Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Earth-Sun distance

  1. Dec 23, 2014 #1
    I was wondering if these distances is perfect to allow life here on Earth. I have did some research on the forum and am ware that the distance changes throughout history but not much. Today Earth has a eccentricity of .0167. If Earth's distant is perfect it should be at 0. Is it safe to say the distant is still perfect? Reason why I brought this up is because there is a well known quote that was attributed by Isaac Newton. In this quote it states:

    "Atheism is so senseless. When I look at the solar system, I see the Earth at the right distance from the Sun to receive proper amounts of heat and light. This did not happen by chance."

    Could it be that Newton was right back then? Or was he in error? I'm not a scientist but this would be an interesting discussion.

    Btw, I'm not here to start an argument. I'm just pasting the quote to see if there's any validity to it. ;)
     
  2. jcsd
  3. Dec 23, 2014 #2

    phinds

    User Avatar
    Gold Member

    He was wrong. It happened by chance. If you bring up any religious arguments that say he was right, this thread will be locked and without religious arguments there ARE no arguments to say he was right.
     
  4. Dec 23, 2014 #3

    davenn

    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    Hi
    welcome to PF :)

    if you want to know more about the good distance of a planet to be from the sun to support life

    google "The Goldilocks Zone"

    keep religion out of any discussions per PF rules :)

    cheers
    Dave
     
  5. Dec 23, 2014 #4
    I see. lol.
     
  6. Dec 23, 2014 #5
    Thanks Davenn. But our moon is also in the the "Goldilocks Zone" is it not? Yet it doesn't support life. Can you explain this?
     
  7. Dec 23, 2014 #6

    russ_watters

    User Avatar

    Staff: Mentor

    What does Earth have that the moon doesn't and why?
     
  8. Dec 23, 2014 #7

    davenn

    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    Russ, You answered whilst I was still typing
    You had the better approach rather than just giving answers as I did

    OK deleted my answers and hopefully the OP didn't read too much of it
     
  9. Dec 23, 2014 #8
    Russ, in short there are differences such as water and atmosphere. The moon does not have that. My point was that it doesn't have to be in the Habitable Zone.
     
  10. Dec 23, 2014 #9

    davenn

    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    you didn't fully answer Russ's Q
    and what I quoted of your comment is a contradiction of the already established habitable zone comments
    so, why did you say that ?

    Dave
     
  11. Dec 23, 2014 #10

    russ_watters

    User Avatar

    Staff: Mentor

    No worries.
     
  12. Dec 23, 2014 #11

    russ_watters

    User Avatar

    Staff: Mentor

    Good start. Prodding a little more (and amplifying davenn's comment...) what about water and/or an atmosphere might require a planet to be in the Habitable Zone?

    Though, no, it isn't necessarily an absolute requirement, but it is a pretty solid one. There are a few other candidates for life elsewhere in our solar system, but they aren't great and the life we may find isn't likely to be very complex.
     
  13. Dec 23, 2014 #12

    marcus

    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    It happens that the Earth is 80 times more massive than the moon, so it has stronger gravity and is able to hold onto much of its atmosphere and water without having them evaporate off into space.

    It's fairly common for planets to be quite a bit more massive than their satellites, i.e. their moons.

    Ooops, I see Russ was already pursuing that line of thought with you, Star28. Maybe I should erase this and retire from the discussion :w
     
  14. Dec 23, 2014 #13

    davenn

    User Avatar
    Science Advisor
    Gold Member
    2017 Award


    Those were some of the answers I wrote, but deleted them cuz Russ and I wanted the OP to discover them :)

    edit: no probs
     
    Last edited: Dec 23, 2014
  15. Dec 23, 2014 #14

    marcus

    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    You get the credit! Clumsy of me to interrupt when Russ was engaging in Socratic dialog, but by now it would be even clumsier to go back and delete, so I'll just let things be.
     
  16. Dec 24, 2014 #15

    Nugatory

    User Avatar

    Staff: Mentor

    14 posts into this thread and no one has mentioned that this quote is bogus? Newton said no such thing.
     
  17. Dec 24, 2014 #16

    davenn

    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    LOL I didn't read close enough to realise he was trying to quote Newton ;)
     
  18. Dec 24, 2014 #17

    phinds

    User Avatar
    Gold Member

    HA ! He was a religious guy so it didn't even occur to me that the quote might be bogus, I was so focused on how wrong the statement is.

