You've likely all seen the news by now.
NASA found a possible sign of life on
Mars.
These tiny spots, barely visible to the
naked eye, are the biggest space news in
over 50 years. If this really is a sign
of life, it would be the most meaningful
discovery in the history of humanity.
But we've been burned by false alarms
before. So, have we really done it this
time?
I'm Alex Mccoan and you're watching
Astramm. Join me today as we dig into
the details of what Perseverance found,
why scientists are excited, and what it
will take to prove we're not alone in
the universe.
In February of 2021, NASA's Perseverance
rover, or Percy to his friends, touched
down on an ancient Martian lake bed. The
Yzero crater was once home to a large
body of water with rivers flowing in and
out, carving deltas, and carrying
sediment. The soil is rich in clay
minerals that can only form in the
presence of water. Percy has been sent
to hunt for ancient microbial life. If
it's going to find them anywhere, the
Yzero crater seems like a good bet. You
see, ancient legs often contain
perclorate, which can be metabolized by
microbes.
Astrobiologists on Earth study microbes
like this in extreme environments to
understand if life could survive in
similar conditions on other planets.
The rover's job is to look for these
possible signs of life, identify and
store the most interesting samples of
Martian rock, and prepare them to be
collected by another space mission for
an eventual return to Earth.
One day in July 2024, while exploring
the edges of the ancient Naret Vales
River Channel, Percy's cameras spotted
something unusual. A rock from the
Bright Angel Formation.
two of the rover's instruments, the
planetary instrument for X-ray
lithocchemistry or pixel and the
scanning habitable environments with
ramen and luminescence for organics and
chemicals or Sherlock for short detected
sedimentary rocks made of clay and silt.
On Earth, these materials are excellent
preservers of microbial life. So Percy
took a closer look and it saw something
amazing.
The rock, also known as Chiava Falls,
was rich in organic compounds like
carbon, phosphorus, and iron arranged
into rings. Affectionately named leopard
spots and poppy seeds. The tiny spots
span 200 micrometers to 1 millimeter in
diameter, but it was enough to raise the
blood pressure of astrobiologists
everywhere.
The light inner part of the leopard spot
is chemically similar to the surrounding
rock, but the dark outer rim is enriched
with iron and phosphorus. It seems to be
evidence of localized iron reduction.
Percy also detected organic carbon-based
compounds in the rock and based on its
texture and geochemical composition, we
strongly suspect this rock was once in
contact with water. Usually when we see
such a combination of organics, water
and iron reduction on Earth is
interpreted as a sign of microbial life.
Suddenly NASA had something very unique
on its hands. Could this mudstone rock
hold the first alien bio signature ever
found?
At the center of this story are two very
special minerals, vivionite and grey.
Vivianite is an iron phosphate. On earth
it forms near metal ores and river
sediments where microbes like geobacttor
metabolize iron instead of oxygen. They
take in iron 3 oxide and release iron 2
as a waste product. The energy given off
by this reaction then powers their
metabolism, a process known as
cheosynthesis.
When the expelled iron 2 reacts with the
phosphate and the water in the
environment, it forms vivionite.
Greygite follows a similar story.
Sulfate reducing microorganisms on Earth
break down sulfate into sulfide which
reacts with iron to make greygite.
But let's be skeptics for a moment and
rule out microbes for now. What else
could have caused these reduction
reactions?
Well, one explanation could be very high
temperatures. The sulfide needed to
produce Greygite could have come from
volcanic gases leaking into groundwater,
but that means the sulfide would have
had to migrate from a hot volcanic
system into a much cooler environment.
And there's been no evidence for such
volcanic or hydrothermal sources nearby.
Another possibility is that sulfate in
the rocks was reduced to sulfide through
reactions with organic matter. But
unless temperatures exceed 150 to 200°
C, these reactions would be very slow
and require a huge amount of energy,
making them unlikely. And studies of the
rocks around this area have shown no
evidence of high temperatures. So
there's no way the surrounding
environment could have got hot enough to
reduce sulfate and form Greygite.
Another possible explanation is acidity.
Both iron 3 ions and sulfate ions
dissolve much more readily in water
under acidic conditions than they do
under neutral conditions, making them
much more prone to reduction through
purely chemical reactions. If the water
on Mars was more acidic than we
anticipated, that could have caused the
spots Percy saw. Perhaps these spots
were just the result of chemical
processes on an alien planet, nothing
more. But then Percy spotted this little
green mineral nestled near the sample
site. A small rock of olivine knocked
the acidic water hypothesis on its head.
Olivine is the fastest weathering
silicut mineral. Unlike other silicone
structures like silicon dioxide for
example, olivine doesn't have strong
silicon oxygen silicon bonds. Instead,
it's made up of negatively charged
silicut ions held together by the
electrostatic attraction with positively
charged magnesium and iron ions. In
acidic conditions, these are displaced
by hydrogen ions, breaking olivine down
into orthosic acid and magnesium ions in
solution. The more acidic the
environment, the more hydrogen ions
there are and the more aggressive the
dissolution of olivine would be.
So the very fact that it exists rules
out the possibility of acidic conditions
causing the strange spots.
