Astronomers who devised a technique to capture direct images of nearby potentially habitable exoplanets have found what could be a world orbiting a star a mere 4.3 light years away from Earth in the Alpha Centauri group.
Details of the technique were published in Nature Communications on Wednesday, and it involves adding a secondary telescope mirror to today's ground-based 'scopes. The extra mirror mitigates the effect of Earth's atmosphere scattering incoming infrared light. A filter or mask is also applied to make it easier to pick out light reflected off a planet orbiting a star.
“Earth’s atmosphere distorts the light due to warm pockets of turbulent air that have different optical properties,” Kevin Wagner, first author of the study and a postdoctoral researcher at the University of Arizona, told The Register. “This causes a sort of blurring effect, which a computer keeps track of in real time, and sends signals to the [secondary] mirror to counteract. This is broadly known as adaptive optics.”
Wagner and his colleagues reckon they have improved upon today's methods, and can capture direct images of planets that are up to three times the size Earth located within habitable zones of stars near our Sun. They tested their new direct imaging technique by observing Alpha Centauri, a system made up of three stars codenamed A, B, and C, located 4.37 light-years away, using the Very Large Telescope in Chile, and made a fascinating discovery.
Planet ahoy, or maybe not
The team were surprised to find what looks like a never-before-seen object around Alpha Centauri A, which they have since nicknamed “C1”. Olivier Absil, co-author of the paper and a research professor at the University of Liege, told us the object was missed in previous observations because the detection methods used weren’t sensitive enough.
“Direct imaging observations have never reached such a sensitivity [before], all other direct imaging experiments are limited to Jupiter-type planets," he said. "In the specific case of Alpha Centauri, even indirect methods such as radial velocities, which are generally more sensitive, but do not provide a picture of the planetary system, have not been able to reach a Neptune-size sensitivity for the orbital distance considered here.”
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The team is hesitant to boast about its latest discovery, however, and have yet to confirm C1 really is a new exoplanet. “At this stage however, without verification via a second observing campaign, we cannot exclude an instrumental artefact of unknown origin, or even the signature of an asymmetrical dust cloud," Absil said.
Wagner told us the team hopes to perform follow-up observations with the Very Large Telescope to verify C1 is, indeed, a newly found planet. If it is it'll be larger than Neptune and in the so-called habitable zone where liquid water may exist.
The data for C1 was collected over a month; the team captured about five million images and made the seven terabytes worth of data publicly available to scour through.
Astronomers will have more opportunities to directly image new exoplanet candidates like C1 in the future. Adaptive optics is going to be used in the METIS instrument for the Extremely Large Telescope currently under construction.
“Members of our team are also involved in building METIS, which will certainly be able to do the job a bit further down the road," Wagner said. "I hope that we won’t have to wait long and that currently available telescopes will deliver an answer, but it will definitely be much easier with METIS.” ®