The date was the 17th May 2013, roughly 3000 Sols, or Martian days since the Opportunity
rover had landed on Mars, and it had just made the most important discovery of its entire
mission.
After kilometers of travelling, it had come to the edge of the biggest crater of the mission,
and along this rim, it found a vein in the ground which scientists named ‘Esperance’.
This vein confirmed that a large body of water was - at one point in the distance past - present
on the Martian surface.
Esperance was a hydrated rock, or a clay, which can only be formed while under a body
of water for a significant period of time.
Opportunity had discovered clues that water existed on Mars in the past, but until this
point it had only found evidence of flooding events.
However, Esperance was likely to be proof of a past ocean.
I’m Alex McColgan, and you’re watching Astrum, and in this sixth video in the Opportunity
series, we will follow this rover’s tracks beyond Esperance, and find out what it saw
and discovered around its winter lodgings at Solander Point.
Even though this huge discovery had been made, Opportunity still had a lot ahead of it.
Mission controllers wanted more evidence of water, and they had their sights set on Solander
Point, about 1.5km further south from Esperance.
Martian winter was starting to come around again, which brings with it a reduction in
sunlight, from the length of the day, to the angle of the Sun in the sky.
To maximise the generation of power for the little rover, Solander point was chosen as
it’s a north facing slope, meaning as Opportunity explores the area, its solar panels would
be angled towards the Sun too.
It was also believed to contain more evidence of hydrated minerals and exposed layering
in the rocks, as spotted by the Mars Reconnaissance Orbiter.
1.5 km doesn’t seem so far away, but Opportunity was a slow rover, with a top speed of only
2cm/s, and it often travelled half that to be safe.
Scientists didn’t want it to crash into rocks, or get stuck in sand dunes, so Opportunity
would move forward a bit, look around for hazards, and repeat the process.
Along the way, the floor underneath Opportunity looked very peculiar.
It was primarily large chunks of rocks, smoothed off at the top, with sand and dust filling
the gaps, almost like a random mosaic.
Flat rocky ground is the ideal terrain for Opportunity, so it made good progress on the
way to Solander Point.
Much like the rest of the mission blueberries were spotted again, rounded rocks a cm or
two across.
By Sol 3390, Opportunity made it to its winter lodgings, and began work on the slope.
Even while working here, energy production was very low, hitting only 270 watt-hours
per day.
Any lower than that, and the rover would have gone into a type of hibernation mode.
This was due to the Martian winter, but also because dust had been settling on the rover’s
solar panels, and there hadn’t been a cleaning event for a while.
This low power mode meant that work around Solander Point was slow, and it wasn’t until
Sol 3530 that a cleaning event finally pushed energy production up to 370 watt-hours per
day.
Cleaning events occur when wind blows extremely fine dust off the panels.
Because Mars is so arid, there’s nothing adhesive about the dust, so even though Mars’
atmosphere is so thin, these dust particles can easily be blown off.
A bit like blowing dust off the cover of a book.
Dust settles on the rover over time, especially during the massive dust storms that are so
big, they can be seen from space.
Around Sol 3519, Opportunity spent the day examining a surface target.
However, embarrassingly, the mesh they use to calculate the distances of objects to the
rover was wrong, meaning the instruments on the arm were off by about 5cm, so the images
taken were blurry and the Alpha Particle X-ray Spectrometer couldn’t properly detect what
it was looking at.
This was quickly rectified, and the usual crisp images started coming back to mission
control again.
A bizarre discovery that was noticed just a few Sols later was something known as Pinnacle
Island.
Opportunity often took days to examine certain patches of ground, but scientists noticed
some variation between one photo, and another taken a few days later.
This rock seems to have appeared out of nowhere.
Mission controllers weren’t so impressed though, putting it down to a nearby meteorite
impact, or even Opportunity bumping the rock into place with one of its wheels.
A flyby of the Mars Reconnaissance Orbiter revealed no fresh impact, so that discounted
that theory.
But mission controllers sent Opportunity on its merry way without investigating the rock
further.
This caused outrage online, with people suspecting aliens left the rock there as a means of communicating
with us on Earth, or that is was a type of fungus that had grown over the 12 days between
photos.
