Astronomers Confirm The Earth-Sized Planet at Proxima Centauri Is Definitely There

Using state-of-the-art astronomical instruments, an international team of researchers has confirmed the existence of Proxima b, an Earth-like planet that’s orbiting the closest star to our Solar System, Proxima Centauri.

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Tau.Neutrino said:

Astronomers Confirm The Earth-Sized Planet at Proxima Centauri Is Definitely There

Using state-of-the-art astronomical instruments, an international team of researchers has confirmed the existence of Proxima b, an Earth-like planet that’s orbiting the closest star to our Solar System, Proxima Centauri.

more…

Good, good.

> They found that Proxima b is 1.17 times the mass of Earth, smaller than the older estimate of 1.3 times. It orbits its star in just 11.2 days. Nailing down the mass of a distant planet with such precision is completely unheard of.

Actually, that is a good point. The mass can’t be nailed down accurately with eclipsing because the orbit may be inclined or elliptical. In the absence of an eclipse it becomes even more difficult. Spectroscopy for example will only give an answer that depends on inclination. So how have they done it? No.

> HARPS has been responsible for discovering hundreds of exoplanets over the last 17 years. ESPRESSO can produce even better measurements.

Not sure if this is the most recent version of the technical article. I think is it. It was written in 2005 and updated 27 May 2020. Accepted by Astronomy and Astrophysics May 2020.
https://arxiv.org/pdf/2005.12114.pdf

“Revisiting Proxima with ESPRESSO

“We analysed 63 spectroscopic ESPRESSO observations of Proxima (Gl 551) taken during 2019. We obtained radial velocity measurements with a typical radial velocity photon noise of 26 cm·s−1. We combined these data with archival spectroscopic observations and newly obtained photometric measurements to model the stellar activity signals and disentangle them from planetary signals in the radial velocity (RV) data.

“The ESPRESSO data on its own shows Proxima b at a period of 11.218±0.029 days, with a minimum mass of 1.29±0.13 M⊕. In the combined dataset we measure a period of 11.18427±0.00070 days with a minimum mass of 1.173±0.086 M⊕. We get a clear measurement of the stellar rotation period (87±12 d). Tentative second planet with a minimum mass of 0.29±0.08 M⊕

So, only minimum mass. That figures. Until the orbital inclination is known every estimate of mass from spectrographic data is going to be an underestimate. Do they estimate inclination and/or eccentricity? Reading on. They don’t even mention orbital inclination. They do mention eccentricity, estimating it as 0.1, similar to the eccentricity of Mars.

Um, the smooth line in the chart below is the assumed long term velocity due to the stellar activity. There’s a lot of variation due to stellar activity rather than planetary motion, even though Proxima is not that much bigger in diameter than Jupiter. The planetary properties come from the difference between this smooth line and the individual data points.