Are there Earth-like planets around our nearest stellar neighbor?
If you live in Earth’s Southern Hemisphere, you’re probably familiar with the Southern Cross, one of the most easily recognizable constellations in the sky. To the left of the cross lies the bright star system of Alpha Centauri. With the naked eye, Alpha Centauri, or Alpha Cen, looks like a single star. But it’s actually two stars—Alpha Cen A and B—and together, they are the third brightest star system in the sky after Sirius and Canopus.
ESO / Digitized Sky Survey 2
Alpha Centauri is the closest star system to our sun, with a distance of just 4.37 light years.
They’re also our closest stellar neighbors, located just 4.37 light years away. That makes the idea of finding exoplanets in the Alpha Cen system pretty exciting. So in 2007, Dr. Debra Fischer and her Yale Exoplanet Group team started looking. With funding from the National Science Foundation, they built a spectrometer called CHIRON for the 1.5-meter telescope at the Cerro Tololo Inter-American Observatory (CTIO) in northern Chile. The acronym CHIRON stands for the CTIO High Resolution spectrometer.
Exoplanets tug on their stars as they orbit, giving the star a slight wobble that can be detected by astronomers. By 2011, CHIRON was up and running, and shown to be capable of detecting star wobbles as small of 1 meter per second. But while a 1-meter wobble might be caused by an exoplanet just two or three times as massive as Earth, an Earth-like planet might only tug on its star by 10 centimeters per second. So Fischer's team set out to improve CHIRON's capabilities.
In 2012, they installed a new fiber-optic system between the telescope and the spectrograph to reduce data errors in the starlight they were collecting from Alpha Cen A and B. The system was based on FINDS (Fiber-optic Improved Next generation Doppler Search) Exo-Earths, which the Yale Exoplanet Group had installed on the 3-meter telescope at Lick Observatory in 2009. FINDS was suppoted by a $45,000 grant from The Planetary Society.
Debra Fischer and Julien Spronck at CITO
Debra Fischer and Julien Spronck on the mount for the 1.5 meter telescope at the Cerro Tololo Inter-American Observatory (CITO) in Chile, where they are searching for planets around Alpha Centauri.
Armed with the FINDS-based fiber system and some improvements to the telescope's guidance system, CHIRON began looking for planets around Alpha Cen A and B. But just a few months later, a team of Geneva-based astronomers using a 3.6-meter telescope at another Chilean observatory dropped a bombshell: they had found a planet orbiting Alpha Cen B.
The new planet, officially Alpha Centauri Bb, has an orbital period of just 3.2 days, and lies just 6 million kilometers from its star. By comparison, Mercury has an 88-day orbit—and its closest approach to the sun is 46 million kilometers. This doesn't bode well for life on the surface, but where there's one exoplanet around a star, there are usually more.
The statistical models used to derive the presence of Alpha Cen Bb from the Geneva team's data are cutting-edge, so additional confirmation of Alpha Cen B's wobbles was needed. In 2013, The Planetary Society pitched in on the effort, funding two blocks of observing time for Fischer's team at CITO. After parsing the results, the Yale group did not find Alpha Cen Bb lurking in their data—though their models suggested they should have, at a marginal level.
Meanwhile, Alpha Cen A and B have been approaching each other, as seen from our telescopes on Earth. They’re now just 4 arcseconds apart. That's too close for astronomers to isolate one star in the telescope. In 2015, the stars will begin to pull away from each other, allowing observations to continue. Until then, the question of Alpha Cen Bb's existence remains unsettled.
In the meantime, both the ESO and Fischer's Yale team are building new, high-resolution spectrometers that will search for exoplanets around other stars—including Alpha Centauri. Fischer's group is building EXPRES, the Extreme Precision Spectrograph. EXPRES will be installed on the 4.3-meter Discovery Channel Telescope at Lowell Observatory, located southeast of Flagstaff, Arizona. The spectrograph will be equipped with a cutting-edge laser calibration system, and The Planetary Society is currently raising funds to help with the project, which we're calling Exoplanets Laser.
Yale Professor of Astronomy Debra Fischer is one of our planet’s most successful discoverers of exoplanets. She has set her sights on Alpha Centauri, where she hopes to find a Earth-sized world in the habitable zone: not too hot, not too cold for life.
The Planetary Society sponsored Alpha Centauri planet search started using a newly upgraded system in May. Here is a quick update including info from project leader Debra Fischer from Yale about their new system.
Do planets circle our closest stellar neighbors, the system loved by science fiction: Alpha Centauri? We don’t know. But, Debra Fischer, Julien Spronck, and their colleagues at Yale University, in part with Planetary Society support, are trying to find out.
European astronomers have made the first planetary discovery in the closest-to-Earth Alpha Centauri star system. Here is some information about the discovery, and insights from Yale Astronomer Debra Fischer, who leads another Alpha Centauri planet search partially supported by The Planetary Society.
An update from Yale’s Debra Fischer about the Alpha Centauri planet hunt, partially sponsored by The Planetary Society, as well as her team’s efforts to remove “noise” from parent stars to help find exoplanets.
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