    Good catch !
     
  19. Dec 24, 2014 #18
    Isn't the modern answer to this kind of question to invoke the anthropomorphic viewpoint?
    Something like...
    We observe these specific conditions conducive to supporting life... because we are alive and require those conditions... in order to be here alive to make these observations... all living creatures will notice that their conditions support what they need to be alive and take notice of these conditions... places that don't support life don't have life to observe the conditions that don't support them.
     
  20. Jan 2, 2015 #19

    BobG

    User Avatar
    Science Advisor
    Homework Helper

    Literally true.

    However, Newton did say (in separate quotes):

    "This most beautiful system of the sun, planets, and comets, could only proceed from the counsel and dominion of an intelligent Being. [...] This Being governs all things, not as the soul of the world, but as Lord over all; and on account of his dominion he is wont to be called "Lord God", or "Universal Ruler". [...] The Supreme God is a Being eternal, infinite, [and] absolutely perfect." (This being three separate sentences from his Principia pulled out of context and grouped together.)

    and...

    "Tis inconceivable that inanimate brute matter should (without the mediation of something else which is not material) operate upon & affect other matter without mutual contact." (from a letter to a colleague)

    Newton may be more famous for developing a formula to calculate the force of gravity (and acceleration due to gravity), but he also had some thoughts about why gravity existed.

    The op's quote, while bogus, does pretty much express Newton's views.

    And I'd say Newton was more spiritual than religious - at least if you're talking about your standard organized religions. He not only believed in a creator, but a creator that would step in from time to time to adjust the universe (as a whole; not a creator that involved himself in minute details such as an individual person). But his views definitely didn't fit either the Protestant or the Catholic religious views (they probably would not have been incompatible with the Unitarian church, but few views are).

    Not that Newton's religious beliefs are very relevant. One can make real observations about the universe and speculate as to why it exists without either seriously hampering the other (unless your religious beliefs require a very literal translation of your religious books).

    Newton's religious or spiritual views give insight into him, as a person. And as valuable as Newton's work on motion, gravity, and optics were, he had some rather bizarre views and practices (such as his work in alchemy, not to mention the poorly thought out experiment where he stared directly at the Sun for two or three hours). He was definitely a very interesting person.
     
  21. Jan 2, 2015 #20
    I think that Newton was wrong by saying that, the positioning of the planets in the solar nebula was completely by chance, as can be seen with other planets in other star systems. As you can see in other star systems some rare planets have been in the Goldilocks zone and most have been in uninhabitable distances. It is all by chance where the planets form and whether they are habitable like Earth
     
  22. Jan 5, 2015 #21
    The Earth's orbit eccentricity varies as a result of the other planets' perturbing its orbit. It is currently 0.0167, but it has an average value of 0.034 and a maximum value around 0.068 (Milankovitch cycles - Wikipedia).

    Circumstellar habitable zone - Wikipedia features several attempts to estimate its extent. Most of them involve estimating where a planet can be if it has liquid water. Estimates of its extent vary widely, because it is dependent on atmosphere thickness and composition, planet rotation, etc. For the inner edge, it's 0.5 - 0.99 AU, while for the outer edge, it's 1.01 - 3.0 AU.

    Venus's runaway greenhouse effect may provide a good lower limit. Its distance from the sun is about 0.72 AU.

    I will attempt to estimate the outer boundary using Water on Mars - Wikipedia discusses the abundance of evidence of the former presence of liquid water on that planet, and [1204.4449] The faint young Sun problem notes the Sun's steadily increasing brightness. About 4 billion years ago, when Mars had lots of liquid water, the Sun was only about 74% as bright as it is today. That means that Mars received as much sunlight as it would if it was orbiting at 1.77 AU today. The Earth also received less, as if it was orbiting at 1.16 AU today. The present mean distances of the two planets are 1 AU and 1.52 AU.

    So a range of 0.75 AU to 1.8 AU is plausible, and it is consistent with several of the estimates.
     
  23. Jan 5, 2015 #22
    I think that the OP's Isaac Newton quote is bogus, for two reasons:

    It seems too much like what someone in the present might write, especially if this was supposed to be Newton's writing in English rather than a translation of his writing in Latin. Here is some of his writing in English: The Project Gutenberg eBook of Opticks:, by Sir Isaac Newton, Knt. He used the spelling "opticks" rather than present-day "optics", and that is the beginning of the differences.

