- Jim Lattis: Welcome to UW Space Place tonight,
we have a guest speaker who has many Madison connections.
Our speaker is a Madison native and also an alum,
got his PhD in physics from the University of Wisconsin
and has spent most of his career
at Goddard Space Flight Center,
the NASA Center, in Maryland, where he is assistant chief
of the Planetary Magnetospheres Lab,
and is the magnetometer instrument specialist, sorry,
magnetometer instrument manager
for a number of magnetometers
that have found their way onto spacecraft
of various sorts, including the one
that's currently orbiting Jupiter,
which he's talked about here before.
But tonight, we're going to hear
about a different area of his research
and one that, for a lot of us, is a little bit surprising
that there's still some question about this,
but we're gonna get a little historical background
about this too, on when did the Moon get an atmosphere.
So help me welcome Ron Oliversen.
[audience applauding]
- Okay, thank you all, it's a pleasure to be here.
My interest in the Moon goes back to the Apollo mission,
you know, as any kid growing up the during the Space Age
wanted to be an astronaut, my eyesight sucks,
so I just had to be the scientist and work at NASA.
And this particular project about the Moon
having an atmosphere got started 13 years ago
when I was back here visiting colleagues,
Fred Roesler in the Physics department,
one of my thesis advisors, and then Ed Merkowitz,
who was also one of his former students,
and we just decided to go out to Pine Bluff Observatory,
point an instrument out there, and just take a look
to see if we could see some traces of the atmosphere,
which we'll discuss later.
But it piqued our interest, and for those of you
who would like to do, say astrophotography
or have gone to an actual observing site,
you know in the desert Southwest or something like that,
you generally don't like the Moon,
because it's up, it's bright,
it makes it hard to see the Milky Way
and all the other interesting objects.
So when I was going to Kitt Peak
to take some of the data that I'll show
at the end of this talk, the people just generally groan
because they knew that means the Moon was coming up
and they didn't, you know, I was bad luck to them.
[audience laughing]
Okay, anyways I just want to deal
with the basic here, lunar phases.
Most of you probably all understand this
and realize you always just see the same side of the Moon,
and the X is pretty much where we are
in the lunar orbit right now.
This Friday, Friday the 13th,
we'll have the next full moon.
But if we could see it, you would find out
that 89% of the Moon is illuminated right now.
And if you just sort of asked
what are the general properties of the Moon,
here are some, you know statistics.
Basically, it's you know, a little more than 1%
the size of the Earth, radius is a little bit
about the quarter.
And I have a picture here taken.
Anyways, this was a video taken by NASA,
a spacecraft called Discover,
it's at about 1 million miles from Earth towards the Sun,
and the whole purpose of the spacecraft
was just to always look back at the Earth.
And so you could see as the Moon went across there,
you know the relative sizes of the Moon.
And I put for comparison the original picture taken
of the Moon by Luna 3, a Russian spacecraft, in 1959.
And what you're looking at was something
that you've never seen before, right,
because it's the far side of the Moon.
Okay, because since we are looking back at the Earth,
we're looking at the side of the Moon
which doesn't face the Earth.
Okay, so anyways, if we back up a little bit
and say how did the Earth, excuse me,
how did the Moon form, then shortly after
the Earth was formed, somewhere within the range
of 30 to 100 million years ago,
a large object which has been nicknamed Thea, size of Mars,
hit the Earth, and had several profound effects.
One, it changed the spin axis of the Earth,
tipped it to the current 23.5 degrees,
but it also spun up the Earth.
And back then you had a five-hour day.
Anyways, the material which was kicked off as a result
of this rather violent collision, quickly coalesced
into one or possibly two moons, became quickly tidal-locked,
so you have the same face facing the Earth again
on the timescale, just weeks to months,
but much closer to the Earth,
10 to 20 times closer than the Earth.
And what that meant was, it was 10 to 20,000 miles
from the Earth, and has been slowly been receding
over the last 4.5 billion years.
Now, this idea that the Moon was formed
by this violent collision in the early solar system
was first put forth by Reginald Daly in 1946.
