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This week NASA announced even more evidence
of plumes erupting from the surface of Jupiter's moon
Europa.
We're becoming increasingly sure that there's
a vast ocean of water beneath Europa's icy crust.
But does that ocean have a life?
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This new evidence of water plumes
was found by the Hubble Space Telescope, which
took ultraviolet images as Europa
passed in front of Jupiter.
Sporadic jets of something appeared
to block some of Jupiter's light.
That material seems to be erupting from Europa's South
Pole.
This is roughly the same location
where a plume of hydrogen and oxygen ions
was also seen by Hubble.
The finding makes it even more likely
that a vast ocean of liquid water
exists beneath Europa's icy crust.
The moon is increasingly looked at as our best chance
to find extraterrestrial life in our solar system.
Today I want to talk about why Europa looks so good for life
and exactly what form that life might take.
At least on Earth, liquid water is
absolutely essential for life.
Every known life form needs at least a little bit.
Having water on Europa doesn't guarantee life there,
but it sure makes it more likely.
But Europa isn't the only gas giant
moon with a possible ice-covered ocean.
Jupiter's moon Ganymede almost certainly has one,
and Callisto may or may not.
Saturn's Enceladus also blasts geysers from its icy surface,
so we're pretty sure there's an ocean down there, too.
Europa's probable water vapor plumes
make an ocean very likely.
But the moon is extra exciting because
of this reddish-brown gunk that covers the surface.
There's a good chance that this is sea salt, perhaps
deposited by geysers that produce those plumes
and then discolored by Jupiter's intense magnetic field.
A salty ocean tells us that the water
must be in direct contact with the rocky surface below.
And for reasons we'll get to, that's
pretty important for life to have evolved there.
Ganymede, on the other hand, probably
has a vast second layer of ice in between its ocean
and the rocky interior.
Saturn's moon Enceladus may be just as promising as Europa.
Its geysers actually produce one of Saturn's rings.
And the Cassini spacecraft found that ring to contain salt.
And why is it so important that the ocean be in contact
with the rocky interior?
Well, in general, it's because life needs energy.
We know that the tidal squeezing from Jupiter's
gravitational field provides the energy that
keeps Europa's ocean liquid.
The same forces drive massive volcanic activity in its system
moon IO, and so it's likely that Europa's rocky interior is also
geologically active.
There's a good chance that this mains hydrothermal vents.
These may be the perfect place for life--
not just to live, but perhaps to have originally evolved.
In fact, it may be that life on Earth
started around its own hydrothermal vents.
This is the iron-sulfur world hypothesis
proposed by Gunter Wachtershauser in the 1980s.
The idea is the first simple life
came into being around so-called black smokers-- volcanic vents
in the deep ocean where noxious gases spew out
from Earth's mantle and water temperatures
exceed 100 degrees Celsius.
Sounds unpleasant, but the regions around these vents
are teeming with life-- 10 to 100,000 times the density
of organisms compared to the sea floor.
Entire specialized ecosystems live around Earth's deep sea
vents.
The foundation of these are the single-celled organisms
that extract energy from the hydrogen sulfide spewing
from the vents.
These support all sorts of complex life-- forests of tube
worms and clusters of clams and mussels
that are crawling with crabs, snails,
and shrimp-like amphipods, octopi,
and the eel-like [INAUDIBLE] top the food chain.
These critters are highly adapted
to the extreme temperatures and sulfur-rich environments.
Perhaps the dominant life on Europa
are also deep-dwelling, sulfur-munching volcanic sea
monsters.
If we believe the iron-sulfur world hypothesis,
then deep-sea vents may be where earth life first originated.
It's believed that an energy source and a rich mineral
content in liquid water are the main ingredients needed
for abiogenesis.
The region surrounding hydrothermal vents have both.
They may have driven a series of peculiar chemical processes,
enabled by the energy differential
and abundant minerals produced by deep sea black smokers.
These, in turn, may have resulted
in a sort of prebiotic chemical metabolism that enabled
evolution into true life.
If this is right, there's every reason
to hope that the same may have happened on Europa.
But regardless of the truth behind this hypothesis, or even
the existence of vents on Europa,
if that moon's ocean is in contact
with a warm, mineral-rich ocean floor,
then perhaps life has found a way.
Now, that Europan ocean is estimated
to be 100 kilometers deep, so it's
gonna take a long, long while before we can get a probe down
to those vents-- if they exist.
However, if life is abundant enough there,
then it'll have left its mark on the rest of the ocean--
molecules, isotopic ratios.
Even preferential handedness-- chirality--
of certain molecules can give away the presence
of biological processes.
We may find this evidence on or just beneath the icy surface,
or even in Europa's vapor plumes.
But if life started at those vents, who's to say
it stayed there?
Another promising habitat for Europan life
also has an earthly analog-- that's
the undersurface of the ice.
That surface is by far the most densely populated region
in the oceans beneath the Antarctic Sea ice.
Crevices in caves beneath the ice
provide protective habitats.
And the process of melting and refreezing
produces an energy gradient that can power metabolisms.
