Earth is the only planet we know of to have sentient life, but astronomers have found two dozen exoplanets that may have better living conditions than our home world.
A team led by Washington State University has identified 24 “super-habitable” planets on over 4,500 known exoplanets that could be a good candidate for life.
They are older, somewhat larger, wetter and slightly warmer than Earth, and these factors, when taken together with a slightly colder and longer-lived star, create better conditions for the development of complex life, the team explained.
While no planet meets all the criteria for “super-habitability”
Even though the worlds are all more than 100 light-years away – too far away to visit – researchers say the discovery can help in the search for life in other parts of the universe.
All the planets discovered by the research team are more than 100 light-years away. They looked at worlds that were potentially “better for life” than Earth. NASA has found some Earth-like K2-18b (pictured) 110 light years away
Lead author Dirk Schulze-Makuch says it’s important to focus space telescope time on likely candidates, and these have the most promising conditions for a complex life.
Just because the team says planets meet the conditions for “super-habitability” doesn’t mean they’re actually habitable as our telescopes can’t yet see their atmospheres – that will come with new technology in the coming years.
For the study, Schulze-Makuch, a geobiologist with experience in planetary habitability, collaborated with astronomers to identify potential super-habitability criteria.
The team, which included Rene Heller of the Max Planck Institute and Edward Guinan of the University of Villanova, searched 4,500 known exoplanets.
In the next few years, a number of space telescopes will come online, including NASA’s James Webb telescope, LUVIOR space observatory and ESA’s PLATO.
The criteria for a “planet to be inhabited” include small islands separated by the oceans rather than large continents. This is a view of the Bora Bora lagoon, an “ earthly paradise ”
|FIRST NAME||AGE OF THE PLANET||RADIUS TO THE EARTH||TEMPERATURE||DISTANCE FROM THE EARTH|
|KOI-5819.01||4.3 billion years||1.16 times larger||81F||2,700 light years|
|KOI-5554.01||6.5 billion years||1.29 times larger||79F||701 light years|
|KOI-456.04||7 billion years||1.77 times larger||58F||3,140 light years|
|KOI-5715.01||5.5 billion years||1.8 times bigger||53F||2,964 light years|
|KOI-5135.01||5.9 billion years||1.85 times larger||88F||4,244 light years|
|KOI-2162.01||7.5 billion years||1.59 times larger||262F||3,144 light years|
|KOI-172.02||7 billion years||1.48 times larger||181F||2,433 light years|
“With the next space telescopes on the way, we will have more information, so it’s important to select some targets,” said Schulze-Makuch.
“We need to focus on a few planets that present the most promising conditions for complex life. However, we must be careful not to get stuck looking for a second Earth because there may be planets that may be better suited to life than ours. “
Habitability does not mean that these planets have life permanently, but simply that they probably have conditions favorable to life and that they deserve further study.
The researchers selected systems with probable terrestrial planets orbiting within the host star’s “liquid water habitable zone”, also known as the Goldilocks zone.
They do not have the ability to tell whether a planet is actually “ wetter than Earth ” as defined by their criteria, but they do predict that those planets that meet other criteria such as size, distance from the star and surface temperature, will have the required water.
Although the Sun is the center of our solar system, it has a relatively short lifespan of less than 10 billion years – it is currently middle-aged.
Since it took nearly four billion years for any complex life to appear on Earth, many stars similar to our Sun, called G stars, could run out of fuel before complex life can develop if life takes longer than it does. did not do on Earth.
In addition to looking for systems with G stars, the team also looked for K dwarf star systems – they are colder, less massive and less bright than the Sun.
K stars also have the advantage of a long lifespan of between 20 and 70 billion years.
This is an impression of the artist Kepler-69c, an Earth-sized exoplanet 2,400 light-years away. It is on the list of potentially “super habitable” planets but its temperature may be too high at 181F
This would allow the orbiting planets to be older and give life more time to advance towards the complexity currently present on Earth.
FINDING SIGNS OF SUPERABITABLE PLANETS INVOLVES A SERIES OF MEASUREMENTS
A super-habitable planet is a more habitable world than Earth for humans.
In order to claim “super habitable” status, a planet must meet certain criteria:
- Orbiting a dwarf star K.
- About 5-8 billion years
- Up to 1.5 more massive than Earth and about 10% larger
- Average surface temperature about 8 ° F higher than Earth’s
- Humid atmosphere with O2 levels of 25-30%, the rest mainly inert gases
- Scattered land / water distributed with many shallow water areas and archipelagos
- Large moon about 1-10 percent of planetary mass at a moderate distance, between 10 and 100 planetary rays
- Has plate tectonics or similar geological / geochemical recycling mechanism, as well as a strong protective geomagnetic field
However, to be habitable, planets would not have to be so old that they have exhausted their geothermal heat and lacking protective geomagnetic fields.
The Earth is about 4.5 billion years old, but researchers say the sweet spot for life is a planet that is between 5 and 8 billion years old.
Size and mass also matter. A planet that is 10% larger than Earth should have more habitable land.
One that is about 1.5 times the earth’s mass would be expected to maintain its internal warming through radioactive decay for longer and would also have stronger gravity to maintain an atmosphere for a longer period of time.
Water is the key to life, and the authors argue that a little more would help, especially in the form of moisture, clouds and humidity.
A slightly warmer temperature, an average surface temperature of about eight degrees Fahrenheit higher than Earth, along with the additional humidity, would also be better for life.
This preference for heat and humidity is seen on Earth with greater biodiversity in tropical rainforests than in colder, drier areas.
Of the 24 best candidate planets, none of them meet all the criteria for super-habitable planets, but one has four of the critical characteristics, making it perhaps much more comfortable for life on our home planet.
“Sometimes it is difficult to convey this principle of the super-habitable planets because we think we have the best planet,” said Schulze-Makuch.
“We have a large number of complex and diverse life forms and many that can survive in extreme environments. It’s nice to have an adaptable life, but that doesn’t mean we have the best of everything. ‘
The results were published in the journal Astrobiology.
Scientists study the atmosphere of distant exoplanets using huge space satellites such as Hubble
Distant stars and their orbiting planets often have conditions unlike anything we see in our atmosphere.
To understand these new worlds and what they are made of, scientists need to be able to detect what their atmospheres consist of.
They often do this using a telescope similar to NASA’s Hubble telescope.
These huge satellites scan the sky and lock onto exoplanets that NASA says could be of interest.
Here, on-board sensors perform different forms of analysis.
One of the most important and useful is called absorption spectroscopy.
This form of analysis measures the light that comes out of a planet’s atmosphere.
Each gas absorbs a slightly different wavelength of light and when this happens a black line appears over a full spectrum.
These lines correspond to a very specific molecule, which indicates its presence on the planet.
They are often called Fraunhofer lines in honor of the German astronomer and physicist who first discovered them in 1814.
By combining all the different wavelengths of lights, scientists can determine all the chemicals that make up a planet’s atmosphere.
The key is that what is missing provides clues to find out what is present.
It is vital that this is done by space telescopes, as the Earth’s atmosphere could interfere.
Absorption of chemicals into our atmosphere would distort the sample, which is why it is important to study light before it has a chance to reach Earth.
This is often used to search for helium, sodium, and even oxygen in alien atmospheres.
This diagram shows how light passing from a star and through the atmosphere of an exoplanet produces Fraunhofer lines that indicate the presence of key compounds such as sodium or helium.