On October 30th 2018, NASA announced the end of the Kepler Space Telescope's
nine-year exoplanet hunting mission, after discovering more than 2,600 new
worlds, including Earth-sized planets in their star's habitable zones. Welcome
back to Launch Pad, I'm Christian Ready, your friendly neighborhood astronomer.
The Kepler Space Telescope was launched in 2009 after astronomers spent the
previous 17 years detecting planets around other stars.
These extrasolar planets - or "exoplanets" - were unlike anything that we've ever
seen here in our solar system before. These were large, gigantic planets that
were orbiting so close to their host stars that they would complete one path
around their star every several days. In fact, some of these planets had orbital
periods measuring in just hours! Astronomers wanted to know if there were
any Earth sized planets orbiting at a safer distance from their host stars,
where the temperatures would be warm enough to allow water to condense on
their surfaces, but not so cold that it would just freeze out entirely. In other
words, could there be Earth sized planets orbiting in stars habitable zones? Now
just because a planet is in a star's habitable zone, it does not guarantee that
the planet automatically has life on it. All it can really tell us is that the
planet is just at a distance where water could be stable on its surface ,and since
water is an essential ingredient for life,
we call it the "habitable zone". Kepler was equipped with a 1.4 meter mirror and a
95 megapixel camera - the largest camera ever flown in space by that time. By
placing a telescope in space, Kepler would be able to detect a drop-off in a
star's light of just one part per 10,000. That's like having 10,000 light bulbs
and turning one of them off. This kind of sensitivity was unprecedented but would
allow astronomers to detect earth sized planets transiting in front of their
host stars. Three sequential transits would be
confirmation that this was due to a planet orbiting its host star. The timing
between the transits would tell us how long a planet took to orbit the star,
which in turn tells us this planet's distance from the star; the shorter the
period the closer the planet the longer the period the more distant the planet.
But astronomers could also learn something else from these transits. By
examining exactly how much light was subtracted from the star, astronomers
could infer the planet's radius. Smaller planets subtract less light from their
host stars while larger planets subtract more light. Kepler would spend the first
four years of its mission staring at a single region of the sky in the
constellation Cygnus. This part of the sky was selected because it lies along
the plane of our Milky Way galaxy, providing Kepler with a rich field of a
150,000 stars to monitor. Almost immediately after it got
to work, Kepler started to detect one exoplanet after another. By 2011, Kepler
was on a roll. It detected the first ever large rocky planet surrounding the star
Kepler 10. This planet, called Kepler 10b, orbits so close to its star that it's
daytime side is hot enough to boil iron. This world would be a lava planet. Its
atmosphere long stripped away by the wind from its star. The discovery of
Kepler 16b revealed the first plane,t ever to orbit a binary star system
straight out of Star Wars. Kepler 20e and 20f became the first two earth sized
planets to be found orbiting a sun-like star. And Kepler 22b became the first
planet detected in a star's habitable zone. Kepler would continue to make one
amazing discovery after another until May of 2013,
when the second of its four reaction wheels failed. With a failure of its
second reaction wheel, Kepler no longer could maintain its stable pointing.
Kepler's primary mission came to an end. But Kepler's operations team knew
that they had an otherwise perfectly healthy spacecraft. All they needed was a
way to point it and keep that pointing stable long enough to do science
operations. The Mission Operations team figured out that if they could orient
Kepler just right, sunlight pressure could be used to help keep the
spacecraft stable. This would give Kepler a new lease on life, and the second light
mission of Kepler, or "K2", was born. But this new orientation also meant that
Kepler would have to point away from the Sun once every 80 days in order to
prevent sunlight from entering the telescope. Even with these new
restrictions, Kepler delivered an incredible amount of new science. It
monitored variable stars, brown dwarfs, and red supergiants just as they went
supernova. But in order for Kepler to change its pointing every 80 days, it had
to make use of its thrusters, which in turn depleted its fuel supply. By October
2018, Kepler had literally run out of gas, and NASA announced its retirement.
In nine and a half years in space, Kepler monitored over 530,000 stars,
detecting 61 new supernovae, and oh yeah, over 2,600
confirmed exoplanets. That's about 70% of all of the exoplanets that
have been discovered to date. But Kepler's contribution will continue to
grow even after its mission ends. That's because it found an additional 2,500
candidate exoplanets, most of which will certainly be confirmed by follow-up
studies. But Kepler leaves behind something far more important than just a
huge stack of planets to study. It tells us that planetary systems are common and
in fact there are more planets than there are stars. It also showed us that
planets come in a wide range of sizes - some smaller than Mars, others larger
than Jupiter. But the most common-sized planet fits somewhere between the sizes
of Earth and Neptune. In other words, the most common type of planet is a
super-earth; something that we don't seem to have here in our solar system. And it
also showed us that our solar system is actually kind of weird. Most of the
planetary systems that Kepler found are very compact with planets clustered so
close to the stars that they would fit well inside the orbit of Mercury,
whereas our solar system seems to be spread out. And this tells us something
about the nature of how our own solar system formed. And Kepler did show that
earth-like planets can and do orbit in their star's habitable zones; it's just
that the frequency of those planets is a bit lower than we would have hoped,
hovering around between 12-20%. But now that we know that planetary
systems are common, the Transiting Exoplanet Survey Satellite is looking
for planets around nearby brighter stars. This will make it a lot easier for
telescopes like the James Webb Space Telescope and the Extremely Large
Telescope to follow up and study those planets in greater detail. And so we say
'so long Kepler, and thanks for all the exoplanets'. So what'd you think of
the Kepler mission? Did it make a discovery that you were particularly
excited about? Let me know in the comments below and I'll be sure to check
them out. And if you I've watched this video all the way to the end, then
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Christian Ready, keep watching the skies.