Astronomers have reported discovering eighteen planets similar to Earth.
One of them is the smallest exoplanet found to date, while another world may have the necessary conditions to harbor life as we know it.
A total of 18 planets the size of the Earth have been discovered beyond the confines of our solar system.
Some of the recently identified worlds are so small that previous surveys had overlooked them.
Researchers from the Max Planck Institute for Solar System Research (MPS), the University of Göttingen and the Sonneberg Observatory, re-analyzed part of the data from the NASA Kepler Space Telescope with a new and more sensitive method that they developed.
The team estimates that their new method has the potential of finding more than 100 extra exoplanets in the entire Kepler mission data set.
So far, more than 4,000 planets orbiting stars outside our solar system have been identified by experts.
Of these so-called exoplanets, about 96 percent are significantly larger than our planet, and most of them are comparable in size to the dimensions of our solar system’s gas giants Neptune or Jupiter.
However, it is likely that this percentage does not reflect the actual conditions in space since smaller alien 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, scientists have revealed.
According to astronomers, the 18 newly discovered worlds fall into the category of Earth-like worlds.
The smallest of them is only 69 percent the size of Earth; the largest is just more than twice the radius of our planet, the researchers have reported.
However, experts say that the newly found worlds have another thing in common: all 18 planets were completely missed in the Kepler Space Telescope data in the previous searches.
The reason, astronomers say, is that 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.
But that may not always be the case.
“Standard search algorithms attempt to identify sudden drops in brightness,” explains Dr. Rene Heller from MPS, first author of the current publications.
“In reality, however, a stellar disk appears slightly darker at the edge than in the center. When a planet moves in front of a star, it therefore initially blocks less starlight than at the mid-time of the transit. The maximum dimming of the star occurs in the center of the transit just before the star becomes gradually brighter again,” the researcher explains.
Bigger planets usually produce deep and clear brightness s of their host stars, so that the subtle variation of brightness from the star in the center hardly plays a role in their discovery.
But when looking at smaller planets things change and are more challenging. Their 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 team of researchers led by Heller 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.
“Our new algorithm helps to draw a more realistic picture of the exoplanet population in space,” summarizes Michael Hippke of Sonneberg Observatory.
“This method constitutes a significant step forward, especially in the search for Earth-like planets.”