Monday, May 7, 2012

Diamonds on the Blackest Velvet (WW111)


Tonight's guest on WW is Nikku Madhusudhan (shown above in a photo by Beverly Schaefer) as we return once more to the topic of extrasolar planets. It's a fascinating field that has grown in leaps and bounds since the first planets were observed around pulsars in the ealy 1990s and around a main sequence star in 1995. Since that time our techniques have expanded and the variety of planetary systems is added to almost daily.

Astoundingly, we can now deduce details about the atmospheres of some of these extrasolar planets, but only the ones relatively large and relatively close-in around brighter stars. But even in this small subset of the infamous "hot jupiters" there is amazing variety. A good part of Dr. Madhusudhan's fame comes from confirming the existence of planets for which Carbon is more abundant than oxygen. Such places were long theorized to exist because Oxygen and Carbon are produced in similar quantities by the proceses in stars that create elements heavier than hydrogen. This "nucleosynthesis" produces a characteristic pattern that we can observe in the abundances of elements within our own solar system (from wikipedia and shown below):


Take a close look. You'll notice a few things. First, the elements created in the big bang, Hydrogen and Helium Dominate - we have not yet come close to processing all of the material in the universe through stars. Secondly, you'll notice the stair-step pattern favoring even-numbered elements. This comes from the relative ease of building up heavier nucleii from "alpha particles," helium-2 nucleii and the greater stability of the nucleii thus formed. But the abundances fall off as the atomic number increases because it gets harder and harder to form larger and larger nucleii since more energy is required. In particular, beyond Iron, nuclear fusion does not yeild any energy, and so you get a pile-up that allows Iron to stand up above the pack.

What about Carbon and Oxygen? Well, these are synthesized largely through an efficient nuclear fusion process called the CNO-cycle in stars a bit more massive than the sun and up. Depending on the specific circumstances of the stellar furnace in question, either one of Carbon or Oxygen can come out a bit ahead. In the building of our own solar system, it was Oxygen. And so we have a solar system whose solids are composed mainly of ices (H2O) and silicate-bearing rocks (SiO4). By weight, Oxygen is not just a significant part of our atmosphere but comprises nearly 60% of the Earth's solid matter too.

Had the balance been different, a system of carbon compounds with different properties would have resulted. By showing that such systems do, in fact, exist Dr. Madhusudhan has expanded our view of the universe and the kinds of variety that exists out there. I hope you enjoy listening to his interview as much as I did. As always, a transcript of my intro is under the cut.



This is certainly one of the most brilliant and beautiful objects in the heavens; under favorable circumstances, the field of view glows and sparkles with innumerable diamonds on a ground dark and rich as the blackest velvet. You’re listening to Western Worlds!

Hello and welcome back for another conversation here on Western Worlds, an AFM*Original show heard right here on Astronomy.fm. My name is Dr. John and I’m coming to you this week, as every week, from the Centre for Planetary Science and Exploration at Western University, 689 miles, as the crow flies, from the Kimberlite of the People of the Parting of the Rocks in London, Ontario, Canada.

The imagery used in our opening quote by Elijah Burritt in 1849 to describe the double cluster has been applied to observations of celestial bodies ever since. However, little did we suspect that simple changes in the abundances of certain elements at the start of solar system formation could create worlds where diamond and other carbon compounds could be major planetary building blocks.

You see, all the elements that go into forming planets are created in stellar furnaces in a process we call nucleosynthesis. As the elements get heavier they become harder and harder to produce and are therefore less abundant. But two of the lightest and most abundant of these rock-forming elements are Carbon and Oxygen. In astronomical terms, nucleosynthesis should produce comparable amounts of each, depending on the specific circumstances of the star in question.

In our solar system we have an overabundance of Oxygen. During the formation of the planets, this oxygen preferentially bonded with hydrogen, silica and iron to produce the solid matter that became the rocky and icy worlds explored by our spacecraft. But that Carbon-Oxygen ratio could have gone the other way in other solar systems leading to exotic landscapes and vastly different geologies.

To tell us a little bit about his discovery of an extra-solar planet rich in carbon and about the atmospheres of extra-solar planets is Dr. Nikku Mad hu sud han, a researcher from Yale University and our guest tonight. It is remarkable how much can be discerned about such distant places, but the character of the worlds we are discovering is more varied than we ever imagined!

Accompanying us tonight is the composition “Elemental” by Opus III.


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