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Since the time immemorial, Earth has been the most habitable planet we could imagine. But now, scientists have broadened this imagination by discovering around 24 planets that may be more suitable for supporting life than Earth. All these planets are outside our solar system. In fact, all of them are located more than 100 light-years away from the Earth.
This discovery does not confirm the presence of any life of the aforementioned planets, but simply identifies the ‘super-habitable’ worlds that possess conditions that are conducive to life.
In this study, led by Dirk Schulze-Makuch, a Washington State University scientist and a geobiologist with expertise in planetary habitability, the research team identified the characteristics of super-habitable planets, which essentially include worlds that are older, a little larger, slightly warmer, and possibly wetter than Earth, along with those that orbit slowly changing stars with longer lifespans than our Sun.
Using these criteria and more, the researchers searched for apt candidates among 4,500 known exoplanets—planets that orbit a star outside our solar system. Subsequently, these 24 contenders for super-habitable planets were identified.
In the near future, these worlds are likely to serve as the go-to ‘targets’ for upcoming advanced telescopes such as NASA’s James Webb Space Telescope, the LUVIOR space observatory, and the European Space Agency’s PLATO space telescope to focus their observation efforts on.
“With the next space telescopes coming up, we will get more information, so it is important to select some targets,” said Schulze-Makuch. “We have to focus on certain planets that have the most promising conditions for complex life. However, we have to be careful to not get stuck looking for a second Earth, because there could be planets that might be more suitable for life than ours.”
Listed below are some of the conditions the research team focused on while shortlisting the super-habitable worlds:
Presence in the habitable zone: Using the Kepler Object of Interest Exoplanet Archive of transiting exoplanets, the researchers selected the probable terrestrial planets that orbit within their host star’s ‘goldilocks zone’—the habitable region around a star where the temperature is just right for liquid water to exist on a planet.
Life expectancy of host star: Our Sun has a relatively short lifespan of fewer than 10 billion years. Moreover, it took nearly 4 billion years for any complex form of life to appear on Earth. Considering this fact, the researchers ignored many stars similar to our Sun, known as G stars, which might die before complex life could develop on orbiting planets. Instead, they looked at K dwarf stars, which are somewhat cooler, less massive, and less luminous than our Sun, and therefore, have long lifespans of 20 billion to 70 billion years. Such long-living stars would effectively allow orbiting planets more time for complex life to develop on them, increasing their habitability scores.
Size and mass of the planets: Scientists also considered the size and the mass of the exoplanets, as they play a notable role in determining how ‘fit’ a world would be to support life. For instance, a planet that is 10% larger than the Earth would have more habitable land, while one that possesses 1.5 times the Earth’s mass is likely to retain its interior heating longer through radioactive decay, while also having a stronger gravity to retain an atmosphere over a longer period of time.
Surface temperature of planets: The surface temperature of planets would strongly influence the formation of moisture, clouds, and humidity, all of which help determine the presence of a key life indicator: water. Planets with a mean surface temperature of about 5°C greater than Earth would be more suitable, as the slightly higher overall temperatures along with the additional moisture would be better for life. Life’s preference for warmth and moisture is evident on Earth too, as we see greater biodiversity in tropical rain forests as compared to colder, drier areas.
Of the 24 top candidates, none managed to meet all the criteria for super-habitable planets. However, one planet does possess four of the critical characteristics, which makes it more capable of supporting life as we know it than our very own home planet.
The findings of this study were published in the journal Astrobiology last month and can be accessed here.
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