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00:00Our galaxy is made up of some 400 billion stars, and at least a hundred billion planets.
00:22How many are like Earth, with an atmosphere, complex geology, flowing water, and abundant
00:50life?
00:56Astronomers are seeking answers in countless photons racing past the Earth, and in whole
01:06new theories about how planets form and evolve.
01:14What they are finding has only sharpened one of the oldest debates in science.
01:23Is biology a powerful and inevitable by-product of cosmic evolution?
01:30Or is life rare in a galaxy shaped by violence and mayhem?
01:37I am.
01:44For millennia we have locked our gaze on that
02:14heavens, hoping for a sign that life exists somewhere beyond Earth.
02:27In modern times, the search for life-bearing planets has become a central quest in a new
02:33age of astronomy.
02:38Giant observatories equipped with a new generation of precision instruments now allow us to
02:44detect planets in solar systems across the galaxy.
02:51And there's a whole new way of seeing that has vastly expanded the search.
03:00Earth in the 21st century.
03:06Computers increasingly shape the way we communicate.
03:11Learn.
03:15Travel.
03:18Grow food.
03:22Buy and sell.
03:27Make things.
03:30The amount of processing power we can put on a computer chip doubles every two years.
03:39This trend, called Moore's Law, has turbocharged the pace of scientific discovery.
03:49Vast centralized supercomputing facilities have sprung up to search for patterns, hidden signals,
03:58in the torrent of data now streaming in from telescopes.
04:09Astronomers, once consumed with taking photographs and making measurements in cold observatories
04:16across countless lonely nights, now write computer programs, analyze data, and build models that
04:30stimulate the complexities of star and planet formation.
04:42Far from settling the question, are we alone?
04:46Their discoveries have reignited one of the oldest disputes in science.
04:59According to the Greek philosopher Aristotle, a perfect planet Earth sat firmly at the center
05:05of a small, orderly universe.
05:12The universe beyond was utterly unpopulated, at least by any creatures other than gods.
05:23Not everyone agreed.
05:25Epicurus of Samos and his followers imagined an infinity of inhabited worlds among the stars.
05:38An ever-evolving cosmos gave rise to a boundless diversity of creatures.
05:47So too, for the modern descendants of Epicurus, our galaxy is filled with life-bearing worlds,
05:55and potentially, alien civilizations.
06:00We just have to find them.
06:06Astronomers have already determined that stars like our sun are not uncommon.
06:13That planets the size of Earth, at the right distance from their parent stars to support
06:18liquid water, could number in the billions.
06:28Yet a very different view has also taken hold, reminiscent of Aristotle.
06:39Biology is so complex, requires such stable conditions, and so much time, that Earth may well be an anomaly,
06:50a rare oasis of life, in a desolate universe.
06:57Who is right?
07:03Back in the early 1960s, the astronomer Frank Drake, a modern-day Epicurean, theorized that
07:11signs of alien intelligence may well be streaming by us, in the form of radio signals.
07:20Employing a radio telescope at Green Bank, West Virginia, he targeted two nearby stars, Epsilon Eridani,
07:28an orange star, just 10.5 light-years away, and Tau Ceti, a yellow star, about three-quarters the
07:37size and mass of our sun.
07:42Since Drake began his work, the search for extraterrestrial intelligence, Ceti, has expanded to hundreds
07:50of astronomers, thousands of stars, and a wide range of radio frequencies.
08:02Searchers have checked and rechecked Epsilon Eridani, Tau Ceti, and many other nearby stars.
08:11So far, after six decades of searching, they've found no repeating messages or anomalous signals.
08:19But they haven't given up, because there are so many more places, and different new ways, to search.
08:33Even as Drake looked for signals, other observers began looking for signs of planets themselves.
08:44The Dutch-American astronomer, Pete van de Kamp, sought evidence in the light of stars.
08:52After comparing photographic plates taken over three decades, he found that several nearby stars
09:00seemed to wobble, as if tugged upon, by unseen massive companions.
09:12In particular, Barnard Star, a red dwarf in the neighborhood of our sun, showed enough movement
09:20for van de Kamp to claim he'd found an orbiting planetary system.
09:33He spotted other nearby wobblers, Lalonde 2185, 61 Cygni, and Epsilon Eridani, the third closest visible star to us.
