The search for exoplanets, planets outside the Solar System, has been one of the great challenges for astronomers in recent times, although it is not proving to be an easy mission.
In an article in Astrobiology, Schulze-Makuch and his team identified 24 exoplanets with characteristics that are very favourable to life or even better than those of Earth, thanks to data from the Kepler mission.
Of the more than 4,000 exoplanets found so far, some were considered theoretically habitable.
These planets, outside our Solar System, are located in the habitable zone, i.e. at a distance from their Sun that allows the presence of water in the liquid state (without freezing or boiling) and are 10% larger than the Earth.
However, it should be pointed out that habitability does not mean that these planets certainly already host life forms, but simply that they have the favourable conditions for its future development.
To get an idea, following these criteria, besides the Earth, our Solar System hosts two other potentially habitable planets: Venus and Mars.
The 24 main “superhabitable” planets are all more than 100 light years away.
Importance of the Sun for the exoplanets
In this selection, the star (or Sun) on which they orbit is of great importance.
Assuming that an orbit around a G-type star, such as the Sun, would be the best place to find a habitable planet, the researchers have, however, elaborated the research according to other evaluations.
Stars like our Sun only have a life span of about eight to ten billion years and it took four billion years for complex life forms to evolve on Earth.
“The Earth is habitable because it is large enough to be geologically active, with a protective magnetic field and enough gravity to hold an atmosphere.
A K-type dwarf star, on the other hand, would be colder and less massive than the Sun, but would last up to 70 billion years, allowing a much longer time for life to emerge and develop.
This is why researchers have focused in particular on those planets that revolve around dwarf stars K, which are less massive, less bright and a little colder but have a longer life span.
This condition gives life more time to evolve, while the larger size of the planet offers more living space.
According to the team, if a planet were ten percent larger, it would have more space to live on.
If it were 1.5 times more massive than the Earth, its interior would retain more heat from radioactive decay, remain active longer and maintain its atmosphere longer.
Also, if a planet was five degrees Celsius warmer than the Earth and had more water, it would enjoy the biodiversity of a tropical rainforest in much of the planet.
The team states that none of the 24 planets found have all these characteristics, but one has four of the critical factors.
The exoplanet KOI-4878.01
Currently the best candidate to host life is KOI-4878.01, an exoplanet orbiting the main sequence star type F KOI-4878.
It is located approximately 1075 light years (329 parsecs) from Earth.
The characteristics of the planet are very similar to those of the Earth, and if confirmed, it would have an Earth Similarity Index (ESI) rating of 0.98 or 98%, which would make it one of the most Earth-like planets found.
The orbital period of the exoplanet is about 449 Earth days.