Original subtitles

As scientists and astronomers peer more closely and with

ever more fidelity at nearby stars, they are discovering

exoplanets, worlds outside our own solar system. Stars with

planets were once thought to be a rarity. They're turning

out to be the norm and not the exception. With some

confidence, scientists now calculate there could be as many

as 40 billion Earth-like planets in our Milky Way galaxy alone.

The first exoplanets were detected in 1992, orbiting a

pulsar, the remnants of a massive exploded star that was now

a fast-spinning neutron star. With data collected from

the Arecibo antennae in Puerto Rico, Aleksandr Volshan

discovered three terrestrial planets orbiting the pulsar PSR

B1257 plus 12. Other pulsars have been detected with dust

clouds and disks orbiting them. This suggests that these

three planets are second generation. The original planets

were destroyed by the stellar explosion, and the subsequent

debris disk enabled these new planets to form. It was

another three years before the first planet orbiting a G

-class star similar to our sun was identified, a gas giant

like Jupiter orbiting 51 Pegasi every four days. Five years

later, another main sequence star was found to have multiple

planets. Exoplanets were not easy to detect. They are tiny,

their light smothered by the light of their star, and they

are so far away.

There are three main methods for planetary detection. The

hardest is direct visual observation via telescope, both on

the ground and in orbit. Some 59 planets have been discovered this way.

More indirect methods are employed, one of which is

the radial velocity method. As a planet orbits, its

gravitational pull causes the parent star to move back and

forth. This tiny radial motion shifts the observed spectrum

of the star by a correspondingly small amount because of the

Doppler shift. With supersensitive spectrographs, the shifts

can be measured and used to infer details of a planet's mass and orbit.

The 3.6-meter telescope at La Silla, Chile has such a

spectrographic instrument called HART and is the leading

exoplanet hunter.

This is Talbotis, one of the first planets discovered

utilizing this method. 51 light-years from Earth, this

planet is massive, some four times the mass of Jupiter. So

far, over 600 planets have been detected by this method.

Another observational tool, and the most successful to date,

is the transit method. A planet that passes in front of its

parent star relative to us produces a slight dimming

of the star's light, which can be detected by sensitive

instruments. Some 1,200 have been located this way.

Until now, it was expected that exoplanets would orbit in

more or less the same plane and in the same direction as the

star's rotation. However, new results unexpectedly show that

many exoplanets actually orbit at a large angle to their

star's spin axis. In the case shown here, Wasp 8b, the orbit

is completely reversed. There are other tools and techniques

in the planet-hunting toolbox, including microlensing,

oculation and TTV or transit timing variation. Often, more

than one technique is used to verify findings.

In fact, revisiting a planet after some time for

verification can lead to surprising results, as in HD

189733b, a hot Jupiter-type planet. On revisiting it, Hubble

discovered the atmosphere was being stripped from it by a

violent stellar flare.

With the Hubble Space Telescope dividing its valuable time

between many varied tasks and objectives, a dedicated planet

hunter called Koro was launched.

The mission was led by the French space agency CNES, with

contributions from ESA, Austria, Belgium, Germany, Spain and

Brazil. Launched in 2006, the mission lasted seven years.

It located two planets around the star Koro 7, one of which

was the first found to display a density similar to Earth's.

In all, it located 32 planets and a hundred others are awaiting confirmation.

The NASA Spitzer Infrared Space Telescope was launched to

study protoplanetary and debris disks around stars and the

curious brown dwarfs, often referred to as failed stars.

Spitzer's infrared capability quickly led to numerous

planetary discoveries and infrared mapping of other known

planets, like hot Jupiter HD 149026b. Some 256 light-years

away in the constellation Hercules, a planet dubbed a hot

Jupiter, it is a sweltering 2,040 degrees Celsius, the

hottest planet yet detected, and also the darkest,

reflecting no sunlight back into space. It speeds around its

star every 2.9 days.

A world just two-thirds the size of Earth, one of the

smallest on record, and only 33 light-years away around the

star GJ 436, planet UCF-1.01 might be the nearest world to

our solar system that is smaller than Earth. The planet, a

rocky world, orbits so close to the star that the surface is

probably molten. As with HD 189733b in the constellation of

Alpacula, it appears to be tidally locked to its star,

showing only one face as it orbits. Spitzer was able to

distinguish the various temperatures of its clouds from 650

to 1700 degrees Celsius. Thermal imaging of these hot giants

has provided more details of these distant worlds. In

2009, the game changed with the launch of the Kepler Space

Observatory.

