Extraordinary claims require extraordinary evidence, and it is
my job, my responsibility, as an astronomer to remind people
that alien hypotheses should always be a last resort.
Now, I want to tell you a story about that. It involves data
from a NASA mission, ordinary people and one of the most
extraordinary stars in our galaxy.
It began in 2009 with the launch of NASA's
Kepler's main scientific objective was to find planets outside
of our solar system. It did this by staring at a single field in
the sky, this one, with all the tiny boxes. And in this one
field, it monitored the brightness of over 150,000 stars
continuously for four years, taking a data point every 30
minutes. It was looking for what astronomers call a transit.
This is when the planet's orbit is aligned in our line of sight,
just so that the planet crosses in front of a star. And when
this happens, it blocks out a tiny bit of starlight, which you
can see as a dip in this curve.
And so the team at NASA had developed very sophisticated
computers to search for transits in all the Kepler data.
At the same time of the first data release, astronomers at Yale
were wondering an interesting thing: What if computers missed
And so we launched the citizen science project called Planet
Hunters to have people look at the same data. The human brain
has an amazing ability for pattern recognition, sometimes even
better than a computer. However, there was a lot of skepticism
My colleague, Debra Fischer, founder of the
Hunters project, said that people at the time were saying,
There's no way that a computer will miss a signal."
And so it was on, the
classic human versus machine gamble. And if we found one planet,
we would be thrilled. When I joined the team four years ago, we
had already found a couple.
And today, with the
help of over 300,000 science enthusiasts, we have found dozens,
and we've also found one of the most mysterious stars in our
So to understand this, let me show you what a normal transit in
Kepler data looks like. On this graph on the left-hand side you
have the amount of light, and on the bottom is time.
The white line is
light just from the star, what astronomers call a light curve.
Now, when a planet transits a star, it blocks out a little bit
of this light, and the depth of this transit reflects the size
of the object itself. And so, for example, let's take Jupiter.
Planets don't get
much bigger than Jupiter. Jupiter will make a one percent drop
in a star's brightness. Earth, on the other hand, is 11 times
smaller than Jupiter, and the signal is barely visible in the
So back to our mystery. A few years ago, Planet Hunters were
sifting through data looking for transits, and they spotted a
mysterious signal coming from the
star KIC 8462852.
The observations in
May of 2009 were the first they spotted, and they started
talking about this in the discussion forums.
They said and object like Jupiter would make a drop like this in
the star's light, but they were also saying it was giant. You
see, transits normally only last for a few hours, and this one
lasted for almost a week.
They were also saying that it looks asymmetric, meaning that
instead of the clean, U-shaped dip that we saw with Jupiter, it
had this strange slope that you can see on the left side.
This seemed to
indicate that whatever was getting in the way and blocking the
starlight was not circular like a planet. There are few more
dips that happened, but for a couple of years, it was pretty
And then in March of 2011, we see this. The star's light drops
by a whole 15 percent, and this is huge compared to a planet,
which would only make a one percent drop.
We described this
feature as both smooth and clean. It also is asymmetric, having
a gradual dimming that lasts almost a week, and then it snaps
right back up to normal in just a matter of days.
And again, after this, not much happens until February of 2013.
Things start to get really crazy. There is a huge complex of
dips in the light curve that appear, and they last for like a
hundred days, all the way up into the Kepler mission's end.
These dips have
variable shapes. Some are very sharp, and some are broad, and
they also have variable durations.
Some last just for a
day or two, and some for more than a week. And there's also up
and down trends within some of these dips, almost like several
independent events were superimposed on top of each other.
And at this time,
this star drops in its brightness over 20 percent. This means
that whatever is blocking its light has an area of over 1,000
times the area of our planet Earth.
This is truly remarkable. And so the citizen scientists, when
they saw this, they notified the science team that they found
something weird enough that it might be worth following up.
And so when the
science team looked at it, we're like,
probably just something wrong with the data."
But we looked really,
really, really hard, and the data were good. And so what was
happening had to be astrophysical, meaning that something in
space was getting in the way and blocking starlight.
And so at this point,
we set out to learn everything we could about the star to see if
we could find any clues to what was going on. And the citizen
scientists who helped us in this discovery, they joined along
for the ride watching science in action firsthand.