09:47Van de Kamp's findings did not stand up to scrutiny.
09:51An error in the telescope itself doomed his results to wide rejection.
09:57But his gut feeling that the stars in the Milky Way host an abundance of planets took hold.
10:11But yet, what astronomers began to see is not what they expected.
10:19In the winter of 1991, engineers at the Arecibo Radio Telescope in Puerto Rico had noticed structural
10:26flaws in the colossal instrument.
10:29They'd ordered it frozen in position.
10:35This limitation gave astronomers Alex Wolgen and Dale Frail the time they needed to observe
10:42a type of collapsed star, a rapidly spinning pulsar.
10:51Most pulsars spin very fast, emitting a flash with each revolution.
10:58One of their targets flashed about 6.2 times each second, but its timing was not predictable.
11:08It seemed to flash faster and slower in a complex pattern best explained by the gravitational tugging
11:15of two dense, rocky planets.
11:30A third, much smaller world would later reveal itself.
11:38Three burned out, zombie planets orbiting the corpse of a dead star.
11:48These are not the only pulsar planets out there.
11:53The oldest known planet, called Methuselah, rides above the Milky Way.
11:59At more than two and a half times heavier than the largest planet in our solar system, Jupiter,
12:05Metuselah lumbers along in a 100-year orbit around a pair of dead stars, a white dwarf and a pulsar.
12:19These discoveries became part of a wider challenge to theories about how solar systems form and
12:24evolve and how planets like Earth come to be.
12:35The reigning idea goes back over two and a half centuries, called the solar nebular model.
12:48This universal model is set in motion by the explosion of a giant star.
12:53So, shockwaves from the blast cause a massive cloud of hydrogen gas to collapse.
13:22This computer simulation shows the remarkable events that follow.
13:29Huge volumes of dust and gas begin to stream into the center of the cloud.
13:36The tighter the cloud is packed, the more it heats up.
13:41A storm erupts.
13:43A raging hurricane of dust, gas and ice crystals.
13:49In its eye, as temperatures rise, a star ignites.
13:57As matter flows toward it, the central region becomes a vast rotating disk.
14:04This disk is shaped by fierce hot winds from the newborn star, which push lighter gases to
14:11the outer zones while leaving dust and rocks to dominate the inner zone.
14:24As the winds die down, planet formation begins.
14:31Around a certain distance, called the frost line.
14:35Planets form quickly, growing large as they scoop up gas, dust and ice.
14:44Inside the frost line, dust grains and rocks coagulate into solid bodies called planetesimals.
14:51Most, perhaps a kilometer wide, but some much larger.
14:59As they collide or merge, they form the planets we know today.
15:10In time, eight emerge, to spin peacefully around the sun ever since.
15:20If our solar system was any guide, astronomers expected to find rocky planets similar to Earth,
15:27Venus and Mars in the sooty inner zones, where iron and silicon would melt and flow together
15:34to make solid planetary cores.
15:39Cool gas worlds, like Jupiter and Saturn, would orbit farther out, in the frosty zone,
15:47where ammonia, methane and water condense into small planets that grow large by gravitationally sweeping up lighter elements.
15:59Even further out, icy titans, like Neptune and Uranus, would crystallize after most of the gaseous hydrogen
16:07had been captured by the older, bigger planets.
16:13It didn't take long for the data to explode this conventional understanding.
16:19As a new age of planet hunting unfolded.
16:29Looking into the southern constellation of Pictor, astronomers examined an infant star
16:37and detected an extra-large newborn planet.
16:48The star, Beta Pictoris, is twice the size of our sun, 50% hotter, and almost nine times more luminous.
16:58It's dense solar disk extends some four times beyond the orbit of our Pluto.
17:12Passing stars have been tugging on the disk, producing waves of turbulence.
17:18The planet, in an orbit twice Jupiter's distance from the sun, is adding to the chaos.
17:27A NASA simulation shows a top view.
17:30The planet's gravity is hurling a stream of debris on a spiral path toward the star.
17:40A side view shows pressure waves created by its slightly tilted orbit.
17:48These waves ramp up collisions between icy and rocky bodies all through the disk.
18:00New models of solar system formation would have to take into account a host of factors at work
18:05in places like Beta Pictoris, the size of the solar nebula, the type of parent star, external influences,
18:21and the interaction of planetary bodies.
