NASA's old exoplanet hunter, the Kepler Space Telescope, continues to provide scientists new discoveries six months after it ran out of fuel.

A team of researchers from the Max Planck Institute, the Georg August University of Göttingen, and the Sonneberg Observatory found 18 more exoplanets that are about the size of the Earth using data from the decommissioned observatory. They claime that one of them is potentially habitable.

To make the discovery, they used a new algorithm that is more sensitive than those that are commonly used to detect exoplanets. They published their findings in the journal Astronomy & Astrophysics on May 13.

A New Way To Search For Exoplanets

Scientists search for exoplanets using the transit method: telescopes, like Kepler, look for temporary dips in the brightness of a distant star. This signifies that a planet in orbit briefly obscures its star's light.

Larger planets are much easier to find because they create a sharper drop in brightness when it passes between its star and the telescope. That is perhaps why exoplanets that are about as big as Jupiter and Neptune seem more common in the universe. About 96 percent of the exoplanets that have been discovered so far are significantly bigger than Earth.

"Standard search algorithms attempt to identify sudden drops in brightness," stated Rene Heller, the first author of the study. "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."

Scientists Discover 18 New Exoplanets From Kepler's Old Data

The researchers tested their new algorithm using data from the K2 mission, which monitored 100,000 stars. They reanalyzed 512 stars that are already known to host exoplanets.

The algorithm confirmed the presence of transiting planets that have previously been discovered. However, in addition, they found 18 new objects that have never before been spotted before.

"In most of the planetary systems that we studied, the new planets are the smallest," claimed Kai Rodenbeck, one of the co-authors of the study.

The smallest exoplanet found is estimated to be around 69 percent of the size of Earth. Meanwhile, the largest one has over twice of Earth's radius.

Most of the new planets found are orbiting very close to their host stars. This means that a lot of them have temperatures well in excess of 100 degrees Celsius. One of them, however, orbits with a safe distance away from its star and might offer conditions that allow life to thrive.

The researchers noted that more exoplanets might be out there but cannot be detected by their new algorithm. Smaller planets that are located far away from their host stars would take longer time to complete one full orbit.

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