TedTest

From the Ted Talk by Ariel Anbar: A needle in countless haystacks Finding habitable worlds

Unscramble the Blue Letters

The universe contains about 100 billion galaxies. Each of those galaxies contains about 100 billion stars. Many of those stars have planets orbiting them. So how do we look for life in all that immensity? It's like searching for a needle in trillions of haystacks. We might want to focus our search on planets that we know can supoprt life as we know it — what we call habitable wrdols. What do such planets look like? To answer that qsueiotn, we don't look out there. Instead, we look at ourselves. At Earth. Because this is the one planet in the universe that we know for certain is habitable. When we look at Earth from space, we see a blue, watery world. It's no coincidence that three quarters of the surface is covered by oceans. Because of its unique chemical and physical properties, water is absolutely essential for all life as we know it. And so we get especially excited about other worlds on which water is abundant. fternltauoy, weatr is very common in the universe. But life needs water in the form of liquid, not ice, and not vapor, and that's a little bit less common. For a planet to have liquid water at its surface, three things are important. First, the planet needs to be large enough that the force of gravity keeps the water mecoeluls from flying off into space. For example, Mars is smaller than Earth, and so has less gravity, and that's one important reason that Mars has a very thin atmosphere, and no oceans at its suacrfe. Second, the planet needs to have an atmosphere. Why? Because without an aseorhtpme, the planet is in a vacuum, and liquid water isn't stblae in a vacuum. For example, our moon has no atmosphere, and so if you sipll some water on the moon, it will either boil away as vapor, or fzreee solid to make ice. Without the pressure of an atmosphere, liquid water can't survive. Third, the planet needs to be at the right distance from its star. Too close, and the surface temperature will ecxeed the boiling point of water, and oceans will turn to vapor. Too far, and the surface temperature will fall below the fiezerng ponit of water, cnsuaig the oceans to turn to ice. Fire or ice. For life as we know it, neither will suffice. You can iingmae that the perfect zone where water stays luqiid looks kind of like a belt around a star. We call that belt the habitable zone. So when we secarh for habitable worlds, we definitely want to look for planets in the habitable zones around their stars. Those regions are the best bets to find pnatles like Earth. But while habitable zones are a pretty good place to begin the search for planets with life, there are a couple of complications. First, a planet isn't nirslaecesy habitable just because it's in the habitable zone. Consider the plneat Venus in our solar system. If you were an aieln aeosotrnmr, you'd think Venus is a pretty good bet for life. It's the right size, it has an atmosphere, and it's in the habitable zone of our sun. An alien astronomer might see it as Earth's twin. But vunes is not habitable, at least not at its surface. Not by life as we know it. It's too hot. That's because Venus' atmosphere is full of carbon dioxide, an important greenhouse gas. In fact, its atmosphere is almost entirely carbon diidoxe, and is almost 100 times tikcehr than our own. As a result, the temperature on Venus is hot enough to melt lead, and the planet is dry as a bone. So finding planets of the right size and distance from their stars is only a beginning. We also want to know about the makeup of their atmospheres. The second complication ermeges when we look a little more deeply at planet Earth. In the last 30 years, we've discovered moericbs lvniig in all sorts of extreme evonmrenntis. We find them in fssriues of rock miles beneath our feet, in boiling waters of the ocean floor, in acidic waters of thermal sgnrips, and in cloud droplets mlies above our heads. These so-called extremophiles aren't rare. Some scientists estimate that the mass of microbes living deep underground equals the mass of all the life at Earth's surface. These subterranean microbes don't need oceans or sunshine. These discoveries suggest that Earth-like planets may be only the tip of the astrobiological iceberg. It's possible that life might persist in aquifers beneath the surface of Mars. Microbes may thrive on Jupiter's moon epuroa, where liquid water ocean probably lies beneath the icy crust. Another oeacn beneath the surface of Saturn's moon Enceladus is the sorcue of geysers erupting into scape. Could these grsyees be raining microbes? Could we fly through them to find out? And what about life as we don't know it, using a liquid other than water? Maybe we are the crazy creatures living in an unusual and extreme environment. Maybe the real hlaibtabe zone is so large that there are billions of needles in those tniliolrs of hatakcyss. Maybe in the big scheme of things, Earth is only one of many different kinds of habitable worlds. The only way to find out is to go out and explore.

