Ever since astronomers confirmed the presence of planets beyond our solar system, called exoplanets, humanity has wondered how many could support life. Now, we are one step closer to finding an answer.
According to new research using data from NASA’s retired planet-hunting mission, the Kepler space telescope, about half of stars similar in temperature to our Sun could have a rocky planet capable of supporting liquid water on their surface.
Our galaxy contains at least 300 million of these potentially habitable worlds, according to the most conservative interpretation of the results of a new study to be published in The Astronomical Journal.
Some of these exoplanets could even be our interstellar neighbors, with at least four potentially within 30 light years of our Sun and the closest one is probably at most about 20 light years from us. These are the minimum numbers for such planets based on the most conservative estimate that 7% of Sun-like stars host such worlds. However, at the expected average rate of 50%, there could be many more.
This research helps us understand the potential of these planets to have the elements to support life. This is an essential part of astrobiology, the study of the origins and future of life in our universe.
The study is written by NASA scientists who worked on the Kepler mission together with collaborators from around the world. NASA recalled the space telescope in 2018 after it ran out of fuel. Nine years of telescope observations revealed that there are billions of planets in our galaxy, more planets than stars.
“Kepler already told us that there were billions of planets, but now we know that a good portion of those planets could be rocky and habitable,” said lead author Steve Bryson, a researcher at NASA’s Ames Research Center in Silicon Valley. California. “Although this result is far from a final value, and the water on the surface of a planet is only one of many factors that support life, it is extremely exciting that we have calculated that these worlds are so common with such confidence and precision. “.
For the purposes of calculating this occurrence rate, the team observed exoplanets with a radius of 0.5 to 1.5 times that of Earth, narrowing down into planets that are likely rocky. They also focused on stars similar to our Sun in age and temperature, roughly up to 1,500 degrees Fahrenheit.
That’s a wide range of different stars, each with its own particular properties that influence whether the rocky planets in its orbit are capable of supporting liquid water. These complexities partly explain why it is so difficult to calculate how many potentially habitable planets there are, especially when even our most powerful telescopes can barely detect these small planets. That’s why the research team took a new approach.
Rethinking how to identify habitability
This new finding is an important step forward in Kepler’s original mission to understand how many potentially habitable worlds exist in our galaxy. Previous estimates of the frequency, also known as the rate of occurrence, of such planets ignored the relationship between the temperature of the star and the types of light emitted by the star and absorbed by the planet.
The new analysis accounts for these relationships and provides a more complete understanding of whether a given planet might be capable of supporting liquid water and potentially life. That approach is made possible by combining Kepler’s final planetary signal dataset with data on the energy output of each star from an extensive trove of data from the European Space Agency’s Gaia mission.
“We always knew how to define habitability simply in terms of the physical distance from a planet to a star, so it’s not too hot or too cold, which left us making a lot of assumptions,” said Ravi Kopparapu, author of the paper and NASA scientist. . Goddard Space Flight Center in Greenbelt, Maryland. “The data from Gaia on the stars allowed us to see these planets and their stars in a completely new way.”
Gaia provided information about the amount of energy that falls on a planet from its host star based on the flow of a star, or the total amount of energy that is emitted in a given area during a given time. This allowed the researchers to approach their analysis in a way that recognized the diversity of the stars and solar systems in our galaxy.
“Not all stars are the same,” Kopparapu said. “And not all planets.”
Although the exact effect is still being investigated, a planet’s atmosphere calculates how much light is needed to allow liquid water to also enter a planet’s surface. Using a conservative estimate of the effect of the atmosphere, the researchers estimated an occurrence rate of around 50% – that is, about half of Sun-like stars have rocky planets capable of harboring liquid water on their surfaces. An alternative optimistic definition of the habitable zone estimates around 75%.
Kepler’s legacy represents future research
This result builds on Kepler’s long legacy of data analysis work to derive an occurrence rate and sets the stage for future observations of exoplanets informed by how common we now expect these rocky and potentially habitable worlds to be. Future research will continue to refine the rate, informing the probability of finding these types of planets, and fueling plans for the next stages of exoplanet research, including future telescopes.
“Knowing how common different types of planets are is extremely valuable in designing upcoming exoplanet search missions,” said co-author Michelle Kunimoto, who worked on this paper after completing her PhD in exoplanet occurrence rates at the University of British Columbia. and recently joined the Transiting Exoplanet Survey Satellite, or TESS, team at the Massachusetts Institute of Technology in Cambridge, Massachusetts. “Surveys targeting small, potentially habitable planets around Sun-like stars will rely on results like these to maximize their chances of success.”
After revealing more than 2,800 confirmed planets outside our solar system, the data collected by the Kepler space telescope continues to shed important new discoveries about our place in the universe. Although Kepler’s field of view covered only 0.25% of the sky, the area that your hand would cover if you held it with your arm outstretched skyward, their data has allowed scientists to extrapolate what the mission data means. for the rest of the galaxy. That work continues with TESS, NASA’s current planet-hunting telescope.
“For me, this result is an example of how much we have been able to discover with just that little glimpse beyond our solar system,” Bryson said. “What we see is that our galaxy is fascinating, with fascinating worlds, and some that may not be very different from ours.”
Source: NASA, Original written by Frank Tavares, NASA Ames Research Center.
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