And in fact, at later seasons it would seem that it does continue up like that.
Let's compare that now to the neutrons.
Now, remember what the neutrons do.
The neutrons are attenuated by hydrogen nuclei.
They are slowed down by hydrogen nuclei.
So if you look at the number of these thermal neutrons, and epithermal,
don't worry about what those two mean, but they're not the fast ones.
The fast ones just come straight out.
These are ones that have been cooled down
by interaction with hydrogen, and look what happens.
Relatively flat, relatively flat.
And then at the same place, this goes up, this go plummeting down through here.
Same place, this starts to go up, this goes
plummeting down, and then who knows up through here.
This is again the problem with the polar
cap, and again, observed over many different seasons.
You could see that there's plenty of water here.
You can take these measurements, and now turn it into a map.
We call it water on Mars in the upper meter of Mars.
But it's really of hydrogen atoms in the upper meter of Mars.
And it looks like this.
Again, favorite regions.
Here's the Tharsis bulge, our favorite three volcanoes.
Here's Valles Marineris.
So now you sort of know where you're looking.
Here is the northern plains, southern highlands, and a ton of
water from sort of 50, 60 degree north all the way up.
A ton, by a ton let's see what this means.
This means something like greater than 30% of the material in this layer.
60 degrees.
Greater than 30% of the materials is hydrogen, is presumably water.
Down here again 60 degrees.
There is a lot of water.
In the crust, even in these regions, in through here, which are
never covered in polar caps, never, never get very cold at all.
We still see regions with, sort of 8-10%.
All these blues, 10% water.
10% in through here, in through here.
Some of the areas are very dry.
These 2% values.
Some of these high lands in through here.
Some of these equatorial regions.
But, there is a lot of water, a lot of, some
type of water in the upper meter of the surface of Mars.
What type of water is it?
Well, it's not liquid water.
The upper meter of the surface of Mars is
still too cold for liquid water to be stable.
The answer is probably some surface ice.
We're used to the idea that the north polar cap is a
big mound of ice, but we're not used to the idea currently,
that this ice extends all the way down through here into these
regions, and that, that some of that subsurface ice could even be equatorial.
Is it true?
Well, how would you find out?
I will give you two ways that it was found out that, yes, indeed, this is true.
First way, fly to a polar region dig, see what you get to.
The phoenix lander landed at about 65 degrees north in
this region here, in one of these very blue areas, where
there's something like more than 30% water in the upper meter,
and it landed and it dug, and here's what it saw.
When this picture came up from the Lander, scientists involved hemmed and
hawed and argued about the different possible things it could possibly be.
But I tell you, you don't necessarily have to argue
too much, you can look at that and, if your first
guess is that it looks like ice just below the
surface of this dusty cover service, your first guess is right.
Let me zoom in a little so you can see a little bit better.
I mean just looking at it right here you can see regions that are, that look
like hard scraped snow in through here and even a little bitty layer of ice that
is maybe even melting the thin part through
here melting through here since it's been exposed,
that's water ice and it is just below the surface over a big chunk of the planet.
I promised you I would show you two, here is
another way we know how extensive that water ice is.
We have enough space craft in orbit around mars
these days staring down that we can find things like
fresh impact craters, regions where we had images and
there was no impact crater, and come back and boom.
There's a brand new impact crater that wasn't there before.
Here's a couple of craters that are curved at about 45 degrees north latitude.
45 degrees north latitude is not that region where you're
in the 30% water, you're in the ten's of percent,
not very much necessarily in that first meter, but slam
a meteor into the surface and what do you see?
You see these bright spots right here,
these are the first images, these bright spots.
The crater is right here, the bottom of the crater has these nice bright spots.
What are they?