An international team of astronomers using ESO’s Very Large Telescope in Chile has found evidence that there is a third planet orbiting Proxima Centauri, the closest system to our own, 4.2 light-years away.
Baptized as Proxima d, it would be the innermost of the worlds identified there and the researchers led by João Faria, from the Institute of Astrophysics and Space Sciences, in Portugal, still treat it as a candidate, in their article published in the journal Astronomy & Astrophysics. . And not without reason: it would be the least massive exoplanet ever detected by the radial velocity measurement method, 25% of that of Earth. This method allows the estimation of the mass of the planets by measuring the wobble that a star makes when being attracted by the worlds that revolve around it.
There has been enthusiasm for Proxima Centauri since 2016, when the first exoplanet was discovered there. Proxima b, as it was called, completes an orbit around its star, a red dwarf much smaller than the Sun, every 11 days. This puts it, in theory, in the star’s habitable zone, a region neither too cold nor too hot, where in principle it would be possible to have water stably on the surface – a prerequisite for life.
Proxima c, the second planet discovered in the system, was found in 2020, with the same equipment that had detected Proxima b. It would be something like a super-Earth or a mini-Neptune, with seven times the mass of Earth, orbiting the star every 5.3 years. He is still treated by most astronomers as a candidate, lacking confirmation.
It is the same situation in which Proxima d now appears, the tiny world discovered with Espresso, the VLT’s spectrograph more powerful and accurate than Harps, responsible for the discovery of the two previous planets. Both instruments essentially do the same thing: they measure the light signature of the observed star and detect variations in wavelengths that indicate the periodic wobble of the star caused by the planets.
The difference is that the Espresso is more modern and operates in a telescope with an 8.2 meter mirror. Harps is installed at the La Silla Observatory, also in Chile, but with a 3.6-meter mirror. It was using it to confirm the presence of Proxima b in 2020 that researchers found a signal indicating a tiny planet with a period of 5 days. Subsequent observations have given more confidence that it is indeed a planet.
More than revealing the richness of the neighboring planetary system, a potential target for future studies with the James Webb Space Telescope, the work confirms Espresso’s potential to discover low-mass exoplanets, a population about which very little is known so far, but must be among the most prevalent types in the galaxy.
This column is published on Mondays, in Folha Corrida.
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