(ORDO NEWS) — Life on Earth began in the oceans. Therefore, when looking for life on other planets, the key factor in potential habitability is the possibility of the existence of liquid water.
To detect liquid water, scientists usually looked for Earth-like exoplanets. However, the long-term existence of liquid water may be possible not only on terrestrial planets.
In a new study, scientists report that maintaining conditions favorable for the existence of liquid water is possible for billions of years on planets that are completely different from Earth.
One of the reasons the Earth has liquid water is due to its atmosphere. The natural greenhouse effect keeps just the right amount of heat needed to form oceans, rivers and rain.
However, Earth’s ancient atmosphere differed significantly in composition from its modern atmosphere. When the Earth was forming, it attracted helium and hydrogen from the solar nebula, forming from them the so-called primary atmosphere. In the course of evolution, the Earth lost its primary atmosphere.
Other, more massive exoplanets are able to pull in more gas and form more massive primordial atmospheres, which they can hold for billions of years in some cases.
Such massive atmospheres can also contribute to the formation of the greenhouse effect, and in a new study, scientists led by Marit Mol Lous of the University of Bern, Switzerland, set out to find out whether planets with such atmospheres can develop the conditions necessary for long-term existence liquid water.
To achieve this goal, the team modeled a large number of different planets and their evolution over billions of years. Not only the properties of the atmospheres of the planets were taken into account, but also the intensity of the radiation of the parent stars and the internal sources of heat of the planets.
While on Earth geothermal heat sources make only a small contribution to the formation of temperature conditions on the surface, in the case of other planets with more massive, primordial atmospheres, this contribution can be significant.
As a result of the simulations, it was found that in many cases the primary atmospheres were lost into space under the influence of intense radiation from the stars, especially on planets located close to the stars.
However, in cases where atmospheric evaporation did not occur, suitable conditions for the formation of liquid water could be formed.
These conditions sometimes persisted for billions of years, and if there was a sufficiently powerful source of heat inside the planet, they could arise at a minimum intensity of stellar radiation and even in the case when the planet did not have a parent star, that is, it was the so-called orphan planet, or planet- a wanderer, the authors found.
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