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The biggest source of methane here on earth is flatulent cows that's right
cow burps and cow farts. Now the methane technically doesn't come from the cows themselves
but from the microbes that live in their gut that help them digest all of the plants that they eat.
Once the digestion is done the cows pass the methane gas and it enters our atmosphere and
becomes a greenhouse gas and contributes to global warming. But what has that got to do
with mars? Well because of its connection to life here on earth it's been considered for a long time
a potential biomarker - a signature that life, at least microbial life, might be present on another
planet. Science is never that simple though because methane can also be produced in geological
processes, you know by rocks. So when the first detection of methane in the martian atmosphere
was made back in 2014 people were obviously excited but also cautious as well you know
we had to repeat the experiment we'd need more measurements from other satellites and rovers and
landers to confirm whether methane had actually been detected. Little did they know then though
that all those extra measurements would just lead to even more confusion and a scenario that we're
only just beginning to explain. Kind of like a science whodunnit this is the story of the
Martian Methane Mystery. Now methane on mars is nowhere near the concentrations that we see
here on earth. In 2019 the methane concentration in the earth's atmosphere was measured at 1886
parts per billion per volume. On Mars it's more like one part per billion per volume. To put that
into context it's like a little pinch of salt in an olympic sized swimming pool and that's
not even a real exact measurement it's actually what we call an upper limit. Essentially we know
the methane has to be less than that otherwise we would have detected it in all the experiments
that have been run over the years either with telescopes here on the ground or satellites in
orbit around mars. And even curiosity rover when it landed on mars in 2012 it put a limit on the
amount of methane in the martian atmosphere of 0.5 parts per billion per volume - that's barely
anything right? It's nothing to write home about so off curiosity when doing other things but then
in 2014 curiosity detected spikes in the methane concentration over the span of about
two months the average out at about 7.2 parts per billion per volume and it's also seen the
normal concentration of methane changing with the seasons as well. That means something
on mars is producing methane seasonally but also with these random spikes as well and we
just don't know what it. Monica: "It just got interesting!" Now since 2018 a satellite that's
in orbit around mars ESA's ExoMars trace gas orbiter has been continuously searching for
signs of atmospheric methane now the methane detector on exomars is supposed to be the
gold standard for detecting methane it's used in industry on earth loads it's also used on the iss
as well to give advanced warning to astronauts if there is like a methane leak or something.
But on mars this gold standard detector didn't detect any methane in the martian atmosphere
and so curiosity's detections of seasonal variation and random spikes were then massively
brought into question if the thing that's like the gold standard didn't detect anything. Now ExoMars
is only sensitive to methane above about three kilometers in altitude in the martian atmosphere
and also its limit on the amount of methane it can detect is only five parts per billion per
volume. You might be thinking well what curiosity detected was lower than that but the problem is
if this methane is perhaps being released let's say by the martian rocks or something like that
at the surface continuously, and curiosity is able to detect that amount that is being pumped out,
that should slowly build up in the atmosphere, get well mixed and should get above concentrations
that ExoMars should then be able to detect. But that's not happening. At the rate that
curiosity is detecting at the ground, if you assume that that's what it's pumping out,
it should have built up to a concentration that exomars can detect in about 28 years! It's
*highly unlikely* that these methane emissions from the ground have only just started in the
past 20 years or so when curiosity just happens to have landed on mars when mars has been around for
4.5 billion years. So once again that leaves us with this discrepancy between what curiosity
measures and what ExoMars measures - it's a classic science mystery that needs solving. And
so the curiosity team especially put their heads together and were like "what could be the possible
explanations for what we've seen?" and the first thing they started with was "is the rover itself
giving out this methane?" Perhaps by rolling over rocks and crushing them and releasing any
trapped gas but the spikes in methane it detected didn't correlate with any movement of the rover,
the rover was always still when it took those measurements, so that was quickly dismissed.
