The date is the 15th December 2010, 2449 sols into Opportunity’s mission to find evidence
of past oceans on Mars.
Up until this point Opportunity had travelled over 25km, investigating rocks, craters and
bedrock, while traversing sand dunes and plains.
The areas it had explored so far contained clues that suggested that these areas were
regularly flooded by water, although it fell short of confirming that a constant body of
water was present there, like an ocean.
Mars’ harsh environment had also started taking its toll on Opportunity with some onboard
motors failing, meaning it couldn’t stow its robotic arm away anymore.
Our persevering champion had just arrived at Santa Maria crater.
But for scientists, the most exciting prospect for the mission was finally on the horizon:
a big, 22-km wide crater where clays had been detected by the Mars Reconnaissance Orbiter.
Clays are significant because they are hydrated minerals, meaning surface water was likely
to have pooled there for lengthy periods of time.
I’m Alex McColgan, and you’re watching Astrum, and together we will follow the journey
of Opportunity, and explore what it saw and discovered around the Endeavour crater.
After spending 3 fairly uneventful months at Santa Maria Crater, Opportunity headed
towards the closest hill on the crater rim, known as Cape York.
Along the way, it came across a few small craters, some of which were very young, with
ejecta from the impact strewn across the place.
But Opportunity didn’t stay for long.
Approaching Endeavour, Opportunity was finally able to see some variation in the landscape
after years of simply crossing flat plains of sand dunes.
Peaks and capes started to rise up on the horizon as Opportunity approached the crater
rim.
On sol 2709, Opportunity finally arrived at Cape York, and specifically a place known
as Spirit Point, named after Opportunity’s sister rover, that had come to the end of
its mission on the other side of the planet only a few months previously.
Opportunity had travelled over 30km up until this point, 50 times further than the original
planned mission distance.
Mission planners decided not to go into the crater, as points of interest were again found
around the rim of the crater.
Bedrock is exposed to the surface there, which allowed Opportunity to study the oldest rocks
it had seen so far on this journey.
It was also around these peaks and capes along the rim where the hydrated minerals, or clays,
were detected by the MRO.
Perched on top of Spirit Point, Opportunity looked over Endeavour crater, providing a
perspective about just how big this crater is.
From the onset, Opportunity began discovering phenomena never before seen on Mars.
You may remember from previous episodes that the soil found around the areas Opportunity
had thus far explored contained countless smooth, tiny, round rocks nicknamed blueberries.
Around Endeavour, no blueberries were to be found.
Instead the soil looks much coarser, the rocks sharper and not as rounded.
Mission controllers were so impressed by the variation of this area compared to the initial
landing site that they said that this section of the mission provided the equivalent of
a second landing site for the price of one.
The first point of interest Opportunity examined was a large ejecta rock called Tisdale 2.
It was unlike any other rock so far examined on Mars.
It had volcanic characteristics, but contained more zinc and bromine than previous seen.
It was determined to be a type of breccia; old rock fragments having been fused together.
This was further evidence for water.
The impact that threw this bit of ejecta likely released hot, underground water that deposited
zinc in the rock.
Just a short distance from Tisdale 2, Opportunity discovered perhaps the most conclusive evidence
that water existed on Mars thus far.
Can you guess what it is from this picture?
Look closely at the bottom of the image, and you’ll see a thin white line exposed in
this outcrop.
A close-up examination of the vein revealed it to be gypsum, the Alpha Particle X-ray
Spectrometer on the rover’s arm detecting the minerals calcium and sulphur, together
making calcium sulphate.
They named this vein the Homestake deposit, and it likely formed from water dissolving
calcium out of volcanic rocks which combined with sulphur, and then was deposited as calcium
sulphate into an underground fracture that later became exposed at the surface.
The impact that threw Tisdale 2 likely had something to do with this vein as well.
If this is the case, it shows that water once flowed through underground fractures on Mars.
Later analysis of the data Opportunity collected showed that not only was this likely to be
gypsum, but also that the water here was much less acidic than it would have been around
other locations on the planet, meaning it could have been more conducive to life.
Martian winter was soon setting in, meaning shorter days and a lower Sun in the sky.
For a solar powered rover that can’t adjust the angle of its solar panels, this is not
the ideal situation.
But, for the first time since the mission began, Opportunity had the opportunity to
spend the winter on a slope aimed towards the Sun, meaning that for this winter, it
would be confined to an area named Greeley Haven.
This area was not only aimed towards the Sun, but was also rocky, meaning Opportunity had
a lot it could examine during these few months.
This 360-degree panorama shows the tracks of Opportunity as it carefully navigated its
way to its winter lodgings.
The fact Opportunity had to wait a few months in one spot was actually handy, as the Mössbauer
spectrometer in the rover’s arm uses radiation from cobolt-57 to determine the composition
of a sample.
However, cobalt-57 has a half-life of only nine months, which wouldn’t have been a
problem for a 3-month mission.
However, Opportunity was now 8 years in, and examining the composition of a rock now took
weeks compared to the half hour it would have taken at the beginning of the mission.
When it was not examining rocks, it could also use the time to study tiny wobbles in
the rotation of Mars to gain insight about the planet's core.
It requires many weeks of radio-tracking the motion of a point on the surface of Mars to
measure changes in the spin axis of the planet, something which couldn’t be done before
as Opportunity was always on the move.
The wobbles they were looking for would indicate whether the interior of Mars is still molten
or not.
Opportunity’s wait also meant it could examine the effects of wind on the dunes of Mars from
a ground perspective, even at a microscopic level using the microscopic camera on the
rover’s arm, checking for slight changes over the months it was stationary.
Months had passed, and winter was turning again to summer.
On sol 2947, Opportunity moved again for the first time since it set up camp in Greeley
Haven.
Luckily, everything that was functioning from before seemed to still be functioning, and
Opportunity headed out to the next point of interest.
MRO data suggested clays where present in this area, and the mission team were determined
to find it.
A beckoning outcrop was spotted around sol 3057, and the microscopic camera revealed
something about it that no-one was expecting.
Much like Opportunity’s landing site, these smooth polished ‘blueberry’ rocks were
observed, however, this time they were very much a part of the rock.
They were also smaller than what Opportunity had seen before, only a few millimetres in
diameter, and not rich in iron like the landing site blueberries.
A few of the exposed blueberries observed had been eroded away, revealing their internal
structure.
Scientists described these blueberries as “crunchy on the outside, and softer in the
middle.
They are different in concentration.
They are different in structure.
They are different in composition.
They are different in distribution.”
It was quite the mystery.
Opportunity had just one more place to visit on its trip around Cape York, and that was
the clay patch dubbed ‘Whitewater Lake’.
On its way there, the Earth and Mars was just going through a phase called solar conjunction,
where Mars is behind the Sun, which blocks communications between mission controllers
and the rover.
This has happened a few times during the course of the mission already, but this time Opportunity
gave mission controllers a bit of a scare, as during the communication blackout, Opportunity’s
onboard computer reset into a standby mode.
Thankfully, communications were restored, Opportunity booted back up properly, and it
carried on to Whitewater Lake.
And it was there Opportunity discovered "Esperance", the pale rock in the upper centre of this
image, which is about the size of a human forearm.
This was it; the treasure scientists had been looking for.
Esperance's composition was found to be higher in aluminium and silica, and lower in calcium
and iron, more so than any other rock Opportunity had examined in more than nine years on Mars.
Testing found that this rock had a clay mineral content due to intensive alteration by water.
Opportunity spent weeks here, making sure the measurements were correct, getting everything
it could get done before Martian winter came around again.
Sights were set on a place called Solander Point, a sun facing slope on the next hill
1.5 km further south.
Opportunity left Cape York on sol 3344, having spent 9 Earth years, or 5 Martian years on
Mars’ surface.
It had found the best evidence out of any Mars mission that neutral ph water once existed
on Mars.
What would the next stage of its mission uncover?
Well, we will have to save that for next time.
Becoming great at science doesn’t have to be dull.
When presented in the right way, it can be fascinating and enlightening.
Passively learning from my videos can be great, but if you want a deeper understanding, I
suggest giving Brilliant a go.
Brilliant has interactive content that makes solving puzzles and challenges about science
and astronomy even more fun and hands-on, plus actively learning means that what you
learn has a better chance of sticking with you.
They go into some really interesting aspects of astronomy which will definitely help you
gain a lot of context to my videos!
So, if you want to try it for yourself, you can sign up for free today by using the link
brilliant.org/astrum/ and that link will also get you 20% off their annual Premium subscription
to get unlimited access to all of Brilliant's interactive math, science and computer science
courses.Thanks for watching!
If you are new to the channel, you are joining us some ways into Opportunity’s mission.
For the whole playlist click here!
A big thank you to my patreons and members, your help really does go a long way.
If you want to support too, find the links in the description.
All the best and see you next time.