Earth is not necessarily the most hospitable planet in the universe for sustaining life, according to a new study.
Researchers have found about 24 planets that are "superhabitable," offering conditions more suitable for life than exist here on Earth.
In fact, some of these planets have even better stars than our Sun, the researchers said.
The new study looked for worlds that would be better at sustaining life than our planet – including those that are older, larger and hotter than Earth – in the hope of helping future searches for life elsewhere in the universe.
The study identified 24 of the "super-habitable" planets. All of them are within 100 light-years of our Sun, making it very difficult, if not impossible, to ever see them up close, but future telescopes could give us much more information about these worlds.
With technological advances in upcoming telescopes – such as NASA 's James Webb Space Telescope , the LUVIOR space observatory, and the European Space Agency's PLATO – researchers hope they will even be able to detect traces of life on planets that are far away.
“With the next space telescopes, we will get more information, so it is important to choose specific targets,” said Dirk Schulze-Makuch, a professor at Washington State University and the Technical University of Berlin, who led the study.
"We need to focus on certain planets that have the most promising conditions to support life. However, we need to be careful not to get stuck looking for a second Earth, because there are probably planets that could be more suitable for life than ours.".
The researchers set out a set of criteria for such superhabitable planets. They then explored the 4,500 known planets outside our solar system in an attempt to identify which ones might meet these important criteria.
This included searching for “K-type dwarf planets,” which are not like sun . Those that resemble our star – known as “G-type” – have relatively short lifespans, and given that our Sun was almost middle-aged before any form of complex life arose, many other similar planetary systems could disappear before they became habitable.
K-type dwarf stars , by contrast, are cooler, smaller and brighter than our sun. They have much longer lifetimes – up to 70 billion years – meaning planets around them would have much more time to develop life.
The researchers also looked for planets that are about 10% larger than Earth, with the idea that they are likely to have a larger habitable zone. More mass would also mean they would retain their core heat longer, and stronger gravity to keep their atmospheres stable.
Superhabitable planets would likely have slightly more water than Earth, especially if it is held in the form of moisture. Also, a warmer climate would make a planet more habitable, with an ideal point being a 5 degree Celsius increase compared to Earth.
None of the 24 planets described in the study meet all of the criteria the researchers set out, despite their sheer number. One of them met four of these criteria, meaning it would theoretically be much more suitable for creating and sustaining life and therefore more likely to be habitable.
“Sometimes it’s hard to get this super-habitable planet theory across because we think we live on the best planet,” said Professor Schulze-Makuch. “We have a large number of complex and diverse life forms, and many of them can survive in extreme environments. Earth is certainly a hospitable host for life, but it’s probably not the best.”
