4

"Close" here is relative. If you look at this explanation: Average distance between two points on a sphere, along with this value from Wolfram Alpha, you will see that the expected distance along the surface between two random points on the surface of Mars is 5335 km.

But the trek between to two landing sites is 3200 km.

Was Mark Watney just lucky, or is there an explanation given for why the two landing sites are closer together than random chance?

  • 3
    Because not all points on Mars' surface are equally useful to NASA? – user1027 Oct 15 '15 at 21:24
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    It points out a flaw in your premise. NASA wouldn't pick the two landing locations randomly, ergo how that compares to the average distance between any two points is not a meaningful comparison. NASA isn't picking from any two points, they're picking from meaningful points for scientific exploration, with some other logic applied like them probably not putting two landers right next to each other, barring something odd like an astronaut being stranded and needing a ride. – user1027 Oct 15 '15 at 23:08
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    @Keen... and if they have a reason you can name, that's the answer to the question. What am I missing? You seem to want to point out a flaw in the premise. There isn't. The only premise is, these two points happen to be closer than random. That is true. The premise is not that NASA would have picked at random. The question is why. You started answering that in your comment, so instead of wrongly attacking a supposed premise, you should be posting an answer. – ThePopMachine Oct 16 '15 at 1:16
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    The difference being only 60% of its expected random value is well within the realm of plausible good luck and most definitely does not warrant the expression "so close". – Michael Borgwardt Oct 16 '15 at 10:22
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    @MichaelBorgwardt: I totally agree it is "within the realm of plausible good luck". The question is asking whether it actually is just luck, or there is a reason given. I still don't see why people are having a problem with this question. Does everyone need to prove a point and jump on the premise: 'it could just be luck' therefore the premise is broken? That is right there in the question from the start. – ThePopMachine Oct 16 '15 at 14:10
8

It's not so coincidental as it might seem. There are some things to keep in mind when going to Mars:

Mars is small: Mars has a circumference of about 21,344 km; no two points can be more than 10,672 km apart. The surface area is about 144 million km^2. As you stated, expected distance along the surface between two random points on the surface of Mars is 5335 km, but the locations of the two sites are NOT going to be random, and in fact they are relatively limited.

Mars is lopsided: For some reason, the majority of lower elevations (with the exceptions of Hellas and Agyre Planitias) are in the northern hemisphere of Mars, and the majority of higher elevations (with the exceptions of some of the volcanic regions) are in the southern hemisphere. There is precious little air on Mars, so the lower you go and denser the atmosphere, and the more air you can grab with your parachute, the safer your landing. Cross off the equivalent of one hemisphere to eliminate areas that are too high. You now have 72 million km^2.

Keep warm and sunny, and go someplace easy to leave: The temperature at the equator in summer generally doesn't go much below -100 F at night, while the poles can get down to -225 F, so cold that the carbon dioxide atmosphere freezes into dry ice. The farther from the equator you go more power it takes to keep warm. In addition, the easiest (and probably lightest) way to get power on Mars is by solar panels. You want to stay places that get lots of sunlight, especially given that Mars gets much less sunlight than earth. Cross off everything more than 30 or 35 degrees from the equator. (Also, you get a little extra boost in getting back to space the closer you are to the equator. It's like free fuel.)

At this point about 62% of the surface of Mars has been eliminated from consideration. You are left with about 55 million km^2, which is close to the equivalent of the combined areas of North America and Africa, in two fairly distinct regions. 'Africa' (Amazonis and Arcadia Planitia) and 'North America' (Chryse and Acidalia Planitia) are actually connected somewhere around 35 to 40 degrees north of the equator, and you might be able to drive from one to the other without getting 'too far north', but the main masses aren't really convenient to each other.

For some reason, 'North America' seems to have gotten a little bit more than its fair share of interesting spots. It's not too big a leap to imagine that two or possibly even three of the Ares missions have landed or will land there. The possible locations for the next Ares mission are either relatively close (generally within 4000 km), or relatively far away (Gale crater, for example, is about 8500 km driving distance).

What Watney did was drive the equivalent of driving from Moose Jaw, Saskatchewan to Fayetteville, NC, which few people would consder to be 'coincidentally close'. But while a car could make the trip in 30 hours according to Google (not accounting for traffic and pit stops), the rover traveled over land at a top speed of 25 km/hour (a little over 15 mph), no more than 4 hours a day, and every 5th day off to replenish his air. He traveled at most a little under 450 km per week (roughly 275 miles).

Very late answer, I know, but I'm replying as much to clarify a couple of things for myself by articulating them (so to speak), and putting them someplace I can reference back to.

11

The implication (from the novel) is that he just got lucky:

I’m lucky. Thirty-two hundred km isn’t that bad. It could have been up to 10,000 km away. And because I’m on the flattest part of Mars, the first 650 kilometers is nice, smooth terrain (Yay Acidalia Planitia!) but the rest of it is nasty, rugged, crater-pocked hell.

That being said, there may have been some operational benefit in having the two sites close to each;

  • The crew of the Ares 3 were tasked with remote-landing the MAV for the Ares 4 mission. Placing the two sites relatively close may have made this easier (due to improved radio reception or shared weather telemetry, perhaps?).
  • This: operational benefit in having the two sites close to each other given that the crew of the Ares 3 were tasked with remote-landing the MDV for the Ares 4 mission. – JRE Oct 16 '15 at 7:15
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    It was the Ares 4 MAV they had to remote-land, not the MDV. I thought Martinez remote-landed the Ares 4 MAV from orbit though, not after they landed at the Ares 3 site. – Scott Whitlock Oct 16 '15 at 16:17
  • @ScottWhitlock - remote-landing from Mars sure looks like pointless waste of mass and outright dangerous due to higher loss-of-control risk and double latency. – Deer Hunter Oct 16 '15 at 17:05
  • @ScottWhitlock - Good point. I've edited – Valorum Oct 16 '15 at 17:49
  • Maybe NASA monitoring the two sites is easier when they aren't so spaced-apart. – Möoz Jan 12 '16 at 21:37

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