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John Grant: Thank you all for being here tonight.
And listening to us tell you a little bit about Curiosity.
So, starting out with why Gale Crater.
Well, here is a map of Mars.
We've landed in six locations before Curiosity.
Why do you need to go for a seventh? Haven't we--
haven't we been all over the planet?
It looks kinda like a shotgun blast to me here
in terms of the yellow marks.
Well, Mars is a smaller planet than the Earth.
But without oceans it's got about the same land area
as the surface of the Earth.
And I travel a fair amount, more than I'd like to
but if I had only been to six places
on the surface of the Earth, I wouldn't know much about it.
Let me give you one example.
There is a place where I used to live
in Western New York, called Letchworth State Park.
It's called the 'Grand Canyon of the East'.
A fabulous place.
But if I had never been out west
and didn't know about the Grand Canyon,
it would be kind of a different story
in terms of where I might choose to go.
But what if the rocks in the Grand Canyon
weren't of interest
and the ones in Letchworth State Park,
even though it's smaller, were.
So what you really need when you are looking
at landing sites is not only do you have to know something
about the planet and where the good places are
but you've got to bring together the expertise
to be able to look at those places
and find out which ones are the most relevant
for the kinds of things
that you want to accomplish with your mission.
So, we started with about 65 landing site candidates
from our Science Laboratory, Curiosity.
We whittled it down to the final four
that you see here in white.
Holden Crater, Eberswalde Crater,
Mawrth Vallis and of course Gale Crater
where we ended up going.
And just to give you a sense of
what we found attractive about those four places
and I'll point out that the yellow ellipsis
that you see here
are all 25 kilometers long by 20 kilometers high.
We've got Mawrth Vallis on the upper left.
There is this stratigraphy,
these layers of rock that we see there
that we see a sense of different kinds of clays
from top to bottom and it's an ancient,
ancient set of rocks that tell us something about
the earliest history of the planet.
A question about Mawrth was
how did those rocks get to be there
and we never really could get a handle on that.
Although work has been moving forward.
Down here in the lower left
we see a place called Holden Crater.
It's about the same size as Gale Crater,
about 100 miles across
and here we see along the side of the crater sediments
that have been washed down into a big fan.
It's the best alluvial system preserved on Mars.
Over here on the lower right we see Eberswalde Delta.
A place where we might go and sample sediments
that have been deposited by water
running down through a river in the ancient past.
The problem or question about these two on the bottom
were they occur relatively late in Mars' history
compared to when we think it was the wettest.
And if we got there
we're seeing a fairly narrow period in the history of Mars.
So we want to know relative to habitability
when those things occurred,
we might want to sample a place with a section
that's preserved is much older.
And that brings us to Gale up here in the upper right.
You'll notice that in this 100 mile across crater,
150 kilometers across,
there is this mountain of material.
Five kilometers or three miles high.
And the layers that are in that mountain
are very much like pages or chapters in a book.
And when we look at the chemistry
or the chemical composition of those layers,
we see a transition from the kinds of things
that were deposited in water in wet conditions
near the bottom to drier things
as we move up through the section.
And so Gale became a chance to sort of read the chapters
related to the changing environment on Mars,
from when it was wetter
to when it's relatively dry today.
And that's why we picked Gale Crater.
Gale Crater lies across this transition on Mars.
What you see here, this topography
where the yellows and the reds are relatively high
and the blues and purples are low.
And Gale right there in the middle
straddles this boundary called the 'planetary dichotomy'.
And what we see here already visible is this mound;
this mountain of material, Mount Sharp.
If we zoom in on the crater proper,
we are looking across here towards the south
and on the north side between the small crater
that you see in the middle of the mountain
is about where we were planning to land.
So we wanted to land and be able to drive directly
over to the flank of the mountain
transitioning up between these layers of material,
these chapters in the book, telling us about
the environmental history of Mars.
But there was another target there.
A small channel that runs down the wall of the crater.
This is a closer view now.
The top of the crater is now to the north,
so I've turned things around on you.
This is an image from
the Mars Reconnaissance Orbiter.
There is this incredible synergy between
the cameras that we have in orbit
and the pictures that we can take of the surface,
and the things that we can do on the surface
to ground truth that data.
This data, we can resolve things
that are about 20 meters across.
