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The year: Sometime a long time from now

The place: Mars

Little Bobby Colonist is going to play out in sand dunes beyond the edge of the domed city where he lives. Terraforming efforts over the last century have made the Martian atmosphere livable, but the air is still pretty thin and it gets deathly cold at night. But Little Bobby can hang out in the dunes as long as he's back by nightfall.

Today though as he's traipsing about kicking rocks, one hits something hard and metallic. Leaning down to look at it, he sees some sort of ancient wheeled device perhaps three feet long. It has some sort of scratched up reflective paneling and six wheels- well, five wheels, but a spot where a sixth would've clearly gone. Inscribed on the side in a very old dialect he can't read is the word Opportunity.

Though he doesn't know it, Little Bobby has just discovered the remains of a long-forgotten mars rover, launched from the Earth-that-was in the 21st century. And, because it's that kind of story, his entire world is about to turn upside down.

Questions:

  • What year could this be? How long would a modern-day mars rover remain identifiable as such to some future-martian colonist? Might pumping large amounts of oxygen into the atmosphere and raising the temperature change this?
  • Little Bobby doesn't recognize the rover and there certainly isn't a memorial or museum of any kind at the site. Is it realistic to say that humanity has established a permanent colony, started terraforming, and forgotten about it's past exploration efforts in this amount of time?
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  • $\begingroup$ I think this question could be 2 questions. 1- how likely is it that today's Martians would be able to find archival information about the early rovers? 2- what condition will the rover be in given that humanity has been actively terraforming $\endgroup$ – Adam Coville Aug 25 '19 at 0:24
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As Mars stands now, probably centuries. Maybe millennia, or even indefinitely. Mars lacks most of the weathering mechanisms Earth has: there's no oxygen so nothing oxides (rusts), there's no water, and while dust storms are fast and kick up a lot of tiny particles, the low atmospheric pressure means that there's simply not a lot of force behind those winds. (It's said on Earth that it's not that the air is moving, it's what the air is moving. On Mars, "what" doesn't amount to much.) Meteorites on the Martian surface can persist for millions of years and still be recognizable.

So, assuming that you're after the bulk structure of a rover and not its electronics (the plutonium core of Curiosity's RTG will be long dead, let alone previous rovers' solar panels), it can last quite a long time indeed. By the time they've landed, the rovers have faced the biggest mechanical stresses they're ever likely to. Maybe the biggest threat is that, over the course of millennia, they end up on the downwind side of a rock and become buried in dust.

But, your Mars is terraformed. What effect will that have?

Surprisingly, for all the intricate detail about what goes into Mars landers, the basic construction of the chassis doesn't come up much. However, it seems reasonable to assume that none of materials that would be on the short list to send to Mars are all that volatile. Plastics don't do very well in low-pressure environments, and there's no reason to send nice oxidizable iron and steel when there's plenty of aerospace-grade aluminum and titanium to go around.

Assuming the rover body is rustproof, it shouldn't be unduly affected by oxygen in the atmosphere, or by increased pressure. (Rovers undergo engineering tests on Earth, so they can handle Earthlike pressure, and gravity for that matter.) If it can avoid being physically weathered (read: hit by a rock) it should be good for a prolonged period, possibly into the centuries.

Incidentally, I would use Curiosity rather than Spirit or Opportunity, partially because it's about five times the size, but mostly because it has a signed plaque and, according to this article, was also signed by the student who named it. Whether these would survive the elements is less certain. (If they were laser-engraved, the signatures should last a fair amount of time if not worn down by dust.) However, I think it's neat to think about.

(Little Bobby should not tamper with the aforementioned RTG. As long as it's in its housing, he's safe, but if he opens it up he may end up inhaling plutonium dust which is, I should stress, not good for you.)

As for whether it would be well-known, probably in general terms but maybe not by sight. At least in my experience with public school history, "how we got here" is a major topic, and rovers as a whole probably played a vital part in establishing a Mars colony. Individual rovers, however, might be less important - especially since we don't know what missions may be launched in the future. There were a number of lunar rovers that were important and impressive in their time but have already been overshadowed by the dramatic accomplishments of our current crop of Mars rovers; the future might hold more of the same that would obscure this particular wreck's place in history - at least for awhile.

As an example: you probably remember, as I do, that Columbus's flagship was the Santa Maria. You might remember that it was a design the English call a "carrack", larger than his other exploration ships. But could you pick it out in a lineup of sailing vessels?

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Hundreds of (Earth) years at least

Reasonable quality solar cells on earth are likely to still be able to produce some electricity after one hundred years. NASA would not skimp on a critical component which is comparatively cheap, so I suggest that Opportunity's solar cells are very likely to be still functional in a hundred years if the dust were cleaned off, definitely still intact. This puts a lower limit of a hundred years on the "recognisable" aspect.

Even with terraforming increasing the water content of the atmosphere, a 180 kg robot designed to survive dust storms is not going to corrode away to nothing in the immediate future. However, the question posits that it must have a legible inscription remaining identifying it as Opportunity. If it remains exposed with dust scouring its surfaces, even the most durable surfaces are likely to be abraded into illegibility after a few hundred years. Alternatively, it may have been buried by dust around the time NASA lost contact with it and only been uncovered a day or so before Little Bobby Colonist kicks a rock at it. In this scenario it could have survived for thousands of years almost undamaged, as have objects on Earth buried under ideal conditions.

However, the answer to the second part of the question makes neither scenario plausible. The first colonists on Mars will be busy building lives there to allow the colony to survive, but within 50-100 years of colonisation, long before terraforming has got well underway, someone will have sought out Opportunity, Pathfinder etc in order to build memorials. Given ground-penetrating radar and the detailed knowledge of their last position, they will find them. It may even be a high priority within a few years of arrival, as Opportunity offers a prime opportunity (pun semi-intended) to examine how well these man made objects have lasted under Martian conditions.

As for future Martians "forgetting" the history of space exploration that allowed colonisation to occur - that would take intentional erasure of history by an omnipotent dictatorship. It is not going to occur "naturally" given the level of documentation of the current era.

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It can last some millenia. The eletronics will be long gone, the plastics will be brittle and the plutonium core won't work (but it can still kill you, plutoniun hates you). The solar panels will be broken and it's pieces will be somewhere nearby. The things that can destroy the rovers are stones moving around, dragged by water as the water cycle reactivates. Mud and being buried won't destroy it, it's made of aluminium, made to survive the chemically active martian soil and the dead martian geology won't crush the sedimentary deposit and turn it into some kind of arenite with a funny metallic aluminiun laced with plutoniun.

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