As part of NASA's Discovery Program, the Kepler Space

Telescope was launched to survey and monitor a fixed field

of stars of the nearby Milky Way trailing behind Earth. It

observed around 165,000 stars, watching for any changes in

their brightness. It has located over 1,100 planetary candidates.

Now these are candidates, but most of them, I'm convinced,

will be confirmed in the coming months and years. That's

more than all the people have found so far in history. A

veritable menagerie of planet types is emerging like Kepler

-16b orbiting two stars,

ice worlds and water worlds like Gliese 1214b.

The Kepler team announced today 1,094 new planet candidates,

bringing the total roster up to 2,326. Of those, 207 are

Earth-size, and we now have 48 that are in the habitable

zone, 10 of which are smaller than two Earth radii. So these

are planets that could potentially be rocky. So it's an

exciting milestone because we are really honing in on truly

Earth-sized habitable planets.

The combined surface and space-based system observations

have led scientists to believe that planets around stars are

the rule rather than the exception, and the average

number of planets per star is greater than one.

Kepler has discovered at least 86 stars with multiple

planetary systems. Kepler-11, for example, has six confirmed

planets orbiting a sun-like star. The Kepler-11 planetary

system is amazing. It's amazingly compact. It's amazingly

flat. There's an amazingly large number of big planets

orbiting close to their star. We didn't know such systems

could even exist. There are certainly far fewer than one

percent of stars have systems like Kepler-11. But whether

it's one in a thousand, one in ten thousand, or one in a

million, that we don't know because we only know one of

them.

The growing number of confirmed planets is

opening up new insights into planet formation.

We're learning so much more about the orbits of planets,

the masses of planets, the sizes of planets, and we're just

beginning. Kepler is still returning data, and we're going

to learn a fantastic amount about the diversity of planets

out there around stars within our galaxy. Around each

star is a circumstellar region called the habitable zone.

Sometimes referred to as the Goldilocks zone, this is a

region neither too cold nor too hot, where a planet could,

under the right conditions, support liquid water

at its surface and in turn could support life.

The first Earth-sized planet in a habitable zone was

discovered around a red dwarf. Named Kepler-186f, it is just

ten percent larger than Earth. Kepler-186f is the first

validated Earth-sized planet in the habitable zone of its

star. It's the outermost of five planets to orbit a star

that is smaller and cooler than the sun. This planet orbits

its star every 130 days, and so this places it in the

habitable zone, where it's in a region where it could have

liquid water on its surface. The star Kepler-186 is 500

light years from Earth in the constellation Cygnus. This

planet Kepler-186f orbits a star that's cooler and dimmer

than the sun. So while we may have found a planet that's the

same size as Earth and receives a similar amount of energy

to what Earth receives, it orbits a very different star. So

perhaps instead of an Earth twin, we've discovered an Earth

cousin. Believed to be a rocky world, its mass and density

are yet to be determined. This is one of the big milestones

that we've been looking for in our attempts to find out if

there are places just like home and if there's life out

there. One of the big steps is to say, is there somewhere

that looks, to all intents and purposes, like Earth? Well,

we don't know just yet, but we know that there are places

that at least look similar.

To date, over 48 Earth-like planets have been located within habitable zones.

Gliese 581 has four known planets. The outer D planet is

thought to be an icy planet that has migrated closer to the

star and would thus be covered by a large and deep ocean.

Kepler 62f is likely to have a rocky composition and is only

40% larger than Earth, making it the exoplanet closest to

the size of our planet known in the habitable zone of

another star. Kepler 62e orbits on the inner edge of the

habitable zone and is roughly 60% larger than Earth. Other

recent discoveries include Kepler 438b, 442b and 440b, a

super-Earth.

The super-Earth exoplanet GJ 1214b orbits its faint red

parent star. This is the first super-Earth exoplanet to have

had its atmosphere analyzed. It has a mass about six

times that of the Earth and appears to be surrounded by an

atmosphere of steam or thick clouds or haze.

Based on observations, scientists believe that of the Sun

-like stars, some 22% have an Earth-sized planet orbiting in

the habitable zone. Assuming 200 billion stars in the Milky

Way, that would be 11 billion potentially habitable Earths,

rising to 40 billion worlds if brown dwarfs are included.