Then the next idea was well could there be some methane leaking from other instruments
and detectors within curiosity rover itself? But you know every system was double and triple
checked and they're pretty sure there's no methane leaking from the rover. The next idea was whether
these methane spikes perhaps correlated with like a direction that the rover was facing in perhaps
towards like a certain rock formation or something that might just be a very high concentration
of methane but again no there was no correlation there. And similarly there was no correlation with
wind direction either, perhaps the wind bringing something over from a very high concentration
of methane somewhere. All of those ideas were thrown out but then one of the curiosity team
scientists Dr John Moores had an idea and he said in an interview with nasa that he took: "a very
canadian way of looking at this" and said: "what if both curiosity and ExoMars are both right?"
I just love this very canadian way of looking at things! Because they realized there was
a correlation with the time of day that the measurements were taken. Up until 2019 all the
methane concentration measurements that curiosity had made had happened at night when there wasn't
much else going on with the rover. So what the team did was then measure the concentration of
methane during the day and noticed that it was much lower it dropped to 0.05 parts per billion
per volume down from the 0.5 parts per billion per volume that averaged out over the night time. So i
guess that's kind of like a 10% of a pinch of salt in an olympic swimming pool - scientists
should never write recipes i'm just gonna put that out there! And guess what the ExoMars satellite
had only ever taken its methane concentration values during the day because it physically
needs sunlight in order to be able to make the measurements. So all of those measurements the day
and the night concentrations have been explained in a paper published recently by Webster and
collaborators, which i'll link in the description below if you want to check it out. And the way
they've explained this day night difference is due to the weather essentially. So at night it's much
cooler the atmosphere is much calmer and methane seeping from the rocks, due to whatever process,
is building up at the surface essentially. But when the sun rises it starts to heat up the air
and then that sets up a classic weather pattern of hot air rising taking the methane with it and then
cold air falling and that mixes it all up in the atmosphere lowering the concentrations to below
what ExoMars can detect during the day. So that study at least gives us one possible explanation
for the discrepancy between the curiosity and the ExoMars measurements but it still leaves a whole
boatload of other unanswered questions the first of which just being what is producing this methane
on mars? Especially these weird spikes and this seasonal variability which is to be honest just
weird. Although given the fact that the weather explained the last problem it's likely that
something to do with the sun and solar radiation could explain the seasonal variability as well.
Perhaps in the summer there's more incidence of solar radiation that melts some ice trapping
methane gas that's perhaps trapped underground, so we don't know how it's gotten underground
whether it is just coming from rocks or maybe there's some microbial life living underground
there perhaps releasing methane we just don't know. The second question that still remains
is why isn't this methane, which is coming from rocks or microbial life we don't know, why isn't
this methane building up in the atmosphere over time? Curiosity landed in Gale Crater and that's
where its detected these higher concentrations of methane at night and including these spikes
as well. Now we don't think there's anything special about gale crater if gale crater is
emitting methane then probably the rest of mars is too so it should have built up to concentrations
that ExoMars can detect but it hasn't. Now we know that methane is stable in the martian
atmosphere for at least 300 years before it does get broken down by the impact of solar radiation,
but 300 years is still enough time for it to build up to concentrations that ExoMars
can detect. So there must be something else, some other process going on, that is somehow destroying
the methane. And whether that is perhaps you know just reabsorption by rocks of the methane? People
propose the idea that static electricity generated by the dust storms and sandstorms, that we see
engulf mars occasionally, could actually be creating static electricity that could destroy
the methane. Or perhaps maybe it's reacting with oxygen in the martian atmosphere as oxygen is
very reactive and perhaps that's getting rid of the methane. There's lots of ideas but we still
don't know which one is actually happening. Either way like whatever is happening on mars
this study that's come out this month has at least given us one piece of this very confusing puzzle
but rest assured there is still a whole heap, a truckload, of unsolved martian methane mysteries!
Before we get to the bloopers a huge thank you to this week's video sponsor
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opportunity to learn and for continuing to support this channel. But now roll those bloopers...
was one thousand eight hundred and sixty six parts pavilion, parts pavilion? parts per billion per
volume - i'm going to trip over that so much in this. On mars however the methane concentration is
more like one parts pavilion... pavilion?! oh my god i said it again parts per billion per volume.
It put a limit on the amount of methane in the atmosphere of 0.5 parts pavilion...
And it can only measure down to about 5 parts pavilion per volume - pavilion?! Why?! WHHHYYYY?!