Open Cloze

The universe contains about 100 billion galaxies. Each of those galaxies contains about 100 billion stars. Many of those stars have planets orbiting them. So how do we look for life in all that immensity? It's like searching for a needle in trillions of haystacks. We might want to focus our search on planets that we know can _______ life as we know it — what we call habitable ______. What do such planets look like? To answer that ________, we don't look out there. Instead, we look at ourselves. At Earth. Because this is the one planet in the universe that we know for certain is habitable. When we look at Earth from space, we see a blue, watery world. It's no coincidence that three quarters of the surface is covered by oceans. Because of its unique chemical and physical properties, water is absolutely essential for all life as we know it. And so we get especially excited about other worlds on which water is abundant. ___________, _____ is very common in the universe. But life needs water in the form of liquid, not ice, and not vapor, and that's a little bit less common. For a planet to have liquid water at its surface, three things are important. First, the planet needs to be large enough that the force of gravity keeps the water _________ from flying off into space. For example, Mars is smaller than Earth, and so has less gravity, and that's one important reason that Mars has a very thin atmosphere, and no oceans at its _______. Second, the planet needs to have an atmosphere. Why? Because without an __________, the planet is in a vacuum, and liquid water isn't ______ in a vacuum. For example, our moon has no atmosphere, and so if you _____ some water on the moon, it will either boil away as vapor, or ______ solid to make ice. Without the pressure of an atmosphere, liquid water can't survive. Third, the planet needs to be at the right distance from its star. Too close, and the surface temperature will ______ the boiling point of water, and oceans will turn to vapor. Too far, and the surface temperature will fall below the ________ _____ of water, _______ the oceans to turn to ice. Fire or ice. For life as we know it, neither will suffice. You can _______ that the perfect zone where water stays ______ looks kind of like a belt around a star. We call that belt the habitable zone. So when we ______ for habitable worlds, we definitely want to look for planets in the habitable zones around their stars. Those regions are the best bets to find _______ like Earth. But while habitable zones are a pretty good place to begin the search for planets with life, there are a couple of complications. First, a planet isn't ___________ habitable just because it's in the habitable zone. Consider the ______ Venus in our solar system. If you were an _____ __________, you'd think Venus is a pretty good bet for life. It's the right size, it has an atmosphere, and it's in the habitable zone of our sun. An alien astronomer might see it as Earth's twin. But _____ is not habitable, at least not at its surface. Not by life as we know it. It's too hot. That's because Venus' atmosphere is full of carbon dioxide, an important greenhouse gas. In fact, its atmosphere is almost entirely carbon _______, and is almost 100 times _______ than our own. As a result, the temperature on Venus is hot enough to melt lead, and the planet is dry as a bone. So finding planets of the right size and distance from their stars is only a beginning. We also want to know about the makeup of their atmospheres. The second complication _______ when we look a little more deeply at planet Earth. In the last 30 years, we've discovered ________ ______ in all sorts of extreme ____________. We find them in ________ of rock miles beneath our feet, in boiling waters of the ocean floor, in acidic waters of thermal _______, and in cloud droplets _____ above our heads. These so-called extremophiles aren't rare. Some scientists estimate that the mass of microbes living deep underground equals the mass of all the life at Earth's surface. These subterranean microbes don't need oceans or sunshine. These discoveries suggest that Earth-like planets may be only the tip of the astrobiological iceberg. It's possible that life might persist in aquifers beneath the surface of Mars. Microbes may thrive on Jupiter's moon ______, where liquid water ocean probably lies beneath the icy crust. Another _____ beneath the surface of Saturn's moon Enceladus is the ______ of geysers erupting into _____. Could these _______ be raining microbes? Could we fly through them to find out? And what about life as we don't know it, using a liquid other than water? Maybe we are the crazy creatures living in an unusual and extreme environment. Maybe the real _________ zone is so large that there are billions of needles in those _________ of _________. Maybe in the big scheme of things, Earth is only one of many different kinds of habitable worlds. The only way to find out is to go out and explore.

Solution

space
trillions
freezing
worlds
haystacks
support
miles
freeze
fortunately
search
planet
living
dioxide
planets
causing
exceed
atmosphere
necessarily
fissures
water
environments
surface
source
ocean
thicker
emerges
stable
molecules
springs
liquid
question
europa
habitable
point
alien
spill
imagine
microbes
geysers
venus
astronomer

