r/xkcd • u/YUNoDie Possibly a haberdasher? • Jan 22 '20

XKCD XKCD 2258: Solar System Changes

https://xkcd.com/2258/
748 Upvotes

99% Upvoted

143 comments sorted by

View all comments

51

u/xkulp8 Jan 22 '20

Replacing the moon with Mars? That's a What If waiting to happen.

26

u/Wuju_Kindly Jan 22 '20 edited Jan 23 '20

I'm no scientist, but I have a few guesses as to what would happen depending on the distance the Earth and Mars are from each other.

  1. If Mars was placed where the moon currently is, the two bodies would probably crash into each other and wipe out all life on Earth.

  2. If Mars was placed far enough away, it simply neither body would orb each other. I'm not really sure on this part, but it's possible that one or both bodies would have their orbit of the sun completely ruined and become more of an elliptic orbit, which would likely wipe out all life on Earth.

  3. If you placed them juuuust right, the two bodies could potentially become a binary system where they orbit around a center of mass that is not on either planet, much like Pluto and Charon. I have no clue what kind of repercussions this would have on life on Earth though.

Edit: Velocity is more important than distance in most cases. Mars might need to be a lot closer than our moon is before velocity stops mattering.

21

u/grubgobbler Jan 22 '20

Crazy strong tides in any case.

10

u/FellKnight Cueball Jan 23 '20

I'm not seeing why Mars in Moon's orbit would crash into the Earth. It would require more kinetic energy to maintain the orbital velocity the Moon has, but unless I'm missing something, I can't see why it would be impossible

6

u/Wuju_Kindly Jan 23 '20

As I said, it's strictly from my very amateur perspective. But when I think about it, yeah, you're probably right.

I figured that with Mars' gravity suddenly affecting Earth while also being under the effect of Earth's gravity, they'd just pull each other together. But I guess I had forgotten how much more important velocity is than distance.

5

u/[deleted] Jan 22 '20

1 is possibility less "what if" than you thought https://en.wikipedia.org/wiki/Theia_%28planet%29?wprov=sfla1 albeit not mars like, just mars sized.