You join us during the final days of the Spirit rover. 344 Martian days, or sols,
have passed since Spirit’s mission boldly began. The whole World was watching as it entered
the atmosphere at over 19,500 km/h before impacting into Mars’ expansive red desert.
During those first sols the lonely rover faced mission-threatening software and hardware issues,
but it defiantly ventured way past its 90 sol life expectancy to share thousands of images of
Mars as well as evidence for the existence of water on the red planet. In the last episode,
we left Spirit climbing to the top of Husband Hill wondering what secrets it will uncover
below the red planet’s surface and whether it will succeed with its grand mission objectives.
I’m Alex McColgan and you are watching Astrum. Join me today to continue with Spirit’s journey
as it reaches the summit of Husband Hill and pushes on to territory NASA never expected
to reach. We will highlight Spirit’s major discoveries and follow our trusted rover to
the very end. This is a journey as full with scientific discovery as it is with adversity,
one whose legacy continues to inspire us to this day, 20 years after it landed.
We rejoin Spirit on the week of its first anniversary of landing on Mars. To celebrate, it
is studying a rock named “Champagne” on the slopes of Husband Hill; yes, even robots need to party!
And as a robot, it enjoys its ‘Champagne’ in the most socially unacceptable way possible: alone and
with full use of its science payload. To recap, this contains: The Rock Abrasion Tool (RAT), which
exposes the fresh surface of a rock of interest, the microscopic imager (MI), that is able to
capture fine details of a rock’s structure to learn about its composition; the alpha particle
x-ray photometer (APXS), used to measure the elemental makeup of a sample, and the Mössbauer
spectrometer (MB) which is used to analyse mineralogy, or the chemical makeup, of the rock.
After these measurements, however, the Spirit team confirmed the existence of a minor short
circuit of 0.1 V. This short wouldn’t affect the day-to-day operations of the rover but it
would make Spirit more vulnerable to subsequent damage. Otherwise, Spirit was doing well, the team
continued to traverse up the soft dusty slopes in increasingly complex manoeuvres to ensure
that our rover didn’t become trapped - a traverse complicated by increased dust in the atmosphere,
reducing the sunlight reaching Spirit’s solar panels. Some of that dust had settled as a coating
layer on the panels, which meant that Spirit’s team needed to be extremely careful with how
they planned their route and power consumption. Nevertheless, en route to Larry’s Lookout, a point
on Cumberland Ridge, Spirit analysed two small rocks of interest - Peace and Alligator - before
imaging a far larger rock much further away, but one the rover can never hope to reach: Phobos,
Mars’ largest moon, a 26 km wide satellite that is due to impact Mars’s surface in 10 million years.
With its imaging tasks completed, Spirit ventured forth across Cumberland Ridge, but only briefly,
before it made an unplanned stop! NASA’s engineers noticed that Spirit had curiously churned up an
intriguing area of soil during its manoeuvres named Paso Robles. But what was it about this
area of soil that captured NASA’s interest? Paso Robles was found to contain incredible levels of
salt and high levels of phosphorus. “We're still trying to work out what this means,
but clearly, with this much salt around, water had a hand here.” A stunning and fortuitous
find about the history of water on Mars, one that preceded another unexpected discovery
through failure that we’ll reveal later. To complete its journey to Larry’s Lookout
Spirit deftly reversed large sections, this manoeuvre helped to relieve pressure on the
failing front wheel; instead of moving forward and pushing the struggling wheel into the ground,
reversing the rover up the slopes dragged the wheel across the surface, saving Spirit energy.
From Larry’s Lookout, Spirit took this panorama on sol 413. To the right we can see Spirit’s tracks,
to the left is a rocky outcrop which is part of the Cumberland ridge,
beyond that lies the Tennessee Valley. This image was made with 108 frames,
each composed of 5 images taken through Spirit’s different filters,
which creates an approximate true colour image. In the centre of the image, 200 m away and 45 m
higher in elevation is the summit of Husband Hill, Spirit’s next destination. This was to
be a difficult and energy consuming journey, but Spirit had a chance encounter that greatly
improved its prospects. Mars dust devils on sol 421 swept over the rover, clearing
a years’ worth of dust buildup and increasing its solar panel efficiency from 60% to 93%!
