
Earth’s Atmosphere Stretches Out to the Moon and Beyond - sohkamyung
http://www.esa.int/Our_Activities/Space_Science/Earth_s_atmosphere_stretches_out_to_the_Moon_and_beyond
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inamberclad
Sure, it's kinda there... It'll count for free radical oxidation of spacecraft
surfaces and cause minute amounts of drag at those altitudes, but it's worth
reminding people that this is in the range of dozens of atoms per cubic meter.
Water boils at body temperature at the Armstrong line, which is only 19.2 km
above sea level.

~~~
DoctorOetker
according to this article:

> The denser dayside region of hydrogen is still rather sparse, with just 70
> atoms per cubic centimeter at 60 000 kilometers above Earth’s surface, and
> about 0.2 atoms at the Moon’s distance.

At the distance of the moon: 200000 per cubic meter so I think it's a bit
higher than you think... of course you don't explicitly mention a height for
the spacecraft surfaces...

~~~
FakeComments
There’s around 10^25 atoms per cubic meter of air at sea level, so talking
about a 10^5 density, a 10^20 reduction in density, is pushing the definition
of “there”. (This also makes it closer to space, at 1 particle per cubic
meter, than Earth atmosphere, by a dozen orders of magnitude.)

For reference, lead in drinking water is actionable at a 10^8 factor, but
beyond that — say 10^12 — we largely talk about it not being there.

There’s basically no case we refer to something attenuated by twenty orders of
magnitude as qualitatively the same.

Edit:

For fun, I looked up what it meant as energy differences — twenty orders of
magnitude is the difference between you jumping and the total energy from the
sun that strikes the face of the Earth each day.

[https://en.m.wikipedia.org/wiki/Orders_of_magnitude_(energy)](https://en.m.wikipedia.org/wiki/Orders_of_magnitude_\(energy\))

~~~
EForEndeavour
Your comment is consistent with why the parent replied to the grandparent: 2e5
is orders of magnitude greater than "dozens." That's still closer to space
than to sea-level atmosphere, but it's not nearly as close as the grandparent
comment stated.

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FakeComments
A density of 10^5 is eight orders of magnitude beyond “ultra high vacuum”,
which is about 10^13 particles per cubic meter — or 10^-12 times normal.
Poster is more correct to say “dozens” (four orders of magnitude) than that
it’s not a vacuum (eight orders before the edge of ultra high).

[https://en.m.wikipedia.org/wiki/Vacuum](https://en.m.wikipedia.org/wiki/Vacuum)

Poster was completely correct that this accounts for only minuscule
interactions such as surface oxidation and teensy drag over prolonged
interactions, and nothing like the “atmosphere” behaves.

~~~
DoctorOetker
at what point exactly did I compare with sea level?

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haberman
I'm surprised this would need to be verified experimentally. Why couldn't a
density gradient like this be derived from fundamental laws?

~~~
macawfish
This is such a good question. Thinking about it reminds me of a quantum
mechanics prof who once explained the way a physicist would model a person
skiing through the forest. The person would be either a sphere or a box,
depending on what's most convenient. The trees in the forest would be
cylinders or boxes. The person skiing would then be something like a sphere
bouncing around through all these cylinders.

And then another time my statistical mechanics prof informed me that "physics
is just drawing cartoons of reality with math." That came as a huge
existential relief by the way.

Popular science holds that physics is the study of "fundamental laws", but
really it's just a special practice of articulating these very stable,
ubiquitous patterns.

When you look at things holistically, you will notice that they are often
irreducably dynamic, complex and full of potential surprises, along with fully
actualized surprises.

So I'd imagine that all these relationships of atmospheric gases with things
like the earth's magnetic field, weather patterns, chemical reactions in the
atmosphere, interactions with extraterrestrial particles, the dynamics of
other magnetic fields, etc. would all make this very difficult to model
accurately.

First principles apply very well to our nice toy models, but the sheer
vastness of existence usually out-scales our toy models very quickly.

~~~
bookmacpro
> Thinking about it reminds me of a quantum mechanics prof who once explained
> the way a physicist would model a person skiing through the forest. The
> person would be either a sphere or a box, depending on what's most
> convenient. The trees in the forest would be cylinders or boxes. The person
> skiing would then be something like a sphere bouncing around through all
> these cylinders.

This way of thinking is a bit flawed.

Convenience is an important aspect, but it's not the entire reason. A
physicist who wants to study how skiers might cause avalanches by
modeling/simulation doesn't care about the details of the people they model
because that's just not important. For what they want to study, it doesn't
matter if they model the human as a sphere or as a real-life model with limbs
and so on. It won't affect the grand picture.

On the other hands, a physicist who wants to study how an avalanche would
crush a person? Then yes, modeling the limbs and the person's physical
properties become much more important.