18:34Astronomers saw this dynamism at work as their planet discoveries piled up.
18:44Several teams focused on detecting wobbles in the light of stars caused by orbiting planets.
18:49As the star moves toward us, then away, it will change color, shifting from blue to red and
18:58back to blue.
19:05This can reveal planets orbiting very close to their stars, even if they lie very far away
19:11from us.
19:17In October 1995, Swiss astronomers Michel Mayor and Didier Quelo used this radial velocity
19:26method to examine the star 51 Pegasi, 50 light-years from Earth.
19:3251 Pegasi is like our sun, but 23% wider and 11% more massive.
19:41Wobbling motions in this star's light implied the presence of a giant planet, 47% less massive
19:49than Jupiter, but one and a half times its size.
19:56Dimidium, as the planet is now called, defied all expectations.
20:03It sits in an orbit that is eight times closer to its star than Mercury is to our sun.
20:12This close-orbiting gas giant is hotter than Jupiter by at least 1,500 degrees Celsius.
20:21How did it get into such a perilous position?
20:27The planet at 51 Pegasi was only one in a string of oddball worlds found patrolling their inner
20:34solar systems.
20:36large rocky planets lined with deep oceans, small gas planets, worlds covered in ice, or lined
20:55with flowing lava.
21:04With discoveries like these, it was our solar system that began to seem like an anomaly.
21:18To understand the full range of planet types, and how they formed within larger planetary systems,
21:26astronomers needed to target entire populations of stars, and to discern details on a finer scale.
21:34In 2009, astronomers developed a new planet-hunting strategy, combining spacecraft, telescopes, and
21:43supercomputers.
21:47Would it show just how unique Earth is?
21:51Or would it tip the scales toward the Epicurean model of a galaxy filled with inhabited worlds?
22:01Astronomers pointed the remarkable Kepler telescope at a group of about 500,000 stars, up to 3,000
22:08light-years away.
22:12Their aim, to detect the slight dimming of a star when a planet sails across its face.
22:25For the technique to work, the planet must orbit along the line of sight between star and telescope.
22:34Using this transit technique, Kepler astronomers, with the help of citizen scientists across the
22:39world wide web, spotted nearly 2,700 new planets.
22:48Kepler's successor, the transiting exoplanet survey satellite, TESS, sweeps across almost all
22:55of the sky, looking at the brightest stars near Earth.
23:02But the types of planets TESS is revealing swings the pendulum back toward Aristotle.
23:11Transit surveys like these tend to find big planets orbiting close in to their stars.
23:23These missions, working in concert with the Hubble Space Telescope and ground-based observatories,
23:29have turned up still more hot Jupiters similar to 51 Pegasi.
23:35Some, facing powerful solar winds, are rapidly losing their atmospheres.
23:46Based on the Kepler data, scientists estimate Jupiter-sized planets, and larger, make up just under
23:53a fifth of all planets.
23:59The most prevalent type, at just over 50% of all known planets, is Neptune-sized, with rock
24:08or ice cores, surrounded by atmospheres of water, ammonia, and methane gas.
24:19Some theories suggest that, deep inside, boulder-sized carbon diamonds rain downward toward their rocky
24:26cores.
24:31The ones detected so far, sit close to their suns.
24:41They may be former Jupiters that lost mass.
24:48Or gas giants that were flung inward by larger cousins.
24:56But in the data, at a point smaller than about two Earth radii, this class of mini-Neptunes,
25:04gives way to dense, rocky worlds that dwarf our planet.
25:14These super-Earths make up 18% of exoplanets discovered so far.
25:24Among them, Kepler-22b is a super-Earth revolving in the habitable zone of its star.
25:38This planet may be a water world, with a deep, global ocean clinging to a massive, rocky core.
25:53Orbiting close to the star 55 Cancri is a rocky planet almost eight times more massive than
26:00Earth.
26:04Its surface is a scorching 2,000 degrees Celsius.
26:15Kepler-452b has an orbit size close to that of Earth, and a parent star similar to the Sun.
26:26The planet is some five times larger than Earth, so it's likely a cloudy world more like Venus.
26:36Then there are the Earth-sized planets, about 11% of the total.
26:42Earth-sized does not make them life-bearing.