Science is ultimately about
falsification. It's not about proving a
hypothesis true. Much more often it's
about proving a hypothesis false. Over
time and through a process of
elimination, all roads seem to point to
the same explanation.
And if that explanation holds up against
enough skepticism for long enough, it
eventually becomes an accepted theory,
testable, reliable, and widely accepted
by the scientific community.
In this paper, the Mars research team
tried to prove that these minerals were
not left behind by ancient alien life.
They started with a null hypothesis and
systematically investigated all the
non-living explanations for what they
found. But after months of study, they
concluded they just couldn't do it. Now,
saying we can't explain how this was
done by something non-living is very
different from saying this is a
definitive sign of life. For one thing,
all our speculation and contained
excitement is based on what we know
about biochemistry on Earth. And no
matter how tempting it may be, we cannot
allow ourselves to assume that just
because something happens one way on
Earth, it would happen the same way on
Mars. Maybe it has a totally different
biochemistry we know nothing about.
NASA's being extra careful not to say
too much too soon. After all, we've been
wrong about potential bio signatures on
Mars before.
Back in 1976, the Viking lander tested
Martian soil for life by squirting it
with nutrients labeled with radioactive
carbon 14. If microbes were present,
they'd metabolize the nutrients into
radioactive carbon dioxide we could
detect. And to everyone's shock, that's
exactly what happened. Excited
scientists thought they had proof of
alien life. But in 2008, NASA's Phoenix
Lander found Martian soil to be rich in
plecchlorate, a powerful oxidant that
destroys organics and releases gas when
heated. What looked like a biological
reason was really just chemistry, a
false positive.
Still, Mars kept dangling hope. In 1996,
a photo of meteorite Alh84001
made headlines. The rock itself was over
4 billion years old from a time when
Mars had liquid water on its surface.
Under the electron microscope, tiny
structures emerged resembling bacterial
colonies. The world stood still.
Researchers thought they were on to
something big. so big that President
Bill Clinton gave a formal announcement
about the discovery. Sounds a lot like
NASA's recent statement of Percy's
discovery, doesn't it? But in 2022,
those squiggles were ruled
non-biological,
explained instead by a water rock
reaction called serpentinization.
Another false alarm. So, is our recent
finding in the Yzero crater another
close call? Or is it proof that the
third time really is the charm? There's
only one way to find out. We have to
bring the sample home for further
testing.
That's where the Mars sample return
mission comes in. It's a complex mission
which requires sending three separate
spacecraft to Mars. Percy has already
completed phase one. It's drilled into
Chiava Falls and tucked away a precious
core sample of the mudstone rock mission
scientists named Sapphire Canyon.
Phase two would be to send another
spacecraft to land near Perseverance,
collect those tubes, and launch them
into orbit around Mars. The third and
final craft would collect the samples
from the orbiter and ferry them all the
way back to Earth. It's a huge task with
an estimated price tag of 11 billion.
The Mars sample return mission was first
announced in 2022 as a joint
collaboration between NASA and issa.
Since then, it has been fraught with
financial struggles and uncertainties,
delaying the project from 2033 to 2040
before ultimately being suspended
indefinitely.
This is despite the National Academy of
Sciences decadel survey, a meeting of
leading scientists who get together
every 10 years to decide the future
priorities for progress in STEM, naming
the Mars sample return as the highest
priority for NASA two decades in a row.
And that was before we discovered this
potential bio signature on our
neighboring planet.
All we can do is hope this puts
political pressure on leaders to
mobilize the necessary resources to pull
it off.
So if we ever do get the Sapphire Canyon
sample back home, what kind of
experiments might scientists run?
There's a good chance that among other
things, they'll be looking for two key
fingerprints of life. The first is
kirality. Amino acids come in two mirror
image versions. right-handed and
left-handed, also known as D and L amino
acids. On Earth, life overwhelmingly
prefers the L version of things, while
non-living materials show more of a
50/50 split.
If the Martian sample shows a
significant chairo preference, either
right or left-handed, that could be a
smoking gun. The second fingerprint is
carbon isotopes. Carbon comes in a few
different flavors, most commonly carbon
12 and carbon 13. Again, life prefers
one over the other. The ratio of carbon
12 to carbon 13 in living things is much
higher than in non-living things. If we
see a similar pattern in the Sapphire
Canyon sample, that could be another
clue that its origin is biological.
You see, you and I may often think of
discoveries like these in quite a binary
way. Either they're a sign of life or
they're not. But NASA has a much more
nuanced take. They recently proposed the
confidence of life detection scale, a
framework for ordering how likely
discoveries actually are to be signs of
life based on a set of criteria. It has
seven levels ranging from we found
something that could be caused by life
all the way to multiple teams have
independently confirmed life more than
once.
NASA hasn't stated where the discovery
in the Ezero crater falls, but I'd guess
probably somewhere between levels three
and four. If the samples come back and
independent labs around the world all
confirm that what we are seeing really
did come from a biological origin, that
would push us up to a level six. Level
seven might even require going back to
Mars and finding the same evidence in a
completely different location.