First, somebody said, you know, what if this star was very young
and it still had the cloud of material it was born from
surrounding it. And then somebody else said, well, what if the
star had already formed planets, and two of these planets had
collided, similar to the Earth-Moon forming event.
Well, both of these
theories could explain part of the data, but the difficulties
were that the star showed no signs of being young, and there was
no glow from any of the material that was heated up by the
star's light, and you would expect this if the star was young or
if there was a collision and a lot of dust was produced.
And so somebody else
said, well, how about a huge swarm of comets that are passing by
this star in a very elliptical orbit?
Well, it ends up that
this is actually consistent with our observations. But I agree,
it does feel a little contrived. You see, it would take hundreds
of comets to reproduce what we're observing.
And these are only
the comets that happen to pass between us and the star. And so
in reality, we're talking thousands to tens of thousands of
comets. But of all the bad ideas we had, this one was the best.
And so we went ahead and published our findings.
Now, let me tell you, this was one of the hardest papers I ever
wrote. Scientists are meant to publish results, and this
situation was far from that.
And so we decided to
give it a catchy title, and we called it:
I will let you work
out the acronym.
So this isn't the end of the story.
Around the same time
I was writing this paper, I met with a colleague of mine, Jason
Wright, and he was also writing a paper on Kepler data. And he
was saying that with Kepler's extreme precision, it could
actually detect alien megastructures around stars, but it
And then I showed him
this weird data that our citizen scientists had found, and he
said to me,
"Aw crap, Tabby. Now I have to rewrite my paper."
So yes, the natural explanations were weak, and we were curious
now. So we had to find a way to rule out aliens. So together, we
convinced a colleague of ours who works on SETI, the Search for
Extraterrestrial Intelligence, that this would be an
extraordinary target to pursue.
We wrote a proposal
to observe the star with the world's largest radio telescope at
Green Bank Observatory.
A couple months later, news of this proposal got leaked to the
press and now there are thousands of articles, over 10,000
articles, on this star alone. And if you search Google Images,
this is what you'll find.
Now, you may be wondering, OK, Tabby, well, how do aliens
actually explain this light curve? OK, well, imagine a
civilization that's much more advanced than our own.
In this hypothetical
circumstance, this civilization would have exhausted the energy
supply of their home planet, so where could they get more
Well, they have a
host star just like we have a sun, and so if they were able to
capture more energy from this star, then that would solve their
energy needs. So they would go and build huge structures.
megastructures, like ginormous solar panels, are called
This image above are lots of artists' impressions of Dyson
spheres. It's really hard to provide perspective on the vastness
of these things, but you can think of it this way.
distance is a quarter of a million miles. The simplest element
on one of these structures is 100 times that size. They're
And now imagine one
of these structures in motion around a star. You can see how it
would produce anomalies in the data such as uneven, unnatural
But it remains that even alien megastructures cannot defy the
laws of physics.
You see, anything
that uses a lot of energy is going to produce heat, and we don't
observe this. But it could be something as simple as they're
just reradiating it away in another direction, just not at
Another idea that's one of my personal favorites is that we had
just witnessed an interplanetary space battle and the
catastrophic destruction of a planet.
Now, I admit that
this would produce a lot of dust that we don't observe. But if
invoking aliens in this explanation, then who is
to say they didn't efficiently clean up all this mess for
You can see how this quickly captures your imagination.
Well, there you have it. We're in a situation that could unfold
to be a natural phenomenon we don't understand or an alien
technology we don't understand. Personally, as a scientist, my
money is on the natural explanation.
But don't get me
wrong, I do think it would be awesome to find aliens. Either
way, there is something new and really interesting to discover.
So what happens next? We need to continue to observe this star
to learn more about what's happening. But professional
astronomers, like me, we have limited resources for this kind of
thing, and Kepler is on to a different mission.
And I'm happy to say that once again, citizen scientists have
come in and saved the day.
You see, this time,
amateur astronomers with their backyard telescopes stepped up
immediately and started observing this star nightly at their own
facilities, and I am so excited to see what they find.
What's amazing to me is that this star would have never been
found by computers because we just weren't looking for something
like this. And what's more exciting is that there's more data to
There are new
missions that are coming up that are observing millions more
stars all over the sky.
And just think:
What will it mean when we find another star like
this? And what will it mean if we don't find another star like