Recent research demonstrates how the molecules in an exoplanet’s atmosphere might disclose whether or not the surface temperature is too high for liquid water in some situations.
Planets in our solar system are either tiny, stony, or huge, gaseous. However, scientists have discovered planets that are somewhat larger than Earth but smaller than Neptune in the vicinity of other stars. These planets may have rocky surfaces or liquid-water seas, but the majority of them are predicted to have atmospheres that are several times thicker and more opaque than Earth’s.
The current study demonstrates how the chemistry of such atmospheres might offer information about what is underneath. Most notably, which planets are too hot to have liquid-water seas. Because liquid water is required for life as we know it, this approach might aid scientists in narrowing their search for possibly habitable exoplanets, or worlds outside our solar system. More than 4,500 exoplanets have been verified in our galaxy, with over 7,700 candidates still awaiting confirmation, but astronomers believe that hundreds of billions of exoplanets exist in our galaxy.
The chemical composition of an exoplanet’s atmosphere can be revealed by NASA space telescopes equipped with spectrometers. A chemical profile of Earth would not disclose images of cows or humans on the planet’s surface, but it would indicate carbon dioxide and methane created by mammals, as well as oxygen produced by trees. None of these molecules would be evidence of life on their own, but when combined, they would indicate that our planet is populated.
The new study identifies which compounds might indicate the presence of hidden seas on exoplanets with diameters ranging from 1.7 to 3.5 times that of Earth. These planets are frequently referred to as sub-Neptunes since Neptune is roughly four times the diameter of Earth.
A dense atmosphere on a sub-Neptune planet would trap heat on its surface, raising its temperature. When the temperature of the atmosphere reaches a specific point, usually around 1,430 degrees Fahrenheit, a process known as thermochemical equilibrium occurs, which modifies the chemical profile of the atmosphere.
After thermochemical equilibrium is reached, and assuming the planet’s atmosphere is principally made up of hydrogen, as is normal for gaseous exoplanets, carbon and nitrogen will mostly exist as methane and ammonia.
In a cooler, thinner atmosphere, when thermochemical equilibrium has not happened, those compounds would be mostly absent. Carbon dioxide and molecules of two nitrogen atoms would be the dominating carbon and nitrogen forms in such circumstances.
According to the findings, an ocean beneath the atmosphere would leave further indications, such as the lack of practically all stray ammonia dissolved in the ocean.
Depending on the pH of the sea, ammonia gas is very soluble in water. When there is a large ocean beneath, the atmosphere should be nearly free of ammonia throughout a wide range of probable ocean pH values, the researchers discovered.
Furthermore, there would be more carbon dioxide than carbon monoxide in the atmosphere; by contrast, if measurable levels of either are present, there should be more carbon monoxide than carbon dioxide in the atmosphere following thermochemical equilibrium.
The James Webb Space Telescope which is scheduled to launch on December 18, will have a spectrometer to search the atmospheres of exoplanets. Scientists are predicting what types of chemical signatures Webb would find in those atmospheres and what they could indicate about these faraway worlds.
As Webb uncovers new planets or conducts more in-depth examinations of known planets, this data might help scientists decide which are worthy of more research, especially if scientists wish to target planets that could support life.