Who wants to go to Mars?

Not me. As the noted astronomer Paolo Maffei once said, the quickest way to get anywhere, no matter how far away, is with our imagination, because with it we're not limited to the speed of radio waves or the speed of light. We're there immediately, and I've been to Mars in my imagination quite a few times.

If we could go back in time three or four billion years in our solar system, I think we'd find that it was quite different than now, and not just because it was a lot younger. Assuming a solar system follows the same laws of physics as do our atoms, then back in the earlier days of our solar system, before it was hit by foreign bodies from outer space, it's quite possible that both our Earth and Mars were somewhat closer to the sun. That might explain why our planet was either semi-tropical or tropical almost all over, and it probably also meant that Mars was well within the ecosphere around the sun, instead of being on the outer fringe of it these days.

Back then, Mars hadn't yet been hit by a large meteoroid which struck it near the equator and punctured its crust. Books I've read don't describe such an event in detail, but we can imagine that if a body hundreds of kilometers in diameter at the temperature of deep space, and probably covered with ice hit and punctured the crust, entering the molten magma beneath, then there would be one horrendously large explosion. Perhaps that explosion was sufficient to
cause a temporary inflation of the planet from within, like the sudden inflation of a balloon. That might break up and throw off the shell of hard surface features and oceans, following which, the suddenly exposed core would reform into its
global shape, and quickly cool to form a new surface, now litttered with the debris and broken rocks and gravel which would settle back from within the gravitational field around it.

Where would the rest of it go? Rocks and water having different specific gravities, and the water bodies being quickly frozen into ice crystals or snowflakes, the two would likely go in different directions. For example, if we look at the asteroid belt further out, it is mostly composed of broken rocks, gravel and sand, and contains about the same mass as that of the skin of a
small planet. And those comets that periodically fly by? Those have been called 'dirty snowballs' and one or two have shown traces of sodium in their tails as they passed by, suggesting a possible origin as sea water.

And that body from outer space would have added both mass and energy to our system, and thus perhaps caused a shift outward in the orbits of others. So we are no longer tropical or subtropical all over, (no more dinosaurs!) and poor Mars got bumped into the fringe of the ecosphere where it is mostly frozen, and now without its original land masses and ocean.

Why would I think something like this? Because there's a reason for everything if only we can find it, and this scenario just might explain why Mars is now just a rusting iron-rich planetary core instead of a complete planet, and why it doesn't have atmosphere, oceans and continents like our planet does. Truth is stranger than fiction, they say, and who knows? Maybe the evidence of past life we're after there is now among the rocks of the asteroid belt, or in the comets.
Maybe we're looking in the wrong places. 

Please Note:

Another interesting point about all this is that the Larousse Guide to Astronomy says that the calculated mean density of Mars is 3.9 grams per cubic centimeter, which is considerably lower than the other three terrestrial planets but similar to the Moon's. This raises the question of whether our Moon was once part of Mars, and possibly material ejected from Mars during that impact with the meteoroid which punctured its crust.