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We only know one planet in our universe that houses life: the Earth. It is therefore logical that humanity has focused its search for life beyond our world on planetary bodies. But a new study suggests that we can leave aside a larger part of the cosmos: the moons.
In a new study published in The Astrophysical Journal, researchers suggest that there are 121 giant exoplanets – worlds orbiting other stars – that could host a potentially habitable moon.
Using data from NASA's Kepler Space Telescope, which has confirmed more than 2,000 exoplanets, scientists have modeled the frequency of formation of gas giant planets like Jupiter and Saturn in the habitable zone of a star, a region where liquid water can exist. the surface of the planet.
From there, the researchers determined how many of these planets could have a single moon, arriving at 121.
Pressing
Life exists on Earth because of several factors, among them:
– The proximity of the sun (which gives us energy).
– Water.
– Our atmosphere.
– A magnetic field that protects us from harmful space radiation.
While we get the energy of the sun, scientists believe that the exomoons could get energy not only from its star, but also from the giant exoplanet. This, they say, makes them potentially "super-habitable".
The idea of planets providing extra energy to their moons comes from observations in our solar system: Jupiter and Saturn do just that for their moons.
Some moons have an elliptical orbit (not quite circular) around their planet that causes a gravitational interaction. The moon is in a hurry between being closer and further. This, called the bending of the tide, causes a warm-up. It's pretty much the same thing if you take an anti-stress ball and hold it tightly: it will generate a little heat (not just the warmth of your hand).
Moreover, as is the case with the moons of Jupiter and Saturn, the magnetism of an exoplanet could protect the moons from cosmic rays, thus increasing its livability potential.
Conservative estimate
The idea of a single potentially habitable moon around an exoplanet is really a conservative number.
Looking at our solar system, our giant planets have many moons: Jupiter has 69; Saturn, 62. And there is no identical composition.
The planetary models suggest that this is the case in the general formation of the planet. So, this increases the chances that giant exoplanets in livable areas have many more moons, thus also increasing chances of one that may be livable.
"Because there are so many … giant planets in the living area around their star, these giant planets should have many moons, as do our giant planets," said Michelle Hill, a student of undergraduate degree from the University of South Queensland in Australia. "So, really these moons could potentially be the life of the world is detected first."
challenges
While the life of discovery on the exomoons is a possibility, the reality is, it will take time. On the one hand, we have not been able to detect biosignatures – signs that something has the ingredients for life – on exoplanets up to now.
In the quest for exoplanets, scientists look for small depressions in the light of a star that indicates that a planet is crossing it, called a transit. But a moon would be much smaller and harder to detect in this way.
"Observations of exomons in the search for life are very difficult because the radiation from the exomoon will be mixed up with the planet," said astrophysicist and Canadian scientist Sara Seager, who is studying exoplanets at MIT.
"The combined light of the exomoon and the planet is already overshadowed by the light of the host star."
Secondly, we have not even confirmed the existence of an exomoon. Only one exoplanet holds any promise, Kepler 1625b, which is 4,000 light-years away from Earth. But in a study published earlier this week, senior author René Heller, an astrophysicist at the Max Planck Institute in Germany, concluded that the jury was still out.
"Depending on how we mass the data (that is, how we try to eliminate noise and stellar / instrumental variability), the object is there – or gone" , he said. This would involve many more observations to confirm or exclude, but the planet only transits once every 287 days. It would take years.
Although their article illustrates the potential livability of exomoons, Hill knows that it will take time, perhaps a decade or more. But on the positive side, the technology is improving.
"Really, the detections of these moons could coincide with the moment when we have the ability to detect any sort of real life signatures that are indisputable," said Hill.
For the moment, astronomers and astrobiologists will turn their eyes to the moons of our solar system, such as Jupiter's Europa Moon and Saturn's Moon Enceladus, with their icy crusts and potential subglacial oceans.
With hydrothermal vents – openings on the seabed that contain mineral-rich and heated materials where life is present on Earth – they are considered two of the most promising candidates.
"I think the prospects of finding life on one of those exotic moons in the solar system are promising," says Heller. "I say that because life on Earth just seems to be everywhere."
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