18 new Earth-size exoplanets pop-up in the old planet Kepler-hunting data

A diagram with the sizes of the newly identified planets compared to Earth and Neptune. Only one of the 18 planets is at a distance from the star, that could potentially allow liquid water to survive on the surface.

Scientists scour old Kepler Space Telescope data have identified 18 more relatively small planets observed by the famous planet-hunting observatory.

While most of the planets close to their parent stars, and burning surface temperatures of up to about 1,830 degrees Fahrenheit (1,000 degrees Celsius), a world that revolves around a red dwarf star in an area called the “habitable zone.” That term is usually defined as the region around a star where a rocky planet could host liquid water on its surface. However, life is never a slam-dunk, and on this world, it is especially difficult because red dwarfs put out killer X-rays, that the life on the nearby planets a challenge, even for microbes.

A new computer algorithm flushed out the hidden planets of the data collected by K2, Kepler is late in life to observe the program. K2 is developed after a number of Kepler’s gyroscopes (devices that make it possible to use a telescope to maintain a consistent orientation in the space) had ceased to work in 2013 after four years of activities in the area, and have exceeded their design life.

Related: RIP, Kepler: Revolutionary Planet-Hunting Telescope runs out of Fuel

Scientists figured out how to stabilize the telescope pointing using the constant pressure of particles streaming from the sun, skipping from time to time to protect the sensors from sunlight. Kepler found her planets using the “transit method,” which looks as a planet passes in front of its parent star it produces a decrease of the brightness.

K2 allowed Kepler to observe of 100,000 more stars for the telescope fuel in 2018, including 517 stars that scientists had already spotted planets orbiting. The researchers behind the new study decided to go back and that stars with a new data-processing algorithm.

“Standard search algorithms to try to identify sudden decrease in brightness,” lead author René Heller, an astrophysicist at the Max Planck Institute for Solar System Research, said in a statement. “In reality, however, a stellar disk is slightly darker at the edge than in the center. When a planet moves in front of a star, so in the first instance, blocks less starlight than on the middle of the time of the passage. The maximum dimming of the star occurs in the middle of the transit just before the star becomes gradually brighter again.”

The new algorithm attempts to chart a more realistic “light curve” or pattern of dimming as the planet moves across the surface of a distant star. This made it easier to find small planets in the data: the new planets, Heller and his colleagues found the range of 70% of the size of the Earth to double our planet’s size. The research team says that their new algorithm also makes it easier to spot small planets in the middle of the natural brightness of the motion of a star, such as those caused by sunspots, and other variables in the observation.

More Earth-size planets could be lurking in the data. Planets that orbit more around a star have a greater chance to be seen, because they pass in front of the star more often. But planets that are further away would have gone unnoticed in the data, because their intersections are less frequent.

The researchers plan to have their algorithm to the rest of the Kepler data, and say that they can lead to 100 new Earth-size worlds.

Two papers on the basis of the research were published this month in the journal Astronomy and Astrophysics.

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