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This is a very dumb question but I am really curious to know the answer. Today I was watching the live streaming of Chandrayan 3 landing on the moon (which it successfully did) and this question came in my mind.

Making a probe land on other celestial planets is extremely difficult but why do we need to make them land if we can extract the data about the constituents of the surface from the measurements of the satellites orbitting the moon ?

What kind of data can't be taken from up above using satellites and can only be obtained by collecting the materials from the surface ?

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    $\begingroup$ Imagine a scientist studying the surface of Earth by only using satellite images but none taken directly from the surface. $\endgroup$
    – Uwe
    Aug 23 at 14:52
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    $\begingroup$ It's easier to land on the surface of Venus then it would be to hover for the ~80 minutes that it's going to survive in its atmosphere, the penetration of which is a requirement to retrieve any "meaningful data". Why was Venus rather than Mars targeted for the first interplanetary landings? $\endgroup$
    – Mazura
    Aug 25 at 19:32
  • $\begingroup$ What makes you think 'we can extract the data about the constituents of the surface from the measurements of satellites orbiting the Moon?' Where is it written that data from satellites can meet all our need? By the way, I suggest landing probes on other celestial bodies is not extremely difficult; just expensive and even then, India seems top have found a way to cut zeroes off the old US NASA costs. $\endgroup$
    – Robbie Goodwin
    Aug 26 at 16:47

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You can always learn more by a closer inspection. You may read articles about materials being detected by spectrometry from orbit, but don't let that give you the impression that humans have the technology to do a full chemical analysis of an arbitrary substance from 200 km away. Here is just a partial list of things you can do on the surface that you can't do from space:

  • Take close-up images (a big one!)
  • Do chemical analyses that require physical processing
  • Physically measure hardness
  • Measure sound or seismic waves through the ground
  • Drill down to get deeper samples

And the list goes on.

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    $\begingroup$ Besides going even a few cm down already can give different results (i.e. not even drilling needed), I would add to the list to be able to make a chemical analysis of a smaller sample. From orbit you always get a spectrum etc. from a relatively large area $\endgroup$
    – PlasmaHH
    Aug 24 at 9:49
  • $\begingroup$ "analysis of an arbitrary substance from 200 km away" Maybe that's why the Chandrayaan-2 orbiter got as close as 100 km :-) $\endgroup$
    – Mast
    Aug 24 at 14:23
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    $\begingroup$ @PlasmaHH: Indeed, helium was discovered on the Sun before it was discovered on Earth. $\endgroup$
    – supercat
    Aug 25 at 15:58
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  1. Politicians that assign funding to space projects like big achievements that appear in the news. They bring votes, development and investments (development and investments also bring votes in the long term).

Space is good in this regard - it is very safe from moral/ethic risks and people all over the world know that landing on a celestial body is a very big deal.

One can, of course, fund education, infrastructure, military power and so on - and get political dividends as well, but few things are less controversial than the space exploration.

  1. There is an actual scientific (and in the long term, practical) interest in landing on Moon or Mars.

One can do a wide diversity of "active" experiments - i.e. doing something to the object of interest and observing the result in contrast to just observing the natural flow of events from far away.

The data obtained from the active experiments are more aligned with whatever we would like to know (this is how exploration works down here as well).

Even some purely observational scientific activities are at all possible only in place - e.g. seismic or atmospheric (even Moon has some atmosphere) measurements.

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  • $\begingroup$ +1 to this. The practical (scientific) aspect of moon travel is negligible and largely pointless. The political aspect, by comparison, is huge and it creates a big PR win for the people involved. Plus every penny spent on the lander is a job created. $\endgroup$
    – Richard
    Aug 25 at 5:59
  • $\begingroup$ You may also want to mention that moon science is propulsion science. Which is rocketry, which is an offshoot of missile technology. Going to the moon means you have the ability to land a nuke anywhere on the Earth with extreme precision $\endgroup$
    – Richard
    Aug 25 at 6:01
  • $\begingroup$ @Richard There are different meanings of pointless. On the other hand, should the government have a penny, it will create a job no matter how it is spent. $\endgroup$
    – fraxinus
    Aug 25 at 6:56
  • $\begingroup$ That's exactly my point. Space science is basically useless. What isn't useless is spending money on science, period. The fact that it's in space is meaningless as long as it gets spent somewhere $\endgroup$
    – Richard
    Aug 25 at 7:03
  • $\begingroup$ Space research useless is not. It pays off later, just like any science. My point was that the space research funding and promotion are based not on the expected profit, but on other factors. $\endgroup$
    – fraxinus
    Aug 26 at 15:01
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You could vaporize rocks and look at what kind of light it shines. This might be possible some day from further than a few centimeters but not yet.

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