Many factors determine whether the planet will have the right conditions for life as we know it to emerge. And now scientists have once again expanded the potential population zone at the expense of clouds.

The habitable zone is a conditional zone around a star in which liquid water can exist on the surface of the planet. The region depends on the activity of the star as well as the characteristics of the planet’s surface and climate. The boundaries of this “belt” usually include some extreme climatic conditions; Under these conditions, liquid water could still be stored on the planet’s surface. The outer limit is generally calculated as the region where a planet with a dense carbon dioxide atmosphere would still be hot enough to have a liquid ocean, and the inner limit is calculated as the region where reflection of water vapor in the atmosphere would prevent the exoplanet from moving. superheating and boiling its oceans.

Unfortunately, our ability to observe exoplanets depends largely on the body’s distance from its star: the closer it is, the more difficult it is to discern the parameters of a potentially habitable world. It is even more difficult to “decipher” these observations, because such planets are very diverse, not all of them are analogues of Venus and Earth.

To prepare for analysis of data from existing observatories and future telescopes of the next generation, scientists are modeling these potentially habitable planets. The authors of the new study focused attention on objects located near the inner border of the residential area.

Previous studies have shown that in the presence of an ocean, the atmosphere on such planets becomes saturated with water vapor, creating a “humid greenhouse effect.” Although these planets cannot provide habitable conditions in the long term, they are stable enough to maintain liquid water on the surface for a long time.

It was believed that an explosive greenhouse effect inevitably occurs after the atmosphere becomes saturated with water. In this scenario, water vapor reaches the stratosphere (which is practically dry on Earth) where it is exposed to ultraviolet radiation. From this, H2O molecules break down into oxygen and hydrogen, and the latter quickly leaves the planet. According to scientists, this leads to loss of liquid water and rapid loss of vitality. But calculations using three-dimensional climate models showed that this pair, on the contrary, can protect the planet from the development of such events.

The problem is that the reflection of clouds is a complex process that depends on many factors, and the accuracy of such calculations can radically change the results and conclusions. To increase the accuracy of the calculations, the authors of the new study supplemented the one-dimensional model explaining the reflectivity of clouds with more complex microphysics of the clouds’ internal structures. The work is available on the preprint site arXiv.

Using the new model, researchers were able to accurately calculate the inner limit of the habitable zone of main sequence stars for the first time, taking into account the physics of clouds. It turns out that the limit depends mostly on four parameters: the radiation of the star, the radius of the planet, the density of clouds and precipitation.

Thus, with sufficient cloud cover, the inner limit of the habitable zone for systems such as Sun-Earth shifts from Earth’s orbit to the orbit between Mercury and Venus. And if you “increase” the parameters of clouds and precipitation, you get even closer to the star. It turns out that inhabited planets such as Earth may be 3.3 times closer to the star, and super-Earths may be 4.7 times closer than previously thought.

Researchers will continue to improve models as telescopes like the James Webb collect observation data. As you may remember, another group of scientists had recently proven that the power of this space telescope was sufficient to search for alien seas on some exoplanets. Moreover, detecting liquid water requires much less observation than researchers claim.