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To date, astronomers have confirmed the existence of 4,144 extrasolar planets in 3,074 systems, with another 5,094 candidates awaiting confirmation. Most of these planets were found by the Kepler space telescope, who spent nine years (between May 2009 and February 2018) monitoring distant stars for traffic signals, where a planet passing in front of a star causes a decrease in brightness.
And yet, even though it is now extinct, the data that Kepler Accumulated over the years continues to lead to new discoveries. For example, a transatlantic team of researchers recently found a signal in KeplerArch s archive data that bypassed detection earlier. This signal indicates that there is a second planet orbiting Kepler-1649, an M-type red dwarf star located 302 light years away.
What is especially exciting about this finding is that this planet (Kepler-1649c) is the most Earth-like planet Kepler has ever come across in terms of size and temperature! As they affirm in their study, which recently appeared in The astrophysical journalThe team confirmed that the planet had 1.06 land masses and receives about 75% of the light that our planet receives from the Sun (meaning it may have similar temperatures).
This planet orbits its star much closer to Earth than the Sun, resulting in an orbital period of just 19.5 Earth days. This is to be expected with planets orbiting within the habitable zones of lower-mass red dwarf stars. And while no flares have been detected in this system, red dwarfs are also known for their flare activity, which could make the planet’s environment challenging for potential life.
As Thomas Zurbuchen, the associate administrator for NASA’s Scientific Mission Directorate, said in a recent NASA press release:
“This intriguing and distant world gives us even greater hope that a second Earth is among the stars, waiting to be found. The data collected by missions such as Kepler and ours Exoplanet Survey satellite in transit (TESS) will continue to produce surprising discoveries as the scientific community refines its abilities to search for promising planets year after year. “
As noted, Kepler He searched for exoplanets by monitoring the stars for periodic drops in brightness, which may be the result of planets passing in front of them relative to the observer (also known as the Transit Method). However, these falls can be caused by a series of phenomena (ranging from natural changes to other objects passing in front of them) and are only the result of exoplanets about 12% of the time.
Previously, Kepler Mission scientists developed a special computer algorithm called Robovetter to search the volumes of data collected by the telescope, which is managed by NASA’s Ames Research Center. This algorithm has the task of distinguishing between the signals produced by planetary transits with the other phenomena known to cause drops in the brightness of a star.
The signatures that Robovetter determines to come from other sources are labeled “false positives,” which is what Kepler-1639c was originally thought to be. Fortunately, scientists knew in advance that the algorithm results would have to be double checked due to the large amount of volume it had to sort, dramatically increasing the probability of errors.
This task is the job of the Kepler False Positive Working Group, which reviews all the signals examined by the algorithm to see if they really could be traffic signals. What they found was that Kelper-1649c had been mislabeled and that it was one of the most unique Earth analog planets discovered to date.
Granted, there are many things that are still unknown about Kepler-1649c, including some key parameters that will help astronomers determine how likely it is to be habitable. These include its atmospheric composition, which has a significant effect on the planet’s ability to warm itself enough for liquid water to exist. Due to the distance between Kepler-1649c and Earth, current size estimates have a significant margin of error.
There are also questions related to the planet’s mass, which would indicate whether it is really rocky or potentially a “water world” (where water constitutes a significant part of its mass). These questions, in addition to what astronomers already know about Kepler-1649c, make him an extremely valuable candidate for follow-up research.
While there are other exoplanets believed to be closer to Earth in terms of size and temperature, Kepler-1649c has the added benefit of orbiting within its star’s habitable zone. Dr. Andrew Vanderburg, a NASA Sagan Fellow at the University of Texas at Austin and lead author of the study, said in a recent NASA press release:
“Of all the mislabeled planets we’ve recovered, this one is particularly exciting, not only because it’s in the habitable zone and size of Earth, but because of how it might interact with this neighboring planet. If we hadn’t examined the work of the algorithm to hand, we would have missed it. ”
The fact that this star system contains another confirmed exoplanet that is also similar in size to Earth was also noted: Kepler-1649b. This planet orbits the star at about half the distance that Kepler-1649c (and is therefore considered analogous to Venus), leading astronomers to suspect that the star may have a third planet in orbit.
With an orbital period of 8.7 days, Kepler-1649b completes four orbits of its star for every nine orbits completed by Kepler-1649c. This type of stable orbital relationship is often indicative of an orbital resonance, which is what three of Jupiter’s largest moons (Io, Europa, and Ganymede) experience. Their orbital periods, 42 hours, 85 hours, and 172 hours days, respectively, adjust to an almost perfect ratio of 1: 2: 3.
In summary, the Kepler-1649 system’s orbital periods could be indicative of an average planet in the system (with an orbital period of approximately fourteen days) that helps stabilize and synchronize its orbits. Or it could be that this latest discovery shows that there are systems in the Universe with 4: 9 resonances, while most of the others are 1: 2 or 2: 3.
To date, a third planet has not been found, which could be because it is simply too small or its orbit is too skewed for Kepler to have detected it using the Transit Method. Ultimately, this question provides astronomers with an even greater incentive to conduct follow-up studies of Kepler-1649. And of course the system provides another example of how common rocky planets are around red dwarf stars.
“The more data we get, the more signs we see that point to the notion that potentially Earth-sized and habitable exoplanets are common around these types of stars,” Vanderburg said. “With red dwarfs almost everywhere around our galaxy, and these small, potentially habitable, and rocky planets around them, the possibility that one of them isn’t much different than our Earth seems a little brighter.”
Since red dwarf stars are the most common in the Universe (they account for 75% of the stars in our galaxy alone), it stands to reason that planets like this might be more common than previously thought. As we find more analogues of Earth orbiting nearby red dwarfs, the chances of determining if they might be habitable increase dramatically.
This discovery also shows that even when scientists work to automate the analytical process, monitoring and double-checking are extremely valuable.
The research team also included members of the Open University, NASA’s Ames Research Center, NASA’s Goddard Space Flight Center, the SETI Institute, the Harvard-Smithsonian Center for Astrophysics (CfA), and the Institute of Science. from the Space Telescope (STSI).
Further reading: NASA, Astrophysical journal letters