So, when NASA says this discovery could
be the clearest sign of life we've ever
found on Mars, they don't mean to say it
is clearly life. But the Mars sample
return mission could finally reveal
whether we've always been alone in the
universe or did we once have a cosmic
neighbor?
Even if our sample turns out to not be
life, it's still an extraordinary
discovery that will help us understand
our own origins even better. See, we
think Mars is like a time capsule of an
early Earth. Unlike Earth, Mars doesn't
have any continental drift or an active
plate tectonic system. Its crust has
been frozen in place for billions of
years, preserved in a way Earth's crust
could never be. The ancient landscapes
on our planet have been erased through
tectonics, erosion, oceans, and
volcanism. So when we study Mars, we're
not just asking whether it once carried
life. We're also peering into a record
of planetary conditions that resemble
Earth at the dawn of biology. In that
sense, Mars is a window into our own
origins, offering clues to what Earth
might have looked and felt like before
life left its mark.
But let's dream for a moment, shall we?
What if the sample does turn out to be
life? Well, most immediately it would
indicate that Mars was habitable far
longer than we imagined since the sample
comes from relatively young sediment.
But more importantly, we'd finally
answer the question, can life exist on
other planets? And in the same breath,
open a Pandora's box of follow-ups. Did
life on Earth start on Mars or the other
way round? Did a meteor from
interstellar space seed life on both our
planets or did it arise spontaneously
twice? Where else could life exist in
the universe? How common is it really?
It would also have implications on the
Drake equation, a probabilistic formula
used to estimate the number of alien
civilizations in our galaxy.
The L value here, which stands for the
fraction of potentially habitable
planets that go on to develop life,
would jump from vanishingly small to
closer to one. Since two out of two
neighboring planets would then have or
have had life at some point, an increase
in this value causes the number of
civilizations in the universe to shoot
up. But crucially, this coefficient only
changes if life on Earth and Mars rose
independently.
If we're related, the products of
panspermia, that still represents just
one biogenesis event, and the outcome of
the equation remains unchanged.
There's a concept known as the 01
infinity rule. In astrobiology, it
represents the idea that life can only
exist in zero, one, or infinite places.
We already know it's not zero. If it's
just one, then we're alone. A single
spark in the dark. But if it's two,
Earth and Mars, then why not five,
5,000, 5 million, or even infinite
places in the universe? Suddenly, life
isn't rare. We're not special anymore.
And personally, I hope that if we ever
discover life out there, it brings us
closer together down here.
When it comes to the search for life on
Mars, we might be looking in the wrong
place.
Recently, I was asked by Timothy Walter
on Patreon about the most likely places
in the solar system to find life outside
of Earth. Mars is certainly a contender.
In the first billion or so years of its
existence, Mars was in many ways similar
to Earth, and it's entirely possible
that life could have emerged on its
surface before the planet underwent
changes that made Mars much less
hospitable. That's why NASA rovers such
as Perseverance are investigating places
like Yzero Crater to investigate those
dried up deltas for any evidence that
life might have once flourished there.
But as I looked deeper into the topic,
it struck me that this might not be the
most likely home for life on Mars. There
is another location that is an even more
likely contender for life. and
incredibly that life, if there might
even still be alive to this day. I'm
Alex Mccoan and you're watching Astramm
Answers, the series where we take
questions you post to us on Patreon and
uncover the answers. And today we're
going deeper than ever before into a
world where a deep biosphere might
thrive. I'm going to answer where I
think is the most likely place to find
life on the planet Mars.
When it comes to life forming though, we
should probably start at the beginning.
It's worth recognizing that we're going
to get a little speculative for this
video, as there are many aspects of the
origin of life, even on Earth, that are
right now still unknown. I did a video
recently on how life likely first came
to be, and one of its key points is that
there's still a lot of debates over the
specifics.
It's also worth noting that we do not
know for certain that life does exist or
ever existed on Mars at all. But there
is some evidence that is intriguing.
NASA's Curiosity rover has detected
methane in Mars's atmosphere, which
mysteriously only emerges at night and
is strangely absent during the day.
Methane on Earth is mostly produced by
living organisms. So, it's an intriguing
indication that life might be on Mars,
too. However, this is not definitive
proof, as there are also non-organic
ways to make methane, as I talk about in
one of my other videos on life on other
planets.
So then why do scientists think that
Mars might be or used to be the home for
life in the first place?
It's all thanks to what Mars looked like
in the first billion or so years after
it formed.
According to our best theories of how
life first came to be on Earth, there
are some key things that you need.
Water, for one, all life on Earth seems
to need it. but also mechanisms for
producing diverse and complex chemical
structures. The raw building blocks of
life from which protoells could arise.
Something like a deep sea thermal vent
would help with that. Or possibly a
volcanic hotring as they would release a
nice spew of minerals and chemicals that
could then hopefully be formed into very
basic protoells if conditions were just
right.
Finally, on the note of those
conditions, you need some kind of
selective pressure to choose some
chemical structures and discard others.
This is quite similar to evolution in
that it wouldn't work if there wasn't a
selective pressure to guide it. For
animals, this could be a scarcity of
food encouraging the survival of those
best able to locate it. But for chemical
structures, it could be something like a
cyclical environment that is sometimes
wet and sometimes dry. Testing to see if
certain structures can survive those
kinds of changes. The structures that
break apart when faced with this stress
test are selected out while those that
survive can move on to the next round of
selection. A sort of evolution but for
rocks.
