It can exist on planets very different from Earth, even if they do not orbit any star.
An investigation has determined that extrasolar worlds very different from our planet could be habitable for billions of years: a dense atmosphere composed of hydrogen and helium can maintain temperatures and conditions suitable for life almost anywhere in the Universe.
Researchers from the University of Bern and the University of Zurich in Switzerland have concluded in a new study that the concept of planetary habitability needs to be revised and made more inclusive with respect to the classical definition: we should not only look for life on worlds similar to Earth Earth, since certain atmospheric conditions could facilitate the elements necessary for the life development on extrasolar planets very different from ours.
Atmospheres and liquid water
According to a press release, there are two key ingredients underpinning the new research, recently published in the journal Nature Astronomy: atmosphere of the planets and the liquid water. According to the authors of this research, the atmospheric characteristics of exoplanets are what would make the presence of liquid water possible for long periods of time, a crucial condition for life to begin to develop.
In their study, the scientists have shown that liquid water could also exist for billions of years on planets that are very different from Earth. This calls into question our current view of the search for potentially habitable planetswhich is strongly focused on discovering scenarios very similar to the one on Earth.
Life on Earth began in the oceans: because of that, we know that the potential for liquid water it is, therefore, a key ingredient for habitability conditions. However, it could not only be viable on terrestrial planets identical to Earth, but also on very different worlds in which the precise elements exist in their atmospheres.
The natural greenhouse effect
As scientists explain, one of the reasons why water can be liquid on Earth is its atmosphere. The call natural greenhouse effect it traps just the right amount of heat, to create the right conditions for oceans, rivers and rain: from that accumulation of liquid water life was possible.
However, the Earth’s atmosphere was very different at the beginning of its history. When the planet formed from cosmic gas and dust, it gathered an atmosphere consisting mainly of hydrogen and helium, the so-called primordial atmosphere. Over time, our planet lost this primary atmosphere and the conditions for the natural greenhouse effect were created.
Using different models and simulations, the researchers found that other more massive planets can accumulate much larger primordial atmospheres, which they can maintain indefinitely in some cases. Such massive primordial atmospheres also can induce a greenhouse effect much like the Earth’s atmosphere todayhelping to create the necessary conditions for the development of liquid water and, later, of some form of life.
Even on nomadic planets
The scientists concluded that primordial atmospheres may be lost on some exoplanets due to intense radiation from stars, especially on worlds that are very close to their host star. But in cases where the atmospheres remainconditions suitable for liquid water may occur.
When enough geothermal heat reaches the surface, that is, from the interior of the planet, not even the radiation of a star like the Sun is necessary for conditions to prevail on the surface that allow the existence of liquid water, which could be maintained until tens of billions of years.
Finally, the specialists indicated that this discovery could greatly expand the horizon for the search for extraterrestrial life forms. According to the results, liquid water could arise even on the so-called nomadic planets or wanderingwhich do not orbit around a star and float freely through the cosmos.
Reference
Potential long-term habitable conditions on planets with primordial H–He atmospheres. Mol Lous, M., Helled, R. & Mordasini, C. Nature Astronomy (2022). DOI:https://doi.org/10.1038/s41550-022-01699-8