Space Fan News #45: Kepler Finds Two Planets That Survived a Red Giant Expansion

Uploaded by tdarnell on 23.12.2011

Hello Space Fans and welcome to another edition of Space Fan News
This week, astronomers have announced the discovery of two Earth-sized planets around
another star using Kepler data.
Now, I know it seems like I say that almost every week, and it's true that now that we've
started looking in earnest, we finding planets all over the place.
But what's remarkable about this discovery is that these planets are orbiting very close
to a star that has already passed through the Red Giant phase of its lifecycle.
Which means that these planets may have survived being engulfed by their parent star.
The star in question is Kepler Object of Interest, or KOI 55, a star much like the Sun.
Or at least, it was.
What we're looking at here, may be the future of our solar system because in five billion
years, our Sun will become a Red Giant like this one.
Red Giants are dying stars that have exhausted most of their hydrogen fuel in their cores.
What happens is as it runs out of fuel, the core will begin to collapse which heats the
outer layers of the star, igniting fusion in these areas.
So now we have a star with hydrogen fusion going on in the outer layers, which heats
it further and causes the star to inflate.
The fusion reaction increases as it expands, and the star gets hotter and brighter, producing
enough energy to increase the star's luminosity by a factor of 1,000–10,000 times its original
brightness and it inflates to around 200 times its original size.
And the star will go on like this for about a billion years before it runs out of fuel
in its outer layers.
Now you can imagine that if there are any planets orbiting close in to that star, they
will likely be in big trouble as it expands.
And, I can assure you, that would NOT be just like downtown.
Astronomers always thought that if a planet were trapped in the outer layers of a star
for a billion years at these temperatures that they would just evaporate, but that doesn't
appear to be the case here.
A team of French astronomers using data from the Kepler Space Telescope were studying small
stellar pulsations of KOI 55, a subdwarf B star consisting of the exposed core of a red
giant that has nearly lost its entire envelope.
Most stars pulsate in brightness a tiny bit, and by studying these pulsations, astronomers
can figure out quite a bit about it: things like its mass, temperature, size and sometimes
even its interior structure.
The study of these pulsations is called asteroseismology.
In order to learn anything about a star from these pulsations, they must be observed 24/7,
sometime for years to get the frequency and minute changes in brightness down.
Kepler is ideally suited for this kind of measurement because that's all its doing:
staring at one spot in the sky for a very long time. Now that Kepler has been up for
a couple of years, the data are finally becoming available allowing us to do some good asteroseismology
on the stars in Kepler's field of view.
So as they looked at the data from this star and attempted to get the frequency of the
pulsations, while they were doing that, the team noticed the presence of two tiny periodic
modulations occurring every 5.76 and 8.23 hours that caused the star to flicker ever
so slightly, at one five thousandth percent of its overall brightness.
I told you Kepler was sensitive.
They eventually found that these two frequencies could not have been produced by the star's
own internal pulsations.
One explanation is that there must be two small planets passing in front of the star
every 5.76 and 8.23 hours. Being scientists, they named these planets KOI 55.1 and 55.2
To complete their orbits so rapidly, they would have to be extremely close to the star,
much closer than Mercury is to our sun. What's more, our Sun is a cool star compared to KOI
55, which burns at about 28,000 Kelvin, or 50,000 degrees Fahrenheit.
They are so close to KOI 55 that they are tidally locked, meaning one side faces toward
the star at all times, the other faces away.
Can you imagine what that must have been like? As the outer atmosphere of KOI 55 engulfed
the planets, they would have been stripped of any water and atmosphere they may have
started with almost immediately.
Then they would have orbited in there for roughly one billion years, friction from being
in the outer layers of a Red Giant star slowing their orbits, causing them to fall inward,
gravity cruelly locking them in an orbit which forces them to face their torment, one side
always pointing towards their tormentor.
Well, that's it for now Space Fans, thank you for watching and, as always, Keep Looking