Potentially Habitable Exoplanet That is Earth-like in Size and Temperature Discovered 300 Light-Years Away

Researchers have discovered an Earth-sized planet that lies in the habitable zone of a star located around 300 light-years from Earth.

The international team of scientists estimate that the planet, dubbed Kepler-1649c, is 1.06 times the size of our own, according to a study published in the Astrophysical Journal Letters.

Furthermore, they say the temperature on Kepler-1649 could be similar to the Earth's given that it receives around 75 percent of the light that our planet receives from the sun. It's host star is a red dwarf, a type of relatively cool, old and small stellar object.

The scientists say that Kepler-1649c orbits the red dwarf very closely (one year is just 19.5 Earth days) but is still located in the so-called habitable zone, the region around a host star within which liquid water could exist on the surface. Liquid water is thought to be key for the evolution of life as we know it.

Nevertheless, red dwarfs are notorious because they sometimes emit gigantic flares, which some scientists think could make the development of life difficult.

In any case, Kepler-1649 is particularly intriguing among worlds that harbor potentially habitable conditions because it is the most similar to Earth, in terms of both estimated size and temperature, of all the planets discovered by NASA's Kepler Space Telescope, which retired in 2018 after running out fuel.

While there are exoplanets discovered by Kepler that are thought to be even closer to Earth in size, and others that may have more similar temperatures, Kepler-1649c is the only the one in the habitable zone that is very close to our own planet when it comes to both of these characteristics.

"This intriguing, distant world gives us even greater hope that a second Earth lies among the stars, waiting to be found," Thomas Zurbuchen, associate administrator of NASA's Science Mission Directorate in Washington, who was not involved in the study, said in a statement. "The data gathered by missions like Kepler and our Transiting Exoplanet Survey Satellite (TESS) will continue to yield amazing discoveries as the science community refines its abilities to look for promising planets year after year."

The scientists discovered Kepler-1649c while reviewing old data collected by Kepler. The telescope used the transit method to identify candidate planets. This involves looking for small dips in brightness, as is observed when planets pass in front of their host star from our perspective. Subsequently, scientists determine whether these dips in brightness are caused by planets or other phenomena.

To sort through the vast amounts of data collected by Kepler, mission scientists created a computer algorithm to help them identify which dips in brightness represented planets. Overall, only around 12 percent of signals turned out be planets. The rest were dubbed "false positives."

However, the computer algorithm made some mistakes when it came to identifying tricky signals, as is the case with Kepler-1649c, which was originally identified as a false positive.

To try and root out these mistakes, a group of astronomers formed the Kepler False Positive Working Group, with the aim of manually reviewing thousands of Kepler false positives in order to confirm that they were not planets. The team discovered Kepler-1649c in the last review of Kepler data that was published three years ago.

Earth, Kepler-1649c
Illustrations of Earth and Kepler-1649c side by side. NASA/Ames Research Center/Daniel Rutter

"In terms of size and likely temperature, this is the most similar planet to Earth that has ever been found with Kepler," Jeffrey Coughlin, a co-author of the study from the SETI Institute, said in a statement. "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."

The system in which Kepler-1649c lies is also intriguing because it contains another planet of similar size that orbits even closer to the host star, around half the distance.

"Out of all the mislabeled planets we've recovered, this one's particularly exciting—not just because it's in the habitable zone and Earth-size, but because of how it might interact with this neighboring planet," Andrew Vanderburg, first author of the paper from the University of Texas at Austin, said in the statement. "If we hadn't looked over the algorithm's work by hand, we would have missed it."

Red dwarfs are the most common type of star in the Milky Way, and there is increasing evidence that many of them harbor planets like Kepler-1649c.

"The more data we get, the more signs we see pointing to the notion that potentially habitable and Earth-size exoplanets are common around these kinds of stars," Vanderburg said. "With red dwarfs almost everywhere around our galaxy, and these small, potentially habitable and rocky planets around them, the chance one of them isn't too different than our Earth looks a bit brighter."

Kepler has revolutionized our understanding of planets beyond the solar system through its observations of tens of thousands of stars. Launched in 2009, the telescope identified 2,600 confirmed exoplanets, although it has also unearthed thousands more potential planet candidates.