Nat Geo_Deadliest Planets
Transcript
00:00In the future, humanity may leave the Earth behind and search for a new home in space.
00:12But where?
00:15Our solar system is a dangerous place.
00:20There are fiery volcanic worlds, planets with 1400 mph winds, clouds of deadly acid, temperatures
00:29hot enough to melt lead.
00:32Among these violent worlds, are there planets where we could one day live?
00:39We're on a voyage to find out.
00:41To explore the planets in our solar system and beyond.
00:46Our mission, to hunt for new worlds, to find a place that one day, we might call home.
00:59Imagine a city with 200 billion stars, so vast that a jumbo jet would take 100 billion
01:22years to cross it.
01:26We call it the Milky Way.
01:34On the outer edges of one of six spiral arms is our own star, the Sun, and its orbiting
01:41planets.
01:48One planet has life, Earth, with its oxygen-rich atmosphere and oceans of water.
01:57Life can flourish here.
02:02But our world is changing.
02:05Climate change is melting the polar ice caps.
02:08Sea levels are rising.
02:11Over the next millennia, land may disappear under the oceans.
02:18Forest areas could become uninhabitable, making the planet dangerously overcrowded.
02:24We'll need more space if we're all to survive.
02:35This is a journey through the solar system and beyond, hunting for our next home.
02:42We'll discover a surprising planet that could support life in its atmosphere.
02:49It is a comfortable temperature and pressure.
02:54I think that life could exist.
02:58But there are also deadly worlds where we stand no chance of surviving.
03:03You couldn't just fly through the system and survive.
03:07You would fry up.
03:11Finding a new home is not going to be easy.
03:14We evolved on Earth.
03:16Where else will we find a planet we can even survive?
03:20Our journey begins with Mercury, the closest planet to the Sun.
03:27Data reveals it has an atmosphere with traces of oxygen.
03:31But could it sustain human life?
03:37Mercury rotates very slowly.
03:39A day here lasts 58 Earth days.
03:44The dark side faces away from the Sun for so long, the temperature plummets to a staggering
03:50300 degrees Fahrenheit below zero.
03:55Around three times lower than the coldest temperature ever recorded on Earth.
04:01At the same time, the side facing the Sun can hit a scorching 840 degrees.
04:08As hot as a blowtorch.
04:12A temperature so brutal that almost all Mercury's atmosphere long ago evaporated into space.
04:21What oxygen is left is extraordinarily thin.
04:24There simply isn't enough of it for us to breathe.
04:31There have to be easier places for us to survive.
04:38Maybe we just need to be further from the Sun.
04:43The next planet out is Venus.
04:49Venus is a close neighbor of Earth, about 26 million miles away.
04:53It is shrouded in a thick atmosphere that completely hides the surface from view.
05:02Scientists used to think that would protect the planet from the Sun.
05:06They imagined Venus's surface to be like early Earth, that tropical forests covered
05:12the land and oceans of water lapped the shores.
05:19Professor David Grinspoon is an astrobiologist at the Denver Museum of Nature and Science
05:25specializing in the evolution of Venus.
05:29People assumed that it was sort of a dripping wet place and in fact the image of a sort
05:33of tropical paradise with tree ferns and maybe even dinosaurs, a kind of primitive
05:39tropical Earth-like place was a common scientific view of Venus really right up until the beginning
05:45of the space age.
05:48The Venusian surface intrigued scientists.
05:52What was really going on beneath the clouds?
05:56In the 1960s and 70s, while NASA explored Mars, the Soviet Union turned its sights on
06:04Venus.
06:05The goal was to land and photograph the planet's mysterious surface.
06:10Codenamed Venera, the Soviet program made countless successful launches, only to mysteriously
06:20lose contact with its probes as they entered the Venusian atmosphere.
06:26In October 1975, the team hit gold.
06:31Venera 9 beamed back the world's first surface images of Venus.
06:38Rather than a lush green world, Venus was a barren desert.
06:45Could humans survive here?
06:50Recently, astronomers have built up a detailed picture of Venus's atmosphere.
06:57Imagine a probe hurtling toward the planet.
07:02What would it see?
07:06Fifty miles above the surface, it hits a thick layer of cloud.
07:11But this is no ordinary cloud.
07:14It's made of vaporized acid, corrosive enough to burn through steel.
07:25Scientists believe that the acid clouds are a byproduct of Venus's violent history.
