At the end of last month, scientists from the European Southern Observatory announced the discovery of Proxima b, the first “exoplanet” ever discovered around Proxima Centauri, the closest start in the Universe to our very own Sun.
The star was discovered using the radial velocity method, which detects small back-and-forth motions induced in the star due to the planet’s gravitational pull. Using this method, scientists were able to determine both the orbital period and mass of the planet.
Proxima b is not only at the correct distance from its start to have the potential to support liquid water on its surface, but it has a mass roughly 1.3 times that of our own world. If this is the case, then it is most likely somewhere around 10% larger in diameter than Earth, could potentially have an Earth-like atmosphere, and the same raw elements as Earth. And most excitingly, Proxima b could potentially even support life on its surface.
While similar, life would be much different on Proxima b
These are incredible similarities that carry with them incredible implications not only for the scientific world, but for the future of humanity itself. Despite these similarities, however, and the planet’s relative close distance at only 4.24 light years away, there are still some fundamental differences between Proxima b and Earth.
One of the more interesting things about the planet is that is doesn’t have a day in which the sun rises and sets like on Earth. Since the planets star, Proxima Centauri, is a red dwarf star, it is much, much smaller, less massive, and dimmer than our own Sun. Because of this, planets in this system need to be much closer in order to receive warmth, which, in turn, means larger tidal forces. In this case, these forces are enough to “lock” the planet into orbit, meaning that the same hemisphere always faces towards the sun, while the other always faces away.
As the planet is locked into orbit around its sun, there will be three constant and different climate zones. The side of the planet facing the star will be constantly scorching, receiving sunlight without ever getting a break. On the other side of the planet, the surface will experience an eternal night and will be dark and frozen, however with spectacular views of the Universe. The border regions between the two, a ring around the planet, will experience eternal dawns/sunsets, and will most likely have the most earth-like conditions.
On the sun-side of the planet, solar flares from its sun could be potentially deadly. Red dwarf starts are generally much more active and variable than stars like our own. It will flare more frequently, and these flares could prove to be cancerous to any organic lifeforms. The magnetic field on Earth effectively shields us from this, though Proxima b will be less likely to have one due to its lack of rotation.
A birthday every 11 days on Proxima b
Because the planet revolves around its sun much quicker than Earth, a year on Proxima b is a mere 11 days long. As there is no axial tilt because of the planets orbit “lock,” seasons would be dependent on how elliptical the orbit of the planet is. If the orbit turns out to be circular, there is a high likelihood that there won’t be seasons at all.
While the planet is much closer to its sun than Earth is to its own, plants on the surface won’t be able to effectively use UVF light. Proxima Centauri is so cool and dim that there is essentially no UV light emitted from it. Additionally, the star emits next to no blue light either, so many of the same molecules that plants on Earth use to get energy wouldn’t thrive on Proxima b.
Since Proxima Centauri is much smaller than our sun, due to how close Proxima b is to it, it would appear massive in the sky. In fact, Proxima Centauri would appear around 10 times s large than the sun does on Earth. Most of the energy from the sun is infrared, so the sun would feel close to the same level of warmth as on Earth. Additionally, there wouldn’t be any danger of sunburn without any UV light.
In the sky on Proxima b, there would be two stars brighter than anything that can be seen from Earth’s surface. Although Proxima Centauri is the closest star to Earth at 4.24 light years away, the stars Alpha Centauri and Alpha Centauri B, which are barely visible from Earth even using professional telescopes, would be very distinct and bright to the naked eye from Proxima b.
If, in fact, life does exist on the planet, it would have evolved to see the stars in the color blue. Since the temperature of Proxima Centauri is much cooler than the Sun, any life would have evolved to “see” longer, redder wavelengths. Since the vast majority of stars in the sky are much hotter and emit much more blue light than Proxima Centauri does, the night sky would be full of blue stars.
Could it be Earth, part two?
Harvard astronomer Avi Loeb, has said that if Proxima b, if habitable, might yet one day save the human species from extinction. The exoplanet is “the most natural location to where our civilization could aspire to move” before the Sun ballons into a red giant and destroys Earth in roughly five billion years.
The slow-burning Proxima Centauri should last another four trillion years (or 300 times the current age of the universe). Time enough for us to rest easy and consider our next move.