0:00:06.327,0:00:07.484
We've all seen movies

0:00:07.484,0:00:09.729
about terrible insects from outer space

0:00:09.729,0:00:12.294
or stories of abduction by little green men,

0:00:12.294,0:00:14.325
but the study of life in the universe,

0:00:14.325,0:00:16.995
including the possibility of extraterrestrial life,

0:00:16.995,0:00:20.087
is also a serious, scientific pursuit.

0:00:20.087,0:00:23.267
Astrobiology draws on diverse fields,

0:00:23.267,0:00:24.160
such as physics,

0:00:24.160,0:00:25.185
biology,

0:00:25.185,0:00:26.170
astronomy,

0:00:26.170,0:00:27.182
and geology,

0:00:27.182,0:00:29.351
to study how life was formed on Earth,

0:00:29.351,0:00:31.013
how it could form elsewhere,

0:00:31.013,0:00:32.895
and how we might detect it.

0:00:33.495,0:00:35.191
Many ancient religions described

0:00:35.191,0:00:38.105
other worlds inhabited by known human beings,

0:00:38.105,0:00:40.074
but these are more like mythical realms

0:00:40.074,0:00:41.517
or parallel universes

0:00:41.517,0:00:42.813
than other planets existing

0:00:42.813,0:00:44.613
in the same physical world.

0:00:44.613,0:00:46.434
It is only within the last century

0:00:46.434,0:00:47.604
that scientists have been able

0:00:47.604,0:00:49.183
to seriously undertake the search

0:00:49.183,0:00:51.384
for extraterrestrial life.

0:00:51.384,0:00:53.296
We know that at the most basic level

0:00:53.296,0:00:55.452
organisms on Earth need three things:

0:00:55.452,0:00:56.345
liquid water,

0:00:56.345,0:00:57.547
a source of energy,

0:00:57.547,0:01:00.005
and organic, carbon-based material.

0:01:00.005,0:01:01.376
We also know that the Earth

0:01:01.376,0:01:03.336
is just the right distance from the Sun,

0:01:03.336,0:01:06.264
so as not to be either frozen or molten.

0:01:06.264,0:01:08.389
So, planets within such a habitable range

0:01:08.389,0:01:09.643
from their own stars

0:01:09.643,0:01:11.880
may be able to support life.

0:01:13.187,0:01:14.349
But while we used to think

0:01:14.349,0:01:15.521
that life could only exist

0:01:15.521,0:01:17.402
in such Earth-like environments,

0:01:17.402,0:01:20.124
one of the most amazing discoveries of astrobiology

0:01:20.124,0:01:22.526
has been just how versatile life is.

0:01:22.526,0:01:24.426
We now know that life can thrive

0:01:24.426,0:01:26.247
in some of the most extreme environments

0:01:26.247,0:01:28.607
that'd be fatal for most known organisms.

0:01:28.607,0:01:30.419
Life is found everywhere,

0:01:30.419,0:01:32.551
from black smoke of hydrothermal vents

0:01:32.551,0:01:34.605
in the dark depths of Earth's oceans,

0:01:34.605,0:01:36.602
to bubbling, hot, acidic springs

0:01:36.602,0:01:38.273
on the flanks of volcanoes,

0:01:38.273,0:01:40.654
to high up in the atmosphere.

0:01:40.654,0:01:43.134
Organisms that live in these challenging environments

0:01:43.134,0:01:45.184
are called extremophiles,

0:01:45.184,0:01:46.791
and they can survive at extremes

0:01:46.791,0:01:47.636
of temperature,

0:01:47.636,0:01:48.437
pressure,

0:01:48.437,0:01:49.434
and radiation,

0:01:49.434,0:01:50.470
as well as salinity,

0:01:50.470,0:01:51.386
acidity,

0:01:51.386,0:01:53.629
and limited availability of sunlight,

0:01:53.629,0:01:54.498
water,

0:01:54.498,0:01:55.881
or oxygen.

0:01:56.988,0:01:59.345
What is most remarkable about these extremophiles

0:01:59.345,0:02:01.399
is that they are found thriving in environments

0:02:01.399,0:02:03.697
that mimic those on alien worlds.

0:02:03.697,0:02:05.908
One of the most important of these worlds

0:02:05.908,0:02:08.681
is our red and dusty neighbor, Mars.

0:02:08.681,0:02:11.736
Today, astrobiologists are exploring places

0:02:11.736,0:02:14.228
where life might once have existed on Mars

0:02:14.228,0:02:16.534
using NASA's Curiosity rover.

0:02:16.534,0:02:18.333
One of these is Gale Crater,

0:02:18.333,0:02:20.062
an impact crater created

0:02:20.062,0:02:21.589
when a meteor hit the surface of Mars

0:02:21.589,0:02:24.271
nearly 3.8 billions years ago.

0:02:24.271,0:02:27.671
Evidence from orbit suggest past traces of water,

0:02:27.671,0:02:28.763
which means the crater

0:02:28.763,0:02:31.185
might once have supported life.

0:02:31.185,0:02:32.841
Planets are not the only places

0:02:32.841,0:02:34.928
astrobiologists are looking at.

0:02:34.928,0:02:37.518
For example, Europa, one of the moons of Jupiter,

0:02:37.518,0:02:39.200
and Enceladus and Titan,

0:02:39.200,0:02:40.349
two of Saturn's moons,

0:02:40.349,0:02:42.595
are all exciting possibilities.

0:02:42.595,0:02:45.018
Although these moons are extremely cold

0:02:45.018,0:02:46.847
and two are covered in thick ice,

0:02:46.847,0:02:50.028
there is evidence of liquid oceans beneath the shell.

0:02:50.028,0:02:52.950
Could life be floating around in these oceans,

0:02:52.950,0:02:54.879
or could it be living around black smoker

0:02:54.879,0:02:56.838
vents at the bottom?

0:02:57.499,0:02:59.321
Titan is particularly promising

0:02:59.321,0:03:00.465
as it has an atmosphere

0:03:00.465,0:03:02.745
and Earth-like lakes, seas, and rivers

0:03:02.745,0:03:04.496
flowing across the surface.

0:03:04.496,0:03:05.929
It is very cold, however,

0:03:05.929,0:03:07.545
too cold for liquid water,

0:03:07.545,0:03:09.382
so these rivers may instead be flowing

0:03:09.382,0:03:10.657
with liquid hydrocarbons

0:03:10.657,0:03:12.953
such as methane and ethane.

0:03:12.953,0:03:14.915
These are composed of hydrogen,

0:03:14.915,0:03:16.943
and, more importantly, carbon,

0:03:16.943,0:03:18.480
which is the basic building block

0:03:18.480,0:03:20.255
of all life as we know it.

0:03:20.255,0:03:22.969
So, could life be found in these lakes?

0:03:22.969,0:03:24.842
Although instruments are being designed

0:03:24.842,0:03:26.513
to study these distant worlds,

0:03:26.513,0:03:28.347
it takes many years to build them

0:03:28.347,0:03:29.537
and even longer to get them

0:03:29.537,0:03:31.134
where they need to be.

0:03:31.134,0:03:33.188
In the meantime, astrobiologists work

0:03:33.188,0:03:35.849
in our own natural laboratory, the Earth,

0:03:35.849,0:03:37.108
to learn about all the weird

0:03:37.108,0:03:39.379
and wonderful forms of life that can exist

0:03:39.379,0:03:40.832
and to help us one day answer

0:03:40.832,0:03:43.065
one of humanity's oldest questions:

0:03:43.065,0:03:44.614
Are we alone?