A second planet could orbit Proxima Centauri

The star closest to the solar system seems to host another world much colder than the Earth.

Lorenzo Santinelli

The planet orbiting the star closest to the sun, Proxima Centauri, could have a neighbor. An international team of astronomers with the participation of the Instituto de Astrofísica de Andalucía, centre of the Consejo Superior de Investigaciones Científicas (CSIC), has announced the discovery of what could be a second planet: Proxima c.

Proxima Centauri is a faint red star just 4.2 light-years away from Earth that houses a potentially habitable planet, Proxima b (a bit larger than Earth). According to indications, this second planet would be much larger and further away from the star.

If it exists, Proxima c would be 5.8 times larger than Earth (or half the mass of Neptune) and would orbit its star approximately once every five Earth years (1.5 times the distance from the Sun) according to scientists in the magazine Science Advances that published the study. Its temperature is approximately -200°C, if it has no atmosphere.

Could it have water?

Unfortunately, given the huge distance between it and the star Proxima Centauri, the planet is also too cold to have liquid water, a key factor for habitability.

The super-Earth

Astronomers say they need new observations to confirm what is now an indication as a planet. Additionally, given its proximity, it is an ideal candidate for follow-up observations, and even images, with next-generation telescopes.

The discovery of the potential planet Proxima c is surprising, because its presence defies current astronomical models of how super-earths form and evolve.

The discovery

The researchers analyzed the "radial velocity" data collected over several years by the instruments HARPS (High Accuracy Radial Velocity Planet Searcher) and UVES (Ultraviolet and Visual Echelle Spectrograph), installed on telescopes operated by the European Southern Observatory (ESO) located in Chile. They tracked the light spectrum of Proxima Centauri over time, looking for regular oscillations that could indicate the presence of an undiscovered planet. This was not an easy task, as the combined measurements of the HARPS and UVES spectrographs covered approximately 17.5 years.

The thorough study bore fruit with the revelation of a possible planet, Proxima c, a super-earth whose confirmation would come from the European Space Agency’s Gaia spacecraft, according to experts.

In addition, scientists are considering looking for Proxima c through direct images, specifically from photographs captured by SPHERE (Spectro-Polarimetric High-contrast Exoplanet REsearch), a tool installed on ESO’s Very Large Telescope in Chile. It’s because the data from the equipment suggests the superland is probably there, waiting to be found, officially. The detected signal is at the limit of the instrumental capabilities, so hopefully the astrometric data of the Gaia satellite will allow to second the existence of Proxima c.

Reference: M. Damasso et al. "A low-mass planet candidate orbiting Proxima Centauri at a distance of 1.5 au". Science Advances, 2020. DOI: 10.1126/sciadv.aax7467

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