NASA’s Sofia Discovers Water on Sunlit Surface of Moon | Hacker News Reader

NASA’s Sofia Discovers Water on Sunlit Surface of Moon

nasa.gov

216 pointsTangerineDream32 comments

It blows my mind a little bit that spectrosocopy is a thing that just happens to be afforded us by physics, and how much less we'd know about the universe if it didn't exist. "Oh, every element has a totally unique signature and all you need to do is look at it to tell what it is, no matter how many miles or light-years away." It's the kind of thing where if it only existed in a sci-fi novel, it would be considered a far-too-convenient plot point.

https://en.wikipedia.org/wiki/Emission_spectrum

It's actually not all that surprising if you approach it from a different angle.

Consider that light is nothing more than electromagnetic radiation; it is generated or absorbed only by changes in electromagnetic potential.

Now also consider that electron orbitals in molecules are discrete and quantized: you can be in this orbital (with such-and-such potential energy) or in that orbital (with a slightly different potential energy) but you cannot exist between those two orbitals.

Therefore, light can only be absorbed or emitted by a molecule if it can precisely force an electron into a different orbital, which in classical terms means that it only works if light has a particular frequency.

As you might imagine, sticking protons (which generate electron fields) at different positions within a molecule, or equivalently adding protons to an atomic nucleus, will change the permissible orbitals very slightly. Consequently, the light that an atom or molecule can emit or absorb will change as well.

How are they able to see the signature water gives off through all the noise that other types of molecules must be sending back? Isn't there even more noise to deal with when doing this over even bigger distances?

To answer your second question first:

Stuff being in the way will of course diminish the signal (by direct absorption or by scattering it). But space is pretty empty. The regular air on Earth contains ~10^19 particles per cm³, and it can take several km of air to start seriously interfering with light. A dense portion of space contains something like 10^4 particles per cm³, and a less dense region maybe 10^-4 particles per cm³. So, once you leave the atmosphere, the noise that's destroying the signal is simply far, far, far weaker than the signal.

Now for your first question. As I mentioned in my first comment, the spectral lines arise from different orbitals. What this means is that there isn't a single line associated with a molecule, but actually several lines. So if you think you see a line from one molecule, you should be able to find the other associated lines, and the more of the lines you can find, the stronger the evidence.

As a couple of people have noted, this isn't a perfect process, so you can get into arguments if your identification is actually correct or not.

Yes, we are really good at denoising. There can sometimes be a couple of possible different "solutions" to the spectroscopy curve, ie. different combination of elements that would lead to the same curve.

It is an extension of our eyesight. We see objects as being a specific color because they selectively absorb or reflect particular wavelengths of light. Our tri-color vision system can seem some large band gaps and our brain calls that a color. Spectroscopy just sees smaller gaps, smaller absorption lines.

But all kinds of complicated material-properties can affect the color our eyes see (to my understanding). That alone wouldn't be useful in this way. It's the fact that these signatures exist at an elemental level, and are consistent across all contexts, and can be teased apart at a cosmic scale that makes the technique so powerful.

Spectroscopy isn't simple. There are huge grey areas. Very well-defined signatures often overlap into a blurry mess of lines. Even within a single element, say hydrogen, there can be different signatures for different ionization states. Rather than clean detections there is often much opinion and debate, for years, before spectroscopy evidence is agreed as a legitimate detection of a substance.

What blows my mind is that travelers from across the galaxy can enter eyes here at Earth's surface to be seen as stars in the night sky.

What blows my mind is how little spectroscopy fingerprint data is available in the public domain!

To wit, considering how ubiquitous camera sensors are, you'd think that we'd have the ability to do spectrosocopic analysis on our smart phones with a simple/cheap adapter by now.

Well you're constantly getting free signals. They just happen to be signals with only three very wide band filters. But you can still identify some materials with them. Like cat fur. :)

Hmmm,

I am fairly certain that this does exist, I remember almost purchasing a spectroscopy adapter for my iPhone way back around 2014. I didn't buy it and I guess it wasn't too popular.

Super cool!

