In 2016, astronomers found a potentially habitable planet called Proxima b around the star Proxima Centauri, which is only 4.2 light years from Earth. Now the researchers have traced a second signal that they believe belongs to a super-Earth orbiting the same star, increasing the intrigue of this neighboring planetary system and its potential.
Proxima Centauri is the closest star to our sun. It is a low mass red dwarf star known as a M class dwarf. The star is in a three star system called Alpha Centauri, including the binary pair Alpha Centauri AB.
All these stars are found in the weak constellation of the Centaur, which cannot be seen with the naked eye.
After the discovery of the first planet around Proxima Centauri, the researchers speculated on the existence of another planet in the system. Astronomers used the Atacama Large Millimeter / submillimeter network of telescopes in Chile to trace the light signals that appeared to be coming from this direction.
The authors of a new study, published Wednesday in the journal Science Advances, were able to examine more than 17 years of radial velocity data from the well-studied star system and determine whether the signal belonged to an orbiting planet.
The radial velocity method is based on gravity and the Doppler effect, in which light increases or decreases in frequency when the source and the objects observed approach or move away from each other.
The stars do not remain completely immobile when they are orbited by planets; they move in small circles in response to the gravitational pull of the planets. These movements modify the light wavelength of the star, going from red to blue depending on the location of the planet. Tracking changes can help astronomers find planets.
Researchers can’t rule out that the signal could be due to the activity of the star’s magnetic field, but the signal they traced occurred over a period of 1,900 days – a strong indicator that a planet is present.
“Even the planetary system closest to us can hold interesting surprises,” said Fabio Del Sordo in an email, study author and postdoctoral researcher in the physics department of the University of Crete. “Proxima Centauri is home to a much more complex planetary system than we knew, and we don’t know how many unknown features are waiting to be discovered.”
Meet the neighbors of the planet
The second planet recently discovered, Proxima c, is probably a super-Earth with a mass larger than Earth but smaller than Uranus and Neptune. Researchers estimate that it completes one Proxima Centauri orbit every 5.2 Earth years.
The first planet found around the star, Proxima b, is six times smaller and 30 times closer to its star, which also makes it warmer, according to the researchers.
Proxima b is 1.3 times the size of the Earth and orbits its star every 11.2 days. It is in an orbit close to Proxima Centauri: only 5% of the distance between the Earth and the sun. They are even closer to each other than Mercury and the sun. But because its star is much colder and weaker than our sun, Proxima b has a temperature which allows liquid water to exist on the surface without evaporating.
Given the proximity of its star, Proxima b is also subject to less pleasant factors like ultraviolet rays and X-rays which are 100 times the intensity of what the Earth receives from the sun. If there is life on the planet, it would be affected by this radiation, but it is pure speculation on the type of effect.
Even if Proxima b is in the habitable zone of its star, which means that liquid water could exist on the surface, this does not mean that it is actually habitable. And the radiation it likely faces has probably stripped away key elements of life like hydrogen, oxygen and nitrogen.
The new planet discovered is intriguing, as further study could reveal the formation of low-mass planets around low-mass stars, the researchers said. And this particular planet overturns the typical theory of super-Earth formation on its head.
It is beyond the system’s “snow line”, which suggests that all water on the planet would be frozen. Super-lands generally form near, but not beyond, the snow line.
“The formation of a super-Earth well beyond the snow line calls into question the training models, according to which the snow line is an ideal point for the accretion of super-Earth, due to the accumulation of frozen solids there, “said Mario Damasso, author and postdoctoral researcher at the Italian National Institute of Astrophysics. “Or it suggests that the protoplanetary disc was much hotter than usual. In general, nothing prevents the existence of Proxima c where we spot it, but formation and evolutionary history are a subject that deserves further investigation. “
The European Space Agency’s Gaia mission, which is creating a 3D mission to our galaxy, could help refine the signal from the second planet and provide more answers in the future.
“Proxima Centauri is the closest star to the sun, and this detection would make it the multi-planetary system closest to us,” said Del Sordo.