07:31Gigantic volcanic eruptions blasted billions of tons of sulfur high into the atmosphere.
07:39There it mixed with water vapor to form concentrated sulfuric acid.
07:47As the probe breaks through the upper atmosphere, it slows to make a low pass over the surface.
07:54The terrain is dominated by dormant volcanoes that tower three miles into the atmosphere.
08:05The channels, forged a million years ago by molten lava, stretch thousands of miles,
08:12one longer even than the River Nile.
08:16Probe sensors reveal an atmospheric pressure 90 times greater than on Earth, large enough
08:23to crush a car.
08:26But the biggest problem is temperature.
08:29The atmosphere is nearly all carbon dioxide.
08:33Just like on Earth, this gas acts like a pane of glass in a greenhouse, letting the light
08:39through, but not the heat out.
08:43On Earth, increased carbon dioxide levels are causing small rises in temperature, but
08:48on Venus, they have pushed the temperature to over 900 degrees Fahrenheit.
08:55But surprisingly, although the surface is hot enough to melt lead, Venus may not be
09:00an entirely lifeless world.
09:04Billions of years ago, primeval Venusian oceans could have been home to simple organisms.
09:15Some scientists believe that when the temperature climbed, the waters boiled away.
09:20This would have killed many of the organisms.
09:23But some may have survived by migrating to the cooler clouds in the upper atmosphere.
09:29Here though, they may have faced an even greater challenge for survival.
09:34The only real problem with the clouds of Venus is that it is extremely acidic, but we keep
09:39finding more and more extreme organisms on Earth that love living in sulfuric acid.
09:46Deep on our ocean floors, volcanic eruptions blast out sulfurous fluids, creating a superheated,
09:53highly acidic environment.
09:59Even here, life abounds.
10:05Colonizing Venus is not an option.
10:10We must head further out, toward the last of the solar system's inner rocky worlds.
10:17This time, it's one that scientists think that we may just stand a chance of living
10:22on.
10:23But the challenges facing would-be settlers go beyond anything we've ever seen on Earth.
10:37Mercury and Venus can never support human life on any large scale.
10:43We pass Earth and move deeper into the solar system.
10:47The next planet is Mars.
10:50Could we one day settle here?
10:52Mars is the one world that most resembles our own.
10:55A Martian day is almost the same length as ours.
10:59Mars has mountains, deserts, and gaping canyons, cut in the distant past by running water.
11:07Traces of that water may still be locked beneath the surface, but to reach it, we would have
11:12to face an ancient danger.
11:15Radiation.
11:18Five billion years ago, when our sun was born, it blasted high-speed energetic solar
11:23radiation out across the whole solar system.
11:29And it's still doing it today.
11:33Without some sort of protection, we could not possibly survive.
11:39We were lucky.
11:41Our world developed a magnetic field.
11:45This shield deflects deadly solar radiation away from the surface.
11:51But Mars has no magnetic field, and that means no protection.
11:57Over many millennia, the solar radiation ripped the atmosphere from the planet.
12:03Mars' water boiled, and most of it evaporated into space.
12:08The surface became a barren desert.
12:14For any future human visitors to the red planet, solar radiation will be a deadly hazard.
12:22Even with the protection of a spacesuit, the radiation can still penetrate.
12:28It tears through the body, bombarding and killing living cells, destroying DNA.
12:38If humans are to live and work on Mars' surface, we'll need some serious protection.
12:45So scientists are developing drugs.
12:50Astronauts would take these specially designed enzymes to mop up the radiation.
13:00Martian homes would need shielding too.
13:04Scientists have developed a special form of polyethylene plastic, lighter and stronger
13:08than metallic shielding, yet just as effective.
13:13The plan is to build it into the structure of Mars' habitats, protecting the occupants.
13:20With this advanced technology, humans could one day consider populating Mars.
13:26But there's another hazard to overcome.
13:31After the radiation stripped the water from the surface, the planet was left covered with
13:35dry iron oxide dust.
13:41Meet the sandstorm, Martian style.
13:45These mini-twisters are babies, dust devils just powerful enough to suck dust up into
13:51the atmosphere.
13:54The problem is what happens next.
13:58Astronomer Ron Greely has been studying atmospheric activity on Mars for over 30 years, knowledge
14:05vital for any human expedition to the red planet.
14:09Greely uses a fan and frozen nitrogen vapor to recreate these twisters in the lab.
14:16They form when the sun heats the surface, causing a pocket of hot gas to suddenly rise,
14:23spinning through cooler air above.
