Exciting discovery: Astronomers have again found evidence of a second planet around our nearest neighboring star, Proxima Centauri. Accordingly, there could be a large, cold super earth in addition to the habitable earth twin. It orbits the star in around 5.2 years, as tiny fluctuations in the star movement suggest. So far, however, the orbit of this planet, unusually wide for a super-earth, is inexplicable.
Our closest neighboring star Proxima Centauri is only about four light years away from us – it is the first system that people with one interstellar mission could achieve. All the more exciting was 2016 the discovery one potentially life-friendly earth twin about this red dwarf. In 2017, astronomers used the ALMA telescope to point out dust rings and the possible heat signal other planets for Proxima Centauri – but the data was still too unspecific.
“Wobbling” of the star as an indicator
Astronomers around Mario Damasso from the Astrophysical Observatory in Turin have now again searched for evidence for a second planet around Proxima Centauri. To do this, they evaluated a good 17 years of observation data from the HARPS spectrometer at ESO’s Very Large Telescope in Chile. They searched for periodic shifts in the Proxima Centauri light spectrum, which typically result from the gravitational influence of a orbiting planet.
This so-called radial velocity method is particularly suitable for the detection of planets that, from our point of view, do not pass directly in front of their star – and therefore do not cause shadowing of the starlight. At Proxima Centauri, however, this is made more difficult by the fact that this red dwarf is very active: it often experiences strong radiation and plasma outbreaks, which can also generate a quasi-regular cycle in the light spectrum.
Planet with an orbital period of 5.2 years
Nevertheless, Damasso and his team found what they were looking for: In the spectral data, they identified regular fluctuations that repeated every 1,900 days. Further analysis showed that the period of this signal differs by 482 days from that of the outbreaks of Proxima Centauri. “This speaks against the fact that this 1,900-day signal is caused by stellar activity,” the researchers report.
The originator of the signal is therefore most likely a second planet around Proxima Centauri – Proxima c. This planet has an orbital period of 5.2 years – 1,900 days – and orbits the star at a distance of 1.48 astronomical units, as the astronomers report. Proxima c could therefore be located almost exactly where the ALMA telescope observed a striking heat signature two years ago.
Super earth far outside the habitable zone
However, this also means that the second planet around our neighboring star is anything but life-friendly: Proxima c lies far outside the habitable zone and, according to initial calculations, could have an equilibrium temperature of freezing minus 234 degrees. The mass of the exoplanet is around 5.8 earth masses. Proxima c would be a very large, cold super earth.
Astronomers do not rule out that Proxima c could be even heavier. Because if the evidence found by the ALMA telescope on a cold, outer dust ring around Proxima Centauri is confirmed, then this could change the mass estimate, as the researchers explain. Proxima c could then weigh a good eight earth masses. “Follow-up observations by ALMA are therefore essential,” stated Damasso and his team.
Too far beyond the snow line?
Unusual, however: This super earth would be the first to go so far beyond the so-called snowline around their star – the limit from which water vapor and other gases freeze out and become ice. According to current theory, rock planets predominantly form within this limit. However, in the case of Proxima Centauri, the snow line is only 0.15 astronomical units – but the super earth Proxima c is ten times farther from the star.
“The formation of a super earth so far beyond the snow line is a challenge for our educational models,” explain Damasso and his team. “Because after these, super earths would have to be created almost directly on the snow line.” Proxima c therefore does not fit into the picture – and so far the astronomers have no clear explanation for this either. Theoretically, it would be possible that Proxima c originally circled in a different orbit or that the snow line was earlier from the star than today.
Further observations are necessary
However, the second planet around Proxima Centauri has not yet been clearly proven – even if the new data make its existence very likely. The astronomers now hope that further observations with the ALMA telescopes and the Gaia satellite from ESA will confirm the planet and also provide further information about its nature. This could also help solve the puzzle of its unusual external position. (Science Advances, 2020; doi: 10.1126 / sciadv.aax7467)
Source: Science Advances
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