Date: July 26, 2010

Title: Another demotion for Pluto? Or is it about to become King of the Dwarfs? Part 2

Podcaster: Marc West

Organization: http://www.mrscienceshow.com
http://www.mrscienceshow.com/2010/05/ep-128-another-demotion-for-pluto.html

Description: Already demoted from the exalted planet club, Pluto could be joined by up to 50 other objects in the ever-expanding “dwarf planet” club if the new definitions of dwarf planet, recently proposed by Australian scientists Charles Lineweaver and Marc Norman, are accepted by the International Astronomical Union. On the other hand, perhaps you would rather regard Pluto as the leading player in the astronomical second division. Rather than being the smallest of the planets, Pluto is set to become the charismatic king of the dwarfs. Marc West had a fascinating chat with Dr Lineweaver about how they derived these new numbers, and also about their work defining the shape and mass of other astronomical bodies.

Part 1 of this podcast was aired on July 5.

Bio: Marc West was a University Medallist in Chemistry at Sydney University, completed a Graduate Diploma in Science Communication at ANU and a Masters of Operations Research and Statistics at UNSW. Having grown up in Sydney, he ventured to Canberra and then London to be editor of Plus Magazine, and now works in Operations Research back in Sydney. Marc has written freelance for a number of magazines and newspapers, including G Magazine, The Canberra Times, The Helix and All Out Cricket Magazine, his article Political Music was published as one of top 50 science blogs of 2008 in The Open Laboratory 2008: The Best Science Writing on Blogs, whilst A sorry saga – the crumbling cookie made the 2009 version. Marc set up the Mr Science Show when on a trip to China, frequently talks on radio with The Diffusion Science Radio Show on 2SER, and co-founded The Beer Drinking Scientists podcast.

Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by John Sandlin because a little astronomy illuminates the darkest nights.

Transcript:

Another demotion for Pluto? Or is he about to become king of the dwarfs?
PART 2 (Part 1 could be heard on July 5)

Marc West: MW
Charles Lineweaver: CL

MW: Greetings and welcome to the 365 Days of Astronomy Podcast, my name is Marc West and I usually broadcast as part of the Mr Science Show , the podcast where science meets pop culture. You can find our website at www.mrscienceshow.com. We like to look at that mysterious grey area between science and pop culture, that area where you’re really not sure if you’re cool. One of the topics that we always like to tackle is astronomy,y and space. Our website again, www.mrscienceshow.com

And this week we’re talking about another demotion for everyone’s favourite astronomical body, Pluto. Not that long ago, Pluto was a fully paid-up member of the planet club, however a few years ago, the International Astronomical Union decided to demote Pluto to a new class of astronomical body called dwarf-planet. This week I spoke to Dr Charles Lineweaver, a senior fellow at the planetary science institute at the ANU in canberra – he has come up with a new definition of dwarf planet that may mean another 50 dwarf planets, so Pluto will hardly be an individual anymore.

THIS IS THE SECOND PART OF AN INTERVIEW WITH DR LINEWEAVER- THE FIRST PART CAN BE HEARD ON THE JULY 5 EDITION OF 365 DAYS OF ASTRONOMY

MW: I was reading recently, on another topic, that astronomers recently discovered a planet so big that they didn’t know whether to define it as a failed star or as a planet. Do you think that the definitions of planets and astronomical bodies, which are based on our solar system, work in other solar systems?

CL: They work if they’re based on fundamental physics, Now you just mentioned the distinction between a planet and a brown dwarf and a star. If you taken a Jupiter and make it bigger and binger and bigger until its about 13 or 15 or 17 Jupiter masses, then it becomes a brown dwarf. And if make it bigger and bigger and bigger until about 80 Jupiter masses, then they become stars as they start to burn Hydrogen in their cores. So thats a fundamental physics distinction because it starts burning H2.

Now the different between a large Jupiter and a brown dwarf is that they burn deuterium. Deuterium is a little easier to burn than H2, and so this is a very physical distinction between brown dwarfs and planets.

So those are distinctions that have nothing to do with our solar system, but to do with the temperatures and pressures needed at the centre of those objects.

MW: And I guess your work on dwarf planets is derived from fundamental physics so it should work everywhere.

CL: That’s right, that’s right. What we did was calculate how much gravity do you need to deform a material of a given compressive strength. The stronger the material, like iron are titanium, the harder it is to deform into a sphere. And so the icy objects should deform into spheres at a radius of 200km and rocky objects should become sphere at 300-350km radius, so theres a difference whether you’re made out of icy or rock.