14:27It sucks up fine iron oxide dust and punches it high into the Martian atmosphere.
14:38The dust devils range in size from about a yard across to features that are as large
14:44as a football field in diameter.
14:46These can be quite large.
14:49That dust has to go somewhere.
14:52Greely believes the mini-twisters could trigger much bigger storms.
14:56We do in fact see local dust storms that grow to global proportions, clusters of individual
15:05dust storms that eventually merge.
15:08The entire planet is enveloped in dust and we can't even see the surface through that
15:13dust.
15:14But it's not just dust devils that can trigger trouble on a global scale.
15:20Blowing across the surface can kick up dust into the atmosphere, building into an overwhelming
15:26storm.
15:27This also happens on Earth.
15:31Satellites photographed a storm raging across the Sahara Desert in Africa, revealing its
15:36enormous size.
15:38The similarity with a storm on Mars is striking and that much dust is going to cause problems.
15:44When humans go to Mars they have to be concerned about the infiltration of this very
15:49fine dust.
15:52It's sort of like baking flour, if you will, very, very fine grain.
15:57The dust is so fine that even the slightest wind can blow it anywhere, clogging up machinery
16:03and air supplies.
16:06Not only is the dust likely to get into every nook and cranny, but there are also properties
16:12of the dust that may pose a hazard.
16:16One of the considerations are the electrostatic charging effects.
16:20When little tiny grains bang together, electrical charges are built up.
16:26Much like shuffling your feet on a carpet, the rubbing action between the grains of dust
16:31creates enormous static electricity.
16:35Up to 20,000 volts can spark between the dust particles.
16:40This could destroy electronics and life support systems.
16:47When we think about the eventual human presence on Mars, we have to understand the dust regime,
16:52we have to understand the electrostatic effects, all related to windblown particles.
16:59Perhaps one day we will conquer Mars' harsh environment, but this is not a world that
17:05would ever feel like home.
17:11We leave Mars and push on out toward the supersized worlds of the outer solar system, the gas
17:18giants.
17:20These offer new and even more extreme challenges in our quest for another home.
17:26First up is Jupiter.
17:31Jupiter is a mysterious world so vast that 1,300 Earth-sized planets could fit inside it.
17:39It's entirely made of gas.
17:42It has no solid surface at all.
17:45Its upper layers are a mass of swirling, counter-rotating clouds.
17:50This is a planet racked with storms and high-speed winds.
17:57Professor Fran Baganel has spent a lifetime studying the atmospheres and environments
18:01of Jupiter and its moons.
18:04Jupiter is spinning extremely fast.
18:06It rotates every 10 hours, and so rotation is very important and drives those east-west
18:12winds that produce the belts and the zones, those stripes across the planet.
18:18Jupiter's high-speed spin generates horizontal bands of clouds that wrap around the planet
18:24like a belt.
18:25When these cloud bands collide, they create massive storms.
18:31The biggest of these is the Great Red Spot, the largest storm in the solar system.
18:40As we approach, the scale becomes clear.
18:44It's three times the diameter of Earth.
18:48Near the spot's boundaries, turbulence spills around the edges.
18:53Hurricanes here travel at more than 250 miles per hour.
18:58It's true that it has a lot of similarities with hurricanes in that the outer edges, it's
19:03swirling around a lot faster, and so indeed the inner parts are more calm.
19:09At first glance, the Red Spot looks similar to hurricanes.
19:14But there is a difference.
19:16Here on Earth, hurricanes feed off the warm waters of the ocean.
19:20But as soon as they hit land, they start to die.
19:24Our storms only last about two weeks.
19:28But Jupiter's different.
19:30The Red Spot has been raging for over 300 years.
19:35The reason why we last such a long time is there isn't a surface on Jupiter.
19:39So it's not as if storms run into a continent and dump its energy.
19:46It just keeps going and going and going around and around.
19:50But the spinning of Jupiter is not enough on its own to drive the Great Red Spot.
19:56Scientists discovered the planet gives out twice as much energy as it receives from the
20:00Sun, suggesting its core must be hot.
20:05This center could be the powerhouse that drives Jupiter's winds.
20:10The core could be worth a closer look.
20:14As we descend through upper layers, vast water clouds envelop our craft.
20:20The pressure is climbing.
20:24Toward the center, it transforms the hydrogen atmosphere to a strange liquefied metal resembling
20:31the element mercury.
