The Closest Exoplanet to Earth Could Be 'Highly Habitable' and with a Dayside Ocean

An artist's impression of the view from Proxima Centarui b, a newly discovered Earth-sized planet just four light-years away. It is unclear if there is intelligent life in the universe, but searches continue to find Earth-sized planets in the habitable zones of their respective stars. Credit: NASA.

Since its discovery in August of 2016, and just around the corner, in astronomical terms, Proxima Centauri b, our closest neighbour has awakened our curiosity, wonder and awe, raising the question of whether it could be capable of sustaining life, its discovery was confirmed by the European Southern Observatory. 

Now researchers employing computer models similar to those used to study climate change on Earth, have found that, under a wide range of conditions, this exoplanet can sustain enormous areas of liquid water on its surface, and that potentially makes the possibility of harbouring living organisms. 

In this new NASA-led study, a team of scientists has investigated various climate scenarios that indicate that Proxima b could still have enough water to support life. The publication is titled “Habitable Climate Scenarios for Proxima Centauri b with a Dynamic Ocean“, and was recently published in the scientific journal Astrobiology. This study was led by Anthony D. Del Genio of NASA’s Goddard Institute for Space Studies (GISS) in New York City and included members from the NASA Goddard Space Flight Center (GSFC), Columbia University, and Trinnovim LLC – an IT company that provides institutional and mission support for the GSFC. Del Genio said: "The major message from our simulations is that there's a decent chance that the planet would be habitable." 

The small cool red-dwarf star of Proxima Centauri is located at just 4.2 light-years from our star The Sun. However, despite its proximity scientists still know very little about this planet orbiting Proxima Centauri, we know that its mass is at least 1.3 times that of Earth and that it orbits it parent star every 11 days. So, Del Genio and his colleagues had to come out with some reasonable guesses about the exoplanet Proxima Centauri b — namely, that it had an atmosphere and an ocean on its surface — for their work to proceed. 

This infographic compares the orbit of the planet around Proxima Centauri (Proxima b) with the same region of the Solar System. Credit: Pale Red Dot.

This exoplanet orbits in its star's habitable zone, which means it lies at the right distance to receive enough light to maintain its surface above the freezing temperature of water. However, in the case for this particular system the distance between the star and the planet is its surface above is very small, meaning that they are tidally locked due to gravitational forces, and so the planet faces always the same side of its parent star, similar like the case between the earth and the moon. 

On a prior simulation published in a paper in the journal Astronomy & Astrophysics it modelled a hypothetical atmosphere on Proxima Centauri b, which rendered the star-facing hemisphere of the exoplanet baked under an intense glare, while a space-facing ocean, on the opposite side the ocean if it had one, it would totally frozen over. Concluding that only a circle of warm sea might exist on Proxima Centauri b, a possibility that Del Genio's team calls "eyeball Earth." 

These new simulations have been more comprehensive than prior ones which also included a dynamic, circulating ocean, a scenario which was able to transfer heat from one side of the exoplanet to the other very effectively. The new findings suggest that the movement of the atmosphere and ocean combined so that "even though the night side never sees any starlight, there's a band of liquid water that's sustained around the equatorial region," in the words of Del Genio. 

He made a comparison with our own planet like in the case of the heat circulation on earth's seaside climates. A good example of this would be how the U.S. East Coast has a more pleasant climate than it would have because the Gulf Stream carries warm water up from the tropics, in contrast to this in California, the ocean currents bring cold water down from the North and so the west coast is colder than it should be, said Del Genio. 

Artist’s impression of Proxima b, which was discovered using the Radial Velocity method. Credit: ESO/M. Kornmesser.

The researchers ran 18 separate simulation scenarios in total, looking at the effects of giant continents, thin atmospheres, different atmospheric compositions and even changes in the amount of salt in the global ocean. In almost all of the models, Proxima Centauri b ended up having open ocean that persisted over at least some part of its surface. 

"The larger the fraction of the planet with liquid water, the better the odds that if there's life there, we can find evidence of that life with future telescopes," Del Genio said. 

Now with the prospects of the next generation of telescopes such as the Extremely Large Telescope currently under construction in Chile, or the James Webb Space Telescope to be launch into space soon, the future looks bright regarding the search for life in our closest planet, Proxima Centauri b 

Sources: livescience, Universe Today,