Despite all the abundance of newly discovered planets outside our solar system, we still have not seen any worlds that can house life. Now that may have changed. A new technique allows us to see a small part of the worlds we are looking for, and on the first outing found a possible one of the closest neighbors of the Sun.
Most planets around other stars (exoplanets) have been found by their effect on their parent star, either by blocking some light or changing its motions slightly. Direct detection is limited to rare cases, such as planets so young that they are still hot enough to be observed in the infrared. Even then, we are still confined to large worlds far enough away from their sun that their light is not lost in the glare. Not the places we go to find life.
However, Kevin Wagner, a graduate student at the University of Arizona, says that this is partly because we were looking in the wrong part of the spectrum. Attempts to detect exoplanets directly were made in the near infrared, with wavelengths less than 10 microns. Yet the planets we are looking for are probably the brightest at slightly longer wavelengths.
As self-defeating as it may seem, Wagner remarked in a statement; “There is a good reason for [these choices] because the earth itself shines on you at those wavelengths. It makes sense that the earth would be brightest at the same wavelengths as the earth-like planets we are trying to find, but that does not make things easy. “Infrared emissions from the air, the camera and the telescope itself are essentially drowning out your signal,” Wagner added.
In Nature Communications, Wagner describes the use of a combination of instruments to enable the Very Large Telescope (VLT) to observe the Alpha Centauri system at wavelengths of 10-20 µm, which emits the radiation of the Earth as well block the two stars.
“We move one star and one star from the cliff paragraph every tenth of one second,” Wagner said. “It allows us to observe each star half the time, and, more importantly, it also allows us to subtract one frame from the next frame, which is all essentially just noise, removed from the camera and the telescope. “
Wagner and co-authors took more than 5 million images in nearly 100 hours, stacking them on top of each other and removing unwanted contributions in a way he compares to the noise-canceling headphones.
In the process, Wagner found a light source he named C1, which apparently lies in the habitable zone of Alpha Centauri A. More needs to be done to eliminate instrumental errors or clouds of dust, but C1 may also be the right thing to do.
“There is one point source that looks like what we would expect a planet to look like, which we cannot explain with the systematic error correction,” Wagner said.
The team hopes to verify the existence of C1, both with follow-up observations on the VLT, and by alternative planetary hunting methods, and to apply the same method to other stars. Nevertheless, the approach has its limitations. Apart from the fact that it takes a lot of time on one of the most expensive telescopes in the world, targets are limited to stars in the area. In addition, Wagner’s technique could not yet find an Earth-sized planet. It will probably be the smallest object about 3-5 times the radius of Earth, making it almost certainly a Neptune-style gas planet as a super-Earth.