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Some planets may be better for Earth life


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Earth is not necessarily the best planet in the universe. Researchers have identified two dozen planets outside our solar system that may have conditions more suited to life than ours. Some of these stars orbit stars that may be even better than our sun.

A study by Washington State University scientist Dirk Schulze-Makuch recently published in the journal Astrobiology characteristic details of potential “superhabitable”

; planets, which include those that are older, a little larger, slightly warmer and possibly wetter than Earth. Life could also thrive more easily on planets revolving around slower changing stars with a longer lifespan than our sun.

The 24 best contenders for super-habitable planets are all more than 100 light-years away, but Schulze-Makuch said the study could help focus future observation efforts, such as NASA’s James Web Space Telescope, the observatory LUVIOR space and PLATO space of the European Space Telescope Agency.

“With the next space telescopes on the way, we will have more information, so it’s important to select some targets,” said Schulze-Makuch, a professor at WSU and the Technical University of Berlin. “We need to focus on some planets that have the most promising conditions for a complex life. However, we need to be careful not to get stuck looking for a second Earth because there may be planets that may be better suited to life than ours.”

For the study, Schulze-Makuch, a geobiologist with experience in planetary habitability, collaborated with astronomers Rene Heller of the Max Planck Institute for Solar System Research and Edward Guinan of Villanova University to identify super-habitability criteria and search among 4,500 exoplanets. known beyond our solar system for good candidates. Habitability does not mean that these planets definitely have life, but simply conditions that would be conducive to life.

The researchers selected planet-star systems with probable terrestrial planets orbiting within the host star’s liquid water habitable zone from the Kepler Object of Interest Exoplanet Archive of transiting exoplanets.

Although the sun is the center of our solar system, it has a relatively short lifespan of less than 10 billion years. Since it took nearly 4 billion years for any complex life to appear on Earth, many stars similar to our sun, called G stars, could run out of fuel before complex life could develop.

In addition to looking at systems with cooler G stars, the researchers also looked at systems with K dwarf stars, which are a bit colder, less massive, and less bright than our sun. K stars have the advantage of a long lifespan of between 20 and 70 billion years. This would allow the orbiting planets to be older and give life more time to advance towards the complexity currently present on Earth. However, to be habitable, planets would not have to be so old that they have exhausted their geothermal heat and lacking protective geomagnetic fields. The Earth is about 4.5 billion years old, but researchers say the sweet spot for life is a planet that is between 5 and 8 billion years old.

Size and mass also matter. A planet that is 10% larger than Earth should have more habitable land. One that is about 1.5 times the mass of the Earth is expected to maintain its internal warming through radioactive decay for longer and would also have stronger gravity to maintain an atmosphere for a longer period of time.

Water is the key to life, and the authors argue that a little more would help, especially in the form of moisture, clouds and humidity. A slightly warmer temperature overall, an average surface temperature of about 5 degrees Celsius (or about 8 degrees Fahrenheit) higher than the Earth, along with the additional humidity, would also be better for life. This preference for heat and humidity is seen on Earth with greater biodiversity in tropical rainforests than in colder, drier areas.

Of the 24 best candidate planets, none of them meet all the criteria for super-habitable planets, but one has four of the critical characteristics, making it perhaps much more comfortable for life on our home planet.

“Sometimes it is difficult to convey this principle of the super-habitable planets because we think we have the best planet,” said Schulze-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 doesn’t mean we have the best of everything.”

A surprising number of exoplanets could host life

More information:
Dirk Schulze-Makuch et al, In search of a better planet than Earth: the best contenders for a super-habitable world, Astrobiology (2020). DOI: 10.1089 / ast 2019.2161

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Some Planets Might Be Better for Earth Life (2020, October 5)
recovered October 5, 2020
from https://phys.org/news/2020-10-planets-life-earth.html

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