In modeling, you choose the model that best fits and represents what you aim
to study. You start off with a complex system of equations and then you slowly
go through and remove the parts that would be irrelevant. You don't need to
account for turbulence if you know that you will never reach the high Reynolds
numbers that require it. You don't need to model cellular biology if you're
just trying to modeling how a piece of tissue stretches.

~~~
macawfish
All great points.

But yeah it was a joke! And basically I remember his joke having a tangential
quip about choosing the shape based on the coordinate system you wanted to
stay in.

And the point I got from it was that in modeling we often use crass
approximations that are oversimplified in order to get a rough picture of
what's going on with respect to certain dynamics, and that one shouldn't
assume that the model resembles the full complexities of real life.

By the way, he was a cosmologist, if that helps you understand a little better
why he was so flippant with the shapes.

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jonnycomputer
I would imagine therefore that Earth's micro-organims occasionally land on the
surface of the moon.

Not a particularly hospital place the moon. But if it _were_ made of cheese,
it'd probably be green by now. (:

~~~
api
Would any be theoretically viable? I imagine a cyst gets blown into space from
time to time but wouldn't last long in a radiation filled vacuum. Solar UV
radiation is intense without the atmosphere. It's why space suit visors look
reflective and why spaceships tend to always be white or shiny.

Bonus: myth: space is dark. You don't get the omnipresent lit sky effect since
there is no atmosphere to scatter the light but if you are anywhere near a
star it is blindingly bright... in the star's direction.

~~~
jonnycomputer
I do not know. But, there have been experiments, and some microbes are more
durable than expected.

[https://en.wikipedia.org/wiki/List_of_microorganisms_tested_...](https://en.wikipedia.org/wiki/List_of_microorganisms_tested_in_outer_space)

[https://motherboard.vice.com/en_us/article/qkvk33/bacteria-a...](https://motherboard.vice.com/en_us/article/qkvk33/bacteria-
are-so-good-at-surviving-in-space-nasa-needs-a-new-way-to-kill-them)

and... well... the moon has been there a while.

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mirekrusin
So humans did not leave earth’s atmosphere after all.

~~~
kerbalspacepro
If we want to just play with words to make them meaningless: humans have never
left the bonds of Earth's gravity.

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SketchySeaBeast
And literally never will.

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zokula
Fun fact! The Earth is inside the sun's atmosphere.

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em-bee
i have been wondering about just that...

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tomrod
Why doesn't the gravity of the moon cause atmosphere to collect around it?

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sandworm101
Because the radiation from the sun pushes it away faster than the moon can
hold onto it. The moon has no, or a lot less of a, magnetuc field to shield
itself.

This happens on earth too, but only for the light gasses like hydrogen and
helium. That's why there is no helium layer at the top of our atmosphere. It
gets pushed out into space by the sun. The process on earth is called called
thermal escape. On the moon it just happens much more quickly and to heavier
gasses.

~~~
sitkack
Shouldn't the dark side of the moon have a small atmosphere then?

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firmgently
There is no dark side of the moon, it's a misnomer - there's a far side from
earth's point of view, but it isn't dark or blocked from the sun
[https://en.wikipedia.org/wiki/Far_side_of_the_Moon](https://en.wikipedia.org/wiki/Far_side_of_the_Moon)

~~~
sitkack
Actually do mean "the side of the moon not in light", like night on the moon
itself.

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MiddleEndian
The same face of the moon is always towards the Earth, but the sun hits all
points of the moon at different times, so no part is perpetually dark. The
"dark side" is just the side facing away from Earth.

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ajuc
So, when will the Moon fall on us?

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dotancohen
This is a terrific question that should not have been downvoted. The article
literally says "the moon flies through the Earth's atmosphere", which implies
drag.

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8bitsrule
A downvote without a (short, simple) statement of reason can be quite impolite
and disrespectful. This is a _perfect_ example.

Not only is it discouraging ( _not everyone_ knows they've made an error...and
so it punishes an innocent question ), it leaves the recipient without knowing
what the problem is.

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ta1234567890
Super interesting. The article says the SWAN instrument measured/detected
hydrogen atoms, is it possible there's other gases/elements there too?

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erbium
Mostly ionized oxygen, sulfur, iron, various random metals and light elements.

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jefurii
The article notes that the study used twenty-year-old archival data from the
ESA/NASA Solar and Heliospheric Observatory (SOHO). It's good to keep that
stuff around, organized so that you can find and use it.

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tempodox
Wow. Apparently, those sensors generate so much data that even 20 years later
one can still make discoveries by evaluating it.

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ValleyOfTheMtns
So, in a way, the Moon has an adopted/hijacked atmosphere?

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danjac
Does this technically make the Earth a gas giant?

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mLuby
Bussard ramscoop here we come!

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buboard
now i need to find a very very very big balloon

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maskedinvader
"... The denser dayside region of hydrogen is still rather sparse, with just
70 atoms per cubic centimeter at 60 000 kilometers above Earth’s surface, and
about 0.2 atoms at the Moon’s distance..."

tldr: Well that's hardly anything, nothing to see here

~~~
sohkamyung
Not quite true. It might affect astronomical observations from the moon:

 _On the down side, the Earth’s geocorona could interfere with future
astronomical observations performed in the vicinity of the Moon._

 _“Space telescopes observing the sky in ultraviolet wavelengths to study the
chemical composition of stars and galaxies would need to take this into
account,” adds Jean-Loup._

~~~
maskedinvader
imagine a gradiant of uv scattering atoms going from a density of 70 atoms to
0.2 attoms ... it should _not_ be quite a interference, for the average
astronomer out there, this is not an issue, simply dealing with the lower
atmosphere is problematic enough.

edit for missing not