He was a geologist, but he did not really have
a very good PR person, because no one really heard
of this idea, and it was then independently
come up with in 1975 by Hartmann and Davis,
and there're also two other astronomers,
Cameron and Ward, were also working on this idea.
So Hartmann and Davis generally
are the people who get credit,
but they weren't the first ones to think of it.
Okay, so after the Moon was created
4.5 billion years ago,
variety of things have happened,
and this is a short video that's put together
by the Lunar Reconnaissance Orbiter mission, a NASA mission,
which has been orbiting the Moon for the last 10 years.
And so after the Moon formed,
you know, it started out in the very molten state,
the Earth was also molten at that point,
so both these bodies were very hot,
and so 4.3 billion years ago,
you had the largest meteor strike on the Moon
to create the south polar Aitken basin,
that's the area gets a lot of attention nowadays.
Gets a lot of attention nowadays
'cause that's where there's ice.
And so when you think about human exploration,
if you go where the ice is, 'cause that means
you can get water.
So, what the animation is showing you
is in the initial bombardment period
3.8 to 4.1 billion years ago,
you created most of the major features on the Moon,
particularly the marias,
because these meteors were then releasing
the molten rock below the surface,
and so the volcanic activity that you're talking about
is not the type of like a big spouting volcano,
but just molten rock flowing out on the surface,
creating this much more flat surface of the Moon.
And then we entered a period from 3.8 to 1 billion years ago
where there was not as heavy,
let's say a reasonable amount of bombardment,
which is still affecting the face of the Moon.
And this is also the period in which you created
certain of the famous Ray craters, most notably Tycho.
Okay, so after all this, meteor activity,
you basically got the two phases of the Moon
that we see nowadays; the near side and the far side,
and what is just obvious, and it was a first surprise
that you can even tell from that very low resolution picture
from Luna 3 that I showed, is the far side
looks radically different than the near side.
Okay, and part of that difference
is not just that the near side has all these extra marias
where you had the volcanic activity
creating these planes, but as a result,
that is the result of the fact that the Moon
on the far side has a much thicker crust,
so even when the meteors were hitting it,
they weren't as likely to bust through to get
to where the molten rock was.
And so the question becomes
why is the far side of the Moon thicker?
I don't think they really know for sure,
a couple of reasons that have some bearing on it.
One, when the Moon first formed,
it would have been very hot,
it would have been close to the Earth
which is also very hot, and so that the front side
is gonna stay hot on the Moon, and so the back side
is gonna cool, or the far side is gonna start to cool
much more rapidly, plus the fact that they speculate
that actually was a second moon created
at the time of the initial impact,
and that that moon eventually then hit
the far side of the Moon and then added extra materials.
And so that might be the reason why it is thicker.
Okay, so we already know the answer
about what caused those craters,
but it was a debate that really was not resolved
until about 60 years ago.
The idea that the craters were first created by meteors
was suggested by geologist Gilbert in 1983,
but then this guy Barrington came along,
one of the premier geologists of the time,
he was the head of the USGS, U.S. Geological Survey,
he went to a meteor crater in Arizona,
incorrectly determined that
that was the remnant of a volcano,
and so his opinion held sway for over 40 years,
until Ralph Baldwin started to look at the issue
and to question that no, maybe meteor crater
was not a volcano, and then finally Gene Shoemaker,
around 1960, was able to prove that the meteor crater
was indeed the result of a pretty sizable object
hitting the Earth and creating that crater
about 50,000 years ago.
Okay, so as we have already mentioned,
these marias are the result of meteor impact
exposing molten rock, which came to the surface,
and a couple of key features about the rocks itself
is they're rich in iron and manganese,
but these do not have any water or hydrated minerals.
So when they talk about areas on the Moon
that have water ice, you're talking shadow regions
or talking about the hydrated minerals,
you're talking more like the highlands.
And if you wanted to go find titanium,
that's actually in the maria regions.
So if anyone can figure out a way to mine that
and bring that back economically,
that's where you would go.
The Chinese have expressed a lot of interest
on their probes going to, rovers going to the Moon
about what can they do in the mining respects.
