The closest planet ever discovered outside the solar system could be habitable with an ocean of day

In August 2016, astronomers from the ESO (European Southern Observatory) confirmed the existence of a planet-like Earth around Proxima Centauri – the closest star to our system solar. In addition, they confirmed that this planet (Proxima b) was in orbit in the habitable zone of its star. Since then, several studies have been conducted to determine if Proxima b could actually be habitable.

Unfortunately, most of this research has not been very encouraging. For example, many studies have shown that the Proxima b sun has too much torch activity for the planet to maintain an atmosphere and liquid water on its surface. However, in a new study conducted by NASA, a team of scientists studied various climate scenarios indicating that Proxima b could still have enough water to support life.

The study, titled "Living Climate Scenarios for Proxima Centauri with a Dynamic Ocean", was recently published in the scientific journal. astrobiology. The study was led by Anthony D. Del Genio of NASA's Goddard Institute for Space Studies (GISS) and included members of NASA's Goddard Space Flight Center (GSFC), Columbia University and Trinnovim LLC for the first time. GSFC.

To break it down, planets like Proxima b – which revolve around M-type stars (red dwarf) – face many challenges in terms of habitability. On the one hand, its orbit close to its star would probably have caused a blistering greenhouse effect at the beginning of its history. It would also be subject to intense radiation (X-rays and extreme ultraviolet flux) and solar wind – which would result in a catastrophic loss of atmosphere and water.

However, there are many things we do not know about the evolutionary history of Proxima b, and there are scenarios in which livability might be feasible. As Anthony D. Del Genio told Universe Today by e-mail:

"Above all, we do not know if Prox even has an atmosphere, and if so, if it has water, without them, life as we know it can not exist. the atmosphere, or that it has formed with an atmosphere but in a stellar system poor in water, or it could have formed with a modest atmosphere and a lot of water, or she could have formed a very thick atmosphere.

"Secondly, Proxima Centauri is a M star or" red dwarf. "These stars are much smaller and cooler than our sun, so a planet must be very close to such a star so that it receives enough starlight for The problem is that M-stars tend to be very active in their lives. "

"Third, at the beginning of their lives, the M-stars are very bright and warm, which means that if Prox b were habitable right away, she could have warmed up and lost her water in the beginning, before life could develop."

Flare activity is of particular concern for Proxima Centauri, which is variable and unstable, even by red dwarf standards. In fact, in recent years, two particularly powerful flares have been spotted from the system. The second was so powerful that it could be seen with the naked eye, indicating that any planet orbiting Proxima Centauri would have a stripped atmosphere over time.

However, as they indicate in their study, there are many possible scenarios in which Proxima B could continue to support life. In addition, there is a range of uncertainties about what is hostile to life that could give Proxima room to maneuver. According to Del Genio, these include the possibility that Proxima b was formed further from its star and gradually migrated inward, which would mean that it was not subject to any conditions. difficult at first.

Secondly, it could have formed ten times more water than the Earth; So, even if Proxima Centauri's high radiation removed 90% of its water, there would still be enough water to have an ocean. It could also have formed with a thick envelope of hydrogen that could have been removed, leaving behind a "living core" atmosphere.

"We just do not know," Del Genio said. "Thus, to provide reference points for future observers, we imagine that it has an atmosphere and water, and we ask, considering the orbital star and the distance of this star, how easy or difficult it is to 'imagining an atmosphere and an ocean that together could produce habitable conditions on the surface (defined as hot enough to support liquid water but not too hot to evaporate everything). "

To address these possibilities, Del Genio and his colleagues conducted a series of 3D simulations using orbital and climate key resolution software for terrestrial and extraterrestrial environments with dynamics (ROCKE-3-D). As a global adaptation of NASA's global E2 Earth climate modeling software, ROCKE-3-D has been used to simulate past and future periods in the Earth's history and a potentially habitable old Venus .

Using this software, the team modeled a range of different types of potential atmospheres for Prox b, which included an Earth-like atmosphere (dominated by nitrogen with small amounts of CO_{2 persons} warm the planet) and a more Marsian atmosphere (pure CO_{2 persons}). They also considered whether its atmosphere would be thinner or thicker than that of the Earth, whether its oceans were more or less salty (deeper or deeper) and whether or not the ocean covered the entire planet.

Last but not least, they wondered if the planet was locked on its star or (like Mercury) had a 3: 2 orbital resonance – where the planet rotates three times on its axis for two orbits. As Del Genio explained:

"For each configuration we imagine, we perform a three-dimensional global climate model adapted from the Earth's climate model that we use to project 21st century warming due to the addition of greenhouse gases to the atmosphere. Our climate for this purpose is that we include a "dynamic" ocean – an ocean that transports warm water to cooler locations – previous studies of Prox b have used a ocean of statis that warms and cools. "

From there, Del Genio and his colleagues found that every case they could think of a planet that had at least liquid water on the surface. They also found that, in the case of a tidal planet, heat transport between the sun and the dark side could also allow the entire planet to be habitable.

"So, if there is an atmosphere and water, Prox B has a good chance of being livable," said Del Genio. "We also found that ocean currents carried warm water from day to night, keeping some parts of the night alive even if they never saw light, and if the ocean was very salty, almost all of the planet could be but with temperatures below the usual freezing point almost everywhere. "

For those who have been treated to a regular diet of bad news about Proxima b, this latest research is very encouraging. Although observations have shown that Proxima Centauri is variable and has produced significant eruptions, there are still many scenarios in which Proxima b could still be habitable. Whether or not the case, however, will depend on future observations. As Del Genio said:

"Unfortunately, because of the Earth, Prox b does not seem to be transiting, which makes it more difficult to detect an atmosphere and its contents, but in the not too distant future, astronomers will be able to monitor the heat emitted in space. " by Prox b in motion in its orbit.Our results show that it should be possible to distinguish a planet with an atmosphere without a cold and thin atmosphere and a warm atmosphere and thick. "

It could also extend to other rocky planets that orbit M type stars (red dwarf), which is even more encouraging. Since these stars represent more than 70% of the stars of the Milky Way galaxy alone, the likelihood that they support potentially habitable planets increases the chances of finding extra-terrestrial life significantly.

In the coming years, next-generation instruments should play a major role in the detection and characterization of exoplanets. These include the James Webb Space Telescope (JWST), the Wide Field Infrared Investigation Telescope (WFIRST) and ground-based instruments such as the Extreme Telescope (ELT) and the Magellan Giant Telescope (GMT). ). And you can bet that some of their time will be spent studying the planet's closest exoplanet!

Explore more:
Satellite weather forecast for Proxima Centauri B

More information:
Anthony D. Del Genio et al. Living climate scenarios for Proxima Centauri b with a dynamic ocean, astrobiology (2018). DOI: 10.1089 / ast.2017.1760