PLANETS OF OTHER SUNS

As of 21 September 2023, there are 5,523 confirmed exoplanets in 4,112 planetary systems, with 932 systems having more than one planet. Most of these were discovered by the Kepler space telescope. There are an additional 1,984 potential exoplanets from Kepler's first mission yet to be confirmed, as well as 977 from its "Second Light" mission and 4,512 from the Transiting Exoplanet Survey Satellite (TESS) mission. [From Wikipedia.] Here is a list of known exoplanets.


Overwhelmingly the most probable types of planetary systems are "similar" and "mixed."  The "ordered" and "anti-ordered" arrangements are extremely rare.  We can see planetary systems in the process of forming, the Orion nebula is particularly full of them, and the relatively random nature of the overall process makes these outcomes easy to understand. The nearest other planetary system to our own is the system of Alpha Centauri. It is a triple star system, and apparently the two sunlike stars in the system do not have planets; only the dimmest star, Proxima is known to have at least two planets, both rocky. Proxima is also the nearest star, 4.2 light years away. The average distance from our sun to a star with planets is about 750 parsecs or roughly 2400 light years!  About 85% of all stars are part of binary systems, but there are four known quintuple star systems!  Better not to try to imagine what orbits of planets might be like in a system with 5 suns!






Speculation about the probabilities of life originating on other worlds besides our earth seems to be utterly pointless and fruitless because we know of only one example of life forming and evolving on a planet, namely the earth itself. Just using the past history of earth as a guide, we can see how relentlessly hostile nature is to the existence of life. In the known history of life on earth, there have been around 6 major "extinction events," in which all life on earth came close to dying completely out!  Any one of these catastrophes could easily have wiped out every living thing on earth, leaving the earth barren of life for the remainder of its existence, until it is destroyed as the sun evolves into a red giant. To the best of our current knowledge, life seems to have begun on earth during or just after the so-called Late Heavy Bombardment, about 3.7 billion years ago. Did the bombardment itself seed life?  This might have been either the worst possible time or the best possible time for the chemical processes that produced self-replicating molecules and the earliest molecular forms of life....  In any case, even if the basic chemistry on which life is based can be assembled with high probability, it can certainly be destroyed with approximately equal high probability. Only time will tell if, on other worlds, life has survived against all odds and has even produced multicellular organisms which can manipulate their environment extensively.




THE FERMI PARADOX

The Future Lies Ahead!