Disclaimer : This article is not based on scientific data, models or predictions. It definitely has no ambition of predicting the actual future. It just follows the 'there is a world where' way of mind, a sci-fy approach.
The Earth looks like it's on a steady orbit around our beloved sun. It may have been so for the past few billion years, but are we certain this will continue?
First of all, it turns out that the earth is already having some trouble to stay on the track. You may have heard of the tidal interaction between two celestial bodies. The best example of this is the rise and fall of the see level, due to the Moon (and thus it's gravity force) rotating around the Earth. The exact same principle applies to each pairs of celestial bodies for which one orbits the other. The earth and sun are subject to this tidal effect. It creates a small energy dissipation, slowing down the speed of the earth. By slowing down, our planet is slowly but surely stepping away from the sun, at the terrifying rate of a micrometer/year
From what is written above it may seems like your grand children have no chance of witnessing the great crash between Mars and the Earth. But that's where the second part of my post comes into place. Is the earth evaporating ?
From what I found doing my researches, the earth's atmosphere is leaking for about 90 tons a year. This is actually not much compared to the actual mass of the Earth 6x10 ^21 tons. This leak seems partly caused by the solar wind, taking away our atmosphere.
I'm not able to provide an estimation of this effects consequence on the Earth orbit change. But what I know for sure, is that a decrease in the mass a body also decrease the gravity force that binds it to all other bodies around it. In this case, it means that when the Earth loose mass, the sun attracts it less. And guess what happens from that ? The Earth slides away from the sun. Again!
Even though this effect is probably even smaller than the first one on the orbit change of our planet, it is the concept of mass loss that is interesting. The solar wind may not stealing a lot of earth mass, but another phenomenon might : Human activity!
In only half a century, we have gone from sending dogs in Low Earth orbit, to bringing huge rovers on mars and sending spacecraft to the outer solar system and beyond. Most of what we send in space today is going to fall back into our atmosphere. But we have started to send object further into space, and these are not planning on returning anytime soon.
Every object we launch out there is a part of the earth that is taken away from it. It may not be much as of today, but with human natural need for expansion and exploration, we might see hundreds or thousands of these sent out everyday in a couple of centuries : for scientific discoveries, planet colonization, or even interstellar travel. The Earth could then see it's mass shrink at a higher rate. As we have previously established, this would also mean the quicker change in earth orbit, going away from the sun faster and faster.
On the bright side, the probability of us being able to remove enough mass from the Earth to reach the mars-ian orbit must be really low, and even lower must be the probability of the Earth being in collision course with the red planet.
But other, more minor consequences may arise from such changes, starting with the duration of a year being increased, or the planet temperature lowered.
I let you list the other consequences, good or bad, that you may see coming from such a change in the comment section below.
But anyway, I want to reassure the more afraid of you about this article : Your grand children should be just fine and not end up in a giant blowup of the Earth against Mars. Maybe I'm wrong though...