Some people even went to the lengths of suing NASA over their reluctance to investigate
Pinnacle Island further by imaging it with the microscopic camera onboard Opportunity’s
arm.
However, before that really got going, as Opportunity looked back on Pinnacle Island,
the mystery was solved.
Opportunity had indeed cracked a rock in half, as can be seen by the tracks left in the sand.
As far as we are aware, this was the first time something like this has happened on its
whole mission.
But the chances of it occurring were likely increased as Opportunity’s arm was getting
less and less mobile through wear and tear.
This means that the rover itself now had to turn in order for the arm to reach specific
objects, instead of the arm simply reaching across.
Another problem that was becoming more and more persistent for Opportunity was the onboard
computer randomly resetting.
Although Opportunity was always able to turn back on, each reset wasted about a day’s
worth of science activities.
By Sol 3749, these resets caused about half the month to be missed.
Mission controllers narrowed the problem down to the onboard flash memory.
Flash memory can get temperamental after repeated use, heightening the risk of losing new photos
before they can be sent back to Earth, and so the decision was made to reformat the entire
drive.
This would not only clear the storage, but also identify any bad cells within the drive
itself, so those cells can then be avoided in the future.
By Sol 3773, the reformatting was completed successfully.
Soon thereafter, Opportunity reached Wdowiak Ridge, south of Solander Point.
As this was going on, a visitor from the outer edges of the solar system was hurtling towards
Mars.
Its trajectory would take it just 130,000km above the planet’s surface, before it continued
on towards the Sun.
This visitor was again not an alien, but Comet Siding Spring, a visitor from the Oort Cloud.
The Oort Cloud is found well beyond Pluto and the Kuiper Belt, millions of icy rocks
in orbits that take millions of years to complete.
Because it had such a long time to accelerate towards the Sun from the furthest point in
its orbit, the trip from Mars to the closest approach to the Sun only took 6 days.
That’s 56km per second.
However, because of the close flyby of Mars, it meant that the spacecraft on and around
Mars where actually in a better spot to witness Comet Siding Spring than we were on Earth.
Mission controllers of the various missions were also a bit nervous about the dust particles
that are ejected from the comet travelling that speed, potentially impacting and damaging
spacecraft in orbit around Mars.
As such, Hubble, as well as spacecraft around Mars, all began observations of this visitor.
Fortunately, mission controllers had already had some practice at this with Comet ISON,
another comet that passed by Mars only the year previously.
Comet ISON, however, was 80 times further away than Siding Spring would be, too far
and too dim for Opportunity to spot.
Unfortunately, it was day just as Siding Spring made its closest approach to Mars, but Opportunity
was able to snap a couple of photos of it just before dawn.
Can you spot it?
Here’s the annotated version of the same image.
As it passed by, none of the spacecraft were damaged by ejected dust particles, but what
they did observe from this flyby was completely unexpected.
As it passed by, it plunged Mars’ weak magnetic field into chaos, albeit temporarily.
Unlike Earth, Mars doesn’t have a magnetic field generated from within its core.
Its magnetic field comes from plasma high up in its atmosphere, which generates a very
weak charge.
This is enough to deflect solar wind coming from the Sun, but solar storms from CMEs and
solar flares push past this induced magnetic field, stripping away atoms from the atmosphere.
Comet Siding Spring had a very similar effect on Mars.
Comets are also surrounded by a magnetic field, again induced from interactions with the solar
wind, this time with the comet’s atmosphere, or coma.
A comet’s coma can reach out for a million kilometres from the comet, meaning that as
Siding Spring passed Mars, Mars was enveloped in its coma for a good few hours.
This merged both magnetic fields for the duration of the event, with charged particles from
both objects interacting strongly with each other, and the atmosphere of Mars lost some
particles to space as a result.
However, apart from the image Opportunity was able to take from the surface, all this
went largely unnoticed by the rover.
2015 was quickly approaching, and Opportunity was heading for Marathon Valley, which would
take the odometer reading of Opportunity to the distance of a typical marathon.
But we will have to save that for next time!
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