exeter. “The effect is to moderate the temperature extremes, thus making the planet more habitable."

Researchers also found planets benefit from this airborne dust as it contributes to cooling the inner edge of these habitable zones. Temperatures can get so high in these zones, they cease to support surface water and become inhabitable, which is what is thought to have happened to Venus.

When a planet loses much of its water, dust can become more prevalent in its atmosphere and in turn cools the planet down. This is known as negative climate feedback, in which the reaction of dust cooling the atmosphere helps to maintain balance and prevent the loss of water.

The scientists also noted that the airborne dust needs to be taken into account when searching for key indicators of life, the same way methane indicates the presence of microbial life on Mars.

They further explain that, given this evidence, astronomers must be especially mindful when searching exoplanets for signs of life as the dust could obscure some of their readings, and the planet might be wrongfully dismissed as inhabitable.

"Airborne dust is something that might keep planets habitable, but also obscures our ability to find signs of life on these planets. These effects need to be considered in future research," said Manoj Joshi, a professor at Exeter.

Another aspect of this study was the consideration of mineral dust, which is known to have a considerable part to play in climate due to its optical properties of redistributing solar radiation. This has been seen on a regional level on Earth and on a global level on Mars.

Using the most advanced climate models available, the team conducted simulations of Earth-sized exoplanets and successfully depicted for the first time just how greatly mineral dust affects whether or not an exoplanet can support life.

The authors note that this study further proves the fact that a planet’s habitability depends on not only the amount of light energy given off by nearby stars, but also the atmospheric makeup.

Moving forward, identifying habitable planets will be a large focus of space exploration missions to discover life outside our solar system.

"It's exciting to see the results of the practical research in my final year of study paying off,” said Duncan Lyster, who led an undergraduate program as part of this study. “I was working on a fascinating exoplanet atmosphere simulation project, and was lucky enough to be part of a group who could take it on to the level of world-class research.”

"Research such as this is only possible by crossing disciplines and combing the excellent understanding and techniques developed to study our own planet's climate, with cutting edge astrophysics,” said Nathan Mayne, at the University of Exeter.

"To be able to involve undergraduate physics students in this, and other projects, also provides an excellent opportunity for those studying with us to directly develop the skills needed in such technical and collaborative projects,” Mayne said.

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