Are any of these worlds close to Earth? In fact, yes. The

closest star to our own is the well-known Alpha Centauri

group, with the bright stars Alpha and Beta Centauri, plus

the faint red star Proxima Centauri, the closest star to

Earth.

Alpha Centauri b is known to be orbited by an Earth-mass

planet, making it the closest exoplanet to our solar system,

a meteor. It is located near 4.37 light-years away, almost within our reach.

Now in its fourth observing campaign, the Kepler spacecraft

continues targeting 16,000 stars for exoplanets. It's

estimated that the onboard fuel supply should last until at

least December 2017. So far, Kepler has found an astounding

1,013 confirmed exoplanets around 440 star systems.

The terrestrial telescopes continue to do the heavy lifting

when it comes to verifying possible planet candidates. The

Harpsk spectrographic instrument Atlassia Chile is being

joined by the Next Generation Transit Survey, or NGTS. It

will search for transiting exoplanets with a focus on

discovering Neptune-sized and smaller planets. NGTS is

designed to operate in a robotic mode. It will continuously

monitor the brightness of hundreds of thousands of

comparatively bright stars in the southern skies.

ESO's Very Large Telescope at Cerro Paranal in Chile,

composed of four individual telescopes, will be improved

with the new Next Generation of Adaptive Optic System called

Sphere. Other improved technologies include the Gemini

Planet Imager at nearby Cerro Pacion, now in operation, and

the SUBARU coronagraphic extreme technology currently being

installed and tested.

New, bigger and more powerful telescopes are in the pipeline as well.

The 30-meter telescope, planned for Manuakea, Hawaii, will

have 492 small hexagon mirrors arranged together to form the

primary mirror 30 meters across.

The GMT, or Giant Magellan Telescope, will be built at the

Las Campañas Observatory in Chile. It will consist of seven

8.4-meter mirrors arranged together to make up the primary mirror.

Work on the mirrors is well underway.

The European Extremely Large Telescope in the Atacama Desert

is due for completion in 2024. It will have a 39-meter

diameter mirror made up of 798 hexagonal mirrors and will be

the largest ever built. It will enable scientists to study

the atmosphere of exoplanets more closely.

Space-based telescopes are advancing as well. The Next

Generation Infrared Telescope, James Webb, is nearing

completion as it goes through rigorous testing.

A scheduled launch in October 2018 will put the 6.5-meter

telescope in orbit as a replacement for the Hubble and

Spitzer telescopes.

Like unto the California Gold Rush, there are planets out

there to be found, and the race is on. TESS, the Transiting

Exoplanet Survey Satellite, is scheduled to launch in 2017.

TESS will scan the entire sky searching for exoplanets using

four state-of-the-art cameras. It will be able to determine

the chemical compositions of exoplanet atmospheres.

Also planned for a 2017 launch is KEOPS. Its function is

to characterize transiting exoplanets orbiting bright host

stars. The satellite is a small package, roughly 1.5

meters square, with a life expectancy of five years.

The European Space Agency has commenced a new program called

Cosmic Vision, set to run from 2015 to 2025, with PLATO, an

exoplanet hunter, expected to be launched in 2024. Other

projects underway include PEGAS, under development in

France, EXCEED, the Exoplanetary Circumstaller Environments

and Disk Explorer, NASA, and FINESSE, the Fast Infrared

Exoplanet Spectroscopy Survey Explorer, due to launch 2019.

The Wide Field Infrared Survey Telescope, WFIRST, is another

NASA observatory designed to perform wide-field imaging for

the planet-hunting community. It will be fitted with a

coronagraph instrument for direct imaging of exoplanets and

debris disks.

Another NASA New Worlds mission is the STARSHADE project,

scheduled for a 2019 launch. It will physically block the

star's light with a parasol to allow direct observation of exoplanets.

NASA is already thinking about a future James Webb

replacement. Called the Advanced Technology Large Aperture

Space Telescope, or ATLAST, it will be 2,000 times more

light-sensitive than Hubble. If all goes according to plan,

ATLAST could be launched between 2025 and 2035.

With these new tools and technologies, it is only a matter

of time before we are able to detect Earth-like worlds

capable of supporting life.

Perhaps one day, even a planet emitting radio or other

signals, indicative of a sufficiently advanced intelligent

civilization. Finally answering that great question, are we alone?