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 bioliln glxeaais. 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 fcuos our search on paelnts 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 scape, we see a blue, watery world. It's no coincidence that three qrtraues of the surface is covered by oceans. Because of its uiunqe 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 coommn in the universe. But life needs water in the form of liquid, not ice, and not voapr, and that's a little bit less common. For a planet to have liquid water at its surface, three things are imtnroapt. First, the planet needs to be large enough that the fcore of griatvy keeps the water molecules from flying off into space. For example, Mars is selamlr than Earth, and so has less gravity, and that's one important reason that Mars has a very thin atmosphere, and no onceas at its surface. Second, the pnleat 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 dsnaicte from its star. Too colse, and the sfacure temperature will exceed the biionlg 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 peecfrt zone where water satys 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 halabbite zones around their sarts. Those regions are the best bets to find planets like Earth. But while habitable zones are a pterty 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 cabron dioxide, an important greenhouse gas. In fact, its apetomsrhe is almost entirely carbon dioxide, and is almost 100 times thicker than our own. As a result, the ttpeearurme on veuns is hot enough to melt lead, and the planet is dry as a bone. So findnig planets of the right size and distance from their stars is only a bnningeig. We also want to know about the makeup of their atmospheres. The second complication emerges when we look a little more depley 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 dltorpes miles above our heads. These so-called ehtoeexpirmls aren't rare. Some sceniittss 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 sugsget that Earth-like planets may be only the tip of the astrobiological iceberg. It's possible that life might pssreit 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 euedancls is the source of geyress eunpitrg 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 wtear? Maybe we are the crazy creatures lniivg in an uausnul and extreme environment. Maybe the real habitable zone is so lrgae 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 kidns of habitable worlds. The only way to find out is to go out and explore.

Open Cloze

The universe contains about 100 _______ ________. 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 _____ our search on _______ 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 _____, we see a blue, watery world. It's no coincidence that three ________ of the surface is covered by oceans. Because of its ______ 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 ______ in the universe. But life needs water in the form of liquid, not ice, and not _____, and that's a little bit less common. For a planet to have liquid water at its surface, three things are _________. First, the planet needs to be large enough that the _____ of _______ keeps the water molecules from flying off into space. For example, Mars is _______ than Earth, and so has less gravity, and that's one important reason that Mars has a very thin atmosphere, and no ______ at its surface. Second, the ______ 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 ________ from its star. Too _____, and the _______ temperature will exceed the _______ 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 _______ zone where water _____ 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 _________ zones around their _____. Those regions are the best bets to find planets like Earth. But while habitable zones are a ______ 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 ______ dioxide, an important greenhouse gas. In fact, its __________ is almost entirely carbon dioxide, and is almost 100 times thicker than our own. As a result, the ___________ on _____ is hot enough to melt lead, and the planet is dry as a bone. So _______ planets of the right size and distance from their stars is only a _________. We also want to know about the makeup of their atmospheres. The second complication emerges when we look a little more ______ 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 ________ miles above our heads. These so-called _____________ aren't rare. Some __________ 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 _______ that Earth-like planets may be only the tip of the astrobiological iceberg. It's possible that life might _______ 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 _________ is the source of _______ ________ 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 _____? Maybe we are the crazy creatures ______ in an _______ and extreme environment. Maybe the real habitable zone is so _____ 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 _____ of habitable worlds. The only way to find out is to go out and explore.

Solution

stars
droplets
large
unique
living
oceans
quarters
geysers
smaller
force
venus
focus
distance
planets
surface
scientists
suggest
vapor
persist
deeply
space
gravity
beginning
common
kinds
temperature
carbon
water
close
extremophiles
enceladus
pretty
erupting
perfect
important
finding
galaxies
billion
stays
habitable
atmosphere
boiling
planet
unusual

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