On Earth, evidence suggests that life
arose within the first billion years
after the planet formed, which is quite
fast on the cosmic scale of things. And
it turns out that on Mars, its first
billion years of existence had these key
factors and more. It also had a thick
atmosphere and a magnetic field to
protect any fledgling life from deadly
solar radiation and to allow bodies of
liquid water to form without evaporating
away. It had volcanism providing energy
from the planet's warm core and those
vital chemical building blocks. Sunlight
also provided helpful energy to the
planet. If the presence of these things
on Earth made it, meaning capable of
supporting the genesis of life, then it
could well make Mars irriable, too.
However, there's a built-in time limit
here. After 1 to two billion years, the
water had all dried up. Mars had cooled
enough that the mechanism powering its
magnetic field had ceased and over just
a few hundred million years later the
atmosphere had been stripped away. This
eventually led to the evaporation of all
the liquid water on the planet with the
only remaining water being locked in the
ice on the polar caps. So life on Mars
would need to have formed during those 1
to2 billion years after the planet's
formation. NASA is working under the
assumption that this is the case and so
they've sent rovers and landers to
investigate craters like Yzero for any
ancient signs of life. Perseverance has
collected 21 rock core samples as of
April 2024, which it got from drilling a
few centimeters into the stony surface
of Mars. Yzero crater once held a large
body of water and a delta. If living
things had made that water a habitat,
their remains could well have dropped
into the bottom of the delta to be
captured in the sediment there. There is
even a chance that they're still locked
into that sediment. Researchers in the
journal Astrobiology found that even
when completely dried up, frozen, and
subjected to intense radiation, certain
kinds of bacteria on Earth could
theoretically survive hundreds of
millions of years without too much ill
effect, just waiting to be thored out
and given water again. This is why
scientists must be so careful about both
forwards and backwards
crosscontamination when exploring other
worlds.
If not there, there is also a chance
that life exists in the water lakes on
Mars today. But Alex, I hear you say
through your screens, didn't you just
tell us that those lakes had all dried
up? What I told you was mostly true, but
not entirely. While it seems unlikely
that there is any water still moving
freely on Mars's surface, there is a
location where water can still be found
and in liquid form deep beneath the
polar caps. In 2018, scientists
announced that they had found an entire
lake trapped deep beneath the thick ice.
Three more were confirmed by 2020. This
is interesting because it mirrors an
ecosystem on Earth called Lake Vosto,
which is also a lake sealed away 4 km
beneath the solar polar ice cap.
Intriguingly, Lake Vosto was found in
the late '90s to house bacteria and even
potentially fish. Some trace DNA was
captured and brought to the surface.
Either way, Lake Vosto is a fascinating
ecosystem that has been sealed away for
15 to 25 million years. Sadly, the
chance of Mars's lake being another lake
Vstto filled with ancient life is
actually quite low. Given the
temperatures on Mars being so much
lower, it's thought that the water
inside the polar lakes there have to be
very salty. This would not be conducive
for most forms of life. And on top of
that, perhaps the Martian legs are not
real after all. A recent study in the
journal Science Advances offered other
explanations for why the radar imaging
thought it saw a lake, suggesting that
reflective dust layers spaced closely
together could create the same effect, a
sort of optical illusion. If this is
what's happening on Mars, the lakes
might not even be there.
So, it seems that Yzero Crater is a
better place to search. But even Yzero
has a point against it. Yzero Crater,
while certainly habitable, is not a
likely place where life could have
formed. It does not contain deep thermal
vents and isn't home to volcanic springs
unlike other parts of the planet like
Columbia Hills. So the question is,
could life have formed and then
distributed quickly enough that it would
make it to craters like Yzero before
Mars underwent its transformation into a
barren world? It's possible, but it's
also possible that it would not.
As the planet cooled and the water
evaporated, any bodies of water would
have found themselves becoming more and
more salty, as any salt concentration
would have ended up with a lower and
lower ratio of water. Again, too much
salt is bad for most forms of life, and
research suggests it could have been a
massive hurdle for the survival of
undeveloped proto cells. Such cells
simply may not have developed the tools
to allow them to survive in such
conditions.
Even more developed Earth life would
have struggled when combined with the
depleting atmosphere and deadly
radiation.
So, it's safer to search where life
would have begun rather than places it
would have distributed.
Thus, volcanic spring sites like
Colombia Hills already seem like a
better place to look for signs of early
life than Yzero Crater. If life never
made it out of the primordial super on
Mars, those initial pools are the places
that make the most sense to look as so
far we're not looking there.
But if you want to talk about where life
on Mars might be right now, volcanic
springs have one other vital feature
going for them. They are gateways to
underground biomes.
Why explore out of the water when you
can follow those nutrients down to their
source?
On Earth, life does not just live on the
surface. There exists a whole world of
life known as the deep biosphere that
exists kilometers beneath our feet. Life
down there has learned to adapt to
living without sunlight and without air
in high temperature and high pressure
environments. And incredibly, it's
thriving.
