Earth is the only planet we know that has life on it. However, scientists say it may not be the best planet in the universe for life.
Scientists have recently identified 24 “superhabitable” planets outside our solar system that may have conditions more suitable for life than Earth. They are all more than 100 light-years away.
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The exoplanets are older, slightly larger, warmer, and wetter than Earth, the study by Washington State University (WSU) found. Some of them orbit stars that may be better than even our sun.
Scientists say life could thrive more easily on planets orbiting changing stars with longer lifespans than the sun at a slower speed.
The lead author of the study Dirk Schulze-Makuch said the study could help focus future observation efforts, such as from NASA’s James Web Space Telescope, the LUVIOR space observatory, and the European Space Agency’s PLATO space telescope.
“With the next space telescopes coming up, we will get more information, so it is important to select some targets,” said Schulze-Makuch, a professor with WSU and the Technical University in Berlin.
The study suggests we don’t need to look for Earth 2.0. There could be planets way more suitable for life than ours.
“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,” said Schulze-Makuch.
To identify the 24 top contenders for superhabitable exoplanets, WSU researchers teamed with scientists from the Max Planck Institute for Solar System Research in Germany and Villanova University in Pennsylvania.
Astronomers created a “superhabitability criteria”, which they used against 4,500 known exoplanets. Habitability does not mean these planets definitely have life, but rather the conditions needed for life to thrive were present.
The researchers selected planetary systems with G stars which have short lifespans of less than 10 billion years – similar to our sun – as well as systems with K dwarf stars.
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K dwarf stars are much smaller and colder, featuring long life spans ranging from 20 billion to 70 billion years. This means orbiting planets can be older, allowing for life to advance as much as it has on Earth.
Scientists consider Earth to be 4.5 billion years old. But the researchers argue that a planet aged 5 billion to 8 billion can nurture life well.
Size and mass are also critical. A planet that is 10 percent larger than Earth should have more habitable land. Scientists expect a planet 1.5 times the mass of Earth would keep its interior heating through radioactive decay longer.
Water is also important for life. Scientists suggest that a little more of it, especially in the form of moisture, clouds, and humidity, would help.
The researchers also considered that a slightly warmer temperature, about 5 degrees Celsius (8 degrees Fahrenheit) more than Earth, would be better for life.
This warmth and moisture preference is seen on Earth with the greater biodiversity in tropical rain forests than in colder, drier areas.
None of the 24 planets met all of the criteria. But one has four of the critical characteristics, making it much more comfortable for life than Earth.
“We have a great number of complex and diverse lifeforms, and many that can survive in extreme environments. It is good to have adaptable life, but that doesn’t mean that we have the best of everything,” said Schulze-Makuch.
The researchers published their study in the journal Astrobiology.