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The “super-habitable” planets may be better for life on Earth

And while scientists look for other planets outside of our solar system, called exoplanets, that could host life, very Earth-like planets may not be the best answer.

“We are so focused on finding a mirror image of the Earth that we may be overlooking a planet that is even more suitable for life,” said Dirk Schulze-Makuch, lead author of the study and professor of astrobiology and planetary habitability at Washington State. University, in an email to CNN. The study was published Monday in the journal Astrobiology.

In the new study, Schulze-Makuch and his co-authors identified 24 exoplanets and candidate exoplanets (planets that have not been positively confirmed as exoplanets). They are all more than 1

00 light-years apart, which could be contenders for super-habitable planets with conditions more suitable for life on Earth.

However, the authors warn that this does not mean that they have confirmed that life exists on these planets. Instead, it means these planets could have conditions conducive to life.

“We feel that while we look for super-habitable planets, that doesn’t mean they necessarily contain life (or even complex life),” Schulze-Makuch said. “A planet may be habitable or super-habitable but uninhabited. This has to do with the natural history of the planet. There may have been a calamity (such as a nearby Supernova explosion).”

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Schulze-Makuch identifies a super-habitable planet as “any planet with more biomass and biodiversity than our present Earth”. Essentially, it would be slightly older, larger, warmer and wetter than Earth, he said.

“The habitability of our planet has also changed over the course of our natural history,” he said. “For example, the Earth in the Carboniferous Period with all of the swamps and rainforest (which produced most of our current gas and oil) was probably more habitable – viable by our definition – than Earth at present.”

Stars with a longer duration

One superabitability factor could actually be the type of star that orbits the planets. Researchers identify a K dwarf star as the most ideal in the study. These stars have a longer lifespan than our sun, so life could potentially persist and thrive on the planets orbiting them.

K dwarf stars are colder, less massive, and even less bright than ours sun, but can persist for 20 to 70 billion years. The planets orbiting these stars would be older and would allow life to reach the complexity we have on Earth.

The Earth is about 4.5 billion years old. But in the study, the researchers suggest that five to eight billion years is actually the “sweet spot” for the formation and evolution of life.

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Our sun has a lifespan of less than 10 billion years, and it took nearly four billion of these for any kind of complex life to evolve on Earth. And stars similar to our sun could actually die before complex life formed on the planets orbiting them.

Other criteria were used to determine the super-habitability of the 4,500 known exoplanets.

The planets were probably terrestrial, or rocky like Earth, and orbited in the habitable zone of their star, which is the distance from the star where liquid water could remain permanently on the exoplanet’s surface.

They looked at the size and mass and estimated that a planet around 1.5 times the mass of Earth would be able to maintain internal warming longer than Earth and would have stronger gravity that would allow it to hold onto its atmosphere. longer.

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Even higher water content on a warmer planet, about 8 degrees Fahrenheit warmer than Earth, may be better suited for life. The study authors compared this preference for heat and humidity to biodiversity in Earth’s tropical rainforests, especially when compared to colder, drier areas.

Of these criteria, Schulze-Makuch thinks the most important is that the planet is hosted by a K dwarf star and that the planet is slightly older than Earth.

While a planet may be superinhabitable and meet only some of the criteria without checking all the boxes, the authors warn that there is much more information that cannot be evaluated about these planets.

Even “a slightly higher temperature could make things worse in times of habitability,” such as the extreme deserts on Earth, Schulze-Makuch warned.

Finding a world that can be lived in

None of the 24 candidates meet all the criteria set out in the study because scientists simply don’t know enough to be able to tell. One of them, named KOI 5715.01, has four of the desirable aspects for a super-habitable planet.

It is located in the constellation of Cygnus about 3,000 light years from Earth. The star is 77% of our sun’s radius and 76% of its mass, with only 34% of our sun’s brightness. And the star is about 5.5 billion years old, or a billion years older than our sun.

The authors provide a bit of a report card for the star orbiting the study based on what they know, which they admit isn’t much.

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“The point is that these preliminary candidates for possibly being habitable or liveable should be selected and prioritized for further investigation,” Schulze-Makuch said. “Furthermore, we need to better understand what makes a planet habitable and how biospheres interact with their natural environment.”

But to fully evaluate these candidates, Schulze-Makuch sees the need for probes or to land on the planet, but all of these are so far away, it’s not likely. However, better remote observations with future space telescopes could help focus more on the details of these planets.

“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.”

Planetary astronomer and scientist Sara Seager sees this study as “a great resource to use as a reference for all”. Seager, also a professor at the Massachusetts Institute of Technology, was not involved in the study.

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“It’s a really nice description of all the ingredients for a habitable world,” Seager said in an email to CNN. “I love the concept of super-habitable exoplanets. The concept is good, like those Olympic athletes among us humans.”

And Seager agrees with what the authors say in the conclusion of their article.

“Observations of habitable or super-habitable exoplanets are still so extremely challenging that nature will ultimately determine which targets we can follow with our next-generation telescopes,” Seager said.

“This is the follow up to see if the planet is actually habitable, if it has water vapor in its atmosphere (indicative of surface water on a rocky planet), potentially measuring the planet and looking for biosignature gas.

“So even though the sample list of exoplanets is quite long, none are within 100 light years and none are suitable for later observations with our next generation telescopes. “

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