In 2018, Deep Carbon Observatory
collaborators, a group of over 1,000
scientists, published that if you added
up all the weight of the living things
beneath the surface of Earth, it would
add up to almost 400 times the carbon
mass of every human on the planet
combined. The deep biosphere covers an
area of nearly 2.3 billion km almost
twice the volume of all the oceans. It
contains 70% of all species of Earth's
bacteria na. Also, viruses and small
worms have been found down there.
Overall, it is thought to be as diverse,
if not more diverse, than the surface.
There has not yet been found a limit to
how deep or how hot life can survive as
records are continually being broken.
Currently, the hottest survived
temperature is 121° C, hot enough to
boil water, which was found with a
bacterium living in a thermal vent.
And the deepest is 10.5 km beneath the
sea level.
Food is hard to come by when your
kilometers deep in rock and metabolic
processes of living things in the deep
biosphere is 10,000 to 1 million times
slower than the surface. With life
ticking so slowly, it transpires that
they can live almost indefinitely. We
don't yet know how old things get down
there. Some species are found at sites
globally, suggesting that although
they're traveling through solid rock to
do so, bacteria are still somehow able
to get around.
We've only in the last decade begun to
grasp the sheer scale of the deep
biosphere on Earth. But all of this is
incredibly insightful when it comes to
life on Mars.
Deep beneath Mars's surface, life could
be well protected from any of the
devastation going on at its surface.
Life is proven to be able to survive
thermal vents, which means that once
life formed in a volcanic region, it
would have been able to seep into the
warmer nutrientrich subsurface through
cracks. It simply would have had to fall
down. And given the long metabolisms
involved, it could still be alive there
today. there could be a thriving
widespread ecosystem alive and well.
Finding out for sure would be difficult.
We find it hard to explore the deep
biosphere here on Earth, requiring deep
sea drilling technology or very deep
mines. On Mars, landers like Insight
struggle to even dig 2 to 3 cm.
But to my mind, that's the most likely
place to search for Martian life today.
Of course, it's worth reiterating that
there are a lot of ifs here. If life
formed on Mars in the first place, if it
managed to make it out of the hot
springs it likely formed in, if it
evolved and adapted like it did on
Earth, only then could it still be out
there. But it's incredible to me to
consider that while Mars's surface might
appear dry and barren, there's the
potential for an entire thriving
ecosystem beneath Mars's soil alive
today. Perhaps that is the cause for the
methane in Mars' atmosphere detected by
Curiosity.
There's always a chance life spread to
legs like Yzero, but my bet if it's
alive today, it will be deeper. I
believe that when it comes to finding
life on Mars, we've barely scratched the
surface.
Do you have a question you'd like us to
answer? Send it over to us on Patreon
and you might be selected for a future
Astramm Answers episode. But for now,
thanks for watching and I'll see you
next time.
The universe is a harsh, brutal place.
Solar winds, high radiation, and extreme
temperatures and pressures make it
largely inhospitable.
And yet, life found a way. It's in you
and in me. And perhaps there is no quest
more epic than the search for life
beyond our beautiful blue home. But
scanning the night sky for possible
neighbors, like most things in
astronomy, comes with its challenges.
Where could they be? What would they
look like? Should we even look for them?
Are they in turn looking for us?
One thing that makes the search for
alien life tricky is that we don't know
exactly what we're looking for. But by
studying ancient life forms on Earth,
scientists can get a clearer idea of the
kind of organisms that are most likely
to be out there and where we might be
best off looking.
I'm Alex Mccoan and you're watching
Astramm. Join me today as we uncover how
scientists actually hunt for alien life,
the unique characteristics of Earth's
earliest life forms, and the surprising
role these ancient microbes play in
guiding the quest to answer the eternal
question, is there anybody out there?
If you were tasked with combing through
a seemingly infinite universe for signs
of life, where would you start?
I reckon I'd start by looking for a
planet similar to ours. Starting the
search in the most hospitable part of
the galaxy seems like a smart move. The
galactic habitable zone is the region of
a galaxy that has the most optimal
conditions for potentially lifebearing
planets to develop. Typically, it's a
spot with enough heavy elements for
Earthlike planets and minimal cosmic
drama like supernova or stellar close
calls. This excludes stars too close to
the center or in the spiral arms of
galaxies since they are full of super
intense harmful radiation.
So far, we've discovered 5,539
exoplanets of all different shapes,
sizes, and compositions.
Scientists are still debating what kind
of atmospheres might be hiding signs of
life on other planets. As far as we
know, life on Earth emerged 3.8 billion
years ago. At that time, our atmosphere
was mainly nitrogen gas, carbon dioxide,
and water vapor. You'd understand then
why some scientists choose this
atmospheric composition as a preferred
focal point. But others aren't so
convinced. They say only searching for
these compounds is limiting since
methane and hydrogen gas atmospheres may
themselves be signs of life. In reality,
it seems to be a bit of a chicken egg
situation. The atmospheric composition
of a planet determines what kind of
life, if any, could emerge on that
planet. But the kind of life that
emerges also affects the composition of
the atmosphere.
Let me quickly explain with an example
from home. Today, Earth's atmosphere is
21% oxygen. That wasn't always the case.
