Proxima b orbits the closest star to our sun – a red dwarf known as Proxima Centauri, which lies 4.2 light years away. It's a rocky, terrestrial planet with a surface -- unlike a gas giant, such as Jupiter -- that is 1.3 times the size of Earth and orbits its star every 11.2 days. It is in a close orbit of Proxima Centauri: only 5% of the distance between the Earth and the sun. They are even closer together than Mercury and the sun. But because its star is much cooler and fainter than our sun, Proxima b has a temperature that is suitable for liquid water to exist on the surface without evaporating.
Researchers estimate that if the planet has an atmosphere, which could be assumed but isn't known, it may be between 86 to 104 degrees Fahrenheit (31 to 40 degrees Celsius) on the surface. Without an atmosphere, it could be -22 to -40 degrees Fahrenheit (-30 to -40 degrees Celsius). To put that in perspective, Earth would be -4 degrees (-20 degrees Celsius) if it didn't have an atmosphere, Reiners said.
Given the proximity to its star, Proxima b is also subject to less pleasant factors like ultraviolet and X-ray flares that are 100 times the intensity of what Earth receives from the sun. In the paper, researchers estimated it to be 400 times the intensity, but recent research has caused them to create a new estimate, they said. If there is life on the planet, it would be affected by this radiation, but it is pure speculation as to what kind of effect.

We don’t even know for sure that Proxima b is a rocky planet, although researchers think this is likely, judging by other planets orbiting small stars. What we do know is that it is within the so-called “habitable zone”, meaning that if water is present on the planet, it could be in liquid form. But many important questions are as yet unanswered. We don’t know if the planet has water, or an atmosphere, or a magnetic field to shield it from the high-energy radiation emitted by its star. What is likely is that the newly discovered planet is “tidally locked” to its star, meaning that only one side receives sunlight. Proxima b might be within the habitable zone, but whether it could host life is quite a different matter.

How many other similar planets could be out there?

Thousands of exoplanets – planets outside our solar system – have been found to date. The first confirmed discoveries were in 1992, when astronomers found planets orbiting a type of neutron star known as a pulsar. The first planet orbiting a sun-like star was discovered in 1995. Since then, missions such as the Kepler space observatory, as well as ground-based observations, have found many more, including a number of Earth-sized worlds within the habitable zone of their stars. But that’s just the tip of the iceberg. Based on Kepler’s results, astronomers have suggested there could be as many as 40bn habitable, Earth-sized planets in our galaxy, travelling around red dwarfs or stars similar to our sun (yellow dwarfs).