One planet in the entire universe—Earth—serves as our model for extraterrestrial habitability. The only planet on which we can be positive that life has arisen is our Earth.
But the prerequisites for life as we know it could not just exist on planets similar to Earth; in fact, researchers have recently identified one type of exoplanet that might support life for billions of years.
The secret is in liquid water that is persistent throughout time. Liquid water was essential for the origin of life here on Earth. Therefore, exoplanets with the potential to maintain liquid water may have a higher likelihood of supporting life as we know it.
Researchers have discovered that a lovely, thick atmosphere of hydrogen and helium may sustain temperatures and conditions favorable for life for a very long time, according to new study conducted by astronomer Marit Mol Lous of the University of Zürich in Switzerland.
According to theoretical astronomer Ravit Helled of the University of Zurich in Switzerland, “one of the reasons that water may be liquid on Earth is because it has an atmosphere.”
It traps just enough heat through its natural greenhouse effect to favorably influence rivers, rain, and seas.
However, the present-day appearance of Earth’s atmosphere was not always the case. The main elements at this time are nitrogen and oxygen, with very small quantities of hydrogen and helium.
The Sun and the Solar System evolved from a cloud of gas and dust, and the planet originally had what is known as a primordial atmosphere, which was mostly composed of hydrogen and helium.
Early mechanisms including irradiation from a very hot young Sun and meteorite bombardment are likely to blame for Earth’s loss of its original atmosphere.
A super-Earth exoplanet, which would be larger than Earth but smaller than Neptune, would be able to preserve its original atmosphere for a lot longer than Earth was able to.
Similar to the atmosphere we have now, such huge primordial atmospheres can provide a greenhouse effect, according to Helled. We thus sought to determine whether these atmospheres may aid in producing the conditions required for liquid water.
The researchers used simulations to carry out this analysis, simulating exoplanets with various core masses, atmospheric masses, and orbital distances from their host stars, which they modeled as being similar to the Sun.
Their findings demonstrated that exoplanets with a dense early atmosphere might actually be warm enough to sustain the presence of liquid water for as long as 10 billion years.
But there are restrictions. The exoplanet must be far from the star—roughly twice Earth’s distance from the Sun—to avoid the powerful solar radiation that might remove a primordial atmosphere. That distance from the Sun for the Solar System makes any water on a planet’s surface likely to be frozen.
The Sun isn’t a planet’s only source of heat, though; certain planets, like Earth, are capable of producing their own heat. Numerous mechanisms, including geothermal activities and the existence of radioactive materials that release heat during their decay, can contribute to this.
The prerequisites for liquid water at the surface would thus be satisfied if a super-Earth exoplanet at that distance from its host star had both a primordial atmosphere and enough internal heating to keep itself warm, the researchers added.
According to theoretical astrophysicist Christoph Mordasini of the University of Bern, “This may come as a surprise to many.”
“Astronomers usually anticipate that liquid water would exist in places near stars that get exactly the appropriate amount of radiation: not too much, so that the water does not evaporate, and not too little, so that it does not completely freeze.”
Since the presence of liquid water is most likely a need for life, and life on Earth most likely evolved over many millions of years, this may substantially broaden the possibilities for the search for extraterrestrial life. Our findings suggest that it may even manifest on so-called free-floating planets, which don’t revolve around a star.
This internal heating approach could be able to sustain life on frozen worlds like Jupiter’s moon Europa and Saturn’s moon Enceladus as well as moons orbiting rogue exoplanets that are floating aimlessly across the cosmos.
For the team’s model, several components must be at the proper locations at the appropriate times. That’s not impossible because Earth and all of its life do exist, but it might not happen quickly.
“While our findings are intriguing, they should be interpreted cautiously. Such planets must have the appropriate level of atmosphere in order to support liquid water for an extended period of time. We don’t know how typical that is,” adds Mordasini.
It is also unknown how feasible it is for life to evolve in such a strange prospective home, even under ideal circumstances. Astrobiologists should answer that query. However, our research demonstrated that perhaps our Earth-centric conception of a planet conducive to life is too limited.
The study was released in the journal Nature Astronomy.