It wasn't until about 2.4 billion years
ago that free oxygen gas started
accumulating in our atmosphere. This is
known as the great oxidation event. The
main theory among researchers is that
cyanobacteria living in the ocean
evolved the ability to photosynthesize
and started releasing oxygen gas faster
than it could react with other
compounds. Eventually, this oxygen
evaporated from the oceans into the
atmosphere, replacing the methane that
was already there. This is an example of
a bio signature of life. The next step
in honing our mission to find alien
life.
Bio signatures are substances, signals
or patterns that could be a sign of
biological activity. This could be as
obvious and direct as a fossil or
something more subtle like the
composition of a planet's atmosphere.
They are important because they indicate
not only the potential presence of life
but also the level of its
sophistication.
It's important to understand that all
bios signatures are really just
potential bios signatures. Because while
they could be signs of life, they could
also be caused by non-living things. A
big challenge scientists face is
battling all the false positives that
arise. There's no official
classification system for bio
signatures, but it's useful to think
about them falling into three
categories. Gaseous, temporal, and
surface signatures. Gaseous bios
signatures are direct or indirect
products of metabolic activity.
The most common manifestation of this is
the composition of the atmosphere. For
example, the presence of haze could be
an indirect byproduct of a methane rich
world.
This could tell us that a particular
planet hosts microbial life similar to
what we had on Earth over 2.5 billion
years ago before the great oxidation
event. It's similar to the example we
explored earlier of how having free
oxygen in the atmosphere could be a bios
signature for photosynthesizing life.
Temporal bios signatures are timebound
changes that can correlate with
biosphere activity. On Earth, the
concentration of carbon dioxide in the
atmosphere rises and falls with the
seasons. Vegetation grows in the spring
and decays in the autumn. This
oscillation is way stronger in the
northern hemisphere than the southern
hemisphere because it has more land
mass. In theory, we can use this kind of
information to see where on an exoplanet
life is most likely to be. However,
nothing is so black and white. Temporal
bios signatures can be caused by abiotic
factors too. The concentration of
methane in Earth's atmosphere, for
example, changes mainly due to its
interaction with water vapor in the
troposphere. So even though the methane
itself is from a biological origin, the
temporal oscillations are dictated by
abiotic factors. I personally find
surface bios signatures the most
interesting.
Basically, every planet reflects some
light from its star. Different materials
on the surface of the planet will
reflect different combinations of
wavelengths of that light. This results
in a unique reflectance spectrum for
every material. Surface features like
rocks, snow, water, and soil can all be
deduced from a reflectant spectra.
Life can also influence the reflectance
spectra of a planet. This is an example
of a surface bio signature. Here's where
it gets super cool. Today, the Earth
appears blue from space because its
oceans reflect a lot of blue light. But
some scientists think that there was a
time when our planet would have been
purple instead.
There's an ancient family of microbes
that produce a protein called
bacteriosin.
Bacterio rodopsin can create energy
without a carbon source, something
plants can't do. It literally just turns
sunlight into metabolic energy the cells
can use. It is thought to be one of the
simplest and earliest bioenergetic
processes to have developed.
But why would it make earth appear
purple? Bacterial redopsin contains a
pigment that reflects a lot of purple
light. This makes its cell membrane
appear purple. An early Earth would have
had oceans full of this organism,
turning the whole planet visibly purple.
While it's just a bit of fun to imagine
a purple Earth, the implications of this
theory mean that these microbes and
others like them could be a very useful
surface bio signature of exoplanets. Of
course, the reflection of purple light
alone doesn't mean much, but if it were
to be combined with evidence of a highly
saline surface, that could start to
paint a more convincing picture.
You see, the specific family of ancient
microbes that produce this purple
protein are called haloilic ara or halo
aa for short. Aa are some of the most
ancient lineages of life on Earth. Even
though they're single-sellled organisms,
they are not to be confused with
bacteria, the two are actually totally
different domains of life, but we won't
go into that. Haloilic means they grow
and survive best in conditions of
extremely high salinity. Halophiles
belong to a large group of organisms
known as extreopiles.
Extreophiles are life forms that are
able to live in very hostile
environments. There are lots of
different kinds of extreopiles that are
well adapted to different kinds of
extreme conditions like very high or
very low temperatures, pressures,
dryness, radiation, salinity, acidity,
and heavy metals or any combination of
those extreme conditions. These
organisms span the globe, inhabiting the
harshest parts of our world. From
sulfuric hot springs in Japan to the
Atakama desert in Chile to sewage
treatment plants in Germany and even a
hypers saline deep lake in Antarctica
where our beloved halo aa were found.
What makes extreopiles so interesting is
their unique biology. As you can
imagine, living in such extreme
conditions forces you to get creative.
Extreophiles biochemistry and physiology
are often modified in very clever ways
to help them adapt to their harsh
environments and this makes them an
astrobiological gold mine.
Many extreophile habitats on Earth are
surprisingly similar to conditions on
other planetary bodies. These regions on
Earth are called analoges and they can
teach us a lot about where we might find
life beyond our home planet.
