# How close would the orbit of Mars have to be to that of the Earth to induce a collision?

When the Earth passes by Mars they exert a slight gravitational pull on each other, but the force is so small that their orbits are not significantly disturbed.

However, if we imagined that the orbits of the Earth and Mars were coplanar and much closer to one another, then there would presumably be some critical distance at which they would move together and collide.

What is that critical distance? In other words, if we shrunk the radius of the orbit of Mars, how much would it have to shrink before a collision would occur by the natural force of gravity between the two bodies?

• Why do you think they would collide? Direct collisions are very improbable without friction. If anything, they would exchange angular momentum and fly off on different paths. Feb 11 '19 at 12:12
• @AtmosphericPrisonEscape Because gravity causes objects to move towards each other. Feb 11 '19 at 12:15
• Why do you think do we not fall into the sun? It also exerts gravity onto Earth. How are satellites able to orbit Earth, instead of falling onto it? Feb 11 '19 at 12:16
• I shrunk the orbit of Mars in a simulator some millions kms, and Mercury, Venus, Mars and the Earth got tossed from the solar system Feb 11 '19 at 21:18
• When you shrunk the orbit of Mars what I think it happens is this. Earth and Mars arent in the same position in their orbits, first Mars orbit is pulled down when Earth gets closer and it ends orbiting closer to the sun than Earth, later when Earth passes again (now Earth is further away to the sun) it's pulled out so it ends orbiting further away, this cycle happens many times until Earth changes its orbits enough as for Mars being tossed away of the solar system Feb 11 '19 at 21:45