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I am interested in long-term data preservation on the Moon in style of Lunar Mission One. To attract the attention of the next civilization on Earth to the message, I think that a beacon similar to Nasca Lines should be drawn on the surface. What will be the most cost-effective way to do so? I already have the following ideas:

• Using craters as dots • Electrically powered tractor could slowly “print” a message by boring dots or channels on surface, • A robot could collect stones and put them into lines or pyramids, • Drawing by creating tracks in lunar dust. • The beacon could be also created by a gradient of a rare and clearly artificial element (but not radioactive) • Aluminum foil could be rolled into image, • Aluminum powder could be spayed by a lander around its location in some geometric form
• Very stable and visibly dye. Which one?

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  • $\begingroup$ This question could fit on WorldBuilding, as it is speculative, but it is possible to give a factual answer (though there are a number of possibilities). $\endgroup$
    – kim holder
    Dec 14 '17 at 17:43
  • $\begingroup$ You can not predict when and where a large meteorit will hit the Moon. Even smaller metorits will destroy and hide the picture partialy. Moon dust may hide the picture too. But a picture visible and recognizable with the naked eye should be extreamly large, 1/20 of the Moon diameter will be about 700 km. The largest Nazca figures are about 370 m, that is 1/2000 smaller. $\endgroup$
    – Uwe
    Dec 14 '17 at 18:00
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According to Is the moon only 60 pixels? on Astronomy.SE, it would appear that to the unaided eye you can't see much more than would fit in 40 to 60 pixels (height & width).

According to Wikipedia, the Moon has a diameter of 3,476 km. Therefore, each "pixel" would have to be dot nearly 58 km in diameter for you to see it from Earth without a telescope. (3,476 / 60 = 57.8 km)

Even a small image will have to be hundreds of kilometers on a side. For example, a simple image consisting of 2 lines, each 10 dots long would require almost 72,000 km2.

If you're going to mechanically alter the face of the Moon you'll need a lot of really big robots and a lot of paint.

It would be a lot cheaper to bury a time capsule and plant either a radioactive marker above it1 or a nuclear powered radio transmitting "I am here" in Morse code. Neither would be visible from Earth but any civilization with the technology to actually visit the Moon would certainly notice the marker.

1 Yes, you explicitly excluded radioactive markers, but they're probably the best option available

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  • $\begingroup$ Surely I expect that it will be visible in a telescope, and maybe even from a lunar satellite, not by a naked eye. In first case dots size should be at least 300 meters, and in the second 30 meters may be enough. $\endgroup$ Dec 14 '17 at 21:09
  • $\begingroup$ We don't have the technology to build a nuclear powered radio transmitting "I am here" in Morse code that will still work in a 100 million years. Nobody is able to proof that his design will work so long. $\endgroup$
    – Uwe
    Dec 14 '17 at 22:10
  • $\begingroup$ @Uwe You're right - I was thinking "a long time", but not "100 million years". $\endgroup$ Dec 14 '17 at 22:20

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