For example, the Atakama Desert in South
America is a very arid environment with
high salinity, high UV radiation levels,
and oxidizing soil, making it quite
similar to Mars. In fact, we've been
studying it as an analog to Mars for
years. Life has been found across the
Atakama desert, but its presence is
highly patchy. In a way, this is good
news. It helps scientists identify the
exact factors that cause life to appear
where it does and therefore where we
might have the best chance to find it on
Mars. The extreophilic yeast exopa is
another example of this. It was found in
high alitude regions of the Atakama and
caught the attention of astrobiologists
pretty fast. Researchers were looking at
how exofial's protein expression changes
in a simulated Martian environment.
After the first 24 hours of exposure,
they found some proteins were
overexpressed and others underexpressed
compared to baseline levels. However,
there were no signs of heat shock
proteins. The compounds organisms
release in response to high stress
conditions. Even more surprisingly, 7
days into the exposure, Exopella's
protein expression patterns were back to
normal. This is a big deal because it
indicates that Exofila is able to
recover and survive under Martian
conditions.
In other studies, exopila show great
resilience to the Earth's stratosphere.
It also showed the highest UVB and UVC
resistance when compared with other
similar yeasts. All this together makes
it a promising model for potential life
on Mars. It may be a stretch to suggest,
but it is possible any Martian life we
might find could be biochemically
similar to this humble yeast.
Certain species of halo aa are also
being studied as exciting
astrobiological models. Specifically,
hello bacterium NRC1 and Helloacterium
lacas profundi. They are both
extreophiles that thrive in high
salinity and are great candidates for
understanding potential life on Mars and
Jupiter's moon Europa. Think about it.
If there is a planet where conditions
are totally different to ours here on
Earth, it makes sense that the life we
may find there could be completely
different. But if the planet does have
similarities to our own, is it really so
crazy to think that life there might
look similar, too?
Mars is a specific focus for our search
for life because it has several similar
early geological processes to Earth.
Scientists have determined that Mars was
possibly much warmer and wetter in its
history. This suggests there could have
been super salty brines on early Mars.
Like we've said, these hypers salient
environments are ideal for halo aa.
Wouldn't it be cool if these ancient
microbes could have been enclosed in
Martian brines lying dormant all this
time? Similarly, Europa is thought to
contain salty oceans two to three times
the volume of Earth's below its
inhospitable surface. This subterranean
ocean might also be chemically rich
thanks to a silicut seafloor and surface
oxidants making it a great candidate for
haloilic life.
In fact, scientists have been testing
this theory by shooting Halo Akia into
space since 1994.
Testing to see the types of harsh
environments they can survive. The first
mission involved the ejection of a
capsule into low Earth orbit. The
short-term exposure results were
promising with the microbes surviving
the initial exposure. The European Space
Agency then designed the expose facility
for medium and long-term exposure
experiments on the outside of the
International Space Station. Three
separate missions were launched in 2008
and another in 2014 testing survival of
various halophilic archa strains in
space. In March 2019, results emerged
from the ISO Biomex experiment. They
reported that microbes from Earth
survived 18 months of space exposure
outside the ISS, suggesting life could
theoretically survive on our neighbor
Mars. Clearly, there's still a lot we
don't know about these microbes. For a
start, they've only ever been studied in
isolation.
How would they interact with a wider
environment?
All the research so far has focused on
sodium chloride. But how would these
organisms fare in other salts?
So even though they seem like promising
candidates with lots of potential, more
research is needed to fully understand
their implications for astrobiology.
So how does knowledge of these ancient
microbes turned astrobiological models
help us in the search for life in the
universe?
Well, within our own solar system,
having intimate knowledge of these
organisms can directly impact where we
send our space missions. For example,
the Spirit rover was sent to the Gusv
crater to investigate a suspected
ancient lake. We already had lots of
evidence for volcanic hydrothermal vents
on Mars, but Spirit discovered lots of
new evidence pointing to hotring
activity in Mars's past. Hot springs are
great places to look for bio signatures
because they can preserve ancient cells
in their chemical precipitates for a
long time. It would be an ideal place to
find fossils of Martian organisms if
they ever existed there.
Beyond the Kyper belt, studying
extreophiles lets us better understand
how life arises and evolves in the
universe. Firstly, it can show us what
traits to look for in distant planets. a
certain spectral fingerprint or a
particular gas in the sky. It also
indicates what the signals we receive
from distant planets could mean about
how hospitable they are. Extreophiles
show us what type of life we might
expect on other planets. And finally,
they push back the limits of life as we
know it to redefine what is possible.
Time and time again,
our searches for signs of life haven't
been very fruitful yet and will likely
take many decades more. Designs are
already in the works for a new
generation of telescopes that will take
to the skies in the 2030s and 2040s. The
Nautilus is a concept telescope that
could be operational by 2033 and would
enable scientists to cover 50 times the
light collection area of the James Webb
telescope thanks to its large aperture.
Another concept put forth by NASA is
designed to observe potentially
habitable exoplanets around sunlike
stars. The Habitable Exoplanet
Observatory or HABEX for short would
look for bio signatures like water and
methane. It would also become the first
telescope with the ability to directly
image an Earthlike exoplanet. They sound
fascinating. I hope they get approved.