    The relation between how much sunlight a planet gets and what temperature it is was not well understood until the late 19th cy. That's when the Stefan-Boltzmann law was discovered. Also, in the 18th cy. and thereabouts, it was widely believed that the other planets had inhabitants much like the Earth's. The Planet-Girded Suns: The History of Human Thought About Extrasolar Worlds is a good history of that notion. In fact, there was a common belief back then that God would not waste a world, that he would not create a world and then not create inhabitants for it (2.3 - Plurality of Worlds and Divine Purpose) So it's unlikely that Newton or any of his contemporaries would have considered the Earth just right for habitation.
     
  24. Jan 5, 2015 #23
    This is where I am...how did gravity come to be? Calculating gravity is one thing but understanding its mechanisms at work in an atomic level and grander scenarios is very breathtaking. Maybe there is a scientific explanation how did gravity come about being. I can't figure it out I'm stumped. It's driving me mad! Literally.
     
  25. Jan 17, 2015 #24
    Given the absolutely enormous number of planets in the Universe (there are about 1011 galaxies each with 1011 stars, and who knows how many planets per star?), the chances are extremely likely that some planets will be in the habitable zone by pure luck. We've already discovered quite a few Earth-sized planets in the habitable zone of their star, and estimates suggest there may be 8.8 billion terrestrial planets in the habitable zone of their star in our galaxy alone! Given that some planets will end up in the habitable zone by chance, it's not surprising we find ourselves on one of these - since we as living beings need to be on a habitable planet by definition.
    It's an effect called anthropic selection - if we find something has a low probability (but not so low as to be almost impossible) and had to be necessary for a planet to be habitable (e.g. being in a stable orbit in the habitable zone of a star), we shouldn't be surprised to see that that unlikely thing applies to Earth - its small-but-not-too-small probability combined with the enormous number of planets in the Universe means it had to happen on a few planets by chance, and Earth had to be one of those planets or else we wouldn't be here to talk about it!

    Personally I've always been baffled when people use the Earth's orbit as an argument that Earth was specially designed as a home for life. If Earth was the only planet in the Universe, then Earth's habitability would be a rather spooky coincidence. (Maybe. Or perhaps that would no more prove the Universe was designed for life as it would prove the Universe was designed especially for plate tectonics, or continental crust, or surface liquid oceans, or a nitrogen-rich atmosphere or other features of Earth - perhaps life would just be something that happened to arise on Earth with no particular cosmic significance to it.) The argument falls completely flat, however, when we look at all the other planets in our solar system and the vast majority of the exoplanets out there (not to mention the huge empty spaces between solar systems with no stars or planets at all, or the regions of the galaxy that are too low in metals or too high in radiation to support life even if Earth-like planets exist, or...) and realise that they can't support life. Why should Earth be so privileged? Why assume Earth was designed for life, when chance alone seems to be perfectly capable of explaining its orbit and the vast, vast, vast majority of the Universe clearly wasn't designed as a home for life? It would be as if the Creator built a city full of structurally unstable buildings, only one of which had enough strength to stay intact after a tornado rips through the city, and pointing to that one building as evidence that the whole thing was created for the purpose of withstanding tornadoes.

    (None of this says God doesn't exist, by the way, only that you can't use the "design" of Earth's orbit as evidence for that. Science seeks to explain the world in terms of natural phenomena, and makes no comment on the existence of God - science and religion are two different things, designed to answer different questions. Earth's orbit and habitability can be fully explained by science, so can't be used to bolster a design argument for God's existence.)

    One final thing: the habitable zone isn't necessarily the only thing making a planet habitable. You have to consider the planet's atmosphere, its size, its water content, abundance of organic matter, long-term climate stability... then there's the evolution of those planets over time (Earth's remained a pleasant home for life for at least 3.8 billion years, albeit with a few mass extinctions, but most planetary scientists agree Venus and Mars were once habitable too and are no longer) and the fact that with tidal heating some planets or moons outside the conventional habitable zone may still be capable of supporting life (Europa, Enceladus, Titan)... not to mention alternative and hypothetical biochemistries!
     
  26. Jan 18, 2015 #25

    Dale

    Staff: Mentor

    With that we will go ahead and close this thread. The science has already been discussed and the religion is not appropriate for the forum.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook