The Opportunity Rover has now come to the end of a very successful mission on Mars,
spending over 15 years operating on its surface.
Being that long on another planet means it has made a lot of fascinating discoveries
and it has a lot of stories to tell about its adventure.
In the previous episodes, Opportunity visited various craters, drilling into rocks to see
into Mars’ past.
It got stuck in sand dunes, but got itself out thanks to the ingenuity and patience of
the mission control team on Earth.
Opportunity also experienced a few mechanical problems, meaning its arm can’t be stowed
any more.
But even with all these hinderances and successes, this series isn’t even halfway through its
mission yet!
I’m Alex McColgan, and you’re watching Astrum, and together we will follow the tracks
of Opportunity, and experience what it saw and discovered on the Martian surface.
We left off last time around Sol 1700, or the 1700th Martian day of Opportunity’s
mission, which equates to about 4 and a half Earth years.
Opportunity had just finished exploring the Victoria crater, an impressive 750m wide crater
with layered cliff faces and exposed bedrock.
It was by far the biggest crater Opportunity had visited yet, but after a successful excursion
around Victoria, mission controllers had their eyes set on a much bigger fish.
This is Endeavour crater, a huge but shallow crater at 22km across and 300m deep.
But why Endeavour crater?
Due to the distances involved, it would take a long time for Opportunity to get there,
so, what’s special about this place compared to anything Opportunity had seen before?
The most compelling reason, and indeed one of the science goals of Opportunity, was to
find evidence of past oceans on Mars.
At this point in 2008, the theory that Mars once held an ocean on its surface was only
just starting to get solid evidence thanks to the Spirit and Opportunity rovers.
Opportunity at this point had discovered that water once existed on the places it had visited,
but these places were no more than shallow flood plains which dried up periodically,
not a true ocean.
On the other hand, the Mars Reconnaissance Orbiter had spotted what was believed to be
clays around Endeavour crater, clays being hydrated minerals which could have only formed
from water being on the surface for extended periods there.
Could Endeavour have been part of a more permanent ocean?
And if there really was a surface ocean, are there clues to indicate that could it have
harboured life?
Mission controllers had to find out.
And so Opportunity left Victoria crater and began its arduous journey south.
The mission team were determined to reach their destination as quickly as possible,
while also keeping a look out for anything of interest along the way.
Opportunity made good time across the Meridiani plains, and by sol 1818 it had travelled more
than 3km.
Nothing noteworthy really happened until sol 1947, where a large rock was spotted.
The mission team decided to investigate, discovering that it was a meteorite which they named ‘Block
Island’.
In fact, large rocks seemed to be the only thing to keep Opportunity busy, later spotting
another one named ‘Shelter Island’, and a third called ‘Marquette Island’.
Marquette Island was of particular interest to scientists though, as they believed this
rock was part of the ejecta from a large meteor impact, meaning this rock would have come
from deep in Mars’ crust.
Scientists could tell because the grains within the rock are coarse with a basalt composition.
The coarseness indicates it cooled slowly from molten rock, allowing crystals time to
grow.
Had it formed near the surface, the crystals within it would have been a lot smaller as
it would have cooled a lot quicker.
Opportunity was never alone on Mars.
It had a sister rover named Spirit, which was exploring the other side of the planet
at the same time.
They both landed on Mars at roughly the same time, and had both far exceeded their original
expected life span of 90 sols, at this point they were 1900 sols into the mission.
Although, just like Opportunity up until this point, Spirit had encountered some mechanical
failures too.
Most notably, one of its front wheels jammed only 700 sols into its mission, meaning it
dragged this wheel along as it travelled.
In a way, I almost think Spirit was NASA’s darling between the two rovers, Spirit often
got more media attention for the things it was discovering on the planet.
However, it was around the time Opportunity explored those rocks that Spirit, on the other
side of the planet, attempted to drive over a sand dune and got its wheels stuck deeply
in the sand.
Spirit’s operators began the long process of attempting to get it unstuck through simulations
and testing on Earth based replicas.
Meanwhile, Opportunity carried on its long journey to Endeavour.
By Sol 2138, Opportunity finally reached a landmark of note, Concepción crater.
It is only 10m wide, but probably the youngest crater visited yet, evidenced by the exposed
rubble and ejecta.
Nothing particularly new was found there compared to any of the bedrock Opportunity has examined
in the past, which was simply sulphate rich sandstone containing peppercorn size spheres,
known as blueberries.
At least the crater provided a contrast to the vast expanse of rolling sand dunes.
Eight months had passed since Spirit got stuck in the dune.
The sand that enveloped its wheels was particularly fine, and the process of excavating Spirit
was exasperated by its jammed wheel.
During this recovery process, another of Spirit’s wheels jammed, meaning only 4 of the 6 now
worked.
The Martian winter approached for Spirit, and it was getting less and less sunlight
to power its batteries, until finally, a low power fault occurred on the rover, and its
systems disconnected from the battery.
Spirit went silent.
Mission controllers attempted for months afterwards to regain contact with the rover, but NASA
eventually called an end to Spirit’s mission.
For the first time since it landed, Opportunity was now alone on Mars.
Opportunity’s long slog over kilometres of sand dunes to reach Endeavour was becoming
taxing for the rover.
Perhaps overly anxious not to have a repeat of what happened to Spirit, mission controllers
decided to reroute Opportunity’s course, a longer route but hopefully a less arduous
one.
This route would also take it by what was named Santa Maria crater.
By sol 2244, Opportunity set a new record for the longest lasting mission on Mars, finally
beating Viking I’s mission duration.
Opportunity could begin to see the rim of Endeavour, spotting the landmarks of Cape
Tribulation, Cape Byron and Cape Dromedary.
However, even 100 sols later, it was only halfway to Endeavour from Victoria.
It had made good time, considering it has a top speed of 5cm per second, and often went
half of that to be safe, with frequent stops to look out for potentially problematic sand
dunes.
You’ll notice the rover’s tracks are ahead of the rover in this time lapse.
This is because there is also a navigational camera on the back of Opportunity, allowing
it to drive forwards or in reverse to evenly distribute wear and tear on the motors.
Although, another reason right now was to protect Opportunity’s extended arm, which
as I mentioned in the last episode, got stuck in this position.
On sol 2449, Opportunity finally arrived at Santa Maria crater.
It’s a 90-meter-wide crater, and was important to mission controllers as there was already
evidence here of hydrated sulphate minerals.
As I mentioned, hydrated minerals can only form under bodies of water over extended periods
of time, so this was an exciting precursor to what they wanted to really investigate
around Endeavour, which was still a tantalising two-year journey away.
Opportunity also stopped here to take a spectacular time lapse of a Martian sunset or two, with
one of the time lapses showing a transit of Mars biggest moon Phobos across the Sun.
Over two Earth years had passed in just this one episode.
Opportunity had soldiered on well beyond its expected mission lifetime of 90 sols, and
even outlived its sister rover Spirit.
It and the mission team had earned a rest at Santa Maria, and they all spent three months
happily examining rocks and unlocking secrets about the history of Mars.
After that, it was onward and upwards for Opportunity towards Spirit Point, a point
around the rim of Endeavour, an inspiring commemoration of the mission’s loss on the
other side of the planet.
And we will save this journey for the next episode!
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