This illustration shows Kepler-186f, the first validated Earth-sized planet orbiting a distant star in the habitable zone. Photo credit: NASA Ames / JPL-Caltech / T. Pyle
Ever since astronomers confirmed the presence of planets outside of our solar system called exoplanets, mankind has wondered how many lives could host. We are now one step closer to finding an answer. According to new research with data from NASAOn the retired planet-hunting mission, the Kepler Space Telescope, about half of the stars whose temperature is similar to our Sun could have a rocky planet that can carry liquid water on its surface.
Our galaxy contains at least an estimated 300 million of these potentially habitable worlds, based on the most conservative interpretation of the results of a study to be published The Astronomical Journal. Some of these exoplanets could even be our interstellar neighbors, with at least four being possibly within 30 light years of our Sun and the closest possibly being about 20 light years or less away from us. This is the minimum number of such planets, based on the most conservative estimate that 7% of sun-like stars host such worlds. However, at the average expected rate of 50%, there could be a lot more.
This research helps us understand that these planets have the elements to support life. This is an essential part of astrobiology, the study of the origins of life and the future in our universe.
The study was written by NASA scientists who collaborated with staff from around the world on the Kepler mission. NASA retired the space telescope in 2018 after it ran out of fuel. Nine years of telescope observations showed that there are billions of planets in our galaxy – more planets than stars.
“Kepler already told us that there are 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 California’s Silicon Valley . “Although this result is far from definitive and water on the surface of a planet is just one of many factors that support life, it is extremely exciting that we have calculated that these worlds are so with such confidence and precision are common. ”
To calculate this rate of occurrence, the team looked at exoplanets with a radius between 0.5 and 1.5 times the radius of the Earth and narrowed them down to planets that are most likely rocky. They also focused on stars that are similar in age and temperature to our Sun, plus or minus up to 1,500 degrees Fahrenheit.
This is a multitude of different stars, each with their own properties that affect whether the rocky planets in its orbit can support liquid water. This complexity is partly why it is so difficult to calculate how many potentially habitable planets there are, especially when even our most powerful telescopes can barely see these tiny planets. That is why the research team took a new approach.
This illustration shows one possible appearance of the planet Kepler-452b, the first near-Earth world to be in the habitable zone of a star similar to our sun. Photo credit: NASA Ames / JPL-Caltech / T. Pyle
Rethinking how to identify habitability
This new discovery is a significant step forward in Kepler’s original mission to understand how many potentially habitable worlds exist in our galaxy. Previous estimates of the abundance of such planets, also known as the rate of occurrence, ignored the relationship between the temperature of the star and the types of light emitted by and absorbed by the planet.
The new analysis takes these relationships into account and provides a more complete understanding of whether or not a given planet can support liquid water and possibly life. This approach is made possible by combining Kepler’s final data set of planetary signals with data on the energy output of each star from an extensive database of the European Space Agency’s Gaia mission.
“We have always known that habitability is defined simply by the physical distance a planet is from a star, so that it is not too hot or too cold. So we made a lot of assumptions, ”said Ravi Kopparapu, author of the paper and a scientist at NASA’s Goddard Space Center in Greenbelt, Maryland. “Gaia’s data on stars enabled us to look at these planets and their stars in a completely new way.”
Gaia provided information about the amount of energy falling onto a planet from its host star based on the flux of a star or the total amount of energy emitted in a given area over a period of time. This allowed the researchers to approach their analysis in a way that recognized the diversity of stars and solar systems in our galaxy.
“Not every star is created equal,” said Kopparapu. “And not every planet either.”
Although the exact effect is still being researched, the atmosphere of a planet shows how much light is needed to allow liquid water to be present on the surface of a planet. Using a conservative estimate of the effect of the atmosphere, the researchers estimated an occurrence rate of about 50% – that is, about half of the Sun-like stars have rocky planets that can absorb liquid water on their surfaces. An alternative optimistic definition of the habitable zone estimates around 75%.
An illustration depicting the legacy of NASA’s Kepler Space Telescope. After nine years in space collecting data showing that our night sky was filled with billions of hidden planets – more planets than stars – NASA’s Kepler Space Telescope ran out of fuel for further scientific operations in 2018. Credits: NASA / Wendy Stenzel / Daniel Rutter
Kepler’s Legacy Charts Futurology
This result builds on a long tradition of analyzing Kepler data to get an occurrence rate and sets the stage for the future Exoplanet Observations of how often we expect these rocky, potentially habitable worlds now. Future research will further refine the rate, reveal the likelihood of finding these type of planets, and incorporate 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 the article after studying exoplanet research at the University of British Columbia Appearance Rates. and recently joined the Transiting Exoplanet Survey Satellite, or Tess, Team at the Massachusetts Institute of Technology in Cambridge, Massachusetts. “Polls targeting small, potentially habitable planets around sun-like stars will depend on such results to maximize their chances of success.”
After more than 2,800 confirmed planets have been discovered outside our solar system, the data collected by the Kepler Space Telescope continues to provide important new discoveries about our place in the universe. Although Kepler’s field of view covered only 0.25% of the sky, the area your hand would cover if you held him at arm’s length towards the sky, his data allowed scientists to extrapolate what the mission’s data would do for the rest the mission mean the galaxy. This work continues with TESS, NASA’s current planetary hunting telescope.
“To me, this result is an example of how much we could discover beyond our solar system with that little look,” said Bryson. “What we are seeing is that our galaxy is fascinating, with fascinating worlds and some not too different from ours.”
Reference: “The Occurrence of Planets in Rocky Habitable Zones Around Solar-Like Stars from Kepler Data” by Steve Bryson, Michelle Kunimoto, Ravi K. Kopparapu, Jeffrey L. Coughlin, William J. Borucki, David Koch, Victor Silva Aguirre, and Christopher Allen , Geert Barentsen, Natalie. M. Batalha, Travis Berger, Alan Boss, Lars A. Buchhave, Christopher J. Burke, Douglas A. Caldwell, Jennifer R. Campbell, Joseph Catanzarite, Hema Chandrasekharan, William J. Chaplin, Jessie L. Christiansen, Jorgen Christensen-Dalsgaard David R. Ciardi, Bruce D. Clarke, William D. Cochran, Jessie L. Dotson, Laurance R. Doyle, Eduardo Seperuelo Duarte, Edward W. Dunham, Andrea K. Dupree, Michael Endl, James L. Fanson, Eric B. Ford, Maura Fujieh, Thomas N. Gautier III, John C. Geary, Ronald L. Gilliland, Forrest R. Girouard, Alan Gould, Michael R. Haas, Christopher E. Henze, Matthew J. Holman, Andrew Howard, Steve B. Howell, Daniel Huber, Roger C. Hunter, Jon M. Jenkins, Hans Kjeldsen, Jeffery Kolodziejczak, Kipp Larson, David W. Latham, Jie Li, Savita Mathur, Soren Meibom, Chris Middour, Robert L. Morris, Timothy D. Morton Fergal Mullally, Susan E. Mullally, David Pletcher, Andrej Prsa, Samuel N. Quinn, Elisa V. Quintana, Darin Ragozzine, Solange V. Ramirez, Dwight T. Sanderfer, Dimitar Sasselov, Shawn E. Seader, Megan Shabram, Avi Shporer, Jeffrey C. Smith, Jason H. Steffen, Martin Still, Guillermo Torres, John Troeltzsch, Joseph D. Twicken, Akm Kamal Uddin, Jeffrey E. Van Cleve, Janice Voss, Lauren Weiss, William F. Welsh, Bill Wohler, Khadeejah A Zamudio, accepted, The Astronomical Journal.