The Presence of Airborne Dust could Indicate that Distant Planets are more Habitable

Scientists have added a vital climate component, the presence of airborne dust, to our understanding of potentially habitable worlds orbiting distant stars. Dust particles can fly through the air from a variety of sources, including weather-lifted soil (an Aeolian process), volcanic eruptions, and pollutants.

Dust is produced in arid and dry areas where high-velocity winds can remove largely silt-sized particles. According to the researchers, planets with extensive airborne dust, like the world depicted in the classic sci-fi novel Dune, could be habitable at a wider range of distances from their parent star, hence expanding the window for planets capable of supporting life.

The University of Exeter, the Met Office, and the University of East Anglia (UEA) collaborated to identify three key dust impacts. Planets circling M dwarf stars, which are smaller and cooler than the Sun, are expected to have synchronized rotation-orbit states, leading in perpetual day and night sides.

Lunar dust collected inside the capsule during some Apollo flights to the moon caused eye irritation and breathing difficulties for the crew when they launched from the moon and regained “microgravity.”

Reactive and poisonous dust, such as lithium hydroxide, have posed a health risk to Shuttle crews, and fine particles from combustion events can be particularly dangerous. Due to the lack of gravity settling, airborne dust and particles tend to be bigger than on Earth under nominal spaceflight conditions.

Dust cools the hotter dayside but warms the cooler nightside, essentially expanding the planet’s ‘habitable zone,’ or the range of distances from the star where surface water may exist, according to the researchers. For these words, the most successful method of detection and characterization is now detection and characterization of possibly habitable distant planets.

The findings, which were published today in Nature Communications, also reveal that airborne dust could play a substantial role in planet cooling near the inner limit of the habitable zone, where it becomes so hot that planets lose their surface water and become habitable, as it did on Venus.

As the world’s water supply diminishes and its seas recede, the amount of dust in the atmosphere can rise, cooling the planet. This is a so-called negative climatic feedback, which delays the planet’s water loss.

Importantly, the findings show that dust must be taken into account while looking for crucial biomarkers indicative of life, such as the presence of methane because it can mask their signs as seen by astronomers.

On Earth and Mars, dust storms have both cooling and warming effects on the surface, with the cooling effect typically winning out. But these ‘synchronized orbit’ planets are very different. The dark sides of these planets are perpetually dark, and the warming effect prevails, whereas the cooling effect prevails on the dayside. The result is that temperature extremes are moderated, making the planet more habitable.

Dr. Ian Boutle

These findings, according to the researchers, signify that exoplanets must be carefully investigated before being ruled out in the quest for habitable faraway worlds.

Dr. Ian Boutle, lead author of the study and jointly from the Met Office and the University of Exeter said: “On Earth and Mars, dust storms have both cooling and warming effects on the surface, with the cooling effect typically winning out. But these ‘synchronized orbit’ planets are very different.”

“The dark sides of these planets are perpetually dark, and the warming effect prevails, whereas the cooling effect prevails on the dayside. The result is that temperature extremes are moderated, making the planet more habitable.”

Mineral dust is recognized to play a significant effect in climate, both regionally on Earth and worldwide on Mars.

Using state-of-the-art climate models, the study team ran a series of simulations of terrestrial or Earth-sized exoplanets, demonstrating for the first time that naturally existing mineral dust will have a significant impact on whether exoplanets can support life.

This study, according to UEA’s Prof Manoj Joshi, demonstrates how the ability of exoplanets to host life is dependent not just on stellar irradiance, or the quantity of light energy emitted by the nearest star, but also on the planet’s atmospheric make-up.

“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.”

Duncan Lyster, who is listed among the paper’s authors, contributed to the study endeavor as part of an undergraduate project. Duncan, who now runs his own business crafting surfboards added:

“It’s exciting to see the results of the practical research in my final year of study paying off. 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.”

The search for habitable planets beyond our solar system is an important aspect of present and future space missions, with many of them aimed at determining if we are alone.

Nathan Mayne, from the University of Exeter, who along with a co-author was able to work on this project thanks to funding from the Science and Technology Facilities Council (STFC) added: “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.”

“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.”

Now is a terrific time to study Physics, with game-changing facilities like the JWST and E-ELT likely to become accessible in the near future and set to provide a big leap forward in the study of exoplanets.