20:33This is the core, a churning furnace at over 40,000 degrees Fahrenheit.
20:40Scientists estimate that the pressure here is 100 million times higher than on the surface
20:45of Earth.
20:46How can I give you a sense of what that feels like as a pressure?
20:49Well, if anyone's had someone step on their toe with a stiletto heel, you know that's
20:54a lot of pressure.
20:55Now, imagine an elephant wearing stiletto heels and standing on one foot on a stiletto
21:00heel.
21:01But to get the pressure at the center of Jupiter, you need to have about a thousand elephants
21:06standing on top of each other, the bottom one on one foot on a stiletto heel.
21:16At these sorts of pressures, humans could never journey to the core.
21:21But could we survive in the upper atmosphere?
21:26The answer to that lies on one of its moons, which has an extraordinary effect on the gas
21:33giant.
21:35It might be dwarfed by Jupiter, but this minuscule world packs a mighty punch.
21:46Our quest for a new home has brought us a long way.
21:51We are 365 million miles from Earth, in orbit around the giant planet Jupiter.
21:59Could we survive here, perhaps in the turbulent upper atmosphere?
22:05That depends on what's happening around us.
22:08On Jupiter, that means looking at its moons.
22:13Io is tiny, but it's the most volcanic body in our solar system.
22:21And living next to a volcano is never a good idea.
22:26Dr. Rosalie Lopez is a volcanologist.
22:30She's come to the Kilauea Volcano Range in Hawaii, one of the closest matches on Earth
22:35to Io's fiery surface.
22:44This is very much what the surface of Io may look like, particularly close to the lava
22:49flows.
22:51There would be lava flows just like this, solid at the surface with underneath us hot
22:56lava flowing.
22:59Like Kilauea, Io spews lava from its superheated interior.
23:05But that's where the similarities stop.
23:08The volume of lava that Io's volcanoes erupt is quite staggering.
23:13If we do a comparison with Kilauea, in five months Kilauea might cover four square miles,
23:21but Io erupts about a hundred times the volume of lava.
23:28One lava flow on Io covered 240 square miles.
23:33On Kilauea, the heat to drive the volcanoes mostly comes from the decay of radioactive
23:39materials deep in the Earth's interior.
23:46But on Io, the activity is generated by something entirely different, tidal heating.
23:54Just as the oceans of the Earth rise and fall with the pull of our own moon, so Io's surface
24:02distorts with the gravity of Jupiter and two nearby moons.
24:07The ground rises and falls by over 300 feet, the height of the Statue of Liberty, every
24:15two days.
24:20Its pulsating surface creates enormous amounts of friction deep inside the crust.
24:26Heat and pressure build, turning solid rock to molten lava, forming lakes the size of
24:33Arizona.
24:39Io's volcanoes are deadly, but they aren't the real killer.
24:44Before the lava can get you, the radiation will.
24:51Just ten minutes on the surface and you're toast.
24:55Even over 200,000 miles away, in Jupiter's upper atmosphere, an unprotected human could
25:02only survive a matter of hours.
25:06The volcanic particles that Io blasts out into space become trapped in Jupiter's enormous
25:12magnetic field.
25:16Jupiter's rapid rotation accelerates them to fantastic speeds.
25:21They're like microscopic cannonballs.
25:24They form a radiation belt around Jupiter, cutting through almost anything in their path.
25:31They're sufficiently intense that a human would receive a lethal dosage within just
25:37ten minutes.
25:39So you couldn't just fly through the system and survive, you would fry up.
25:47This intense bombardment would destroy your flesh and the organs inside, everything.
25:54We just don't have the technology to protect ourselves from radiation this fierce.
26:00Jupiter is one planet we'll never call home.
26:06But our next stop offer more hope.
26:10Saturn's radiation levels are lower, but it's not a danger-free zone.
26:16From Earth, Saturn appears almost featureless, but its appearance is misleading.
26:27Its rings may look solid, but in fact they're mostly made up of billions of chunks of ice
26:33and rocks, ranging in size from pebbles to blocks as big as a car.
26:40All of them are moving faster than a high-speed bullet.
26:45But Saturn's real danger lies within its atmosphere.
26:49Like Jupiter, the planet has bands of high-speed counter-rotating winds.
26:56Clouds race around the planet at over 1,000 miles per hour.
27:01Along the edges where two bands meet, tiny particles collide, brushing past each other,
27:08generating an enormous electrical charge.
