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Astronomers using a new technique may not only have found a super-Earth on a nearby star, but they may also have directly imaged it. And it could be nice and cozy in the living area around Alpha Centauri.
Giant planets are much easier to see than Earth-sized planets. Regardless of the detection method used, the larger planets are simply a bigger needle in the cosmic haystack. But overall, astronomers are very interested in planets similar to Earth. And finding them is much more difficult.
We thought that we would have to wait for the ultra-powerful telescopes being built before we could directly visualize the exoplanets. Facilities such as the Giant Magellan Telescope and the Extremely Large European Telescope will bring enormous observational power to the task of imaging exoplanets. But a team of researchers have developed a new technique that could get the job done. They say they envisioned a planet the size of a sub-Neptune / super-Earth orbiting one of our closest neighbors, Alpha Centauri A.
The team presented their findings in a Nature Communications article titled “Imaging of low-mass planets in the habitable zone of? Centauri. The lead author is Kevin Wagner, astronomer and Sagan researcher at the University of Arizona.
“These results demonstrate the feasibility of imaging exoplanets of the rocky habitable zone with current and future telescopes.
From “” Imaging of low mass planets in the habitable zone of? Centauri. “
While astronomers have already found low mass exoplanets, they have never felt their light. They watched the planets reveal themselves by shooting their stars. And they saw the light of the stars that host these planets plunge as the planet passes in front of the star. But they never directly imagined one. Until now, maybe.
This new method of detection boils down to infrared. One of the challenges of imaging Earth-sized exoplanets in the infrared is to discern light from an exoplanet when that light is eliminated by all of the star’s background infrared radiation. Astronomers can search for exoplanets in wavelengths where the background infrared is diminished, but at those same wavelengths temperate Earth-like planets are weak.
One method is to look in the near infrared (NIR) part of the spectrum. In NIR, the thermal glow of the planet is not as washed out by the star. But starlight is still blinding and millions of times brighter than the planet. So just looking in the NIR is not a total solution.
The solution may be the NEAR (New Earths in the AlphaCen Region) instrument used in this research. NEAR is mounted on the Very Large Telescope (VLT) of ESO (European Southern Observatory) in Chile. It works with the VISIR instrument, also on the VLT. The group behind NEAR is the Breakthrough Watch, which is part of Yuri Milner’s Breakthrough Initiatives.
The NEAR instrument not only observes in the desirable part of the infrared spectrum, it also uses a coronograph. The Breakthrough group believed that the NEAR instrument used on an 8-meter terrestrial telescope would allow better observations of the Alpha Centauri system and its planets. So they built the instrument in collaboration with ESO and installed it on the Very Large Telescope.
This new discovery is the result of 100 hours of cumulative observations with NEAR and the VLT. “These results,” write the authors, “demonstrate the feasibility of imaging rocky habitable zone exoplanets with current and future telescopes.”
The 100 hour commissioning cycle was intended to demonstrate the power of the instrument. The team says that based on about 80% of the best images from this race, the NEAR instrument is an order of magnitude better than other viewing methods “… hot planets the size of a sub-Neptune in much of the living area of? Centauri A. “
They also, perhaps, found a planet. “We are also discussing a possible detection of exoplanets or exozodiacal discs? Centauri A ”, they write. “However, an instrumental artefact of unknown origin cannot be ruled out.”
This is not the first time that astronomers have discovered exoplanets in the Alpha Centauri system. There are a few confirmed planets in the system, and there are other candidates as well. But none of them have been directly imaged as this potential new planet, which bears the placeholder name C1, and which is the first potential detection around the system’s M-dwarf, Proxima Centauri.
Follow-up observations should confirm or cancel the discovery. The researchers say it’s possible the signal is an instrument artifact. “We are also discussing a possible detection of exoplanets or exozodiacal discs? Centauri A ”, they write. “However, an instrumental artefact of unknown origin cannot be ruled out.”
It’s exciting to think that a hot Neptune-class exoplanet could be orbiting a Sun-like star in our nearest neighbor star system. One of the goals of Breakthrough Initiatives is to send a light sailing spacecraft to the Alpha Centauri system and give us more detailed insight.
But this prospect is out of reach at the moment. And in some ways, this discovery isn’t so much about the planet as it is about the technology developed to detect it.
The vast majority of the exoplanets discovered are gigantic planets similar in mass to Jupiter, Saturn and Neptune. They are the easiest to find. But as humans on Earth, we are primarily interested in planets like ours. The Earth-like planets in the habitable zone of a star excite us about the prospects for life on another planet. But they can also tell us a lot about our own solar system and how solar systems in general and are evolving.
If C1 turns out to be a planet, then the Breakthrough group has achieved a vital enterprise. They are the first to detect an Earth-like planet by direct imaging. Not only that, but they did it with an 8-meter ground telescope and an instrument specially designed and developed to detect these types of planets in the Alpha Centauri system.
The authors are convinced that NEAR can perform well, even compared to much larger telescopes. The conclusion of the article contains a description of the overall sensitivity of the instrument. Then they write: “Would that in principle be enough to detect an Earth-like planet around?” Centauri A (~ 20 µJy) in just a few hours, which meets the expectations of ELTs. “
The E-ELT will have a 39 meter primary mirror. One of its capabilities and design goals is to directly image exoplanets, especially smaller ones, the size of Earth.
Of course, the E-ELT will be an extremely powerful telescope that will undoubtedly fuel scientific discovery for a long time, not only in imaging of exoplanets, but in various other ways. And other giant telescopes on the ground will also change the imaging game of exoplanets. What took hours for NEAR to see may take just a few minutes for the E-ELT, Thirty Meter Telescope, or Giant Magellanic Telescope to see.
NEAR cannot compete with these telescopes and was never meant to.
But if these results are confirmed, then NEAR has succeeded where no one else has succeeded, and for a fraction of the cost of a new telescope. Regardless, what NEAR has accomplished likely represents the future of exoplanet research. Rather than large-scale surveys like Kepler and TESS, scientists will soon be able to focus on individual planets.
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