# Moon Doom: Sun, Jupiter, collision, or deep space **URL:** \ **Category:** Factual Questions\ **Created:** [December 21, 2009, 6:30pm UTC](https://boards.straightdope.com/t/moon-doom-sun-jupiter-collision-or-deep-space/522095 "2009-12-21T18:30:21Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![Super\_Kapowzler](https://avatars.discourse-cdn.com/v4/letter/s/a698b9/32.png) [@Super\_Kapowzler](https://boards.straightdope.com/u/Super_Kapowzler)\ **Post date:** [December 21, 2009, 6:30pm UTC](https://boards.straightdope.com/t/moon-doom-sun-jupiter-collision-or-deep-space/522095/1 "2009-12-21T18:30:21Z")
The moon slips from it’s orbit at about 2"/year. Couldn’t the “separation date” be calculated, knowing speed, density, mass? Will the Moon make it out of our solar system? Which has the better chance of devouring said Moon once it flys away: Sol or Jupiter? (the two major gravitational competitors.) Or will it hit Venus upside the head in the greatest collision in our system witnessed by man? Rock on Moon! I never was much for Venus. Or will it deep-six “SPACE 1999” style? ---
**Author:** ![RandMcnally](https://avatars.discourse-cdn.com/v4/letter/r/b782af/32.png) [@RandMcnally](https://boards.straightdope.com/u/RandMcnally)\ **Post date:** [December 21, 2009, 6:35pm UTC](https://boards.straightdope.com/t/moon-doom-sun-jupiter-collision-or-deep-space/522095/2 "2009-12-21T18:35:16Z")
The moon won’t slip its orbit because as it gets further away from the Earth it begins to slow down. As it slows it gets pulled into the Earth again. As it gets closer it speeds up then begins to pull itself away. It is like a yo-yo. ---
**Author:** ![pan1](https://avatars.discourse-cdn.com/v4/letter/p/e495f1/32.png) [@pan1](https://boards.straightdope.com/u/pan1)\ **Post date:** [December 21, 2009, 6:39pm UTC](https://boards.straightdope.com/t/moon-doom-sun-jupiter-collision-or-deep-space/522095/3 "2009-12-21T18:39:00Z")
Odds are the eventual resting place of our moon is our sun. The moon is in orbit around the sun as much as it is in orbit around earth. If it get’s free of Earth, it’s not going anywhere new in relation to the sun. After that - it will get blown into space as it’s cooked atoms when the sun explodes or it will remain as part of the burnt out core of Sol. ---
**Author:** ![pan1](https://avatars.discourse-cdn.com/v4/letter/p/e495f1/32.png) [@pan1](https://boards.straightdope.com/u/pan1)\ **Post date:** [December 21, 2009, 6:43pm UTC](https://boards.straightdope.com/t/moon-doom-sun-jupiter-collision-or-deep-space/522095/4 "2009-12-21T18:43:32Z")
I forgot to mention the orbital lifespan of the moon - the time it will take until it flys away - is 50 billion years. The sun’s got about 3-4 billlion until its bigger than earth’s orbit. I suspect the math from there is simple. ---
**Author:** ![The\_Hamster\_King](https://avatars.discourse-cdn.com/v4/letter/t/8edcca/32.png) [@The\_Hamster\_King](https://boards.straightdope.com/u/The_Hamster_King)\ **Post date:** [December 21, 2009, 6:46pm UTC](https://boards.straightdope.com/t/moon-doom-sun-jupiter-collision-or-deep-space/522095/5 "2009-12-21T18:46:47Z")
The Moon is receding from Earth because Earth is gradually transferring some of its rotational momentum to the Moon through tidal forces. Eventually the system will reach a stable state where the rotational period of the Earth matches the orbital period of the Moon and the Moon will stop receding. Of course, long before that happens the sun will turn into a red giant and cook both the Earth and the Moon, but the important point is that the recession will not continue indefinitely. ---
