Privileged Planet: frantic search for others (Introduction)

by David Turell , Wednesday, June 23, 2021, 20:15 (1038 days ago) @ David Turell

There-must-be-life-out-there research is frantically proceeding just like the origin-of-life research folks are constantly trying to achieve success, to no avail:

https://www.sciencedaily.com/releases/2021/06/210623113820.htm

"A new analysis of known exoplanets has revealed that Earth-like conditions on potentially habitable planets may be much rarer than previously thought. The work focuses on the conditions required for oxygen-based photosynthesis to develop on a planet, which would enable complex biospheres of the type found on Earth.

"The number of confirmed planets in our own Milky Way galaxy now numbers into the thousands. However planets that are both Earth-like and in the habitable zone -- the region around a star where the temperature is just right for liquid water to exist on the surface -- are much less common.

"At the moment, only a handful of such rocky and potentially habitable exoplanets are known. However the new research indicates that none of these has the theoretical conditions to sustain an Earth-like biosphere by means of 'oxygenic' photosynthesis -- the mechanism plants on Earth use to convert light and carbon dioxide into oxygen and nutrients.

"Only one of those planets comes close to receiving the stellar radiation necessary to sustain a large biosphere: Kepler-442b, a rocky planet about twice the mass of the Earth, orbiting a moderately hot star around 1,200 light years away.

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"By calculating the amount of photosynthetically active radiation (PAR) that a planet receives from its star, the team discovered that stars around half the temperature of our Sun cannot sustain Earth-like biospheres because they do not provide enough energy in the correct wavelength range. Oxygenic photosynthesis would still be possible, but such planets could not sustain a rich biosphere.

"Planets around even cooler stars known as red dwarfs, which smoulder at roughly a third of our Sun's temperature, could not receive enough energy to even activate photosynthesis. Stars that are hotter than our Sun are much brighter, and emit up to ten times more radiation in the necessary range for effective photosynthesis than red dwarfs, however generally do not live long enough for complex life to evolve.

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"'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.'"

Comment: The Earth is very, very special, but hope springs eternal that we inhabit something that is not so special. Why?