Over the next 160 sols Spirit tackled its way to the top. The increase in energy supply meant that
Spirit was able to upload its data every sol with the Odyssey orbiter, allowing the team to
capture lots of information en route including on samples Paso Robles 2, Big Clod, Paso Dark,
Methuselah, Keystone, Pittsburgh, Independence and Franklin without filling up its limited storage.
On sol 581, Spirit reached the first summit of Husband Hill, but our hard-working rover
had no intention to stand idle. It took a 360º panorama composed of 653 images,
for the first time imaging the entire deck of the rover in a panorama.
Look how clean those panels are! During the nights on top of Husband Hill,
Spirit also imaged both moons, Phobos and Deimos in order to measure their orbits more accurately.
In the panoramic image McCool Hill and Ramon Hill are off into the distance in the centre.
McCool Hill was to be its winter destination, an area where Spirit could park up and angle its
panels to the sun to maximise its energy capture over the darker months. But it never reached it.
So let’s continue with Spirit’s journey to see what it can achieve in its final 2.6 kms of life.
On the descent of Husband Hill, Spirit was able to collaborate with the Hubble
telescope to help calibrate data with atmospheric opacity readings, a sky survey
and calibration target readings. These helped with the accuracy of Spirit’s measurements.
Incredibly, Spirit’s capability increased several times in its life, despite being
142 million kilometres away from its team of engineers. The multitasking rover installed an
update as it was climbing Husband Hill, giving it the ability to drive sections autonomously,
and another on sol 1067 allowed Spirit to decide if and when to upload images and
whether to extend its arms to examine rocks. Spirit gained independence as it matured.
There was one decision that the NASA controllers still took on the descent of
Husband Hill, though: which rock to analyse out of a choice between two: “Comanche” and “Miami”.
Commanche was chosen, and it turned out to be a rich subject to analyse. On sol 690,
Spirit discovered that Comanche was 1/4 magnesium iron carbonates,
around 10 times higher than any rock previously analysed on Mars. Carbonates are important in
further understanding the hydrological history of Mars as they are formed in the presence of water,
but dissolved by acid. So their discovery in high levels suggested that more neutral and hospitable
bodies of water existed that could have been home to primitive life much earlier in Mars’ history.
A great discovery, but Spirit continued on tirelessly and it reached its next checkpoint
on sol 744 (Visuals showing Home Plate). Home Plate features layered and weathered rocks,
including this feature found on the outskirts. It’s hard to imagine this
being shaped by anything other than flowing water!
But it was the flow of time that was shaping Spirit. The rover was charging towards the
north facing slopes of McCool Hill in March 2006 when one of its wheels failed. Exhaustive tests
back on Earth at the JPL test facility replicating the failure could not get the wheel moving again,
Spirit was now only making progress by dragging the locked right-front wheel.
Martian winter was coming, too, and as the light fades so too do Spirit’s reserves. With
these two factors combined, NASA made the call to abort the drive to McCool hill in
favour of Low Ridge Haven. The rover found a spot with an incline of 11º,
which was sufficient to see Spirit make it through another Martian winter.
For around 8 months, Spirit remained on the ridge taking images of its surroundings. In
one of the images, engineers spotted two subjects that were possible iron
meteors. These were given the names: Zhong Shan after the Chinese Antarctic base,
and Allan Hills after an area in Antarctica where several Martian meteorites have been
discovered. Including the most well known and noteworthy of these, ALH84001.Found in 1996,
NASA scientists suggested that this Martian meteorite may contain fossilised extraterrestrial
life and released this image you may recognise as it became front page news the world over.
Once the Martian winter was over, Spirit had far more energy to use and it ventured out once
again. In March 2007, Spirit unwittingly excavated a surprising discovery. In the
soft and red Martian soil, Spirit’s failed wheel gouged the Martian surface exposing
bright white silica. Not evidence for life, per se, but the next best thing. Evidence
for the potential of life. In our video on the origin of life we talked about deep sea vents
and areas where hot gases and material from below the crust meets the Earth’s
surface. Some create the potential for life to start, others offer life a haven for growth.
