Since when exoplanets – planets that orbit other stars – have been confirmed by science, humanity has been thinking: after all, how many of them can harbor life? There is still no right answer to that question, but a new study by NASA scientists who worked on the Kepler mission brings us closer to the answer: possibly half of the stars with a temperature similar to the Sun’s could have in its orbit , a rocky planet with liquid water on its surface.
For the study, data were used from the Kepler space telescope, which was retired in 2018. In that, nine years of observations made by the telescope revealed that there are billions of planets in our galaxy – so much so that there are more of them than the stars, and the data indicate that the Milky Way has about 300 million potentially habitable worlds, with some candidates being as close as 30 light years from the Sun, while the closest possibly is 20 light years away from us.
The scientists combined Kepler’s planetary signal data with star energy data obtained by the European Space Agency (ESA) Gaia mission. Gaia collected information about the amount of energy a planet receives from its star based on the total energy emitted during a given period. The exact effect of this is still being studied, but in a conservative estimate of the effect of light on the atmosphere, half of the sun-like stars would have rocky planets that may have liquid water on the surface. Thus, scientists were able to direct the analysis including the diversity of stars and solar systems in the Milky Way.
“Kepler has already shown us that there are billions of planets, but now we know that most of them can be rocky and habitable,” says Steve Bryson, the study’s lead author. He points out that this result is not a final definition, and that water is just one of several factors necessary for the occurrence of life. Even so, the accuracy of the discovery is incredible: to calculate the occurrence rate, the team observed exoplanets with equivalent radii between 0.5 and 1.5 times the radius of the Earth, and filtered out those that are likely to be rocky. In addition, they also focused on stars that are similar in age and temperature to the Sun.
In the end, this gives us different stars with varying characteristics that influence the ability of planets to have liquid water. It is complex, but it shows why it is so difficult to calculate how many potentially habitable planets there are. Even so, this discovery is an important step in understanding how many of these worlds exist in our galaxy; previous estimates of the rate of occurrence of the planets did not consider the relationship between the temperature of the star and the types of light supplied and absorbed by the planet. This new analysis includes these relationships and gives a more complete understanding of a planet’s ability to have liquid water.
It is not the first time that Kepler’s data has resulted in discoveries even after the end of its activities; at the beginning of the year, a planet similar in size to the Earth was discovered amid the mission data. The surprising results of this study were produced based on a great deal of analysis of Kepler’s data, and it builds the bases for future observations of exoplanets as often as we expect from these rocky and potentially habitable worlds. Now, for future studies, the data will be refined and should inform the chances of finding these planets in addition to feeding the plans for the next stages of the search for exoplanets.
The study will be published in The Astronomical Journal and can now be accessed in the arXiv repository.
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