So what does all this volcanic activity do?
Well, it actually does give you an atmosphere,
and so over the period
from one billion to four billion years ago,
you've got a chart here
showing you peaks that you had an atmosphere
and how much of an atmosphere you had by the pressure.
And you can see around maybe 3.4, 3.5 billion years ago,
the Moon actually had atmosphere
almost 1% of the Earth's atmosphere,
which would mean that its atmosphere was more dense
than Mars's current atmosphere,
which is a little less than 1% of the Earth right now.
So it never had a really big atmosphere,
you can see I've marked on the left,
the 1%, the 0.1% marks, and then on the right,
I've marked where 0.01% is.
But what you notice is, you've got peaks
anytime at a lot of volcanic activity,
yeah, you get an atmosphere,
but once the event volcanic activity stopped,
the atmosphere just seems to go back to zero.
So, the question that we're gonna address
for the rest of the the talk is;
does the Moon have an atmosphere now?
And I titled it like this,
when did the Moon get an atmosphere, not so much
that it one day decided to have an atmosphere,
but the endeavor for people to figure out
that the Moon really did have an atmosphere,
because they really wanted to believe that the Moon
had an atmosphere, and they just couldn't prove it.
The idea of the Moon having an atmosphere
at least goes back to the 1st century AD or CE,
depending on your preferences, when a Greek philosopher
Plutarch, in the form of a dialogue that he wrote,
just discussed the idea that when he looked at the Moon,
thought that those dark regions were oceans,
and he thought all those light regions were land.
And they even speculated maybe that the Moon was habitable.
Now bear in mind, for a century they had no idea
that the Moon is a rocky body, they just knew
that it was something up in the sky.
They also speculated maybe the Moon is the place
where all the souls went after people died,
but nevertheless, they took what they saw around them,
which was obviously water and land,
and said, "Maybe that's what we're seeing in the sky."
That idea certainly continued.
And Plutarch was actually quoted by several scientists
and philosophers up until the 1600s.
He was quoted by Galileo and also Kepler.
And so the advent of the telescope,
something that Galileo did not invent,
but was one of the early users and made an improvement,
he drew one of the early maps of the Moon.
He does get credit for recognizing mountains
and making measurements of how tall those mountains were,
but he wasn't the first person to draw the map,
he's just a person who gets the credit
because he wrote Starry Messenger in 1610.
The person who did it before him
was Thomas Harriot, an English astronomer,
but he didn't publish.
He worked for Sir Walter Raleigh
and then later, another earl named Henry Percy
who kept him employed, but the guy never published anything,
and so even though he is a well-respected scientist
of the time, no one knew what he did
outside of the circles that he talked in.
So using more than, you know, people using telescopes,
you had an English clergyman, John Wilkins, come along
who wrote this book entitled
Discovery of a World in the Moone .
And he then put in, in print actually that he thought
the Moon had an atmosphere.
And this book had several propositions,
and I've just highlighted a couple of them
relevant to this talk, and the other one being
that he also thought it was very probable
that the Moon had inhabitants, and he actually proposed,
I don't wanna say a space vehicle,
but he proposed some means by maybe we could get
to the Moon, thinking ahead.
And so he came up with a name for the inhabitants
that you would meet, Selenites.
And so he was forward-thinking on that,
but again, the basis of the idea was "Okay,
"I've got these things around me here on Earth,
"I now know that the Moon actually is a, is a body
"that is going around the Earth,
"and so if I think it's Earth-like,
"then it should have an atmosphere like I have on Earth,
"and it should have creatures, animals and plants."
And we're all familiar however with the another notion
that the Moon is cheese, [audience laughing]
and it actually turns out
that in 1546, a writer from England, John Heywood,
actually came up with the idea, who was then quoted later
by John Wilkins, basically making fun
of what he considered simpletons
or people who were just ignorant, who would believe
if they saw the reflection of the Moon in a body of water,
or a lake or stream, that that somehow
represented a wheel of cheese.
So that's not meant to be a compliment.
