Privileged Planet: we are still very special (Introduction)

by David Turell , Saturday, July 03, 2021, 15:15 (1240 days ago) @ David Turell

Most exoplanets do not look habitable:

https://www.universetoday.com/151637/most-exoplanets-wont-receive-enough-radiation-to-s...

"To date, astronomers have confirmed the existence of 4,422 extrasolar planets in 3,280 star systems, with an additional 7,445 candidates awaiting confirmation. Of these, only a small fraction (165) have been terrestrial (aka. rocky) in nature and comparable in size to Earth – i.e., not “Super-Earths.” And even less have been found that are orbiting within their parent star’s circumsolar habitable zone (HZ).

"In the coming years, this is likely to change when next-generation instruments (like James Webb) are able to observe smaller planets that orbit closer to their stars (which is where Earth-like planets are more likely to reside). However, according to a new study by researchers from the University of Napoli and the Italian National Institute of Astrophysics (INAF), Earth-like biospheres may be very rare for exoplanets.

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"Led by astrophysics Prof. Giovanni Covone of the University of Napoli, the team focused on whether or not exoplanets discovered so far get enough Photosynthetically Active Radiation (PAR) to allow for the development of complex biospheres.

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"Specifically, photosynthetic organisms relied on solar radiation that ranges from 400 to 700 nanometers on the electromagnetic spectrum to carry out “oxygenic photosynthesis” – which corresponds roughly to the range of light that the human eye can perceive – aka. visible light. This is of significant concern to astrobiologists since Sun-like stars (G-type yellow dwarfs) are rare, with an estimated 4.1 billion in the Milky Way galaxy (between 1% and 4%).

"It is main sequence M-type red dwarfs that make up the majority of stars in our Universe, accounting for roughly 75% in our galaxy alone. Compared to Sun-like stars, red dwarfs are cooler and less luminous and are known for their elevated flare activity and producing a significant amount of radiation in the ultraviolet band. In addition, based on the current census of rocky exoplanets, red dwarfs are considered to be the most likely place to find Earth-like planets.

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“'Since red dwarfs are by far the most common type of star in our galaxy, this result indicates that Earth-like conditions on other planets may be much less common than we might hope. This study puts strong constraints on the parameter space for complex life, so unfortunately it appears that the “sweet spot” for hosting a rich Earth-like biosphere is not so wide.”

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"These findings are reminiscent of previous research conducted by Manasvi Lingam and Abraham Loeb, a postdoctoral researcher and the Frank B. Baird Jr. Professor of Science at Harvard University (respectively). In a 2019 study, titled “Photosynthesis on habitable planets around low-mass stars,” they demonstrated how planets that orbit red dwarf stars may not recieve enough photons to support photosynthesis."

Comment: For life fine-tuning is one requirement, but a special Earth orbiting a special star is just as important. It doesn't answer dhw's strange concern as to why God made the universe so huge and filled with so many weird processes if He only wanted humans. His same concern applies to why the bush of evolved life is so big. My view is God knew what had to be created to achieve His goals. dhw somehow knows better.