Hello Space Fans and welcome to another edition
of Space Fan News.
In this episode, as NASA’s Kepler Space
Telescope ends its mission once and for all,
ESA’s GAIA Space Telescope offers new data
prompting a reassessment of the estimate of
rocky habitable Earth-sized worlds found by
Kepler.
This new information reduces the number of
potentially habitable rocky worlds considerably.
On the same week that the Kepler Space Telescope
finally ran out of fuel, ending its nine year
mission, new light (so to speak) has been
shed on some of Kepler’s finding requiring
a reassessment of the number of potentially
habitable rocky worlds that Kepler found while
it was in operation.
GAIA is an astrometric space telescope that
measures the brightness and positions of billions
of stars.
Launched in 2013, Gaia is creating an ultraprecise
3D map of stars in our Milky Way.
This map includes position information for
1.7 billion stars and distance data for 1.3
billion stars.
Gaia is providing the most accurate data of
its kind every produced and it is adding valuable
insight into our knowledge of the Milky Way
Galaxy.
OK, so what has Gaia done to Kepler?
Remember that Kepler finds exoplanets using
the transit method and from the tiny dips
in brightness astronomers can learn several
things.
First, the amount of the dip is directly related
to the brightness of the star.
The size of a exoplanet is derived from the
percentage of the stellar disk that is blocked.
Big planets block a larger amount of light
than smaller ones.
Makes sense, right?
Secondly, how many times you see this dip
over time tells you something about its orbit.
If Kepler was far away and looked at the Earth
passing in front of the sun this way, it would
see a dip that occurred every 365 days.
That tells astronomers something about its
distance from the star.
And this is usually the number people use
to see if it’s in the habitable zone or
not.
So couple these light curves from Kepler with
what we already know about the star: it’s
type, size, temperature and all that good
stuff, astronomers piece together a picture
of what the planet may be like: things like
how big the planet is as well as how far away
it is from the star.
That’s not a lot of information to go on
to give us a complete picture, like whether
there is an atmosphere or not, but it’s
a good start.
What Gaia did was give better information
on the brightnesses of the stars in Kepler’s
original field of view.
Remember Kepler stared for five years at the
constellation Cygnus to specifically look
for earth-sized transits.
And over those five years, Kepler found 30
roughly Earth-sized worlds in orbit around
stars located in that stars’ habitable zone.
When Gaia looked at those stars, it returned
observations that some of those 30 candidate
worlds orbited stars much brighter that previously
thought.
And since the light curves measured by Kepler
are proportional to both the stars brightness
and the planets size, if the stars are brighter,
that means the planet must be bigger.
Why?
The brighter a star is, the hotter it is and
it pumps out more heat.
If the star is brighter and hotter, then the
light curves seen by Kepler must have come
from bigger planets, so they are larger than
Earth-sized.
Hotter stars also mean the habitable zone
has moved further out and the planets Kepler
THOUGHT were in the habitable zone, actually
aren’t any more.
So what’s the damage?
Of the 30 planets that Kepler thought were
earth-sized and in the habitable zone, now,
with these new Gaia observations, only between
2 and 12 are thought to be.
Yeah, I know, that’s disappointing, but
let’s remember that it was Kepler who showed
us that there are more planets in the galaxy
than there are stars over 50 percent more!
So there is still plenty of opportunity here,
this doesn’t really affect some of the other
candidates we’re all juiced about, like
TRAPPIST-1, Ross 128b and all those that weren’t
found by Kepler.
I’m interested to see how, if at all, the
Gaia data affects those estimates.
I would imagine not much since they are pretty
close by and we know a lot about those stars.
Still, you never know.
I’m really impressed by what Gaia is doing,
on the surface its mission isn’t sexy, measuring
brightness and position is pretty boring stuff,
but that information is vital in getting to
the more interesting stuff, like whether a
planet is in a habitable zone and if it’s
Earth-sized.
Another interesting thing is that astronomers
aren’t sure how big a planet can get and
still be rocky.
I guess past a certain point, rocky planets
cannot be sustained and they are still trying
to get a handle on those limits.
Well, I just want to say so long Kepler and
thanks for all the exoplanets.
I have a shirt made to commemorate the Kepler
mission on Teespring, the shirt is down below
the video if you want to take a look.
I had one shipped to me but I haven’t gotten
it yet.
I’ll probably have it for the next video
though.
That’s it for this episode Space Fans, I
want to thank all of Deep Astronomy’s amazing
and supporting Patreon Patrons who, along
with OPT Telescopes - a leader in telescopes
worldwide - make sure these episodes are produced
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Thank you all so much.
Thanks to all of you for watching and as always,
Keep Looking Up!