[audience chuckling]
Okay, so in 1792, we have an English gentleman,
he was a lawyer, independent means.
And so to him, he got his own telescope,
he may have built it himself,
and then he made observations looking through the telescope.
And one of the conclusions that he came to,
and it wasn't an uncommon thing, is you stare at a star,
and he watched the Moon as it goes across
occulting that star, and when that happened,
he saw instances in where the star
appeared to be in front of the Moon.
And the only way that that could happen, he reasoned,
was if the Moon had an atmosphere.
It's called refraction,
a couple slides I'll show a demonstration of that,
and he was very passionate about, this proved
the Moon had an atmosphere.
And he wrote a long article.
I have read many, many pages of this to try
and get an understanding for his frame of mind,
but the one thing you got is he was very enthusiastic,
and he believed what he saw
demonstrated the Moon had an atmosphere.
You had a premier--
premier, premier?
Scientist mathematician
named George Airy, who basically didn't wanna commit
to the Moon having an atmosphere.
And so he sort of said, maybe it has an atmosphere,
but it could also be attributed
to maybe something about the optics you're using,
or maybe it's the Earth's atmosphere,
or maybe it's just a physiological issue
with the eyes' perception.
In 1897, a UW astronomer here at Washburn Observatory
just echoed this belief that the Moon
just had to have an atmosphere, it just had to.
We just hadn't found it yet, but it's got to be there.
And you can see from his, his quote is basically saying,
everyone who studies the Moon of consequence
recognizes that the Moon has to be an atmosphere,
you just have this other scientist guy named Peschel
who's putting physics into the equation,
and sort of demonstrating that if the Moon
has an atmosphere, it can't be much of one,
and it's gonna be really hard to detect.
And so they did make an observation right here
that indicated that if the Moon had an atmosphere,
it's less than 1/5,000th of the Earth's atmosphere.
In this particular case, again it's a matter
of using refraction, and as you look there,
you see your line of sight.
As you're looking at a star, if there is an atmosphere,
then the light to the star looks like it's bent,
and so the position of the star then seems to change.
And so Comstock's approach was he put that device
I showed you on the previous slide, here,
that filar micrometer, and it has two crosshairs on it.
And he put one on one star, and one on another star,
and he measured the distance between the two stars;
you've got a micrometer, it gives you the distance,
and it kept measuring those distances as the star
was being eclipsed by the Moon.
Happens very quickly, and he basically couldn't prove
that the distance between these two stars ever changed,
and so he just got what he determined as an upper limit.
So then in 1946, another UW Washburn astronomer
used a slightly different technique.
Any of you who are amateur astronomers
may be familiar with the diffraction limit of a telescope
that's determined by the size of the telescope.
And so if you have good optics and you have good seeing,
then it's possible to see this diffraction pattern
around a star.
So what Whitford did is, using a high speed photometer,
in just measuring what the total light output
from the Sun was, from the star, but electronically
measuring it very fast, and watching as that star
got occulted by the Moon.
So if you do that, what you see
is if you have a diffraction pattern,
you'll see that you have a bunch of secondary peaks.
And so he measured this, and found that the pattern
that he got exactly matched what you would have
if the Moon had no atmosphere, 'cause if the Moon
had an atmosphere, it would smear out
this diffraction pattern.
And so in Science Newsletter , as it says there,
September 21st, 1946, very bold letters,
"Moon Has No Atmosphere," we're done,
thank you for coming to my talk.
There's nothing left to say. [audience chuckling]
But people didn't quit, 1955, you had Elsmore and Whitfield
said "Okay, we're gonna try this,
"we're gonna look for that diffraction again,
"but we're not gonna do it in the visible
"like everyone has been trying to do.
"We'll try to do it in the radio."
And so in this case, they had IC 443,
that's an extra galactic galaxy and in the Crab Nebula,
they watched the Moon go over these,
they looked at the radio and tried to see
whether or not there was any indication
that the radio waves were being refracted.
We can say that they got a positive answer,
but it was a positive answer pretty much consistent
with slightly better than zero.
