The primary goal of contemporary astronomy is to search for extraterrestrial life. All organisms on Earth require water, prompting scientists to postulate that locating water in space is essential for finding Earth-like life elsewhere. Discoveries indicate that substantial amounts of water exist in space, often in surprising locations. For example, researchers have identified frosty Calderas on Mars and water geysers on Saturn’s Moon Enceladus, among other sites, including the worlds of water surrounding other stars.
Nonetheless, water-rich exoplanets do not necessarily mimic Earth. A prevalent category of exoplanets known as Sub-Neptunes can be 2-4 times Earth’s radius, typically composed of more gas and ice. Researchers have determined the density of these sub-Neptunes, suggesting they may possess a substantial inner layer rich in water, encased in hydrogen layers. This structure diverges from Earth’s, which features thin surface oceans and expansive underground water reserves.
Additionally, scientists have found numerous sub-Neptunes in close orbit to their stars, revealing that they maintain elevated equilibrium temperatures. Consequently, these exoplanets are unable to sustain liquid water layers; instead, they exhibit a vapor atmosphere above a water layer in a state between liquid and gas, referred to as supercritical.
Gas and supercritical fluids dominate over liquids, resulting in Steam Worlds that are inflated compared to colder sub-Neptunes. Their larger radius is sensitive to temperature changes, causing them to expand as they move away from their host star and contract as they approach it. Although scientists have developed computer models of steam worlds previously, outcomes varied as they overlooked either contraction effects or aged deformation.
In pursuit of a clearer understanding of these steam worlds, a collaboration between US and UK scientists generated dynamic simulations of the known exoplanet GJ 1214B to assess its transformations over 20 billion years. Their model featured planets orbiting a red star with a mass less than seven times that of Earth and a radius exceeding 3.3 times Earth’s, with equilibrium temperatures around 540°F (280°C). They structured the model planet across five distinct layers: an inner iron core, varying upper and lower mantle compositions, a high-pressure ice layer, and an external fluid water envelope.
To monitor the temperature changes within their steam world over time, the research team focused on its interior rather than the outermost layer. For planets with vaporous outer layers subjected to solar evaporation, internal temperatures can exceed expectations since atmospheric gases can trap more heat than escape to space. This explains why Venus, the second planet from the Sun, is hotter than Mercury, the closest planet to the Sun.
The team found that their model exoplanet generally cooled and contracted over its lifespan. Starting with a radius over 3.3 times Earth’s and internal temperatures near 1,300°F (700°C), within less than 10 million years, its radius reduced to 2.9 times Earth’s with an internal temperature of 260°F (130°C). After 100 million years, it measured 2.7 times Earth’s radius, while internal temperatures dropped to -190°F (-120°C). Ultimately, after 20 billion years, the model planet’s radius was 2.6 times that of Earth, with a frigid interior temperature of -400°F (-230°C).
The final findings revealed a cooler interior exoplanet, smaller than earlier models of water-rich sub-Neptunes, indicating that it remained tightly compressed and did not lose mass. A denser planet holds less steam in its outer layers. Additionally, its inner ice layer was influenced by chemical transformations between ice and cold plasma, exhibiting properties of both liquid and solid forms, termed superion ice.
The researchers conceded that their model may not accurately reflect real sub-Neptunes, as they assumed pure water layers within the steam world. In reality, these layers likely contain chemical impurities, accompanied by an outer hydrogen and helium gas shell. Nonetheless, they posited that these outcomes could aid international researchers in better deciphering the entirety of Sub-Neptunes, as they indicate a potential relationship between a sub-Neptune’s radius, its density, and the age of its host system. All three characteristics are currently under examination in ongoing missions like JWST and Gaia.
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Source: sciworthy.com