NASA believed that the silica deposit was made in one of two environments:
hot spring deposits, where hot water dissolves silica in one place and then deposits it
elsewhere, like hot springs or geysers. or ii) acidified steam blasting existing rocks
stripping them of much of their minerals leaving mostly silica behind, areas known as fumaroles.
Whichever it was, both environments are very supportive of microbial life
on Earth! Incredible to think, if Spirit had not malfunctioned,
if it and NASA had given up too early, this discovery would never have been made.
Spirit spent the next few months circling Home Plate and in June
2007 received another life-saving spring clean of its solar panels.
Spirit boosted its power generation from a dip of 120 w/h back to over 600!
On November 6th, Spirit navigated to the western side of Home Plate and took another panorama. NASA
published this photo as a “Astronomy Picture of the Day”, which on first inspection looked like
every other photo taken of the Martian landscape. But it was soon to receive worldwide attention!
Can you spot it? Hiding in plain sight is a suspected humanoid life-form. Let’s zoom in to
what was dubbed ‘Little Bigfoot’. On the right of the image we can also see Spirit’s tracks
from Husband Hill! We are now a few hundred metres away from the end of Spirit’s journey.
Martian storms had been increasing in recent months, leaving the solar
panels heavily covered with dust as well as blocking up to 99% of the light through the
atmosphere. Survival was becoming harder and operations were now much reduced from its peak.
The ageing Spirit was generating only 128 w/h which is less than the 150 w/h it requires to
keep itself warm If the heating fails then the rover’s components will eventually fail, too.
Two small cleaning events took the energy output of the solar arrays to 372 w/h. This
gave the rover enough energy to charge its batteries and begin to move again.
But the flow of time is always cruel. Spirit began to experience unexplained memory gaps
in April 2009 with the rover now only 4 metres away from its resting place.
On sol 1892 Spirit hit incredibly soft dusty soil at a location named Troy,
where Spirit would make its last stand. Underneath its wheels was jarosite,
which is a mineral of iron(iii) sulphate. Jarosite has remarkably low cohesion meaning
that achieving enough traction to move was proving impossible. Despite efforts by the
JPL back on Earth to explore techniques to escape the sand trap no progress was made. On sol 2155,
NASA reclassified the mission as a stationary research platform. While there our rover took
measurements of the atmosphere and several more images, including its last panorama from Troy.
Spirit was still able to perform soil studies and extraction tests because the functionality
of its arm was still excellent. Spirit needed to have a busy research schedule to use the power it
was generating to maintain good battery health. But the final winter was approaching for Spirit,
and it was a bitter one. Over the next few months, the power generation continually dropped,
and by sol 2196 it was again down to the critical 150 w/h. Sometime on sol 2208,
it is believed Spirit suffered a low-power fault.
On a lifeless and quiet planet, Spirit’s end was never going to be dramatic, but that’s not to
say Spirit went gently into that good night. Now forgotten by many who watched Spirit’s landing,
it came to rest on the edge of Home Plate, alone, with two broken wheels,
a drained battery and a legacy of scientific discovery.
In its life of 2088 sols, Spirit journeyed 7.7 kilometres and transferred over 128,000 images
back to Earth. Its mission was an overwhelming success, achieving its objectives to further
the understanding of the history of water – and the chance for life – on Mars. Its name
lives on in the name of asteroid 27452 Spirit, and the Perseverance rover is
carrying its memory today; with this, a family portrait of the Mars vehicles.
Spirit’s story is one of overcoming. Both the Spirit and Opportunity rovers
lived up to their names given to them by a seven year old girl called Sofi;
names inspired by the struggles and promise of her own childhood. So it’s fitting that as
the Spirit’s internal heaters turned off, as it froze under the Martian star-scape,
the rover’s story came full circle and found its end right where it began with Sofi’s:
“It was dark and cold and lonely. At night,
I looked up at the sparkly sky and felt better. I dreamed I could fly there.”
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