So they could sort of say, okay, if it's got something
rather than, you know the earlier number
that I quoted from Comstock, 1 part in 5,000,
they now said, "Okay this is a really really small number."
10 to the minus 14th, I'll show another description
of that in a bit.
But they kept looking.
Well, then basically what we have, and as I grew up,
a product of the Space Age,
and the textbook telling me exactly as Whitford had said,
"The Moon has no atmosphere."
So the standard argument that you would have made
or seen in a textbook at this time,
is that if you looked at star occultations,
you've got no fading of the signal.
Nothing that gradually causes it to blink out,
and so there is no atmosphere.
Obviously, there's no clouds, nothing in the weather.
And even if there were, people made arguments
going back to Bessel, pretty much saying that
the Moon, because of its mass, has a low escape velocity,
it gets very hot during the day.
In one of the early slides there,
it gets up to 250 degrees Fahrenheit during the day,
and so as a result, if you do have any gas,
it's going to escape eventually.
If the gas becomes ionized, then the gas
is going to be swept away with the solar wind.
So it's just like, even if there was an atmosphere,
it's just not going to just hang around.
So this is the second time in which we're done, right,
there's just no atmosphere.
Well, okay, as I mentioned, you know,
product of the Space Age here,
and we did have the Apollo program,
and so we're sending spacecraft to the Moon
'cause we got to understand the Moon.
And then you get something like this from Surveyor in 1967.
In the lower right there, you're looking at a picture
of the limb of the Moon and the, excuse me,
yeah, the limb of the Moon, but the Sun has set.
If the Sun has set and there is no atmosphere,
you cannot have any glow of the sunlight over your horizon,
it's just got to be dark.
Well, it's not dark.
So there's something above the surface of the Moon.
You don't know if it's gas or you don't know if it's dust,
but there's something.
So now there's something, and you start asking yourself
the question about, okay, what is it?
Is the source of the material you're looking at something
that comes from the solar wind?
The solar wind is just a bunch
of high-energy charged particles
that are flowing off the Sun at all times.
Is it material that's somehow being released
from the regolith of the Moon's surface, what is it?
So on Apollo 12, 14, and 15,
they put what they call a cold cathode gauge,
which basically is this cold plate,
and you make it cold plate because then things
will settle on it and stay there, right.
And so they could measure the fact that something
was settling on that plate,
but they didn't know what it was.
And so in Apollo 17, they actually had an experiment
to try and determine out some of the actual composition
of this atmosphere.
And they couldn't determine the composition during the day,
because during the day, as the Sun heated up everything,
the Apollo spacecraft, the sent module which was left
as well as all the experiments with outgas, right.
And for those of you who may not be familiar
with outgassing, think about your car, right.
You've got the plastics in your car
that get heated up during the summer, UV radiation,
and you come in and you end up with this thin film of gas
on your windshield on the inside, right.
So that's what's happening on the Moon.
So they'd have to wait until they got night time,
so all the outgassing of what man had left
in the Apollo program would go away,
and then they could start to see there was some stuff
left over that was lunar in origin.
But I'm gonna put lunar in quotes there
because what they detected was helium,
hydrogen, argon, and neon.
And you'll notice I listed as one of the sources
captured solar wind.
All four of those elements are very prominent
in the solar wind.
So it wasn't obvious that what you were detecting
was coming from the Moon, it could just be coming
from the solar wind and just temporarily
creating an atmosphere there.
Okay, so now we have some evidence of something,
and so as scientists, we wanna be motivated,
and we have to convince some funding agency
to continue our work so you got to give them reasons, right.
Okay, so number one reason is that it's actually
the most common form of an atmosphere in the solar system.
So if we wanna understand the atmosphere
around say Mercury or a large satellite,
or icy moons around Jupiter and Saturn,
then the Moon would be a good place to start,
because they all have this type of atmosphere in common.
Very thin, but nevertheless an atmosphere.
And that atmosphere at this level
is called a surface bounded exosphere.
And all that really means is that
the density of the atmosphere is so low
that the gas particles never interact with one another.
Right now you have gas particles in this room,
I believe in the range about 20 quatrillion,
bumping into one another.