The camera has a resolution of six meters per pixel.
And we can see that channel now
coming in from the upper left
and draining out into a fan of sediment.
We call this an alluvial fan.
And there are many examples of this on Earth
that we see in places for example like Death Valley.
So this became a very important
secondary target,
to the layers in Mount Sharp,
for our exploration.
Well, here is the view from the surface
after Curiosity landed.
This is one of my favorite images
from the mission
because to me it's almost like
you are standing in Death Valley
looking up the west at the Panamint Mountains.
And seeing this fan of material,
you can see the bright outline of Peace Vallis,
this channel coming down and the sloping sort of
deposit of sediment that's being
laid down by that river some time in the past.
We are way down at the very far end of that
where we landed with Curiosity.
In fact we weren't even sure if we were going to be
on those sediments.
Now here is an overhead view,
this time from the HiRise camera,
which can image things that are about three feet across.
It has a resolution of about 25 centimeters
or about a foot.
You can see where Curiosity landed,
the two blue spots over here on the left.
And those are the tracks of the rover.
When we landed, because we had
mapped the surface of our landing ellipse
before we got down to the surface of the planet
we knew that there were some different terrains
that we were likely to sample, depending on where we landed.
And because we landed at that spot there,
we happen to be very close to
three different kinds of material
that were sort of like a Rosetta Stone
we thought for understanding the geology of our traverse
as we went across to Mount Sharp.
The most of the material for
the left two-thirds of the image was one type
and the lower right corner was another,
and then the brighter whitish-blue stuff up there
is a third.
Seeing this juncture of these three different materials
knowing that they held to clues to
what was going on in Gale and that they might be related
to that alluvial fan,
drove us literally in the opposite direction
than we intended once we got down on the surface.
Mount Sharp is down to the left--
to the lower left, your left, my right.
We went east, we went to your right.
And it paid off.
Very soon after we got started,
we started to find these outcrops.
The pebbles that you can see
weathering out, that are rounded.
Becky Williams who is here tonight
was the lead author on a science paper
that first described these
as 'deposits related to that river
flowing down that side of the canyon'.
Now, in Death Valley it doesn't,
it doesn't rain very often.
But when it does, that water comes out fast.
And I can almost imagine
when I see these sorts of things,
you know water up to my thigh kinda thing
draining across the surface depositing these gravels.
What an amazing and different place
this must have been
three, three and a half billion years ago.
We got into this place called Yellowknife Bay
and here's our dried up lake sediments.
This is a mudstone.
We drilled down into this rock.
The rocks weren't red, they are gray.
They tell us something about the conditions in the past.
When we look at the chemistry it tells us
that these clays that are in here were deposited
in conditions that were relatively neutral,
that is not too acidic, not too basic.
But we've already sampled
sediments washed down in a river
and ancient lake deposits.
And we haven't even gotten to Mount Sharp yet.
So, clearly the first bit of information
that we got back from Curiosity,
really sort of set us on our ear,
in terms of understanding Mars as a planet
and how it evolved.
Since leaving Yellowknife Bay
and these ancient lake deposits
we've been traversing across a landscape
that's littered with sedimentary rocks.
You can see some of those here in the foreground.
And we've been sampling these as we've gone,
trying to understand more about the relationship
between sediments washed down in this river,
Peace Vallis and out onto this fan of sediments
versus the sediments that have been
shed off the side of Mount Sharp.
There's still kind of an uncertainty
in terms of where some of these
different sediments have come from
and what their origin is in relationship
to the timing of the formation of this big, huge mountain
in the middle of the-- of the crater.
But as you can see this image,
we haven't lost sight of Mount Sharp.
It's always sort of been dead in our sights.
And we are actually more than half way there
from when we left the Yellowknife Bay area.
And in fact we see images like this almost daily
with Curiosity and it reminds us exactly
why we came here and why this is the goal.
Because you can see the layers here
that I described earlier as sort of chapters in a book.
And you can see here
how they transition from sort of darker
and grayer layers near the bottom
to lighter sediments at the top.
And knowing what we already know about Gale Crater
from our exploration of these lake and sediments
washed down in the fan,
we are very eager to get here and understand more
about the evolution of the Martian climate
as these sediments were deposited.
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