Proxima d is one of the smallest exoplanets ever discovered, weighing only a quarter of the Earth’s mass. It is also the third exoplanet found to orbit Proxima Centauri. And although its surface is probably uninhabitable, its detection suggests that there are still many exoplanets that can be discovered just outside the gates of the solar system. And who knows? For example, an alien civilization lives on one of them.
Proxima d joins Proxima b and c for a triple-planet system in our closest neighbour, showing us once more that multi-planetary systems are very common and that low-mass M-dwarfs are full of surprises. Is this the last planet orbiting Proxima? Time will tell. pic.twitter.com/987PBStlFn
— ESPRESSO Science Team (@espresso_astro) February 10, 2022
“The discovery shows that our nearest stellar neighbor is full of interesting new worlds. We are within reach of further discoveries, studies and research. ” said Portuguese astrophysicist João Faria.
To date, almost 5,000 exoplanets have been discovered and confirmed, and thousands more discoveries await the imaginary list of exoplanets.
How to find an exoplanet
There are two main ways to search for planets outside the solar system. The most widely used technique is the so-called transit method, in which the telescope observes stars for a long time to detect faint, regular drops in brightness that signal an orbiting planet passing between the Earth and the star.
The second popular approach is the radial velocity (or wobble) method. When two bodies, such as a star and a planet, are gravitationally bound, one does not orbit the other. Instead, they orbit their common center of gravity, the so-called barycenter. The bar center of the solar system, for example, is just off the surface of the Sun.
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This causes the star to sway slightly in place, which in turn affects the light that hits us, causing the Doppler shift. As the star moves away from us, the wavelengths of its light stretch slightly. When it moves towards us, they compress themselves again. Astronomers then look for these regular Doppler shifts, which lead them to discover new exoplanets.
Both of these methods are more reliable in detecting larger exoplanets because they block more light from the star or create more pronounced stellar fluctuations. Currently, only 36 exoplanets less massive than Earth have been discovered.
Two-year observation
Signs of the existence of Proximy d appeared as early as 2020, when astronomers used an instrument called ESPRESSO, which focused on research around Proximy Centauri. At that time, they used the method of radial velocity and thus confirmed the existence of Proximy b, an exoplanet weighing 1.2 times the mass of the Earth.
However, there was another, much weaker signal in the data. Something seemed to be orbiting the star in a regular five-day period. However, the signal was so weak that much more observation was needed.
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In the end, the team actually discovered that it was an exoplanet. It was so small that it caused the star to move back and forth at only 40 centimeters per hour. The ability to detect such a gentle and slight movement at a distance of 4.2 light years is almost impossible.
“After several observations, we were finally able to confirm that this signal really indicates the existence of a new candidate for the planet. I was excited and it was a huge challenge to detect such a small signal, “the astrophysicist described.
Proxima d weighs about 0.26 times the mass of the Earth and orbits its axis once every 5.12 days. Unfortunately, this means that it is too close to the star for life to be on it.
Detection of new exoplanet, Proxima d, orbiting the star closet to the Sun: Proxima Centauri https://t.co/RKI63mdMIU @THAT @NASA pic.twitter.com/LjYEJ3VjVQ
— ♄ Charles W. Clark ħ (@g8ge) February 10, 2022
Discovery however, it suggests that the current low numbers of smaller exoplanets may have been due to the human inability to detect them reliably and that finding them is only a matter of time and technology.
“This success is extremely important. This shows that the radial velocity method has the potential to detect populations of light planets such as ours, those that can potentially host life as we know it, ”wrote the official report by the ESPRESSO scientist Pedro Figueira.
The third planet orbiting Proximy Centauri is called next c, is about six times more massive than Earth and orbits its star once every 5.2 years, which means it is too cold to be habitable. So far, the most likely candidate for an exoplanet that could host life is Proxima b. However, if this is indeed the case, we will have to wait a while longer.
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