So when you get to an exosphere--
And the Earth does have an exosphere, right.
It's that transition region from atmosphere to outer space.
So typically on the Earth, we say above 50 to 60 miles,
we enter into, to outer space,
and so that's where our exosphere begins,
but our exosphere goes out 10, 20,000 miles.
Okay, so reason number one, just basic knowledge,
we wanna understand this type of environment
that is found on the Moon, in other bodies
around our solar system.
Reason number two, space weather.
We're very much interested in studying
the time varying conditions due to our Sun,
that includes radiation, solar wind,
as well as corona mass ejections.
These are the large explosions on the surface of the Sun
that send out billions of tons of material
that then have the ability to create aurora.
I understand that week and a half ago,
they were possibly aurora seen in Wisconsin,
I don't know if anyone saw any, whether or not it was clear,
I know there was an alert to do so.
And it'll affect satellites and communications,
has potential to affect the power grid.
So the Moon just represents another platform
of which we can study these events
besides the satellites that we already have out there
to study space weather, and then the observations
that we made on the ground.
But the Moon represents a good laboratory
to look at these effect.
And then the third reason, sort of why NASA exists,
is human exploration.
Okay, so there's a lot of talk about going back to the Moon,
hopefully putting a man and woman back on Moon by 2024,
that's an ambitious program, but that's the goal.
But to do that, you really wanna understand
what's going on at the surface of the Moon.
And so there are various explanations for this glow
that was first seen in Surveyor 6,
but that is not completely understood.
There's a lot of charging that goes on
at the surface of the Moon,
so you have electrostatic issues.
And this was demonstrated in the Apollo program,
because what they were not expecting
were the spacesuits to get dirty, okay.
It's not that they didn't realize
that there was dust on the Moon,
what they didn't expect was all this dust
to stick to their spacesuits.
And so by sticking to their spacesuits,
you have got a problem that you have to deal with
if you're gonna build a habitat on the Moon, right,
because you effectively, you need a mud room,
someplace to come in and make sure that this dust
does not get into your living quarters,
because otherwise it's gonna clog up your air system, okay.
So you need to understand the surface processes.
Okay, so how do we create an atmosphere?
So now we've got an atmosphere on the Moon,
not very thick, but we do have one.
And so there're various processes that could be used
to create that atmosphere, okay.
I've already mentioned, thermal desorption,
that idea is just like snow sublimating in the wintertime,
just going from solid to gas.
Photostimulated absorption, that's what you're seeing
when you see that residue in your car windows,
UV radiation liberating some of the gases from that polymer.
And okay, so that's a direct energy transfer
from an energetic photon.
Iron sputtering, now you're talking about material
hitting the surface of the Moon
and releasing the particles, solar wind constantly
going on, except when the Earth is near full moon,
then the Moon is in the Earth's magnetotail.
I should have pointed it out in an earlier slide,
but the effect here is, it's when the Moon
is in the Earth's magnetotail, it is shielded
from the solar wind, but then the Moon is then being hit
by the magnetospheric ions,
which are in the Earth's magnetosphere.
And then finally, just micrometeor bombardment
hitting the Moon from all directions at all times, okay.
So that's going on on a sporadic fashion,
and then there are well known.
When we have a meteor shower here on the Earth,
say the Perseids in August,
you got a meteor shower going on at the Moon, okay.
And then finally, the one that we start out with,
we know we do get a atmosphere from the volcanic outgassing.
Okay, now that's not really going on very often now,
but there are occasionally evidence of gas coming out
from the Moon still.
Okay, so that's how you create an atmosphere,
how do you lose an atmosphere?
You can lose an atmosphere very easily.
Like I said, something gets hot,
the particles get more energetic, they pick up speed,
and then it's sort of like the graph on the lower left.
Here's like driving on the highway.
Most of the cars are driving at one speed,
but you always have those cars that are zooming ahead,
and if they zoom fast enough, they escape the Moon.
Okay, now that process can be helped along
by radiation pressure from the Sun
literally blowing the gas particles off,
away from the Moon
once they've escaped the surface.