27:11Theory suggests that when the charge gets too great, the electricity arcs between the
27:16clouds, producing giant lightning bolts.
27:20NASA's Dr. Kevin Grazier is a planetary scientist who specializes in atmospheric conditions
27:26on Saturn.
27:27We have a chance for a lot of charge transfer between one band and the other, creating large
27:32voltages, creating huge lightning bolts.
27:36To get an idea of just how huge Saturn's bolts are, compare them with Earth.
27:44Lightning here can hit 50,000 degrees Fahrenheit in a split second.
27:51Striking the ground, it's hot enough to create a tube of solid glass, stretching down 15 feet.
28:00But compared to Saturn, that's a tiny spark.
28:05A single storm on this gas giant can cover the whole of America.
28:10And you can also get storms that last for years.
28:14Storms on Earth last for a week or two.
28:16Storms on Saturn last for weeks, months, years.
28:22With such an unstable atmosphere, even attempting to enter Saturn's clouds is deadly.
28:31As we push out and pass the featureless world of Uranus, we're heading for the very edge
28:37of our solar system.
28:40But out here, there are challenges that will test human visitors to their limits and beyond.
28:54In the future, humankind will journey to distant worlds, searching for new planets we could
29:00live on.
29:02Next stop, Neptune.
29:07At over 3 billion miles from Earth, observing this gas giant is a tough job, so astronomers
29:13go high, very high, way above Earth's clouds and pollution to get a clearer view.
29:21This is the Keck Observatory, 14,000 feet up on the summit of Mauna Kea in Hawaii.
29:29The telescopes here are so powerful, they could see a flickering candle on the surface
29:35of the Moon.
29:37Dr. Heidi Hamel has been researching Neptune for over 20 years.
29:45Coming to Keck gives her the chance to study this distant world.
29:48We'd see a beautiful blue planet, but that blue is not water like on our planet.
29:55That blue is the atmosphere of hydrogen, a little bit of helium, and most important,
30:01a smidge of methane.
30:05Methane may not have water, but it does have clouds, and these clouds allow Hamel to discover
30:10whether humans could survive this alien world.
30:16Standing out against the blue atmosphere, the clouds are easy to see.
30:22They form when methane freezes in Neptune's super-chilled upper atmosphere.
30:31The Keck telescope swings toward Neptune.
30:39Hamel takes a series of photographic shots, tracking the white clouds as they move around
30:44the upper atmosphere.
30:47Measuring the time and distance they move between two points, she can calculate just
30:53how fast the winds are blowing.
30:56The result comes as a shock.
30:59Some of the winds that we've clocked on Neptune do seem to be some of the fastest
31:03in the solar system.
31:05Some of these little white puffy clouds that we've tracked are really fast.
31:10They blow almost as fast at some latitudes as 1,200 miles per hour.
31:18Could we survive such powerful storms?
31:22To get an idea of how destructive these winds are, we have to compare them to storms on
31:27planet Earth.
31:33One of our most devastating winds is a tornado, a supercharged rotating column of air that
31:42forms in the atmosphere and touches ground with catastrophic results.
31:50On May 3, 1999, at 7.25pm, the suburbs of Oklahoma City were hit by a Category 5 twister.
32:01It cut through the heart of the area, ripping through property, tossing vehicles like toys,
32:08and tearing tarmac from the highway.
32:13This recorded wind speeds of 318 miles per hour, the fastest ever witnessed on Earth.
32:21On Neptune, it would be nothing more than a light breeze.
32:29Clearly, surviving this gas giant's winds would be impossible.
32:37But Neptune's ferocious storms could save human lives here on Earth.
32:43Studying those violent winds could help us understand our own weather systems better,
32:48improving our prediction of the most deadly storms.
32:53The reason is Neptune's simplicity.
32:56On Earth, the atmosphere, the land, and the oceans all interact.
33:01But Neptune has no land or water.
33:04Its weather is easier to predict.
33:07Huge winds every single day.
33:09The weather on the giant planets is simpler.
33:12You've got gas.
33:14And that is a simpler thing for a scientist to model in their computer.
33:21Scientists can use Neptune to test weather models for Earth.
33:25Computer simulations that mimic how weather systems interact.
33:32If they can successfully predict the weather on Neptune, then they're one step closer to
33:38accurate forecasts for Earth.
33:42But in our quest for another home, one thing is clear.
33:48Humans could never visit this alien world.