Original Text

The universe contains about 100 billion galaxies. Each of those galaxies contains about 100 billion stars. Many of those stars have planets orbiting them. So how do we look for life in all that immensity? It's like searching for a needle in trillions of haystacks. We might want to focus our search on planets that we know can support life as we know it — what we call habitable worlds. What do such planets look like? To answer that question, we don't look out there. Instead, we look at ourselves. At Earth. Because this is the one planet in the universe that we know for certain is habitable. When we look at Earth from space, we see a blue, watery world. It's no coincidence that three quarters of the surface is covered by oceans. Because of its unique chemical and physical properties, water is absolutely essential for all life as we know it. And so we get especially excited about other worlds on which water is abundant. Fortunately, water is very common in the universe. But life needs water in the form of liquid, not ice, and not vapor, and that's a little bit less common. For a planet to have liquid water at its surface, three things are important. First, the planet needs to be large enough that the force of gravity keeps the water molecules from flying off into space. For example, Mars is smaller than Earth, and so has less gravity, and that's one important reason that Mars has a very thin atmosphere, and no oceans at its surface. Second, the planet needs to have an atmosphere. Why? Because without an atmosphere, the planet is in a vacuum, and liquid water isn't stable in a vacuum. For example, our moon has no atmosphere, and so if you spill some water on the moon, it will either boil away as vapor, or freeze solid to make ice. Without the pressure of an atmosphere, liquid water can't survive. Third, the planet needs to be at the right distance from its star. Too close, and the surface temperature will exceed the boiling point of water, and oceans will turn to vapor. Too far, and the surface temperature will fall below the freezing point of water, causing the oceans to turn to ice. Fire or ice. For life as we know it, neither will suffice. You can imagine that the perfect zone where water stays liquid looks kind of like a belt around a star. We call that belt the habitable zone. So when we search for habitable worlds, we definitely want to look for planets in the habitable zones around their stars. Those regions are the best bets to find planets like Earth. But while habitable zones are a pretty good place to begin the search for planets with life, there are a couple of complications. First, a planet isn't necessarily habitable just because it's in the habitable zone. Consider the planet Venus in our solar system. If you were an alien astronomer, you'd think Venus is a pretty good bet for life. It's the right size, it has an atmosphere, and it's in the habitable zone of our sun. An alien astronomer might see it as Earth's twin. But Venus is not habitable, at least not at its surface. Not by life as we know it. It's too hot. That's because Venus' atmosphere is full of carbon dioxide, an important greenhouse gas. In fact, its atmosphere is almost entirely carbon dioxide, and is almost 100 times thicker than our own. As a result, the temperature on Venus is hot enough to melt lead, and the planet is dry as a bone. So finding planets of the right size and distance from their stars is only a beginning. We also want to know about the makeup of their atmospheres. The second complication emerges when we look a little more deeply at planet Earth. In the last 30 years, we've discovered microbes living in all sorts of extreme environments. We find them in fissures of rock miles beneath our feet, in boiling waters of the ocean floor, in acidic waters of thermal springs, and in cloud droplets miles above our heads. These so-called extremophiles aren't rare. Some scientists estimate that the mass of microbes living deep underground equals the mass of all the life at Earth's surface. These subterranean microbes don't need oceans or sunshine. These discoveries suggest that Earth-like planets may be only the tip of the astrobiological iceberg. It's possible that life might persist in aquifers beneath the surface of Mars. Microbes may thrive on Jupiter's moon Europa, where liquid water ocean probably lies beneath the icy crust. Another ocean beneath the surface of Saturn's moon Enceladus is the source of geysers erupting into space. Could these geysers be raining microbes? Could we fly through them to find out? And what about life as we don't know it, using a liquid other than water? Maybe we are the crazy creatures living in an unusual and extreme environment. Maybe the real habitable zone is so large that there are billions of needles in those trillions of haystacks. Maybe in the big scheme of things, Earth is only one of many different kinds of habitable worlds. The only way to find out is to go out and explore.

Frequently Occurring Word Combinations

ngrams of length 2

collocation	frequency
liquid water	4
habitable zone	4
habitable worlds	2
surface temperature	2
habitable zones	2
pretty good	2
microbes living	2

Important Words

absolutely
abundant
acidic
alien
answer
aquifers
astrobiological
astronomer
atmosphere
atmospheres
beginning
belt
beneath
bet
bets
big
billion
billions
bit
blue
boil
boiling
bone
call
carbon
causing
chemical
close
cloud
coincidence
common
complication
complications
couple
covered
crazy
creatures
crust
deep
deeply
dioxide
discovered
discoveries
distance
droplets
dry
earth
emerges
enceladus
environment
environments
equals
erupting
essential
estimate
europa
exceed
excited
explore
extreme
extremophiles
fact
fall
feet
find
finding
fire
fissures
floor
fly
flying
focus
force
form
fortunately
freeze
freezing
full
galaxies
gas
geysers
good
gravity
greenhouse
habitable
haystacks
heads
hot
ice
iceberg
icy
imagine
immensity
important
kind
kinds
large
lead
lies
life
liquid
living
makeup
mars
mass
melt
microbes
miles
molecules
moon
necessarily
needle
needles
ocean
oceans
orbiting
perfect
persist
physical
place
planet
planets
point
pressure
pretty
properties
quarters
question
raining
rare
real
reason
regions
result
rock
scheme
scientists
search
searching
size
smaller
solar
solid
sorts
source
space
spill
springs
stable
star
stars
stays
subterranean
suffice
suggest
sun
sunshine
support
surface
survive
system
temperature
thermal
thicker
thin
thrive
times
tip
trillions
turn
twin
underground
unique
universe
unusual
vacuum
vapor
venus
water
waters
watery
world
worlds
years
zone
zones