Okay, and so you actually have an example
on the right there.
A model showing you in the panel,
the second panel down that says model,
what you needed to create the data that was obtained
in the first panel on the right, which is to say,
if you look in the opposite direction of the Moon
at new moon, then you see that there is an enhancement
in the sky of sodium emission.
So it turns out that sodium is being blown off the Moon,
basically like a comet tail that goes behind the Moon
in the anti-solar direction.
And then again, just mentioning that if your particle
becomes ionized, then you can have it swept away
by the solar wind.
So what does that leave us?
Okay, so what that leaves us is the Moon
has what we said, the surface-bounded exosphere,
just a very thin atmosphere, source is both solar wind
and material coming from the regolith.
And I've listed the six most common elements
or molecules in the atmosphere.
Again, over a huge range of temperatures,
because it gets minus 270 degrees
when you get nighttime there for two weeks,
then it goes up to 250 degrees during the daytime.
And in the end, what this atmosphere on the daytime size,
is around a 100,000 to 1,000,000 particles
per cubic centimeter, right.
So a cubic centimeter is a little over 3/8 of an inch,
and that compares to the atmospheric pressure
in this room,
where you got 20 quadrillion particles
per each cubic centimeter.
So you can count the differences
is about 14 or 15 extra zeros on that.
Okay, so this is all good.
So to explain a little bit about what I and my colleagues
have done, we need to understand a little bit
about how we took the data, as well as a little bit
about anytime you're looking at the Moon,
what you're looking at.
Okay, the Moon is a very bright object, right,
and it's reflected sunlight.
So you have the Sun illuminating the Moon.
If you have an atmosphere, that atmosphere itself
can emit some light.
You then are looking at the Moon, but that light
has to go then through the Earth's atmosphere.
So anytime you're looking at something
with respect to the Moon, you've got to be able
to disentangle those three effects.
What comes from the Sun, what comes from the Moon,
and what is the Earth doing to your observation.
A typical--
This is a typical spectrum of what the sunlight looks like,
it's the rainbow, okay.
If you look in high resolution,
you see a bunch of dark lines.
Those dark lines are letting you know
what the composition of the Sun is,
it lets you know what the temperature of the Sun is,
it lets you know about the magnetic field of the Sun,
it lets you know about the velocity.
A bunch of information that you can determine
by analyzing all those little dark lines.
Okay, so that's the background
that you have to look at any light that comes from the Moon.
So the way people have gone about it is say,
"Jeez, that's an awful lot of light that comes from the Sun.
"I don't wanna look at that.
"Let me look at a very select region of stuff
"that might be coming from stuff that could be there,
"or I know that is there, somebody else has found it."
So a favorite spot then
is to look at that very small segment
in that box, and those two very dark lines
are created by sodium gas.
And so if you look at a profile,
then this is what the solar spectrum looks like.
This is the intensity as you're going through
this very small, yellow region of color,
and those very deep lines are the signature of sodium atoms.
Okay, so people doing that.
Then on the left here, you see this all going up,
there in that very streak light,
is away from the limb of the Moon,
but all that multicolored stuff you see at the bottom
again is a scattered light from the Sun,
but by concentrating on a very small part of sunlight,
they were able to isolate the fact
that they could see emission from sodium atoms.
So this happened a little over 30 years ago,
and it's illustrated a little better here.
A few years after that, somebody actually
blocked out the Moon,
used something called the coronagraph,
blocked out the Moon, looked at that very small region
of the yellow part of the sunlight, and took a picture.
And now you can see the size of the sodium cloud
around the Moon.
It's several times the size of the Moon.
It's very thin, but it's big.
And you're seeing the size because the Moon
is losing this sodium, right.
I mentioned earlier that there's a sodium tail
being blown away from the Moon.
Okay, so this was sort of an introduction to get myself
and my colleagues motivated, as I mentioned,
the interest in the Moon from about 13 years ago,
and then ultimately we went down
to Kitt Peak National Observatory near Tucson,
and used the McMath-Pierce, a solar telescope,
to make our own observations to try and study
the atmosphere of the Moon.