26:47The Earth-sized planets are discovered by the TESS satellite.
26:54HD 21749, 53 light-years from Earth, is an orange K-type star 70% the size of our Sun.
27:06Earth-sized planets, planet C, maintains such a close orbit that its year is only eight Earth days long.
27:15Its surface is rocky, likely hovering around 400 degrees Celsius.
27:24Neighboring planet B is a hot mini Neptune, 23 times the mass of Earth.
27:32Even a deep layer of clouds, temperatures average around 150 degrees Celsius.
27:47This planet, 1.3 times the mass of Earth, closely orbits the star LHS 3844.
27:57With a year lasting only 11 Earth days, its surface would be lined with pools of lava.
28:06Finally, the Sun-like star Pi Mensa hosts a planet twice the size of Earth.
28:17Its surface temperature is over 900 degrees Celsius.
28:23Still, as observational and computational techniques advance, there are glimmers of hope for finding
28:32Earth-like planets.
28:38Red dwarfs are the galaxy's most plentiful star type.
28:42They are hard to see, lightweight, cool and much fainter than the Sun.
28:51Other planets orbit close in, their years rushing by in just a few days.
29:00Among them, Proxima Centauri, the closest star to our Sun.
29:08With barely 12% of the Sun's mass, it's only 2% as bright.
29:20After extensively studying the star for more than 18 years, astronomers have confirmed
29:26at least one Earth-sized planet.
29:32Proxima Centauri b completes an orbit in a little more than 11 days.
29:41It revolves at the distance where water could be liquid, just like Earth.
29:51Like many red dwarfs, Proxima Centauri has a stormy temperament.
29:57Large flares blasting with deadly ultraviolet, X-ray and gamma radiation, likely eroding away
30:05any atmospheres its planets may have.
30:13Find Proxima Centauri b, part of a breed of so-called eyeball Earths.
30:25These planets orbit so close to their parent stars that they become gravitationally locked,
30:34with one side facing perpetually in, and the other out.
30:52One side is always arid and scorched by solar flares.
31:02The other, enshrouded in thick ice.
31:10Can a watery ring, with fertile land and life forms, exist in the twilight zone between them?
31:28Here is another candidate.
31:30TRAPPIST-1 is an ultra-cool dwarf star that hosts at least seven planets, all bunched into
31:37close orbits.
31:40All are made of rock, but with densities that suggest an abundance of water.
31:48At just 11% the diameter of our sun, this star puts out just 5 one-hundredths the sun's light.
31:55Fortunately, there is another source of heat.
32:06Like tussling siblings, the planets jostle one another's orbits.
32:13Tidal friction causes them to heat up from within.
32:22Those closest to the star are likely steamy and hot.
32:28Those farthest are icebound.
32:36The fourth planet out, slightly smaller than Earth, has the potential for liquid water.
32:47You probably won't find an advanced civilization here.
32:57In time, astronomers using space telescopes or ground-based instruments will widen their
33:02discoveries to include more planets farther from their stars.
33:08What they have found to date has already transformed theories of how our solar system formed, while
33:15dramatically altering the odds that we will find other life-bearing planets.
33:24Soon after our star ignites in this new view, Jupiter forms in the icy, gas-rich region beyond
33:30the frost line.
33:34It quickly cuts off the flow of matter to the inner solar system, slowing the formation of
33:39rocky worlds.
33:44Scientists have used supercomputers to project Jupiter's path amid countless small objects
33:49that fill the early solar system.
33:52The rings show the orbits of myriad would-be planets.
33:57Flashes mark collisions between them.
34:01The blue ring tracks the orbit of Jupiter.
34:06As it grows, Jupiter increasingly responds to the gravitational pull of the growing sun, as
34:13as well as the pushing and pulling forces from Saturn.
34:20Its orbit begins to shrink.
34:26Named for the turn a sailboat takes into the wind, scientists call Jupiter's inward move
34:32the grand tack.
34:39But the rising giant does not swallow, it flings out of the solar system, or pushes toward the
34:44sun.
34:48Chaos reigns, as once smooth orbits turn into a disordered swarm.
34:54The simulation shows Jupiter reaching the orbit of present-day Mars.
35:00At this time, Saturn begins to pull it back out.
35:08Jupiter's grand tack would have dramatically reduced the mass of the inner solar system.