Other upcoming missions that are going to be looking for water on the moon:

- Lunar IceCube, a 6U CubeSat designed to prospect for lunar water will launch on EM-1, the first Artemis mission. The 14 kg CubeSat will search for water in ice, liquid, and vapor (in the Moon’s very tenuous atmosphere) forms and includes an Iodine-based electric propulsion thruster

- Lunar Flashlight CubeSat, another of EM-1’s 13 secondary payloads, will search for ice in permanently shadowed lunar crater regions using an onboard laser.

We discussed these missions in Orbital Index a few weeks ago: http://orbitalindex.com/archive/2020-09-30-Issue-84/#lunar-i...

Wrong. Better: "NASA/DLRs Sofia Discovers Water on Sunlit Surface of Moon"

Telescope and some of the instruments are powered by German engineering! https://en.wikipedia.org/wiki/Stratospheric_Observatory_for_...

Greetings from Germany ;-)

Ist es nicht der Fall, dass fast alle moderne sachen irgend einen ursprung in Deutsche technik haben?

>We had indications that H2O – the familiar water we know – might be present on the sunlit side of the Moon

Doesn't every part of the Moon get some sunlight over the lunar cycle?

Some parts of some craters are in permanent shadow.

This is true, but the phrasing "might be present on the sunlit side of the Moon" is problematic and reinforces the belief (also reinforced by the phrase "dark side") that the Moon has a light and dark side. (At least in the case of 'dark side' an argument could be made that it means 'dark to (historical) human knowledge.' It's hard to defend "sunlit side.")

Tidal forces from Earth have slowed the Moon's rotation to the point where the same side is always facing the Earth—a phenomenon called tidal locking.

https://en.wikipedia.org/wiki/Far_side_of_the_Moon

But every side faces the sun at some point. The first paragraph of that article even says so.

Context: NASA keen to show SOFIA's worth https://www.nature.com/articles/d41586-020-00685-2

> SOFIA’s publication rate is now starting to creep up, and last year it was 33 papers. The ultimate goal is 75 to 100 papers per year, says James Jackson, associate director for research at the Universities Space Research Association, the Maryland-based group that manages SOFIA. “More than 150 was a stretch goal,” he says.

I don't think a number is the right target here. Discoveries or theories might be a better goal, not just the number of papers published

> The coronavirus pandemic is likely to keep it grounded for some time and threatens a planned deployment to New Zealand later this year.

How long can this modified 747SP fly? I wonder how they were going to fly it to New Zealand and if there were any refuel stops. Would be a nice treat to catch that at your local airport.

Maybe I'm airing some bit of dirty astro laundry here, but on my last looking at SOFIA (a decade ago?), it was not a very cost-efficient or preferred option compared to just sending a NASA SMEX (satellite) mission up with similar instruments? Is that still the case?

I.e. for the amount you spend flying the plane around, and the increase in collecting area needed compared to going all the way to space (much smaller mirror if you just go to space), we could've gotten more by sending a 30cm satellite into orbit.

Is that right? Or am I out of date?

If comets are icy things, and are constantly crashing into the Earth and the Moon, why shouldn't we expect water on the moon?

Because the Moon doesn't have an atmosphere, so any water that gets slightly hot vaporizes and goes away into space.

So, at least near the surface and on areas where the Sun light reaches, it's not obvious at all that we would find any water.

Shouldn't the moon's gravity keep it there?

I think it's not so much the presence as it is the amount. Given the moon's lack of atmosphere, low gravity, and exposure to solar wind, you might expect the water to quickly boil off into space. But apparently it sticks around for quite a while.

> concentrations of 100 to 412 parts per million – roughly equivalent to a 12-ounce bottle of water – trapped in a cubic meter of soil spread across the lunar surface

This is incredible. Is there speculation that there could be a resevoir of ice underneath the soil? As in, could they dig a well and attempt to melt it (somehow) for collection?

Pure ice would require a 2,500 times increase in water proportions. That’s a big increase.

It does seem reasonable that sub soil not heated to 260 degrees every two weeks for two weeks at a time would contain a lot more water. But when Lunar Prospector was crashed into Crater Shoemaker, the plume was mostly soil never exposed to sunlight and water density was minuscule.

12 fluid ounce: ~355ml (excerpt likely meant fluid ounce). 12 ounce: ~340g

Does this mean that there could be life on the moon?

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