A new study suggests that rocky planets that formed early in our Galaxy's 13.2 billion-year history produce environments that are more friendly to life than planets that formed later. The researchers say that planets formed earlier in the history of the Milky Way are more likely to form suitable geological formations, magnetic fields, and other conditions that we know are conducive to the evolutionary survival of life.
Illustration: Artist's depiction of a potentially habitable extraterrestrial planet, Kepler-1649c, orbiting its main red dwarf (Credit: © NASA/Ames Research Center/Daniel Rutter)
"The geology of planets is very important for the survival of life, and the best geological conditions seem to exist only in the planets that formed in the early days of the Milky Way, and it is difficult to reproduce after that," said Craig O'Neill, director of the Macquarie Planetary Research Center at Macquarie University in Sydney. ”
O'Neill and his colleagues study exoplanets in the Milky Way— planets in the orbits of stars other than the Sun.
"Because of the distances, we have limited information about exoplanets, but we can learn about factors like location, temperature, and some geochemical projections," O'Neill said, "which allows us to simulate how they formed."
The research team stuffed these parameters into a star formation simulator and computed them using a processor at the National Computing Foundation Centre at the Australian National University in Canberra. The researchers found that planets that formed relatively early in the history of the Milky Way are more likely to develop a geological formation that acts like a built-in incubator, and that the surface is cool enough to allow life known to evolve.
O'Neill said that in many ways, the lack of such geological formations is bad news for the formation of life. "This doesn't just affect surface temperatures, it also means that the core of the galaxy remains hot, hindering the formation of magnetic fields," he said, "without a magnetic field, the planet would lose its barrier to stellar radiation and thus tend to lose its atmosphere, so life would be more difficult to maintain." A planet needs to be lucky enough to have the right location, the right geochemical properties, and the right timing to allow life to flourish. ”
In addition, the geochemistry of planets is also influenced by the era of their formation, as the chemical composition of galaxies has been changing over time. Later, for example, as supernovae exploded, more heavier material was scattered through the galaxy, while lighter material (such as hydrogen and helium) needed to form stars and planets became scarcer.
These new findings were presented in the Goldschmidt Online Conference 2020, held between June 21 and 26.
Related knowledge
Extrasolar planets, or Exoplanets for short, are planets located outside the Solar System that do not orbit the Sun. As of the end of June 2020, a total of 4,281 exoplanets have been confirmed, of which about 71.3% were discovered through transit; these planets belong to 3,163 planetary systems, of which 701 are multi-planetary. The Kepler mission has detected 18,000 planetary candidates, including 262 candidates located in potential habitable zones.
In the Milky Way, it is estimated that there are billions of stars (between 100 billion and 400 billion planets if each star has at least one planet)[2][3][4][8], with planets not only around the stars but also freely moving planetary-mass objects,[9] and the closest known exoplanet is Proxima Centauri b.
Almost all of the exoplanets that have been discovered are within our own galaxy, but there are a small number of extragalactic planets that may be detectable. In a January 2013 report by the Harvard-Smithsonian Center for Astrophysics, it was estimated that there were "at least 17 billion" Earth-scale exoplanets in the Milky Way.
For hundreds of years, many philosophers and scientists have believed that planets should exist outside the solar system, but there is no way to know how common planets are or how similar they are to the planets of the solar system. In the 19th century, many detection methods were proposed, but in the end all astronomers got negative results. The first confirmed detection occurred in 1992, when several Earth-like-like objects orbited the pulsar PSR B1257+12. The first detection of planets found in stars in the main sequence zone appeared in 1995, when a giant planet with a 4-day orbit was discovered in nearby Pegasus 51. Due to advances in observational technology, the number and efficiency of detections have increased rapidly since then [5]. Some exoplanets are directly imaged by large telescopes, but the vast majority of exoplanets are detected by radial velocity measurements. In addition to exoplanets, "extraterrestrial comets" (comets outside the solar system) have also been discovered and are perhaps common within the Milky Way.
By Elizabeth Howell
FY: Sonic Hedgehog
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