Super-habitable planets may be better for life than Earth

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Site Writing Technological Innovation – 10/06/2020

Better planets than Earth

The Earth is not necessarily the best planet in the Universe, guarantees a trio of astronomers from Germany and the USA.

They have identified two dozen planets outside our Solar System that may have more suitable living conditions than those offered by our planet. And some of the stars where these exoplanets orbit may also be “better than our Sun” to support life.

Dirk Makuch and his colleagues detailed the characteristics of what they call “super-habitable planets”, which include those that are older, slightly larger, slightly warmer and possibly more humid than Earth.

Life as we know it could also thrive more easily on planets that revolve around more stable stars with a longer life expectancy than our Sun.

Unfortunately, for those who can imagine that this resolves any concerns about our environment – they could simply migrate to a better planet – the top 24 candidates for super-habitable planets are all more than 100 light years away.

“With the next space telescopes coming, we will be able to capture more information, so it is important to select some targets,” said Makuch of Washington State University. “We have to focus on certain planets that have the most promising conditions for complex life. However, we have to be careful not to get stuck looking for a second Earth because there may be more suitable planets for life than ours.”

Having used data from the retired Kepler telescope, astronomers are eyeing the more detailed observations that will be possible with the James Webb, Plato and Luvior space telescopes (Large Ultraviolet Optical Infrared Surveyor), the latter is a concept announced last year and still has no construction start date.

Planetas super-habit

Mapping of known exoplanets and their relationship with the habitable zone.
[Imagem:┬áDirk Schulze-Makuch et al. – 10.1089/ast.2019.2161]

Super-habitability

Makuch and his colleagues – who call themselves geobilogues – started by establishing criteria for super-habitability, and then analyzed the approximately 4,500 exoplanets known beyond our Solar System in search of good candidates – by the way, habitability, whether super or not, does not mean that these planets have life, only the conditions that could sustain or lead life.

The starting point was the well-known “habitable zone”, the region of a planetary system where the distance from a planet to its star guarantees a temperature capable of maintaining water in a liquid state.

The next item was the “useful life” of the star. Although the Sun is the center of our Solar System, it has a life expectancy of less than 10 billion years. Since it took almost 4 billion years before any complex life form appeared on Earth, many stars similar to our Sun, called G stars, may run out of fuel before complex life develops.

In addition to looking for systems with cooler G stars, astronomers have also analyzed systems with K-ring stars, which are slightly cooler, smaller and less luminous than our Sun. K stars have the advantage of a life expectancy of 20 billion and 70 billion years. This would allow the orbiting planets to be older, in addition to giving more time for life to advance to the complexity currently found on Earth.

On the other hand, to be habitable the planets must not be so old as to deplete their geothermal heat and have no more geomagnetic fields of protection against the radiation of their own star and space. The Earth is about 4.5 billion years old, but researchers say the sweet spot for life would be a planet between 5 billion and 8 billion years old.

Size and mass are also important. A planet 10% larger than Earth would probably have many more habitable dry zones. The trio’s calculations indicate that a planet about 1.5 times the mass of the Earth would be ideal for maintaining its internal heating for a longer time through radioactive decay and would also have a stronger gravity, to retain the atmosphere for a period of longer time.

Finally, water is the key to life, and astronomers argue that a little more water than there is on Earth would help, especially in the form of dew, clouds and moisture. A slightly warmer temperature – about 5 C higher than the average temperature on Earth, would also be better for life. This preference for more heat and higher humidity is associated on Earth with greater biodiversity in tropical forests than in colder and drier areas.

Planetas super-habit

Details of the candidate planets to be considered “super-habitable” – with greater habitability than Earth.
[Imagem:┬áDirk Schulze-Makuch et al. – 10.1089/ast.2019.2161]

We don’t have the best of everything

Among the 24 habitable planet candidates identified so far, none of them meet all the criteria to be considered a super habitable planet, but one of them, known as KOI 5715.01, has four of the critical characteristics, making it possibly much more comfortable for life than our home planet.

“It is somewhat difficult to convey this principle of super-habitable planets because we think we have the best planet,” said Makuch. “We have a large number of complex and diverse life forms, and many that can survive in extreme environments. It is good to have an adaptable life, but that does not mean that we have the best of everything.”

Bibliography:

Article: In Search for a Planet Better than Earth: Top Contenders for a Superhabitable World
Authors: Dirk Schulze-Makuch, Ren Heller, Edward Guinan
Revista: Astrobiology
DOI: 10.1089 / ast.2019.2161

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