MUSIC

CL: Oh well, the one thing we are talking about here is that as science make progress occasionally we have to reclassify things – in some sense nature is a continuum and some of these worlds are a little arbitrary – but just like H2 and D2 criteria, the idea of being round or not is something thats valid all over the Universe – and so this is not some arbitrary semantic game we’re playing, its whether the gravity is strong enough to make something round, and this will be the case when talking about the planets round Alpha Centauri, or anywhere else in our galaxy or the Universe.

MW: Now that you mention that, I guess the definition of what a planet is – it needs to clear its area, or words to that effect – are there some fundamental physics that could be used to shore up that definition?

CL: Oh yes – there are. If you have a debris disk – its called an accretion disk – when stars form they always have acc disks around them, and if you have alum of material in that disk, material falls onto it and onto it, and if that lump is really big it can gather lot of hydrogen and helium and become what’s called a gas planet. But our little Earth did not have enough mass early on and was unable to form a gas giant – luckily for us our Earth is not made of Hydrogen and Helium but is made of rock – and you can look outside your window and you’ll see rock and not Hydrogen and Helium.

MW: You mention in your report that there are 5 basic shapes in the Universe – would you like to talk bout that?

CL: Yes! Thats something in the report that I find really interesting but has been overlooked by almost everybody because of poor Pluto and the emotional attachment people have to Pluto!

The different shapes – I’ve divided every shape in the Universe into these 5 categories. The small object category is – you’ll see in front of you a pen, a telephone, a piece of paper, a tree and these are all objects whose shapes are determined by the forces between molecules and atoms – not by gravity but by electronic forces – but the electrons in one atom and the electrons in another atom. And there are all sorts of crazy shapes – and I call that just dust as dust is all kinds of crazy shapes,

But if you increase the size of anything, whether thats a pen or paper or a tree, as you get more and more massive, try to keep it the same shape, you wont succeed as the self gravity will pull it into a shape thats more or less a potato – so we have two shapes now, dust and potato. Potato is where gravity has started to become important compared to the electronic forces. So you have weird dusty shapes at the small scale where electrons dominate. And then you have potato shapes where gravity and electronic forces are about the same. And then you get even larger, get more mass together and you get sphere. So you have dust, potatoes and spheres.

Then its gets a bit more complicated. One other shape is disk shaped, like the rings of Saturn or the plane of the solar system – all the planets orbit the sun in a disk. And if you look at galaxies, you’ll see disk galaxies. So disks are objects that have a lot of angular momentum compared to how much much velocity – how much dispersion of their velocity there is. They have not been able to get rid of their angular momentum but they have been able to get rid of their energy. So these are objects that go round and round in a disk like the rings of Saturn, like the disk of a galaxy. These are high angular momentum.

Now theres another kind of object called a Halo – these halos are basically spherical. They haven’t collapsed like the sun and the earth and the moon, or all the other planets, into spheres.. But rather they are made out of discrete objects like stars, and these stars are orbiting and forming like a swarm of bees – but they are also spherical. So I wouldn’t call them spheres, Id call them halos because of their swarmy nature. And clusters of galaxies are also similar – instead of stars sarong around, you have galaxies swarming around inside a cluster.

So you have halos, disk, spheres, potatoes and dust. And those are the 5 categories you can read about in the paper if you have a good look it.

MW: Well its a good read! I enjoyed it!
CL: Oh good, its got nice punctures too!
MW: Its got fanatic pictures!

MUSIC:

MW: Well thats all we have time for in todays 365 days of astronomy podcast. If you liked what you heard today then of course you should keep listening to the 365 days of astronomy podcast, but you should also get over to my podcast at www.mrscienceshow.com. You can leave comments on any of the shows or blog posts we’ve got up, you can engage with me on twitter, and you ca also become a facebook fan.

I hope you enjoyed todays show, my name is Marc West and I hope to see you soon on the Mr Science Show, the podcast where science meets pop culture, and also soon on the 365 days of astronomy podcast.

THIS IS THE SECOND PART OF AN INTERVIEW WITH DR LINEWEAVER- THE FIRST PART CAN BE HEARD ON THE JULY 5 EDITION OF 365 DAYS OF ASTRONOMY

End of podcast:

365 Days of Astronomy
=====================
The 365 Days of Astronomy Podcast is produced by the Astrosphere New Media Association. Audio post-production by Preston Gibson. Bandwidth donated by libsyn.com and wizzard media. Web design by Clockwork Active Media Systems. You may reproduce and distribute this audio for non-commercial purposes. Please consider supporting the podcast with a few dollars (or Euros!). Visit us on the web at 365DaysOfAstronomy.org or email us at info@365DaysOfAstronomy.org. Until tomorrow…goodbye.