[MUSIC PLAYING] 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? [MUSIC PLAYING] 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. [MUSIC PLAYING]
