The search for exoplanets at Alpha Centauri

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The search for new exoplanets orbiting the three stars of the Alpha Centauri star system is intensifying, despite significant viewing challenges and solar activity that precludes life around one star.

The system’s two sunlike stars, Alpha Centauri A and B, orbit each other closely while Proxima Centauri, a tempestuous red dwarf, hangs onto the system tenuously in a much more distant orbit. In 2016, astronomers discovered an Earth-mass planet around Proxima Centauri, but the planet, blasted by radiation and fierce stellar winds, seems unlikely to be habitable. Astrobiologists think the other two stars are more likely to host temperate, Earth-like planets.

Maksym Lisogorskyi, an astronomer at the University of Hertfordshire in Hatfield, U.K., tried to find them with an instrument on the European Southern Observatory’s (ESO’s) 3.6-meter telescope in Chile. He and his colleagues looked for Doppler shifts in the spectral lines of the stars’ light that would be caused if a planet tugged them back and forth. But Lisogorskyi told the meeting that the stars’ surfaces are turbulent, and prone to flares that also jiggle the spectral lines, masking the subtle signals from any Earth-size planets. “The lines do all kinds of things,” he says. Although Alpha Centauri has been a primary target for the planet-finding instrument since it was inaugurated in 2005, it has seen nothing so far.

Also hampering observations are the current positions of the two stars. As viewed from Earth, they are very close together, making them harder to study individually, Lily Zhao of Yale University told the meeting. More precise observations should become possible as their 80-year orbit carries them farther apart. In the meantime, Zhao and her colleagues have succeeded in ruling out the presence of giant planets around either star, based on a decade’s worth of data from three instruments on different telescopes. “There are no Jupiters in the system, but there may be plenty of Earth-sized planets still to discover,” she said.

I am skeptical of the conclusions of the astrobiologists who think there may be habitable Earth-like planets in orbit around the close binary. Binary formation makes planetary formation difficult, and even if they are there the stars’ orbits would make stable orbits unlikely. Nonetheless, the research is good, as the techniques learned will be applicable elsewhere.


One comment

  • Localfluff

    Even our nearest star is so dim that it cannot be seen with the naked eye. No telescope can resolve its surface, it’s just a dot, a pixel. It’s only slightly larger than Jupiter in volume, but much heavier. About 70% of stars are red dwarfs like this, and they are lethally active. While Solar radiation is what feeds all of life on earth, the hard UV radiation from red dwarfs seems difficult to deal with. All molecules is machine gunned by the radiation. Lots of energy for sure, but how to make use of it? Given the practically infinite combinatorics of biochemistry, which includes human engineering, I suppose that it is possible. And once a working patent is found, it will spread everywhere.

    A Jupiter would’ve had potentially habitable icy moons, with oceans protected from the stellar flares, and at any distance from the star since the energy would be tidal instead of stellar. But our neighbor dwarf star doesn’t have such, too bad.

    We’re really lucky with our neighborhood anyway. Red dwarfs are so common and here we have one next doors 4.3 ly away. Its distant companions are two quite Sun like stars. Sirius b is a white dwarf, a very exotic kind of materia orbiting an especially hot and large star 6 ly away. And the nearest known brown dwarf is at the same distance. It’s like a museum, all the most exotic, but yet harmless, objects are nearby. The first interstellar space probes have good targets.

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