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In August 2016, astronomers from the European Southern Observatory (ESO) announced the discovery of an exoplanet in nearby Proxima Centauri system. The news was greeted with considerable enthusiasm because it was the closest rocky planet to our solar system, orbiting the habitable zone of its star.
Since then, many studies have been conducted to determine if this planet could really support life.
Unfortunately, most research done to date has shown that habitability probabilities are not good. Between the variability of Proxima Centauri and the planet closely linked to its star, life would struggle to survive there.
However, taking the life forms of the early Earth as an example, a new study by researchers at the Carl Sagan Institute (CSI) showed how life could have a chance to fight on Proxima b after all.
Artist's view of the Proxima b surface, gravitating around the red dwarf star. (ESO)
The study, recently published in the Monthly Notices of the Royal Astronomical Society, was conducted by Jack O-Malley-James and Lisa Kaltenegger, Research Associate and Director of the Carl Sagan Institute at Cornell University.
Together, they examined the surface UV flux levels that the orbiting planets would encounter the M-type stars (red dwarf) and compared them to those of the primordial Earth.
The potential habitability of red dwarf systems has been a topic of debate for scientists for decades. On the one hand, they have a number of encouraging attributes, of which one of the most common is their common point.
Red dwarfs are essentially the most common type of star in the universe, accounting for 85% of the stars in the Milky Way.
They also have the greatest longevity, with lifetimes of up to billions of years. Finally, they seem to be the stars most likely to host systems of rocky planets.
This is evidenced by the large number of rocky planets discovered in recent years around nearby red dwarf stars – such as Proxima b, Ross 128b, LHS 1140b, Gliese 667Cc, GJ 536, the seven rocky planets orbiting TRAPPIST-1.
Artist's view of planets orbiting TRAPPIST-1, an ultra-cool red dwarf star. (ESO)
However, red dwarf stars also present many barriers to habitability, the least of which is not their variable and unstable nature. As O & # 39; Malley-James explained to Universe Today via email:
"The main barrier to the habitability of these worlds is the activity of their host stars." Regular stellar flares can bath these planets with high levels of biologically harmful radiation. X-ray shots and the particle fluxes from host stars put the atmospheres of these planets at risk of disappearing over time if a planet can not replenish its atmosphere fast enough. "
For generations, scientists have struggled to question the habitability of planets that revolve around red dwarf stars.
Unlike our Sun, these low-mass ultra-cold dwarf stars are variable, unstable and prone to sudden outbreaks. These torches emit a lot of UV rays of high energy, harmful for life as we know them and able to clean up the atmosphere of the planet.
This greatly limits the ability of any planet orbiting a red dwarf star to give life to life or to stay habitable long. However, as previous studies have shown, it largely depends on the density and composition of the planet's atmosphere, not to mention the fact that the planet has a magnetic field or not.
To determine if life could last under these conditions, O Malley-James and Kaltenegger examined the conditions that reigned on planet Earth about 4 billion years ago.
At that time, the surface of the Earth was hostile to life as we know it today. In addition to volcanic activity and a toxic atmosphere, the landscape has been bombarded by ultraviolet rays in a similar way to that of the planets that M-type stars orbit currently.
To remedy this, Kaltenegger and O-Malley-James modeled the surface UV environments of four nearby "potentially habitable" exoplanets – Proxima-b, TRAPPIST-1e, Ross-128b and LHS-1140b – with various atmospheric compositions . These range from those similar to the current Earth to those with "eroded" or "anoxic" atmospheres – that is, those that do not block UV radiation well and that do not have an ozone layer. protective.
Artist's view of an exoplanet orbiting a red dwarf star. (ESO / M. Kornmesser)
These models showed that as atmospheres dwindled and ozone levels decreased, more high-energy ultraviolet light could reach the ground. But when they compared models to what was present on Earth about 4 billion years ago, the results were interesting. As O & # 39; Malley-James said:
"The unsurprising result was that surface UV radiation levels were higher than those we know on Earth today, however, the interesting result was that even UV levels for planets surrounding most stars active, were all lower than the Earth We know that the recent life of the Earth is based on youth, so the arguments for life on the planets in the star systems M may not be so disastrous after all . "
It basically means that life could exist on neighboring planets such as Proxima b, even if it is subjected to high levels of radiation. If you consider the age of Proxima Centauri – 4,853 billion years old, about 200 million years older than our Sun – the arguments in favor of a potential habitability could become even more intriguing.
The current scientific consensus is that the first forms of life on Earth emerged one billion years after the formation of the planet (3.5 billion years ago). Assuming that Proxima b is formed from a protoplanetary debris disk shortly after the birth of Proxima Centauri, life would have had enough time to not only emerge, but also to gain a meaningful footing.
Although this life may consist only of unicellular organisms, it is nevertheless encouraging. In addition to letting us know that there may well be life beyond our solar system and on nearby planets, scientists have constraints on the type of bio-signatures that can be discerned when their study. As O & # 39; Malley-James concluded:
"The results of this study argue in favor of a focus on life on Earth a few billion years ago – a world of unicellular microbes – prokaryotes – that lived with high levels of UV radiation. ancient biosphere could well be superimposed on habitable planets around active M stars, so could provide us with the best clues for our search for life in these star systems. "
As always, the search for life in the cosmos begins with the study of the Earth, because it is the only example we have of a habitable planet. It is therefore important to understand how (that is, under what conditions) life has survived, flourished and responded to environmental changes throughout the geological history of the Earth.
Although we know only one planet that supports life, this life has been remarkably diverse and has changed dramatically over time.
Be sure to watch this video on these latest discoveries, courtesy of the ICS and Cornell University:
This article was originally published by Universe Today. Read the original article.
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