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“Super-habitable”: exoplanets with a life span of up to 70 billion years

“Somewhere on another planet orbiting a very distant star, perhaps in another galaxy, there may well be entities as intelligent as we are and interested in science. It̵

7;s not impossible, “says Nobel Prize-winning physicist Murray Gell-Mann.” I think there are probably many. Most likely none are close enough to interact with us, but they could be out there very easily. “

The Gell-Mann entities could inhabit one of two dozen planets outside our solar system, researchers have identified that they could orbit stars that have created conditions more suitable for life on Earth, according to a study by Dirk Schulze. -Makuch, a professor of the Center for Astronomy and Astrophysics at the Technical University of Berlin, Germany and Adjunct Professor at the School of Earth and Environmental Sciences Washington State University and author of Cosmic biology: how life could evolve on other worlds.

The super-habitable planets

Schulze-Makuch’s research identifies the characteristics of potential “super-habitable” planets which include those that are older, somewhat larger, slightly warmer and possibly wetter than Earth. Life may also thrive more readily on planets revolving around slower-changing stars with longer lifespans than our sun, perhaps, according to some speculations, leading to advanced civilizations capable of manipulating the basic structure of space and weather.

The 24 major 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.

“The Ocean Galaxy”: Many of the 4,000 known exoplanets of the Milky Way may be aquatic worlds

“With the next space telescopes on the way, we will have more information, so it is important to select some targets,” said Schulze-Makuch, professor at the WSU and the Technical University of Berlin. “We need to focus on a few planets that present the most promising conditions for complex life. However, we must 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. “

There are among the 4,500 known exoplanets

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 archive of transiting exoplanets.

“Kepler’s Sweet Spot” – Earth in the center of the “Habitable Zone” of the Milky Way

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.

Planets of the star K: duration of 70 billion years

In addition to looking at systems with colder G stars, stars similar to our Sun that could run out of fuel before complex life can develop, the researchers looked at systems with K dwarf stars, which are a bit colder, less massive. and less bright than our sun. K stars, says the Washington State team, have the advantage of a long lifespan of 20 to 70 billion years, allowing planets in orbit to be older and giving life more time to advance to the complexity it currently found on Earth.

Super-habitable features

Geomagnetic fields: 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.

Mass. 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.

Surface temperature and water. 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 of the criteria for super-habitable planets, but one has four of the critical characteristics, making it perhaps much more suitable 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’s nice to have an adaptable life, but that doesn’t mean we have the best of everything. “

Source: Dirk Schulze-Makuch et al, In Search for a Planet Better than Earth: Top Contenders for a Superhabitable World, Astrobiology (2020). DOI: 10.1089 / ast 2019.2161

The Daily Galaxy, Max Goldberg, via Washington State University

Image credit: Shutterstock license

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