Tag: Alpha Centauri

Possible exoplanet detected in habitable zone around Alpha Centauri A?

10:47 am

The uncertainty of science: Scientists have detected faint evidence that suggests the existence of a Neptune-sized exoplanet circling the sunlike star Alpha Centauri A.

After analyzing 100 hours of data gathered by NEAR in May and June of 2019, the scientists detected a thermal fingerprint in the habitable zone of Alpha Centauri A. The signal potentially corresponds to a roughly Neptune-size world orbiting between 1 and 2 astronomical units (AU) from the star, study team members said. (One AU, the average Earth-sun distance, is about 93 million miles, or 150 million kilometers.)

But that planet has not yet been confirmed, so it remains a candidate for now.

This result is very uncertain at this moment, so we should constrain our enthusiasm. If true, however, it would signal the possibility of more exoplanets circling the stars of the nearest stellar system. Alpha Centauri is actually three stars, a binary of two sunlike stars circled at great distance by the red dwarf Proxima Centauri. Scientists already think there are exoplanets circling Proxima, with one about the size of Earth.

What makes this particular interesting, if true, is that the exoplanet was detected not by the slight wobble its gravity caused in the star, or by a transit across the face of the star, but by its own light. If the detection is real, this would be I think the first time that an exoplanet has been seen directly, even if that detection comprises a few tiny pixels of light.

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The search for exoplanets at Alpha Centauri

8:56 am

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.

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Plotting the interstellar path to Proxima Centauri

8:40 am

Scientists have calculated the slingshot route that Breakthrough Starshot’s tiny interstellar spacecraft should take in order to reach Proxima Centauri while also gathering the maximum scientific data while zipping past the binary stars of Alpha Centauri.

The solution is for the probe’s sail to be redeployed upon arrival so that the spacecraft would be optimally decelerated by the incoming radiation from the stars in the Alpha Centauri system. René Heller, an astrophysicist working on preparations for the upcoming Exoplanet mission PLATO, found a congenial spirit in IT specialist Michael Hippke, who set up the computer simulations. The two scientists based their calculations on a space probe weighing less than 100 grams in total, which is mounted to a 100,000-square-metre sail, equivalent to the area of 14 soccer fields. During the approach to Alpha Centauri, the braking force would increase. The stronger the braking force, the more effectively the spacecraft’s speed can be reduced upon arrival. Vice versa, the same physics could be used to accelerate the sail at departure from the solar system, using the sun as a photon cannon.

The tiny spacecraft would first need to approach the star Alpha Centauri A as close as around four million kilometres, corresponding to five stellar radii, at a maximum speed of 13,800 kilometres per second (4.6 per cent of the speed of light). At even higher speeds, the probe would simply overshoot the star.

While most of this is hardly revolutionary, this is still the first time anyone has done the hard math based upon a real mission concept.

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Russian billionaire backs interstellar project

9:00 am

The competition heats up: A Russian billionaire has announced a $100 million investment in an effort to use lasers to propel cellphone-sized spacecraft on an interstellar voyage to Alpha Centauri.

Called Breakthrough Starshot, the programme is based on an idea that has been around for decades: the solar sail. The theory is that a lightweight space sail could harness the momentum carried by photons in order to travel without fuel.

The Breakthrough Starshot team is betting that a burst of concentrated lasers, fired from the ground, could rapidly accelerate a mobile-phone-sized device equipped with microelectronics and a tiny sail — providing much more energy than could be harnessed from the Sun. Whereas NASA’s plutonium-powered New Horizons spacecraft took nine years to reach Pluto, the “nanocraft” envisioned by Breakthrough Starshot would pass by the dwarf planet and exit the Solar System in three days.

The project’s initial US$100-million budget covers only research and development of such a spacecraft. But Breakthrough Starshot’s ultimate goal is to demonstrate proof of concept for an international programme that would send a fleet of nanocraft into space. Doing so would require the group to surmount enormous scientific and engineering challenges in developing the necessary laser technology, materials and communications systems.

This technology is related though not identical to an earlier story about using lasers to power spacecraft.

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Astronomers have discovered that the nearest star to the Earth, Alpha Centauri, has an exoplanet only slightly heavier than the Earth.

3:28 pm

Big news: Astronomers have discovered that the nearest star to the Earth, Alpha Centauri, has an exoplanet only slightly heavier than the Earth.

Alpha Centauri is actually a triple star system, with two sunlike stars in a tight orbit around each other and a third star far out orbiting them both. The exoplanet orbits one of the inner stars every 3.2 days.

More details from Nature here.

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