33:53Yet there is a near neighbor, a world without storms and with a solid surface.
34:02This is Triton, one of Neptune's 13 moons, super chilled and covered in frozen nitrogen
34:09snow.
34:12It would be big enough for us to live on.
34:15The question is, could we?
34:19Dr. John Spencer from the Southwest Research Institute in Colorado has been exploring the
34:25life-threatening hazards of Triton's icy climate.
34:30The surface of Triton is probably quite bizarre close up.
34:33We have frozen carbon dioxide, frozen carbon monoxide, frozen methane on the surface, but
34:40also a great deal of frozen nitrogen.
34:42It might form snow drifts and be crunchy underfoot.
34:47Any human exploration of Triton's savage surface is life-threatening.
34:53At 390 degrees Fahrenheit below zero, we'll need some special space gear.
35:00With assistant Eddie Goldstein, Spencer uses liquid nitrogen to replicate Triton's environment.
35:07It allows him to see how materials will behave on this super cool world.
35:12If you were to build a spacesuit that would function at Triton temperatures, you'd need
35:16something kind of flexible to make it out of.
35:18You might think you might use some kind of rubber material.
35:21At room temperature, rubber is soft and pliable, ideal for creating airtight seals on astronaut
35:28life support systems.
35:30But drop the temperature to minus 350 degrees Fahrenheit and it's a different story.
35:36And just because something is flexible on Earth does not mean it is flexible on Triton.
35:45The rubber molecules are flexible at warm temperatures.
35:49But drop them into chilled nitrogen, they become rigid as steel.
35:54The rubber hardens and shatters like glass.
36:03The search is on for materials that remain flexible at super low temperatures.
36:10Scientists are looking at familiar substances, fabrics that you may be wearing at this very
36:15moment.
36:16Could nylon be used in the super chilled world of deep space?
36:22And it's interesting because it's just as flexible even after it's cold.
36:28And it's not because nylon is anything special.
36:31It's because the nylon was woven into tiny threads.
36:36The secret of the nylon's flexibility lies in the weave.
36:42The fibers remain pliable because each strand is as thin as a human hair.
36:50So you might be able to make suits out of some material like this if you just treat
36:54it in a different way that takes into account this very unusual environment that we have
36:58out there.
37:00Even if humans do manage to walk on the surface in high-tech space suits, there is one other
37:06danger lurking beneath Triton's surface.
37:11All we see is these rather vague streaks, jets of material coming up from the surface.
37:17These dark marks are the clues to Triton's hidden menace.
37:22Beneath the frozen surface lie oceans of liquid nitrogen.
37:27As the sun warms the moon, the nitrogen turns to gas.
37:32This pressurized gas explodes as a geyser, blasting moon dust high into the atmosphere.
37:44The black dust finally settles on the white surface, leaving dark streaks.
37:51Back in the lab, Spencer recreates the spectacle.
37:55So what we're going to do is put the nitrogen in a situation where it's contained within
37:59this flask, just as it might be trapped underneath a layer of glaze ice on Triton itself, and
38:05the pressure would build up and that would produce a jet that could maybe shoot up six
38:10or ten miles.
38:13Just like...
38:14Hey, we've got a geyser!
38:19Just as the pressure builds in the glass flask, on Triton, pressurized nitrogen, trapped under
38:26the surface, blasts moon dust into space.
38:32A world of violent geysers and crushing cold.
38:40With the right technology, humans could one day walk on the surface, but it's not a world
38:45we could easily colonize.
38:48Within our solar system, this is the end of the search.
38:56This far from the sun, any planet is cold and barren.
39:02After Neptune, there are only small, dead, icy worlds like Pluto.
39:10Beyond is the unknown.
39:14Out here, the possibilities are endless.
39:17But out here, perhaps we will one day find a place to call home.
39:26Today, astronomers are piecing together incredible new evidence in the search for distant worlds.
39:37Planets that could support human life.
39:42Our sun is only one of 200 billion stars that make up our galaxy, the Milky Way.
39:49Any of these stars could have planets, just like our solar system.
39:56Tracking them down is the ultimate scientific quest, and king of the planet hunters is Dr.
40:03Jeff Marcy.
40:05Our Milky Way galaxy is a glorious but enormous place.
40:09It contains 200 billion stars, and it's 100,000 light years across, and so we have to pick
40:15and choose which stars to observe.
40:19This is the Lick Observatory in California, where planet hunters like Marcy come.
