Space Fan News #49: There Are More Planets than Stars in Our Galaxy


Uploaded by tdarnell on 11.01.2012

Transcript:
Hello Space Fans, here we go again!
As I mentioned yesterday, JWST and the Space Telescope Science Institute have a big booth
at the AAS this year and I want to start today by showing you a couple of interesting clips
showing a gigantic video wall that they put up today. Here is Dr. Frank Summers of the
Space Telescope Science Institute showing some galaxies on it.
And here he is again discussing
galaxy collisions.
This wall shows images 100 mega pixels in size on an enormous screen in unprecedented
detail. Shown here is NGC 281, an H II region in the Perseus Spiral Arm of our galaxy which
is hosting a cluster of young, massive stars.
Soon, I imagine we'll all have one of these in our living rooms, and if I had one, I can
promise you this is precisely how I would use it. But for now, we have to rely on NASA
to show them to us this way.
OK next up exoplanets. Lots of exoplanets.
You know, I knew there was going to be lots of news from the AAS regarding exoplanets
this year. Kepler has been announcing planet discoveries more or less non-stop, observatories
from around the world have been sifting through loads of images looking for them and novel
techniques are being invented to improve both our accuracy and rate at which we find these
planets from other stars.
So I knew to expect lots of new exoplanets to be added to our catalog of known worlds.
But I didn't in a million years expect what I learned today.
If you didn't believe it before, then I don't think you can deny it now: we live in the
golden age of exoplanet discovery. Never has there been a more exciting time to look up.
Today was a wonderful reminder of what I went through in the late nineties when a professor
of mine told us how the Hubble Deep Field was taken. I couldn't believe what it represented.
The number of galaxies that appeared in an image taken while looking at a tiny, speck
of sky, with each little smudge an entire galaxy filled with billions of stars... well,
I was utterly breathless and it was the inspiration for the first video I ever uploaded to YouTube
in 2006.
I still think that image is the most important we've ever taken.
I was forever humbled that moment on, I felt humanity needed to get over itself; all of
the importance we place on ourself seems to me somehow misplaced. As Carl Sagan said,
we are standing on the shores of the cosmic ocean, and we have only waded in ankle deep.
Well Space Fans, it's moments like this that got me into astronomy in the first place.
I mean, I've been doing this a long time and sometimes I get caught up in my daily life
and I forget the bigger picture. It's natural, we all do that. But today I read a press release
that brought it all back and i haven't felt this way since my first encounter with the
Hubble Deep Field. This is why we study the universe.
An international team of astronomers from the European Southern Observatory used a technique
known as gravitational microlensing to measure how common planets are in the Milky Way.
Most exoplanets are found using one of two methods: measuring dips in brightness as the
planet passes in front of the star, called transit photometry and is how Kepler finds
them, or measuring the spectral doppler shift of the star as the planet tugs on the star
as it orbits, and that is called the radial velocity method.
Both of these techniques are biased however toward finding planets that orbit relatively
close to their parent stars and transit photometry finds only those planets that have a specific
orientation: if the planet doesn't pass between us and the star, we don't see it.
Gravitational microlensing reduces this bias considerably because it can detect planets
farther out, although the planet's orbital alignment is still important. Here, astronomers
watch what happens when a massive object passes in front of a very distant background star.
The gravitational field of the star and any planets it might contain bends and magnifies
the light from that distant star, acting like a lens.
This produces a light curve whose characteristics tell astronomers a lot about the foreground
object.
In many cases, this foreground body is a star. If it has any planets, even ones in relatively
far-flung orbits, they can generate secondary light curves, which indicates there is something
else there.
The great thing about this technique is that there are literally billions of background
stars to measure against. Scanning the sky, looking over each one gives us a lot of statistics
to work with, way more than Kepler can.
So, these astronomers combed through data gathered from a variety of Earth-based telescopes,
which scanned millions of stars in our galaxy from 2002 to 2007, six years, looking for
microlensing events.
What they found is staggering.
The team determined that about one-sixth of our galaxy's stars harbor Jupiter-mass planets,
HALF have Neptune-like worlds and nearly TWO-THIRDS host super-Earths.
Incredible. On average, there are 1.6 planets to every star in the Milky Way galaxy. Planets
are everywhere. And this only covers the planets orbiting from one half to ten astronomical
units. There are no doubt many, many more than if we could look further out from the
star.
Notice I said on average. Clearly not every star has a planet in orbit. Many have none,
while many others have several.
What's more, as if that wasn't enough, the team confirmed that low-mass planets, such
as rocky planets, super-Earths and Neptune-like planets are much more abundant than giant
planets such as Saturn and Jupiter, up to an estimated six to seven times more.
So all this means there are more planets in our galaxy than there are stars within it.
The Milky Way contains roughly a 100 billion suns, and now we know it also holds roughly
160 billion planets.
I think I'll leave things at that for now Space Fans. For me, this was a lot to absorb
and I'm still getting my head around the implications. There was another press release about Kepler
finding that planets in orbit around double stars are pretty common, but that just seemed
redundant in comparison with this news, so I left it out.
There are links to that if you want to read about it in the description box, so feel free
to check em out.
Well... Okay..., thank you guys for watching and, as always, Keep Looking Up.