Via the NASA site, comes this announcement that the Opportunity rover has happened across yet another large nickel-iron meteorite on the plains of Terra Meridiani. Study of an earlier such find has yielded some really fascinating insights into the Martian environment into which it careened, apparently a very long time ago:
Opportunity found a smaller iron-nickel meteorite, called "Heat Shield Rock," in late 2004. At about a half ton or more, Block Island is roughly 10 times as massive as Heat Shield Rock and several times too big to have landed intact without more braking than today's Martian atmosphere could provide.First of all, let me just say that I looked at these images of this pitted rock, sitting on the sands of Mars, and paused a moment to say, yet again: "Good gods! That's the surface of freakin' MARS!!"
"Consideration of existing model results indicates a meteorite this size requires a thicker atmosphere," said rover team member Matt Golombek of NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Either Mars has hidden reserves of carbon-dioxide ice that can supply large amounts of carbon-dioxide gas into the atmosphere during warm periods of more recent climate cycles, or Block Island fell billions of years ago."
In my office, I have a couple of framed images from Opportunity and Spirit. Every now and then, a client asks me if I took them. And I have to chuckle, for the obvious reasons, and also because the pictures look so lovely, but so commonplace. "Planet" is such an abstract concept. Tickles the intellect, but leaves the glands largely untouched. Now, it's those moments when the reality of a "World" jumps out of these pictures that I just get grabbed but hard. Never gets old.
Anyway, back to the meteorites: I was struck by the above-quoted passage. The very existence of these large, space-borne rocks on the surface speaks to a time when there was enough of an atmosphere to slow them down to the point that they would not get pulverized by the impact. That. plus the numerous finds of near-surface water ice (including some pretty spectacular recent ones) lend further support to models for an earlier Mars which possessed a much thicker atmosphere and probably a very significant amount of surface water. Much of that atmosphere is locked up as dry ice at the poles, a whole lot more adsorbed into the regolith and rocks. Much of the water, it seems, is sitting close to the surface in permafrost (though the possibility of subterranean liquid aquifers can't be ruled out).
First of all, this makes it even more probable that the conditions for the emergence of life were present on Mars for periods of time which compare most favorably with the interval on early Earth in which abiogenesis is theorized to have occurred. Mars, it seems, had what it takes to get itself populated.
Second, it makes it clear that a little bit of site selection research could drop a crewed mission on a patch of Martian land which could provide a rich source of water, and so save a whole lot of mission mass which would have been devoted to consumables. That means a lot more payload, even if you factor in the additional gear for extraction (long-distance pressurized rover, anyone?).
I actually hope that substantial fossilized but no extant life is found. Changes the whole ethical calculus of colonization-focused missions if there's something alive down there. It gets harder to argue for terraforming when it might obliterate an extra-terrestrial biosphere (imagine the emails from Robert Redford!). It would probably be a show-stopper for intrusive habitation (and I can't say that's a bad thing, mind you, but it would be almost as much of a bummer as a boon). The science would be outrageous, but the promise of a Martian branch of human civilization would be a bust for a very long time...if not forever.
This is not to say that coexistence with Martian life might not be possible. After all, it probably thrived under conditions on Mars which would also be favorable to us (thicker atmo, more water). Indeed, the arrival of Humanity on Mars could be the best thing that's ever happened to the natives.
And wouldn't that be an interesting Bizarro version of colonizations past!