Illustration of an Earth-sized exoplanet believed to be habitable like Earth. Photo: NASA Ames/SETI Institute/JPL-Caltech
HOUSTON, kilat.com – Scientists claim to have discovered very habitable planet like, Earth. Even better.
Earth is the only known inhabited planet and life depends on water, so efforts to identify exoplanets that can host life have focused on Earth-like worlds.
But some researchers think there are other types of planets that could offer life conditions as good as, or even better, than Earth. In fact, some scientists think focusing solely on Earth-like worlds may be too “anthropocentric and geocentric” and blind us to exobiological possibilities.
“We’re too focused on finding Earth’s mirror image that we might ignore planets that are even more suitable for life,” Dirk Schulze-Makuch, an astrobiologist at Washington State University and the Technical University of Berlin, told space.com.
In search of potentially highly habitable exoplanets, Schulze-Makuch and his team investigated the Kepler Object of Interest Exoplanet Archive, focusing on 4,500 planetary systems that may have rocky planets within their star’s habitable zone, where liquid water could persist. The researchers published their findings in a 2020 paper in the journal Astrobiology.
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In addition to seeing planetary systems with yellow dwarfs like our Sun, scientists are also looking at orange dwarfs, which are cooler, fainter, and less massive than our Sun.
“Our sun is actually not the best kind of star to accommodate a planet with a lot of life in it,” Schulze-Makuch told Space.com.
Orange dwarfs are about 50% more common than yellow dwarfs in the Milky Way. While our Sun has an estimated lifespan of less than 10 billion years, orange dwarfs have a lifespan of 20 billion to 70 billion years.
Since complex life took about 3.5 billion years to appear on Earth, the longer lifespan of orange dwarf stars could give planets within their habitable zone more time to develop life and increase biodiversity.
Earth is about 4.5 billion years old, so researchers speculate that the sweet spot for life is planets between 5 billion and 8 billion years old.
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A planet’s size and mass can also influence how well it can support life, the researchers wrote. Rocky planets larger than Earth would have a more habitable surface area, and potentially a thicker and more stable atmosphere.
A planet with a mass about 1.5 times Earth’s mass would likely retain its interior heat for longer, which in turn would help keep its core liquid and its protective magnetic field active for a longer span of time during which life might have a chance to emerge and evolve.
Worlds slightly warmer than Earth by about 8 degrees Fahrenheit (5 degrees Celsius) might be very habitable, as they could have larger tropical zones that on Earth encourage more biodiversity. However, warmer planets may also need more humidity, as greater heat can expand deserts.
Also, a planet with the same land area as Earth but broken up into smaller continents may be more habitable. When continents become very large (such as the continent of Gondwana in Earth’s past, about 500 million years ago), their centers are far from the oceans, often turning the interiors of large continents into vast and inhospitable deserts.
In addition, Earth’s shallow waters have greater biodiversity than the deep oceans. So scientists speculate that planets with shallower waters could support more life.
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Habitable Planet?
In all, Schulze-Makuch and team identified 24 potentially highly habitable planets. None of these worlds met all of the researchers’ criteria for a habitable planet, but one met at least two -KOI 5715.01.
KOI (Kepler Object of Interest) 5725.01 is a planet about 5.5 billion years old and 1.8 to 2.4 times the diameter of Earth orbiting an orange dwarf about 2,965 light years away. It may have an average surface temperature of about 4.3 degrees F (2.4 degrees C) cooler than Earth, but if it has more greenhouse gases than Earth to trap heat, it may be very habitable, the researchers wrote.
Schulze-Makuch’s potentially very livable world favorite of these 24 is KOI 5554.01. The planet is about 6.5 billion years old, with a diameter of 0.72 to 1.29 times the diameter of Earth, orbiting a yellow dwarf about 700 light-years from Earth.
“I really like the average surface temperature – around 27 degrees C (80 degrees F),” says Schulze-Makuch. “And it’s probably the size of Earth, and a little older than Earth.”
The 24 potentially highly habitable planets are more than 100 light years from Earth. This makes them too far away for NASA’s Transiting Exoplanet Survey Satellite (TESS) spacecraft to capture high-quality images from to learn more about them.
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However, Schulze-Makuch notes that future spacecraft, such as the recently launched James Webb Space Telescope, NASA’s LUVOIR space observatory mission concept and the European Space Agency’s PLATO space telescope, could shed light on these worlds.
“We caution that while we are looking for habitable planets, that doesn’t mean that they have to contain life,” said Schulze-Makuch. “A planet can be habitable or very habitable but uninhabited.”
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