Kepler data reveals most Earth-like exoplanet in size and temperature yet
A review of early data returned by NASA's Kepler mission has revealed one of the most Earth-like exoplanets discovered so far. Located 300 light-years away, the new planet is slightly larger than our own, is estimated to have a similar temperature, and orbits in the habitable zone of its parent star.
Like going through the pockets of an old suit in search of overlooked cash, revisiting old scientific data can often reap remarkable benefits. A case in point is the data sent back by NASA's Kepler space telescope. Though the unmanned orbital observatory was retired in 2018, the information it gleaned is still telling scientists a great deal about planets orbiting stars outside the solar system.
According to NASA, Kepler-1649c was overlooked by initial analysis, but this wasn't due to carelessness. Kepler looked for exoplanets by measuring dips in the light curves of various stars. Such a dip can be caused by a planet passing between the star and Kepler like a mini-eclipse. However, planets aren't the only cause of such dips. Other phenomena, such as the natural variability of the star or passing clouds of cosmic dust can produce what is called a false positive 88 percent of the time.
To avoid these false positives and speed up analysis, NASA used a computer algorithm called Robovetter. The space agency realized early on that this approach wasn't perfect, so it set up the Kepler False Positive Working Group, which is tasked with reviewing the Kepler data with a finer computer comb to see which false positives are really false negatives. In other words, misidentified exoplanets.
With Kepler-1649c, the group hit the jackpot with the closest analog to the Earth yet seen. The rocky exoplanet is only 1.06 times larger than Earth and it receives 75 percent as much light from its sun as the Earth does, meaning that it may have a similar temperature – although the composition of the planet's atmosphere remains unknown which could affect its temperature. Most importantly, its orbit is inside the habitable zone of the star Kepler-1649. That is, the area where liquid water can exist on a planet's surface.
NASA says that though some exoplanets are closer to Earth in size and some closer in temperature, and a number have been found inside their star's habitable zone, this is the first one to match so closely in all three critical categories.
However, the agency stresses that Kepler-1649c may not be all that pleasant. Its parent star, which it orbits once every 19.5 Earth days, is a red dwarf. This is a type of star prone to throwing out deadly stellar flares that are loaded with radiation. In addition, the calculations used have a very wide margin of error that could affect habitability.
On the plus side, the planet's orbit appears stable, so it should have a long life, and red dwarfs are the most common type of star in our galaxy, suggesting that such Earth-like planets are very common as well.
"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," says Andrew Vanderburg, a researcher at the University of Texas at Austin. "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."
The research was published in The Astrophysical Journal.