[Lex Computer & Tech Group/LCTG] Jupiter

[Michael Alexander]

Ken Pogran wrote: “According to one theory, one such impacting object was so large that a major piece of it broke off upon impact and flew out to became the earth's moon, which would explain why our moon is so different in terms of size and orbit from those of other planets.”
That theory is probably inconsistent with the fact, established from samples of moon rocks brought back to earth, the moon’s elemental composition is similar to the earth’s.
Also, with regard to the idea that Jupiter’s gravitational field has protected the earth:  Imagine an object whose path will lead it to collide with our planet.  Rarely will a path be such that it would be significantly influenced by Jupiter’s gravitational field.  (Jupiter’s orbit around the Sun is very large, and the time it takes to complete the orbit is very long.). In fact, one could turn the idea inside out and argue that Jupiter deflects extraterrestrial objects toward Earth, so they become meteors and meteorites.
    – Mike Alexander


On Friday, October 22, 2021, 3:50 PM, Ken Pogran <pogran at alum.mit.edu> wrote:

john rudy wrote on 10/21/21 9:29 PM:

 
https://www.space.com/jupiter-impact-flash-october-2021-photo-video
 
Its huge gravity causes it to be a vacuum cleaner picking up stuff that might otherwise fly into earth.  This is an interesting story


The point John makes is actually one element of the Rare Earth Hypothesis, which "argues that the origin of life and the evolution of biological complexity such as sexually reproducing, multicellular organisms on Earth (and, subsequently, human intelligence) required an improbable combination of astrophysical and geological events and circumstances." [Wikipedia]

>From the Wikipedia article:

"According to the hypothesis, complex extraterrestrial life is an improbable phenomenon and likely to be rare throughout the universe as a whole. The term "Rare Earth" originates from Rare Earth: Why Complex Life Is Uncommon in the Universe (2000), a book by Peter Ward, a geologist and paleontologist, and Donald E. Brownlee, an astronomer and astrobiologist, both faculty members at the University of Washington."
 
I saw this book in paperback in a bookstore not too long ago, and finished reading it just recently. (My wife thought it a very odd choice indeed for a "summer beach read"!)

One of many elements of the hypothesis is that, as John wrote, Jupiter serves as a "vacuum cleaner picking up stuff that might otherwise fly into earth."  Ward and Brownlee argue that, before Jupiter (and, to a lesser extent, Saturn) formed, the inner planets like earth were regularly bombarded by asteroids and other large space debris. (According to one theory, one such impacting object was so large that a major piece of it broke off upon impact and flew out to became the earth's moon, which would explain why our moon is so different in terms of size and orbit from those of other planets). 

Some of these impacts would have been so energetic that they would have effectively "sterilized" the earth of any life that might have existed.  But once Jupiter formed, it shielded the earth from further large impacts because of its size and position in the solar system, removing  one factor that inhibited the development of life on earth.

This only one of many elements of the Rare Earth Hypothesis. I find the Hypothesis quite compelling. 

Winkler mentioned it ever-so-briefly in his "Intelligent Life" talk on October 6 as counterpoint to the earlier, more prevalent notion (attributed to Carl Sagan, I believe?) that our sun is a very average star,  the earth is a very average planet, and life should therefore be a very average occurrence throughout the universe.  

The Rare Earth Hypothesis, on the other hand, argues that while very primitive life forms may well abound  elsewhere in the universe, there is so much uncommon about the earth's situation (astrophysically and geologically) that the likelihood of complex life existing elsewhere is extremely small.

Ken Pogran



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