35:15If a super-Earth had formed, it was likely obliterated or driven into the sun.
35:23From then on, the planets that formed or survived were bound to be relatively small.
35:33Ironically, Jupiter's destructive foray may have sowed the seeds of life by ferrying in
35:39large numbers of icy bodies.
35:46Destructive impacts continued, possibly bringing an end to the life-bearing chances of Mars.
35:54Earth was not out of the woods.
36:01Scientists theorized that early in its life, our planet was hit by a wayward Mars-sized world,
36:07called Theia.
36:21Instead of destroying the young Earth, the angle of impact created a splash of debris that would
36:27coalesce into the Moon.
36:37Over time, the Moon's gravity acted to slow Earth's orbit and steady its spin.
36:46Tidal effects from the Moon's gravity churned the seas.
37:13Helping to create conditions for life to emerge.
37:28Jupiter continued to serve as a benefactor.
37:34Working in tandem with Saturn, the gas giant shoved Uranus and Neptune off to the edge of interstellar
37:41space.
37:44That disrupted the orbits of millions of comets, flinging them toward the Sun.
38:01These icy projectiles are thought to have delivered massive amounts of water to our fledgling world.
38:15Ironically, one of the very first planetary systems to be examined, by both Pete Vandekamp
38:20and Frank Drake, turns out to be arranged remarkably similar to our own.
38:27Epsilon Eridani has a cloud of icy debris left over from the system's formation in about the same place as our Oort cloud.
38:39A second disk of rocky bodies, equivalent to our Kuiper belt.
38:46And a gas giant planet at the outer edge of a ring of asteroids, like our Jupiter guarding
38:53our main belt.
38:58Astronomers don't yet know, but there could be a world like ours.
39:10The search for other Earths has long focused on the habitable zones of stars, where Earth-sized
39:17planets might settle into stable orbits.
39:23There, they'd have time to develop atmospheres, ocean currents, volcanism, and other factors
39:30that helped spawn life here.
39:35But the tangled history of our solar system shows that making a life-bearing planet is a
39:40matter of rare circumstance and considerable luck.
39:46Accordingly, some astronomers are seeking to redefine the search, focusing instead on finding
39:52the specific conditions that could support life.
39:58The most habitable planets, they say, may not be exactly like Earth.
40:04In a class all its own, a super-habitable planet could be about one and a half times
40:09the size of Earth.
40:16It orbits an orange-colored K-dwarf star, cooler and longer-lived than the Sun.
40:23Set in the habitable zone of its star, the planet is lined with abundant water.
40:29A molten interior spins off a robust magnetic field.
40:36Together with a thick atmosphere, it deflects cosmic rays and solar radiation that pose a danger
40:42to life forms.
40:44Geological activity produces a patchwork of dry land forms, kept low by erosion.
40:53With stable conditions over long periods of time, the chances are good that chemistry and energy
40:59come together to spawn life and generate a habitable climate.
41:08From the thousands of extrasolar planets discovered so far, scientists have distilled a list of 24
41:14super-habitable planets with these general characteristics.
41:18planets and planets.
41:19How will we know if there is life there or on any other candidate?
41:35Future space telescopes will be equipped with instruments to search for oxygen, methane, and other markers of biology as starlight filters through their atmospheres.
41:47Giant new ground-based observatories may take actual pictures of planets, opening a window into their rotation rates, climate, seasons, oceans, even the presence of vegetation.
42:15In the absence of evidence like this, a skeptical follower of Aristotle may conclude that our planet remains wholly unique.
42:24But the new Epicureans, with ever more powerful technologies, hold to a different vision.
42:34They believe the sheer number of planets in our galaxy means we must not be alone.
42:47If our world developed intelligent life forms curious about their place in the universe, then so too did another.
42:57Even now, its inhabitants may be examining images of a yellow G-type main sequence star somewhere in the Milky Way.
43:09They see a tiny pale blue dot tucked into a remarkably circular orbit.
43:16Earth's
43:28The fact that the planet is enough, are more and more корабly experts of other planets, and so one hundred, to be the greatest star- jakieś star-city creatures.
43:35wonder after pouring over their data and running planetary formation models is it
43:45big enough or special enough to support life
44:05you
44:07you
44:35Transcription by CastingWords