Using a newly developed system for mid-infrared exoplanet imaging, astronomers from the Breakthrough Watch Initiative say they can now use ground-based telescopes to directly capture images of exoplanets about three times the size of Earth within the habitable zones of nearby stars. Their initial observations, made with ESO’s Very Large Telescope at the Paranal Observatory in Chile as part of the NEAR (New-Earths in the AlphaCen Region) program, resulted in the detection of a warm sub-Neptune-sized planet in the habitable zone of Alpha Centauri A, part of the star system nearest to Earth.
Mid-infrared images of Alpha Centauri AB: (a) high-pass filtered image without point spread function (PSF) subtraction or artifact removal; the Alpha Centauri B on-coronagraph images have been subtracted from the Alpha Centauri A on-coronagraph images, resulting in a central residual and two off-axis PSFs to the SE and NW of Alpha Centauri A and B, respectively; systematic artifacts labeled 1-3 correspond to detector persistence from Alpha Centauri A, Alpha Centauri B, and an optical ghost of Alpha Centauri A. (b) zoom-in on the inner regions following artifact removal and PSF subtraction; regions impacted by detector persistence are masked for clarity; the approximate inner edge of the habitable zone of Alpha Centauri A is indicated by the dashed circle; a candidate planet detection is labeled as ‘C1.’ Image credit: Wagner et al., doi: 10.1038/s41467-021-21176-6.
Alpha Centauri, also known as Rigil Kentaurus, Rigil Kent and Gliese 559, is the closest stellar system to Earth.
This triple system is made up of the bright binary star formed by Alpha Centauri A and B, plus the faint red dwarf star Alpha Centauri C.
The two brighter components are roughly 4.35 light-years away from us. Alpha Centauri C, better known as Proxima Centauri, is slightly closer, at 4.23 light-years.
Compared to our Sun, Alpha Centauri A is of the same stellar type G2, but slightly bigger. Alpha Centauri B, a K1-type star, is slightly smaller and less bright.
Alpha Centauri A and B orbit a common center of gravity once every 80 years, with a minimum distance of about 11 times the distance between the Earth and the Sun.
“We achieved the capability to directly image planets about three times the size of the Earth in the habitable zone of Alpha Centauri A,” said Dr. Olivier Absil, director of the PSILab (STAR Research Institute/Faculty of Sciences) at the Université de Liège.
In 2016, Breakthrough Watch and ESO launched a collaboration to build a thermal infrared coronagraph, designed to block out most of the light coming from the star and optimized to capture the infrared light emitted by the warm surface of an orbiting planet.
In addition to helping drastically reduce the light of the target star and thereby reveal the signatures of potential terrestrial exoplanets, the coronagraph modifies existing instrumentation to optimize its sensitivity to infrared wavelengths, enabling it to detect potential heat signatures similar to that emitted by the Earth.
Building upon these advances, the astronomers conducted more than 100 hours of observation beginning in 2019, to hunt for exoplanets within the habitable zones of Alpha Centauri A and B.
This artist’s conception shows a hypothetical rocky exoplanet in the Alpha Centauri system. Image credit: Michael S. Helfenbein.
“We were amazed to find a signal in our data,” said Dr. Kevin Wagner, an astronomer at the University of Arizona.
“While the detection meets every criteria for what a planet would look like, alternative explanations have to be ruled out.”
“Verification might take some time and will require the involvement and ingenuity of the larger scientific community.”
“Only a few years ago, we set out on a search for possible Earth-like planets circling Alpha Centauri A and B,” said Dr. Pete Worden, executive director of the Breakthrough Initiatives.
“We built the machinery that could do the job, and now a candidate planet has revealed itself. The power of concerted, global scientific collaboration is quite astonishing.”
“When we collaborate on a global scale, we discover new worlds, and we keep advancing,” said Yuri Milner, founder of the Breakthrough Initiatives.
“The identification of a candidate habitable-zone planet in our celestial backyard will continue to power our curiosity.”
The team’s paper was published in the journal Nature Communications.
_____
K. Wagner et al. 2021. Imaging low-mass planets within the habitable zone of α Centauri. Nat Commun 12, 922; doi: 10.1038/s41467-021-21176-6
