In their tireless search for signs of extraterrestrial life, astronomers have coined the intriguing term “Goldilocks Zone” when referring to the habitable zone of a star body: the distance from a star where liquid water can be present on the surface of a planet is not too hot, not too cold, but fair.
New research by astronomers based on decades of data has identified new criteria that can help assess the potential habitability of a planet.
The study, called the “Goldilocks Project”, presented by a team of astronomers from the University of Villanova at the 235th meeting of the American Astronomical Society in Hawaii, has identified what has been coined as “Goldilocks stars,” star systems where they hope to find the best planets for possible extraterrestrial life.
Many are already familiar with the concept of the habitable zone, the distance from a star in which liquid water can be present on the surface of a planet, not hot enough to vaporize it, not so cold that everything would be frozen.
That explains the reference to the story of Goldilocks and the Three Bears, where a blond girl enters an empty cabin in the forest, tries three bowls of porridge and discovers that one is “fair, neither too hot nor too cold! ”
The Goldilocks area around a star is like that. However, although we definitely consider liquid water as a vital ingredient for life, it is not the only criterion in our search for potentially habitable planets.
According to astronomers at the University of Villanova, the best stars for life are one step along the Hertzsprung-Russell star type table, that is, K-type stars. These are orange stars that are a bit colder than the sun, and a little warmer than a red dwarf.
Different stars Burn at different temperatures depending on their size and age. The chart pictured is called a Hertzsprung – Russell diagram and it helps visualize the concept. pic.twitter.com/xvdt20Rj7a
– Ryan H (@TheRealRyan_H) April 2, 2019
“The K dwarf stars are in the” sweet spot “, with intermediate properties between the rarer, brighter but shorter-lived solar stars (G stars) and the more numerous red dwarf stars (M stars),” Villanova astronomer and astrophysicist Edward Guinan explained, who presented the new study with a colleague, astronomer Scott Engle.
“K stars, especially the warmest ones, have the best of all worlds. If you are looking for planets with habitability, the abundance of K stars increases your chances of finding life. ”
Guinan, Engle and their students have been monitoring a series of F and G stars in ultraviolet and X-rays for the past 30 years as part of their Sun in Time program, and red M-type dwarfs for 10 years as part of the program Live with a red dwarf.
Both programs have been helping to assess the impact of X-rays and ultraviolet radiation from the stars in question on the possible habitability of their planets.
The study has also been measuring age, rotation rate and X-rays and far ultraviolet radiation in a sample of mostly cold G and K stars.
In their investigation, they used the NASA Hubble Space Telescope, the Chandra X-ray Observatory and the XMM-Newton satellite of the European Space Agency for their observations. Hubble’s sensitive ultraviolet light observations of hydrogen radiation were used to evaluate the radiation of a sample of approximately 20 orange dwarfs.
“Hubble is the only telescope that can do this kind of observation,” Guinan said.
Guinan and Engle discovered that the radiation levels around the K stars were much more benign for the accompanying planets than those found around the red dwarfs.
K stars also have a longer lifespan and, therefore, the migration of the habitable zone occurs more slowly, pointing to the suggestion that K dwarfs could present the ideal place to look for signs of extraterrestrial life.
Guinan and Engle also observed some of the most interesting K stars that host planets, including Kepler-442, Tau Ceti and Epsilon Eridani.
“Kepler-442 is notable because this star houses what is considered one of the best Goldilocks planets, Kepler-442b, a rocky planet that is a little more than double the Earth’s mass. Therefore, the Kepler-442 system is a Goldilocks planet housed by a Goldilocks star! “Guinan said.
In another fact that inspires optimism, there are three times more K dwarfs in our galaxy than stars like our Sun.
Approximately 1,000 K stars are within 100 light years of our Sun, which makes them the best candidates for exploration.