In August 2016, astronomers from the European Southern Observatory (ESO) announced the discovery of an exoplanet in the neighboring system of Proxima Centauri. The news was received with great enthusiasm, since this was the rocky planet closest to our Solar System that also orbited within the habitable zone of its star.
Since then, multiple studies have been conducted to determine if this planet could really sustain life.
Unfortunately, most of the research so far has indicated that the probability of habitability is not good. Between the variability of Proxima Centauri and the planet blocked by the tide with its star, life would have difficulties to survive there.
However, using primitive Earth life forms as an example, a new study by researchers at the Carl Sagan Institute (CSI) shows how life might have a fighting chance in Proxima b after all.
The study, which appeared recently in the Monthly Notices of the Royal Astronomical Society, was conducted by Jack O & # 39; Malley-James and Lisa Kaltenegger, associate researcher and director of the Carl Sagan Institute at Cornell University.
Together, they examined the levels of surface UV flux that planets that orbit M-type stars (red dwarf stars) will experience and compare it with conditions on the primordial Earth.
The potential habitability of red dwarf systems is something that scientists have debated for decades. On the one hand, they have a number of attributes that are encouraging, one of which is not the most common.
Essentially, red dwarfs are the most common type of star in the Universe, and they represent 85 percent of the stars only in the Milky Way.
They also have the longest lifespan, with lifetimes that can last up to billions of years. Last but not least, they seem to be the most likely stars to house rocky planet systems.
This is demonstrated by the large number of rocky planets discovered around neighboring red dwarf stars in recent years, such as Proxima b, Ross 128b, LHS 1140b, Gliese 667Cc, GJ 536, the seven rocky planets orbiting TRAPPIST-1.
However, red dwarf stars also present many impediments to habitability, one of which is 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 eruptions can bathe these planets with high levels of biologically damaging radiation, and for longer periods, the attack of X-ray radiation has charged the particle fluxes of the host stars placing the atmospheres of these planets at risk of being stripped away over time if a planet can not replenish its atmosphere fast enough. "
For generations, scientists have struggled with questions about the habitability of planets orbiting red dwarf stars.
Unlike our Sun, these ultra low and low mass dwarf stars are variable, unstable and prone to outbreaks. These flares emit a large amount of high energy UV radiation, which is detrimental to life as we know it and capable of eliminating the atmospheres of a planet.
This places significant limitations on the ability of any planet that orbits a red dwarf star to give life or remain habitable for a long time. However, as previous studies have shown, much of this depends on the density and composition of the atmospheres of the planets, not to mention whether the planet has a magnetic field or not.
To determine if life could last under these conditions, O & # 39; Malley-James and Kaltenegger considered what the conditions were like 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 was bombarded by UV radiation in a manner similar to that experienced by planets orbiting M-type stars today.
To address this, Kaltenegger and O & # 39; Malley-James modeled the UV surface 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 that have "eroded" or "anoxic" atmospheres, that is, those that do not block UV radiation well and do not have a protective layer of ozone.
These models showed that as atmospheres thin out and ozone levels decrease, more high-energy UV radiation can reach the ground. But when they compared the models with what was present on Earth, about 4 billion years ago, the results were interesting. As said O & # 39; Malley-James:
"The surprising result was that the UV levels on the surface were higher than those we experience on Earth today, but the interesting result was that the UV levels, even for the planets around the stars more active, they were all lower than those experienced on Earth, their youth, we know that young life sustained on Earth, so the case of life on planets in stellar systems M may not be so serious, after all " .
What this means, in essence, is that life could exist on neighboring planets like Proxima b at this time despite being subjected to severe levels of radiation. If you consider the age of Proxima Centauri (4,853 million years), which is approximately 200 million years older than our Sun, the case of possible habitability may become even more intriguing.
The current scientific consensus is that the first life forms on Earth emerged a billion years after the formation of the planet (3.5 billion years ago). Assuming that Proxima b was formed from a disk of protoplanetary debris shortly after the birth of Proxima Centauri, life would have had sufficient time not only to emerge, but also to obtain a significant foothold.
While that life may consist only of unicellular organisms, it is encouraging nonetheless. In addition to informing us that there might very well be life beyond our Solar System, and on nearby planets, it gives scientists limitations on what kind of biosignatures can be discerned by studying them. As O & # 39; Malley-James concluded:
"The results of this study build the case to focus on life on Earth a few billion years ago, a world of unicellular, prokaryotic microbes that lived with high levels of UV radiation." This ancient biosphere may have the best coincidences with the conditions in the habitable planets around active M stars, so they could provide us with the best clues in our search for life in these star systems. "
As always, the search for life in the cosmos begins with the study of the Earth, since it is the only example we have of a habitable planet. Therefore, it is important to understand how (ie, under what conditions) life could survive, thrive and respond to environmental changes throughout Earth's geological history.
While we may know of a single planet that sustains life, that life has been remarkably diverse and has changed drastically over time.
Be sure to watch this video about these latest findings, courtesy of CSI and Cornell University:
This article was originally published by Universe Today. Read the original article.