Researchers have discovered that the atmospheres of tidally locked exoplanets may be hidden by a layer of clouds on their dark sides, making it difficult to detect their atmospheric composition and potential habitability.
The Trouble with Red Dwarfs
Before we even delve into the list, here’s an important point: Red dwarf stars are by far the most abundant type of star in our Milky Way galaxy — so it is perhaps not surprising that most of the exoplanets we’ve discovered so far circle around these common stellar objects. That refers, of course, to the fact that most habitable worlds will almost certainly be located around these small, cool stars. But it is also a topic that poses great challenges.
Neither of these conditions bode well for habitability as we understand it on Earth since planets in such tight orbits around red dwarfs are subject to high levels of stellar flaring and risk becoming tidally locked. Tidal locking results when a planet’s rotation period is the same length as its orbital period, so that one side permanently faces the star and the other remains in darkness forever. Such a large temperature variation between day and night would render the planet uninhabitable — unless it has a thick atmosphere to moderate the temperatures.
Cloudy Deception
But astronomers have a neat trick up their sleeve for figuring out which it might be: measuring how big of a temperature difference there is between the poles and the night sides of those planets. This large temperature difference is a telltale sign that no warm little atmosphere exists to spread the warmth.
A new paper on the arXiv preprint server suggests that such a simple trick might actually be more complex than we previously thought. The scientists say large, thick clouds on the night side of a tidally locked planet might mask the temperature signal so that it would look as though no atmosphere was present at all.
Their models suggest that a planet with a thick atmosphere would show temperatures on the day and night sides differing by only about 50K, for example, closer to those in a dry part of Earth. However, that change in temperature could still be enough to initiate the creation of thick clouds on the dark side. In that case, these clouds would serve as an insulating blanket and the dark temperatures recorded by Webb in transmission spectra would be way cooler than its surface temperature.
Conclusion
The Black Side of Exoplanets Might Have Rains that Never Leave Nighttime HorizonsadminPinterest Image IconPinterest IconFlipboard Icon Print IconHelperand not just with hidden water: On Monday, scientists learned that the dark side may be drenched in daytime weather with no way to dry out. Benjamin SultanAtmosphere clouds exoplanet BrunoVergresNo place would hype up a rainy day like Kepler-7b. In the future, scientists will have to employ advanced methods to detect and study the atmospheres of such planets in more detail to determine whether they could host life. This result underscores the difficulties and revelations that come as we are only scratching the surface when it comes to understanding the rich tapestry of exoplanets.
Astronomers have a clever trick to detect whether a tidally locked planet has an atmosphere: by measuring the temperature difference between the day and night sides. If the temperature difference is dramatic, it suggests the planet lacks a significant atmosphere to distribute heat.
However, a new study published on the arXiv preprint server shows that this simple trick may not be so straightforward. The researchers argue that thick clouds on the dark side of a tidally locked planet could skew the temperature measurements, making it appear that the planet has no atmosphere, even if it does.
According to the researchers’ models, a planet with a thick atmosphere would have relatively moderate temperature differences between its day and night sides, similar to a dry region on Earth. But this temperature shift could still trigger the formation of dense clouds on the dark side. These clouds would then act as an insulating layer, causing the measured temperature of the dark side to be much colder than the planet’s actual surface temperature.
Conclusion
The discovery that exoplanets’ atmospheres may be hidden by clouds on their dark sides complicates the search for potentially habitable worlds. Researchers will need to develop more sophisticated techniques to accurately detect and analyze the atmospheres of tidally locked planets, in order to better understand their potential for supporting life. This finding highlights the ongoing challenges and surprises that emerge as we continue to explore the diverse and complex nature of exoplanets.
