New Earth-Sized Planet Discovered Inside Star’s Habitable Zone

An artist's concept of Kepler-1649c orbiting around its host red dwarf star. This newly discovered exoplanet is in its star’s habitable zone and is the closest to Earth in size and temperature found yet in Kepler's data. NASA/Ames Research Center

Exoplanet hunter Kepler may have bowed out in 2018, but a dedicated team of scientist have been reviewing thousands of signals from the final data release. Now, they've announced the discovery of a new Earth-sized world located in the habitable zone of its star.

The planet is known as Kepler-1649c and it orbits a red dwarf star roughly 300 light-years from Earth. The system was home to an already interesting planet, dubbed a “Venus-twin,” given the amount of light it receives from its star. As reported in The Astrophysical Journal Letters, Kepler-1649c is about 6 percent bigger than Earth, a bit smaller than its companion. It orbits its star in about 19.5 days, but given that the star is much dimmer than the Sun, it receives about three-quarters the light Earth gets.

“In terms of size and likely temperature, this is the most similar planet to Earth that has ever been found with Kepler. It’s incredible to me that we just found it now, seven years after data collection stopped on the original Kepler field. I can’t wait to see what else might be found in the rich dataset from Kepler over the next seven years, or even seventy,” co-author Jeff Coughlin, from the SETI Institute scientist said in a statement.

A comparison of Earth and Kepler-1649c, an exoplanet only 1.06 times Earth's radius. NASA/Ames Research Center/Daniel Rutter

The space telescope used the transit method to detect exoplanets – waiting for a regular blip in light that may signify a planet passing (transiting) in front of its star. The primary mission of Kepler lasted for four years and observed nearly 200,000 stars. The dataset is so huge the first selection is done by computer algorithms before humans take a look at it.  

The process is not 100 percent fool-proof, so researchers have been looking at data again. The Kepler False Positive Working Group manually review interesting signals that are most often not due to planets, and yet Kepler-1649c was found hidden among them.

“There are an incredibly large number of signals in the initial detection stage that aren’t due to planets, such as those due to variable stars and spurious noise from Kepler’s electronics,” Coughlin said. “It took us years of studying these signals in-depth to gain the human expertise to distinguish them reliably, and then years more to write the computer algorithms to do it automatically.”

Though it has a promising location and size, these are certainly not a guarantee for habitable conditions on this planet – red dwarfs tend to flare violently making the chances for a livable world small. Despite that, researchers believe that discoveries such as this are a reason to be optimistic about finding a true Earth-like planet.

"The more data we get, the more signs we see pointing to the notion that potentially habitable and Earth-sized exoplanets are common around these kinds of stars,” lead author Andrew Vanderburg, a NASA Sagan Postdoctoral Fellow at the University of Texas at Austin, said. “With red dwarf stars almost everywhere around our galaxy, and these small, potentially habitable and rocky planets around them too, the chance one of them isn't too different than our Earth looks a bit brighter."

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