Space Fan News #60: Billions of Habitable Earths; Oldest Planetary System; Deepest Deep Field Ever

Uploaded by tdarnell on 30.03.2012

Hello Space Fans and welcome to another edition of Space Fan News.
OK, this is getting ridiculous. In the course of just a few years we've gone from not knowing
if there were ANY other planets in the galaxy outside of our solar system, to finding hundreds,
then looking at surveys at finding evidence for millions, then billions, then hundreds
of billions of planets in our galaxy alone.
About 160 billion to be a little more precise.
Well now astronomers working on ESO's HARPS planet finder are announcing that of those
hundreds of billions of planets in our galaxy, many of the ones that are small and rocky
like Earth are very common and that there are tens of billions of them
Oh, and they also happen to lie in the habitable zone of the planet.
Oh, and there are about one hundred in the Sun's immediate neighborhood.
Oh, is that all? No big whoop.
With this announcement, the HARPS team is telling us that around 40% of the most common
star in the galaxy, red dwarfs, have an Earth-sized planet in orbit within the habitable zone
of the star.
That comes out to tens of billions of Earth-sized planets that could have liquid water in our
What they did was they chose a sample of 102 red dwarf stars and looked at them for over
six years.
(They didn't do that all at once, they took a break or two every once in a while)
During that time, within that 102 star sample, they found nine super-Earths (these are planets
between one and ten times that of Earth), and two of those where within the habitable
They were able to estimate how heavy they were and how far away they were from the star.
Then they combined all this data, including observations of stars that didn't have planets,
and looking at the fraction of existing planets that could be discovered - and did what astronomers
do best: extrapolated using statistics to estimate how common different sorts of planets
are around red dwarf stars were.
I know, it's disappointing isn't it? You were hoping they would look at every star to see
the planet there? Yeah, me too, but what're you gonna do, astronomers gotta eat.
Anyway, they found that the frequency of occurrence of super-Earths in the habitable zones of
stars is 41%.
What's also interesting about this study is that they didn't find many massive planets,
like Jupiter and Saturn. Those appear to be rare around red dwarf stars.
Now, because there are a lot of red dwarfs close to the Sun, this new estimate means
that there are probably about 100 of these super-Earths in habitable zones in our neighborhood
- which they're defining as stars closer than 30 light-years.
I know, big neighborhood - it's not like downtown.
Next, astronomers from the Max Planck Institute for Astronomy in Munich have found what they
believe to be the oldest planetary system ever seen.
The system is known as HIP 11952 and this star has two planets in orbit around it: HIP
11952b - which orbits once every seven days - and HIP 11952c - which has a year of 290
This star system is in the constellation Cetus the Whale and lies 375 light years away.
Now this system is not all that remarkable as solar systems go, it's basically a star
with two gas giants in orbit, we've seen plenty of these.
Remember, we've confirmed roughly 750 exoplanets so far in our search and as I mentioned in
the previous story, we're getting a good sense of how many of the different kinds of planets
there are out there.
And this one's pretty ordinary, except for one detail.
This star is estimated to be 12.8 billion years old.
So here's the thing: we know that planets form from detritus left over from the formation
of the central star. The gas, dust, ice, etc that didn't make it into the star, usually
forms planets orbiting around it.
But we really don't know much more than that about what it takes to have planets form and
make a solar system.
So far of the planets we've found, we've learned that most stars that have planets in orbit
around them have something called high metallicity, which is a fancy way of saying they have a
lot of elements in them heavier than helium.
Why is that important?
Well for starters, we're pretty confident that the early universe consisted primarily
of hydrogen and helium and all the heavier elements came later from the deaths of these
early stars through supernovae.
So a big question we'd like answered is: are metals (elements heavier than helium) required
to have planets? How metal-poor can a star be and still have planets?
Well this star, HIP 11952, is almost all hydrogen and helium, it is very metal-poor, and given
the age of the star, 12.8 billion years, these planets probably formed when the galaxy was
just a baby and this is the first metal-poor star ever found to have planets.
This discovery sheds a little more light on what it takes to make a planetary system and
the metallicity question, what we need to do now is find more planets around these metal-poor
OK, finally since it seems to be ESO day at Space Fan News, astronomers there using the
VISTA telescope have released an image that is the widest and deepest ever taken of the
night sky.
And yes, that includes my most favorite picture ever: the Hubble Ultra Deep Field.
This image was created from over six thousand separate images with a combined, effective
exposure time of 55 hours.
See, in astronomy, if you take a lot of short exposure images each with a small amount of
photons and add them together, you get an image with more photons and a brighter object.
For example, taking two 100 second exposure images, each with a very dim galaxy you can
barely see, and put them together using a computer, you get a brighter image that would
look the same as if you had exposed it for 200 seconds.
They do it this way to keep the noise down. One day, I'll do a video explaining this process.
But here, this image represents the ultimate coaddition. Six thousand images yielding a
view of the sky as if we stared at it for 55 hours. Combining all these images together
brought out very faint galaxies we couldn't see in the individual exposures.
For comparison, the Ultra Deep Field taken by Hubble contained around 10,000 galaxies.
This image, called the UltraVISTA deep field, looked in a similar, apparently empty patch
of sky. But when processing these images was complete, UltraVISTA revealed over 200,000
galaxies, and includes some of the most distant ever seen by humanity.
Think about this for a minute: This is what we see when we stare at an empty part of sky
for a really long time, collecting every feeble photon that strikes the detector. Everywhere
we look is filled with galaxies, and each galaxy holds hundreds of billions of stars.
Truly understanding what's represented by this image, we are confronted with the fact
that humanity - sitting on our little planet orbiting our little star in only one of these
galaxies - is really nothing all that remarkable. We occupy no special place in the cosmos,
we are not central to anything.
Have a nice day!
Well, that's it for this week Space Fans, thank you for watching and, as always, Keep
Looking Up.