Around two dozen planets that may be even more suitable for life than Earth have been discovered outside our solar system.
While the search continues for planets similar to our own that could potentially harbour alien life, researchers may have found planets that are even better than Earth.
A study recently published to Astrobiology, led by Washington State University scientist Dirk Schulze-Makuch, revealed 24 exoplanets that can be considered ‘superhabitable’. These planets are older, a little larger, slightly warmer and potentially wetter than our own.
Life could also more easily thrive on planets that circle more slowly-changing stars with longer lifespans than our sun. All of these 24 planets are located more than 100 light years away and, according to Schulze-Makuch, this research could help more powerful future telescopes focus on discovering many more planets.
“With the next space telescopes coming up, we will get more information, so it is important to select some targets,” he said.
“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.”
For the study, researchers searched the 4,500 or so known exoplanets for ones that might be superhabitable, meaning they harbour the right conditions for life but may not necessarily have life. They then selected planet-star systems with probable terrestrial planets orbiting within the host star’s liquid water habitable zone. These were sourced from the Kepler Object of Interest Exoplanet Archive of transiting exoplanets.
What we look for
Stars like the sun, known as G stars, have relatively short lifespans, meaning that fuel could run out before complex life can develop. In addition to looking at systems with cooler G stars, the researchers also looked at systems with K dwarf stars, which are somewhat cooler, less massive and less luminous than our sun.
These stars have a lifespan of between 20bn and 70bn years – unlike our sun, which has less than 10bn years. This would allow orbiting planets to be older and give more time for life to advance to a level seen on Earth. But planets can’t be so old that they have exhausted their geothermal heat and lack protective geomagnetic fields.
A planet that is 10pc larger than Earth and has a mean surface temperature 5 degrees Celsius warmer than ours would be better for life, researchers said. Of the 24 planets identified, none were found to have all of the needed characteristics to be deemed superhabitable. However, one planet does have four of them, making it potentially much more comfortable for life than our home planet.
“It’s sometimes difficult to convey this principle of superhabitable planets because we think we have the best planet,” said Schulze-Makuch. “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.”