So what does that life look like?
If Earth's ice-loving organisms are anything to judge by,
then we're again talking single-celled organisms.
But a number of complex species also
live in these frigid environments.
Several types of fish, for example,
have antifreeze powers-- proteins
that protect their fluids from freezing and livers that
can extract ice crystals from their blood.
But why restrict ourselves to the ocean floor or ocean roof?
Life is found throughout earth's oceans.
However, ours are much shallower--
11 kilometers at the deepest.
And life throughout those depths depends on biological activity
at the surface.
Ultimately, their energy and nutrients
come from sunlight-powered microorganisms,
like algae and plankton, at the ocean's surface.
Europa's ocean roof doesn't have an abundant energy source,
and certainly not one that could power
a 100-kilometer deep biosphere.
But who knows?
It may be that the ocean floor vents are blasting
enough energy and nutrients upwards to support
all those alien whale things and tentacled monstrosities
and merperson cities that I know we're all really
hoping to find.
So when will we know?
NASA's Europa Clipper is expected
to launch in the 2020s, and will vastly improve
our knowledge of the moon.
The original plan was a lightweight spacecraft
carrying several instruments.
It would survey the surface with high-resolution imaging
and infrared scans, probe the interior
with radar and magnetic mapping, and use
a variety of instruments to sniff out
the chemical composition of the atmosphere, surface deposits,
and the giant vapor plumes.
The observations taken with these instruments
would then help NASA decide a promising site
for a future possible lander.
However, in its 2016 budget, Congress threw a spinner
in the works-- well, sort of.
They allocated a lot more money to NASA's Europa program
than requested, but also added a mandate
that NASA include a lander on the mission
and that it launch by 2022.
That'd be great and all, except it adds a lot of extra weight
and development time to the mission,
and it also makes it pretty hard for NASA
to scout out the best landing spot.
NASA is considering doing this as two separate missions--
if that's even allowed under Congress's decree.
We might wonder whether we should just
let NASA do what it does best.
But it's hard to turn down extra funding,
so let's see what those geniuses at NASA can come up with.
On the other hand, we may learned a lot--
even before a new probe reaches Europa.
By training Hubble spectrographs on Europa,
it may be possible to see the absorption of Jupiter's
light, due to specific molecules in those water plumes--
molecules that tell us even more about the plausibility of life
in that ocean.
But to really know, we probably do need to land that probe
and somehow peer beneath the ice.
Who knows what we'll see?
Give us your best guess in the comments.
And we'll see you next week on "Space Time."
Last week we talked about the weirdness
of quantum entanglement and the implications
its results have for the nature of reality.
Unsurprisingly, you guys had a lot to say.
A couple of you asked what result
you would get if you measured one
particle with a vertically-aligned measurement
device and a second particle with a horizontally-aligned
device.
Well, first, the simplest observable difference
between the predictions of a local hidden variable
theory versus pure quantum mechanics
is if you measure the spins of both particles
with the same measurement axis.
In that case, the pure quantum, no-hidden-variable prediction
is that you'll always measure opposite spins.
With the local hidden variable theory,
you'd expect to sometimes measure spins
in the same direction, depending on the relationship
of the chosen measurement axis with the hidden spins
of the particle.
If, instead, you measure one spin in one direction
and the other at 90 degrees, then the pure quantum
prediction is that the second particle is aligned one way 50%
of the time and the other way 50% of the time.
That's because the measurement of its entangled twin forces
its alignment to be 90 degrees to its own measurement axis.
That leads to 50% alignment in either direction.
By contrast, a local hidden variable prediction
is that the second particle doesn't
care how the first was measured, so it aligns itself
according to its original spin, which probably won't
lead to an even 50/50 split.
Alex Trusk very reasonably asks me to define
what I mean by observer.
So I've done this in a couple of the quantum videos before,
but it bears repeating.
The definition of observer sort of
depends on what interpretation of quantum mechanics
you're going with.
However, no mainstream interpretations
demand any sort of conscious observation.
Rather, observation may just mean any interaction
that destroys quantum coherence between
the entangled particles.
Another way of saying that is that this measurement
interaction effectively entangles
the measured particle and its partner
with a macroscopic system so complex
that we no longer observe clean quantum effects.
David21686 and a couple of others
point out that John Stewart Bell had another possible solution
to this whole seeming paradox-- that is super determinism.
Now, that's a huge topic, and I think we'll do a video on it.
But for now, let me give you Bill's own explanation
of this way out.
He says there is a way to escape the inference
of superluminal speeds and spooky action at a distance,
but it involves absolute determinism
in the universe-- the complete absence of free will.
Suppose the world is super deterministic
with not just inanimate objects running
on behind-the-scenes clockwork, but with our behavior--
including our belief that we are free to choose
to do one experiment rather than another-- absolutely
predetermines, including the decision by the experimenter
to carry out one set of experiments rather than another
the difficulty disappears.
There's no need for a faster-than-light signal
to tell particle a what measurement has been carried
out on particle B because the universe, including particle A,
already knows what that measurement and its outcome
will be.
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