We've come a long way and still have a
long way to go, but we are not giving up
our epic mission to find other life
forms and their homes beyond the bounds
of our planet. Our distant relatives
will just have to wait a little longer
to be found.
Life is a mysterious thing.
As far as we are currently aware, Earth
is the only place in the universe where
life exists.
Life is so prevalent on Earth because of
a combination of many factors, including
Earth's distance from its star. It is
situated in the solar systems Goldilock
zone in a region that is not too hot or
too cold.
We also have a magnetic field that
protects us from solar and cosmic
particles.
We have an oxygenrich atmosphere which
we can breathe.
We also have an abundance of water on
the surface.
These and a few other factors combined
allow life to exist as it does here.
But a quick look around the solar system
reveals nothing on the surface of any
celestial body that is even close to
resemble the green and blue lush surface
of Earth. So, does this mean there's no
life in the solar system? Well, the
simple answer is we don't know. But
there are a few places we are still
interested in checking out just to be
sure.
I'm Alex Mccoan and you're watching
Astramm. And together we will travel
through the solar system and see where
the most likely places to find life
could be.
Here's our sun. It's a very nice and
stable type of star known as a Gtype
main sequence star. Not a good place to
look for life as far as we know though.
Certainly nothing like life on Earth
could survive the thousands of degrees
temperature on the surface. We would
have to expand our concepts of what life
could be. Perhaps beings of energy
rather than traditional elements. Neil
deGrasse Tyson said he wasn't opposed to
this idea.
>> I don't see why not except uh by the way
mass is energy. Energy is mass. So I can
imagine an alien species that is energy.
Um I can imagine it
>> like a pound of energy.
>> I can allow my brain to accept the
possibility.
>> However, the possibility is extremely
remote. So, I think we can leave the sun
and move safely onto Mercury.
Mercury does not tick many boxes in
regards to what would be needed for life
to form. It has a very tenuous
atmosphere and is far too close to the
sun.
This combination means that the
temperatures on the day side rise to
over 400°
and the night side can drop as low as
-70°.
It has been discovered that Mercury was
geologically active in the past, but the
last eruption was thought to be 1
billion years ago.
Many extinction events would have
happened during Mercury's history that
would have most likely prevented life
from getting anywhere.
There is water ice to be found in the
permanently dark craters around the
planet's poles, but we theorize that
only liquid water can support life.
Mercury seems to be a dead, inactive,
and sterile planet.
The next place to visit is Venus. Venus
does have a rather substantial
atmosphere, but the problem is that it
isn't quite far enough away from the sun
to be in the Goldilock zone.
On Venus's surface, it is even hotter
than Mercury, well over 400° C all over
the planet.
This is due to the greenhouse gases in
the atmosphere.
Carbon dioxide make up 96% of it. This
heat means that water could not stay in
liquid form on the surface.
There is a slight possibility, however,
that there could be some form of
microorganisms high in the clouds of
Venus that would use UV light from the
sun as an energy source.
The temperature and pressure high in the
atmosphere is much more hospitable than
on the surface. So this possibility
exists.
But moving on, one of the best bets in
the solar system is Mars.
It is situated nicely in the Goldilock
zone and has an atmosphere.
The big problem with Mars, though, is it
lack of a magnetic field.
The magnetic field on Earth prevents the
solar wind from the sun, stripping away
the particles in the upper atmosphere.
Because Mars doesn't have this, its
atmosphere has been stripped of all but
the heaviest molecules consisting of 96%
carbon dioxide.
At one point in its history, it did have
some surface water as can be evidenced
by dried up rivers and lake beds.
However, today that water has gone. And
if there was any life on the surface,
this is most likely gone, too.
Scientists have been keen to find
evidence in rocks with the Viking
missions and looking for methane in the
atmosphere with the rovers currently on
the planet, but they have so far found
only traces of evidence.
But NASA are not deterred. Finding solid
evidence of life on Mars is now one of
their primary objectives. So, they
clearly think there's still a good
chance of finding something.
There are a few telltale signs that life
exists or could have existed on Mars.
There are possible bio signatures like
methane in the atmosphere often the
byproduct of life. Scientists can't
quite agree on where the quantity of
methane gas comes from and life is a
definite possibility.
We also have 34 meteorites on Earth
which originated from Mars. These are
highly valuable as they are the only
samples of Mars that we possess.
A few of these meteorites even contain
what looks to be fossilized bacteria,
although they are much smaller
formations than any terrestrial bacteria
on Earth. Sadly, this is not conclusive
evidence as these formations could also
be explained by natural processes.
At this point in time, there are a
couple of possible places to find life
on Mars.
One would be about 10 m under the
surface. Water can be in liquid form
this far down and any life would be much
more protected from cosmic and UV
radiation.
The other theory is that microorganisms
could exist under the polar ice caps.
Potential evidence of this could be the
darkening of these spider patterns next
to the gizers on the poles.
The darkening could be these
microorganisms as they photosynthesize
the sun's UV light from under the
surface.
But with all the attention Mars is
getting from the global scientific
community, I guess that we will know
conclusively whether there is life on
Mars within the next 30 years.
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