As most of you probably already know, water is generally considered to be essential for life (as we know it). Consequently, we focus on the existence of water in our search for extraterrestrial life.
Interestingly, our ideas about water on planets may have been a tad too Earth-centric. Swiss researchers have recently determined that liquid water can exist for billions of years on exotic planets that we would previously have ignored.
Exoplanets we may have previously overlooked could potentially harbor exotic habitats for billions of years! - (Image Credit: Thibaut Roger - Universität Bern - Universität Zürich Thibaut Roger (CC BY-NC-SA 4.0))
A group of researchers affiliated with the University of Zurich and the University of Bern in Switzerland published a paper in the peer-reviewed science journal Nature Astronomy in which they took a closer look at the conditions necessary to sustain liquid water for very long periods of time.
Professor of Theoretical Astrophysics at the University of Zurich, Ravit Helled, explains that one of the reasons that liquid water can exist on the surface of Earth is its atmosphere. Helled: "With its natural greenhouse effect, it traps just the right amount of heat to create the right conditions for oceans, rivers and rain."
Millions of years ago, our atmosphere was very dissimilar to what we see today. When our planet first formed out of dust and cosmic gas, it accumulated an atmosphere consisting primarily of the light elements Helium and Hydrogen, forming a primordial atmosphere. Throughout its evolution, however, Earth lost this primordial atmosphere.
It turns out that exoplanets that are much larger than Earth tend to accumulate far bigger primordial atmospheres. In some cases, these planets may hold on to these atmospheres forever. These types of planets can construct greenhouse effects akin to that of Earth. The team was interested in learning if these conditions allow liquid water to exist.
Extensive modeling
To find out, the researchers simulated the development of an enormous amount of planets over extensive periods of time. In addition to the characteristics of the planets' atmospheres, the team took into account the strength of the radiation from each planet's star as well as the planets' own internal heat that radiates outward.
On Earth, geothermal heat has little impact on surface temperatures, but on planets with enormous primordial atmospheres, it can have a much more considerable impact.
It appears that numerous planets lose their primordial atmosphere as a result of interaction with the massive radiation they receive from their host star. This goes double for planets that orbit in close proximity to their star.
Liquid water, sustained for billions of years
Nevertheless, the researchers discovered that if a primordial atmosphere survives, the right conditions to sustain liquid water can exist. Perhaps, even more intriguing is the fact that heat from a star is not even necessary as geothermal heat that researchers all the way to the surface can already be sufficient.
An extensive variety of conditions allow for the existence of liquid water - (Image Credit: Thibaut Roger - Universität Bern - Universität Zürich CC BY-NC-SA 4.0)
Marit Mol Lous, Ph.D. student and main author of the research paper, stated that Perhaps most importantly, their results indicate that these conditions can persist for immensely long periods (up to tens of billions of years, in fact).
As it is believed that it took several billions of years for life to emerge on our own planet, it is essential that the existence of water is sustained for long periods of time.
With that in mind, many more exoplanets can now be considered a candidate for being capable of sustaining life; these new findings may considerably expand our horizons in the search for life beyond Earth.
Be sure to check out the paper listed below for more detailed information about the research
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