**Author:** ![Der\_Trihs](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/der_trihs/32/233_2.png) [@Der\_Trihs](https://boards.straightdope.com/u/Der_Trihs)\ **Post date:** [December 21, 2009, 9:13pm UTC](https://boards.straightdope.com/t/moon-doom-sun-jupiter-collision-or-deep-space/522095/6 "2009-12-21T21:13:59Z")
> [@The\_Hamster\_King](#): > > The Moon is receding from Earth because Earth is gradually transferring some of its rotational momentum to the Moon through tidal forces. Eventually the system will reach a stable state where the rotational period of the Earth matches the orbital period of the Moon and the Moon will stop receding. > > Of course, long before that happens the sun will turn into a red giant and cook both the Earth and the Moon, but the important point is that the recession will not continue indefinitely. I recall reading some years ago that presuming that the Sun or the end of the universe doesn’t intervene, the Moon would indeed do what you say. However, it would then start to move back towards Earth. The Earth/Moon system loses energy over time, radiated as gravity waves. Over a very long time this would result in a decaying orbit and eventually the Earth and Moon would collide and merge. ---
**Author:** ![Find\_Friends](https://avatars.discourse-cdn.com/v4/letter/f/c37758/32.png) [@Find\_Friends](https://boards.straightdope.com/u/Find_Friends)\ **Post date:** [December 21, 2009, 10:44pm UTC](https://boards.straightdope.com/t/moon-doom-sun-jupiter-collision-or-deep-space/522095/7 "2009-12-21T22:44:47Z")
Nice member name/question combination, BTW. > [@Super\_Kapowzler](#): > > Or will it hit Venus upside the head in the greatest collision in our system witnessed by man? Rock on Moon! I never was much for Venus. Are you “from Mars” then? 😉 Seriously, though, questions like these make me wonder how many people have any real sense of the emptiness of the Solar System. (That is, planetary widths versus their average distances to the sun, and mutual separations, especially minimums.) Recently I calculated the likelihood that a comet crossing the earth’s orbit would strike the earth. By “crossing” I mean that it is neither too far “north” or “south” of the elliptic. (These other possibilities alter the question of probability, but let’s say that we know ahead of time that the comet won’t miss the earth either such way.) Now, I don’t remember the exact figure, but it was in the neighborhood of 60,000 to one. That’s based on the diameter of the earth versus the length of its orbit, and projecting that the comet is exactly on the ecliptic. I realize that the earth’s gravitation would affect the comet’s orbit as it approaches, but I’m figuring that it would be equally likely to cause the comet to just miss as pull ity in. Now, the orbit of the earth is wider that that of Venus by about a 4 to 3 ratio. This is partially offset by Venus’ smaller diameter, but not by much. More significant is that the moon has a diameter that makes a difference, whereas a comet has a compact nucleus so small as to be negligible. We could almost just as soon imagine a mathematical point striking the earth as a comet. Again, to make a realistic projection we must take into account the north/south factor. Now,if the moon is fleeing its orbit from the earth, we need not quite extend the question of a full sphere of Venus’ orbit versus the cross-section of Venus; it would be somewhere in between, and much closer to a circle-comparison than a sphere-comparison. Bu the ratio would be pretty huge, and the probability extremely low. ---
**Author:** ![Super\_Kapowzler](https://avatars.discourse-cdn.com/v4/letter/s/a698b9/32.png) [@Super\_Kapowzler](https://boards.straightdope.com/u/Super_Kapowzler)\ **Post date:** [December 22, 2009, 12:00am UTC](https://boards.straightdope.com/t/moon-doom-sun-jupiter-collision-or-deep-space/522095/8 "2009-12-22T00:00:37Z")
That’s too bad. I was hoping that bitch Venus would get her come-uppance. No one deserves to have a Moon-rock upside the head more than a hussy whom preaches “Free-Love” while wakeboarding on a Mollusk.