I'd like to advance a theory on the likelihood that our planet's Habitable Zone was once upon a time during the earlier stages of our Solar System's formation actually much larger than it is today; which is to say, its distance from our Sun's location was greater than it is today, therefore it may have applied to the area in which Mars or the asteroid belt now resides.
50 million years ago, when it is theorized a Mars-sized planetoid may have collided with the Earth to form our moon, was the heat coming from the Sun's region then greater than it is today?
In the past, astronomers wondered at the much larger gap between Mars and Jupiter, theorizing there may have been a planet there, once. (Astronomer Heinrich Wilhelm Matthäus Olbers dubbed this hypothetical planet "Phaeton".) It's not hard to imagine a planet formerly between Mars and Jupiter having been slammed into by a giant asteroid, nor is it it hard to imagine, perhaps, many such-sized planets having existed in this region, perhaps all of which were destroyed from chaotic collisions. Whatever occurred during these formative stages of our solar system, the results are plain to observe today with telescopes: the asteroid belt remains, trapped in orbit about our Sun. Ceres appears to be the largest remaining chunk of whatever destructive collisions occurred way back then. Perhaps certain chunks went ricocheting out towards Mars - two of which became captured by it's gravity, and are today known as Phobos and Deimos.
But what about our Goldilocks Zone? It's not hard to imagine that perhaps, back then--the heat from our developing Sun may have reached farther out. For all we know, the Goldilocks Habitable Zone extended as far as where that missing fifth planet may have been located (referred to as either Phaeton and/or also Theia, today).
In my raw theorizing, I have developed this idea that perhaps homo sapiens sapiens are descended from the Phaetons or the Theians, presuming either of these hypothetical planetoids were occupied by an advanced civilization. Maybe they even surpassed our own level of technology, and figured out that their own Habitable Zone was shrinking, and would eventually encompass Mars. Perhaps they devised a rudimentary form of space travel--a solar ark, so to speak--sufficient enough to carry a core group of them across safely to Mars.
Perhaps they did this to escape the asteroid they observed headed straight towards them. Whatever the case may be, it's interesting to speculate on the possibilities surrounding the notion that the Habitable Zone may have once had a greater circumference.
Perhaps Mars once held life, as has been pointed out many times before by scientists speculating. Maybe the Goldilocks Zone shrank, from having accommodated Phaeton or Theia, to having accommodated Mars, for a new period lasting millennia. And maybe (just maybe), this Shrinking Zone continued to get smaller...until it finally reached the Earth.
Maybe our ancestors were prepared for this, and successfully transferred themselves, once again, by planet hopping from Mars to Earth . . . just in time to benefit from the next, smaller Habitable Zone--which we find ourselves in today.
It makes sense if, indeed, the heat being generated from our Sun was greater, back then. It would explain a lot about the water currently being observed on Ceres. It would help corroborate the new theory that perhaps life on Earth was seeded from Theia or Phaeton. It's not entirely out of the realm of possibility that this "seeding" may have something to do with the impact which rendered the asteroid belt and possibly our Moon.
The thing to keep in mind, is we must never underestimate the outlandish magnificence or grandeur of nature. We tend to think of it as being mechanistic, that is, accidental collisions resulting in life. But what if some of what occurred was orchestrated by advanced beings: our forefathers? It's easy to scoff at such notions, today. Yet beware of scoffing away the proverbial baby with our tossed-out bathwater. It's what keeping an open mind is all about.
So, what if our Moon was placed here by design? Maybe architects placed the Moon as a sort of "plumb bob" to intentionally rectify its axis to 23 degrees, just so, in order to fine-tune this third planet from the Sun to accommodate life?
The mystery of the formation of our Solar System has been studied with closer scrutiny since the invention of the telescope and continues to this day with the advent of modern science. Today, scientists continue to make new and startling discoveries about the real nature of our solar system. We should all be paying more close attention. If we all think this through together, we might get somewhere.
We are drawing closer towards more clues that will help provide the answers we are seeking. Answers to the questions of our origin, and its true nature. We must continue to exercise our thinking muscles and remember to speculate wildly! For the actual answers may be far more shocking than we are currently prepared for.