At the Max Planck Institute for Solar System Research (MPS), Georg August University in Göttingen and the Sonneberg Observatory, Scientists have discovered 18 Earth-sized planets beyond the solar system. The worlds are so tiny that earlier surveys had overlooked them. One of them is one of the smallest known so far; Another could offer friendly conditions to life. The researchers reanalyzed part of the data from NASA's Kepler Space Telescope with a new and more sensitive method they developed. The team estimates that its new method has the potential to find more than 100 extra exoplanets in the entire Kepler mission data set.
Up to now, we know more than 4000 planets that orbit stars outside our solar system. Of these exoplanets, about 96 % are bigger than our Earth, most of them more comparable to the dimensions of the gas giants Neptune or Jupiter. However, it is likely that this percentage does not reflect the actual conditions in space, since small planets are much harder to track than large ones. In addition, small worlds are fascinating targets in the search for Earth-like, potentially habitable planets outside the solar system.
The 18 newly discovered worlds fall into the category of planets the size of the Earth. The smallest of them is only 69 percent the size of Earth; the largest is just more than twice the radius of the Earth. And they have another thing in common: the 18 planets could not be detected in the Kepler Space Telescope data so far. The common search algorithms were not sensitive enough.
In their search for distant worlds, scientists often use the so-called transit method to search for stars with recurring brightness drops periodically. If a star has a planet whose orbital plane is aligned with the line of sight of the Earth, the planet conceals a small fraction of the starlight as it passes in front of the star once per orbit.
"Standard search algorithms try to identify sudden drops in brightness," explains Dr. René Heller of MPS, first author of current publications. "In reality, however, a stellar disc appears slightly darker on the edge than in the center. When a planet moves in front of a star, therefore, it initially blocks less starlight than in the middle of transit. The maximum attenuation of the star occurs at the center of traffic, just before the star gradually becomes brighter, "he explains.
Large planets tend to produce bright and deep variations in brightness of their host stars, so that the subtle variation of brightness from the star in the center to the tip hardly plays a role in their discovery. The small planets, however, present immense challenges to scientists. Its effect on the stellar brightness is so small that it is extremely difficult to distinguish it from the natural fluctuations of the brightness of the star and the noise that necessarily comes with any type of observation. The René Heller team has now been able to demonstrate that the sensitivity of the transit method can be significantly improved, if a more realistic light curve is assumed in the search algorithm.
By: Preeti Narula