They don't have to be extraterrestrial -- that's more the author's poetic language than any hard science-oriented speculation -- but he hopes we remain open to the possibility that we may find them someday, and they may be closer than we’d think.
The rockets are coming
Among other things, Bradbury's Martians are his hope for the future, and what happens to them is telling.
Once members of a thriving civilization, in many ways further advanced than our own, the Martians are destroyed when humans come.
We don't destroy them by force, exactly -- the official cause of death is "disease," but we kill them more fundamentally by sheer dominance of will.
Even before the first rocket lands, the passive Martians have not only felt the coming threat, but have fallen under the spell of Earth dreams and expectations.
At first, this empathic pliability actually aids the Martians in their defense of the planet, and they ambush our explorers with dreams and ghosts. But the rockets keep coming -- with increasing numbers of Terrans inside -- despite the clear danger Mars poses.
Interplanetary destiny made manifest
This seemingly foolhardy determination -- the "indomitable human spirit" -- eventually pays off in unintentional genocide.
By the time we send a fourth expedition to the Red Planet, we find almost all of the Martians recently destroyed by a simple earthly disease, presumably carried there by one of our previous rockets.
The carnage was inadvertent, but inevitable; humans will dominate, and therefore did.
Bradbury’s people are postwar Americans, sure of their ascendant place in the world, and by extension, the universe.
Are Martians dreamt or born?
Bradbury suggests that we humans shape reality to suit our own expectations.
We Terrans never had a chance of fruitful interaction with Martians because our own will distorts the Martian reality, making ours dominant. The Martians are pushed into the wilderness, left to appear, when they appear at all, as shimmering mirages, or in the guise of humans.
Of course, this failure of the imagination makes life simpler. Humans need not evince interest in the people they have shoved aside, though they see evidence of the Martians' displaced civilization all around them.
Nor does it occur to the human settlers to care about Martians’ well-being, or fear that the natives might try to take their land back.
Instead, the Terrans throw themselves into adapting Mars for their own purposes.
And naturally, Mars is easily molded.
The return of the oppressed
But despite humanity’s effective victory, the Martians aren’t done with us yet. Even in retreat, they flicker on the edges of outlying settlements and open minds, subtly influencing Terran lives simply by their continued existence.
The stories of this long twilight of the Martian people are various and strange.
One man finds himself talking with a Martian on a deserted highway, but neither human nor Martian appears solid to the other. Each one believes that the other is a shadow of the past and that his own reality is the true one. While the practical Terran blames the whole experience on too much whiskey, the reader isn’t so sure.
Other Martians appear to humans as shadows of lost loved ones -- as regrets for what might have been, or as longing for the past. The overwhelming need of human minds destroys one Martian who would rather become human than wander lonely in a Mars that no longer exists.
Significantly, every human wants the Martian to "be" someone else. Unable to control his own malleable identity, the Martian is destroyed by the conflicting expectations of humanity.
They let us make them different from us
Why don’t the surviving Martians fight the destruction of their world? Why don't they even protest?
Ravaged by disease, cut off from their technology and their land, perhaps they simply no longer have the resources to fight.
And perhaps it's something else.
Hathaway, a member of Bradbury's fourth expedition, takes it upon himself to the virtues of their culture, as evidenced by the artifacts left behind, sums up the difference between the Martian and Terran mindsets.
"We Earthmen have a talent for ruining big, beautiful things," he complains to his captain.
The Martians, on the other hand, "probably don’t mind us being here any more than they mind children playing on the lawn, knowing and understanding children for what they are."
And anyway, Hathaway hopes, "perhaps this will all change us for the better."
Lessons of a Red Planet
Did this change take place?
Not within the settlers. As more people arrive from Earth, the alien frontier increasingly resembles the mother planet, both physically and socially.
Mars never gets under the skin its new inhabitants; we never become the Martians. When war breaks out on Earth, nearly all the settlers evacuate the colony, even though it means suffering and destruction.
Their hearts are back "home" on Terra. And sadly, the last remaining Martians don’t stage a comeback after we are gone -- the effects of our presence linger.
Another chance to say hello
However, after the Red Planet sits silent for many years, a small group of humans escape war-torn Earth. Hoping to cut themselves off from Earth society and create new lives, they call themselves Martians.
Hathaway’s hopes for Mars proved too optimistic for the early pioneers, but bear fruit in these sadder, wiser Terrans -- no longer colonists, but true immigrants.
While the aboriginal Martians are now long gone, these newcomers are willing to take Mars as they find it and respect what the planet can teach them.
And of course Bradbury, as science fiction's master eulogist and moralist, hopes the same is true of us, his readers -- that we will finally hear the Martians when they whisper in our ears.
Although the component stories in The Martian Chronicles are older, the book itself turns 50 years old this year.