40:26He scans the night sky, searching for new worlds orbiting distant stars.
40:32But he has to pick carefully.
40:35Luckily, there's this marvelous catalog called the Hipparchos Catalog that has over 100,000
40:41stars that are all very nearby.
40:43And what we've chosen, logically, are the nearest, in fact, the nearest 2,000 stars.
40:48They're all within about 200 or 300 light years of the Earth.
40:52So if you imagine the little Earth floating in the blackness of the universe, and you
40:56imagine a glass sphere extending out about 300 light years, we are observing and hunting
41:02for planets around those stars within that sphere.
41:05Okay, Bernie, I think we can go to the next star.
41:10The next one will be Barnard's star.
41:13Every star takes hours of painstaking observation.
41:18Lick's 3-meter telescope locks on to its target.
41:24But even with all its magnification, a planet circling a distant star is too small and faint
41:31to be seen directly.
41:34The real challenge in planet hunting is that planets, by their intrinsic nature, don't
41:41produce their own energy.
41:42They shine by reflected light, and if they're warm, they glow a little bit.
41:47But they are, in fact, about a billion times fainter than the host star around which they're
41:53orbiting.
41:54So astronomers have perfected an ingenious technique to find these invisible worlds.
42:00So we use a trick.
42:02And the trick is, we watch the star, not the planet.
42:06As a planet orbits the star, the planet pulls gravitationally on the star, making the star
42:12wobble to and fro.
42:15To show how a planet pulls on a star, Marcy uses a simple demonstration.
42:21Okay, so here we have a bag of rice, and it's going to simulate the planet.
42:27And I'm the star.
42:29And what happens, of course, is that the planet orbits the star, like so, and as the
42:35planet orbits the star, the planet pulls back on the star and makes the star wobble.
42:41You might be able to see my body wobbling back and forth, and it's wobbling because,
42:46in fact, the sack of rice is pulling on me.
42:50And of course, the analog is quite perfect, because the sack of rice acts as the planet,
42:55my body is the star, and this rope serves as gravity.
43:03And of course, all we see with our telescopes is the star.
43:06We can't detect the planet at all, so we just watch stars to see if they wobble to and fro.
43:12And if they do, they must have a planet.
43:15To date, hunters like Marcy have found over 200 new planets orbiting distant stars.
43:25But can they determine what those worlds are like?
43:29Marcy believes so, by calculating how far the new world is from its star.
43:35The longer it takes the planet to go around the star, the farther the planet must have
43:40been from the star.
43:41Close-in planets go around fast.
43:44Distant planets take a long time.
43:45The Earth, of course, taking one year.
43:48Marcy's discovered one world, 1,100 times the mass of Earth, that orbits eight times
43:55closer to its parent star.
43:58Another planet is so close, it races around in just three days, making its surface thousands
44:04of times hotter than Earth.
44:07Some of the planets we've found orbit so close to their stars that the temperatures are thousands
44:13of degrees.
44:15Those kinds of temperatures, ordinary metals like iron and nickel and titanium, not only
44:20melt, they vaporize.
44:23Instead of clouds of water, the atmospheres of these deadly worlds are filled with clouds
44:29of metallic vapor.
44:32But Marcy's convinced that not all alien worlds are so savage.
44:39He's decided to look at smaller stars that burn less intensely.
44:44Could their orbiting worlds be more like Earth?
44:48What we hope to do in the next year is a glorious quest.
44:51We're going to observe low-mass stars and hunt for Earth-like planets.
44:56They're orbiting close, but next to a dim star, the temperature won't be too hot nor
45:01too cold, but just right for life.
45:06Out here, countless worlds are waiting to be discovered.
45:11Perhaps some will have breathable atmospheres and oceans of water, allowing life to flourish.
45:20But finding them is a huge challenge.
45:24So far, scientists have drawn a blank, and judging by the deadly environments on the
45:29planets that make up our own solar system, it's not going to be an easy job.
45:36From the crushing heat of Venus, to the erupting volcanoes of Io, to the 1,400 mile-per-hour
45:48winds of Neptune, the worlds we have discovered are too savage for even our most advanced
45:58technology.
46:01The only planet that offers hope for human colonization is Mars.
46:10If we could overcome the dust and the solar radiation, one day we could live here.
46:21Maybe in the future, when Earth's climate is too extreme, Mars will become home.
46:29Until that day, humans will have to adapt, continuing to thrive in a constantly changing
46:39world.