And this is a unique structure,
no other telescope building looks like this, okay.
It's a seven on its side, and I've got several pictures
that I'm just gonna go through, 'cause I wanna highlight
how unique this is.
60% of this structure is actually underground,
it's a three mirror system.
There's one mirror up at the very top,
you see one, and then you see two at the very bottom,
and then bouncing light up to mirror three,
and then into your observing room.
And I'm just gonna show you some pictures,
and this effort here will show you a lot of students
who have helped out over the years.
They've been very helpful.
And it's just been my most fun as a NASA scientist
is being able to do observing.
And this telescope is just totally unique to do that.
And the view from inside is just this tunnel,
and you've got these mirrors to bounce light around,
and that bounces it around into this room.
And the room basically is a laboratory.
And so we set up this instrument,
and we're gonna look at even a smaller part
of the yellow spectrum than I showed you earlier,
because we really wanna isolate the sodium emissions.
And I'm just showing you different pictures in here.
The thing I wanna point out is all the equipment
you're looking at is older
than any one of those students in that picture.
[audience laughing]
Okay, it was the 1960s control panel,
the latest upgrade was 1983.
And I think the oldest person there was born in '89,
but I don't wanna identify her.
[audience chuckling]
The way that this worked for us
is the reason we like this telescope.
It was designed to look at the Sun,
and it was designed to create a very big image of the Sun.
And since the Moon is about the same angular size
as the Sun, this is what the image
you got to see of the Sun.
And so what we would do is we would look
right off the edge of the Moon
and see if we could detect
the sodium emission from the Moon.
This was not at all clear to us that we could do this,
the Moon is a very, very bright object.
And we were therefore very pleasantly surprised.
So, this is just one of those deep features
that I showed you a few slides ago from sodium.
And so what you're looking at there is you see
we're interested in the bright bumps in the middle.
Everything else is either from the sunlight,
reflected sunlight, or it's from the Earth's atmosphere.
So in the top one you see the deep dip,
that's the solar Fraunhofer line, and you see
where the atmospheric absorption features
are marked in blue,
and then you got this peak of emission of sodium on top,
potassium at the bottom.
And what we care about is how bright is that peak
and how wide is it.
That was our objective and from that,
we're gonna try to figure out what's going on.
So we would look at this and we would go off
from the surface of the Moon at different locations,
to try and map out this distribution.
You saw what the big picture look like
in that earlier picture, when I showed you
the Moon blocked out with an occulting disk,
and you saw how big the cloud is.
Here we're actually trying to measure
the physical properties of the sodium.
In this particular case, what's the temperature of that gas,
and what are its philosophies, what are its kinematics?
But what you notice, we don't really need to worry
about the details, right, but what you notice
is that the sodium emission is much more extended
than the potassium emission.
Now, we already knew that sodium
was brighter than potassium,
other people had shown that,
but here, we're making it very clear how much more extended
the sodium is than the potassium.
And then if we take that a little further,
what you see, the details don't matter
other than potassium is on the right, sodium is on the left,
and you see that the structure of the width of the line
is very different between the two gases.
Okay, the sodium on the left, top left,
has a much more symmetric looking set of dots,
so whatever that width of that line is doing
and whatever it means, it doesn't seem to care
if you're looking at it before full moon,
the waxing phase, or after full moon,
the waning phase, whereas potassium,
the state of the atoms
are very different in the waxing phase
versus the waning phase.
And if you look at the bottom set of two things,
and if you look at the intensity,
you'll see that that where both of them decrease
towards full moon, the decrease in potassium
is much more severe, as well as
something seems to be going on
around full moon with sodium
that we can't see in potassium.
Basically, we couldn't detect potassium at full moon at all.
Okay, I have hit my highlights of what
I'm trying to talk about, so I thank you.
And for those of you who are interested in green flashes
just as a atmospheric phenomenon,
I have a picture of one,
which we took from the solar telescope.
When I was down there, we saw green flashes routinely.
I mean I've literally seen probably a 1,000 green flashes.
Okay, anyways, thank you.
[audience applauding]