Friday, June 29, 2012

The Core of it All!
Do all planets have a solid core?

A planetary core is the innermost layers of a planet that can be either liquid or solid. It is the densest part of a planet’s interior and contains a large fraction of the planet’s mass. The core can vastly range in size from planet to planet. The core of Mercury is nearly 85% of the planet’s radius while the inner and outer core combined in the Earth consists of only 55% of the radius. 

With recent observations of large gaseous exoplanets orbiting close to their stars astronomers think that due to outgassing, the loss of the planet’s atmosphere due to interaction with the stellar atmosphere, they may lose so much of their atmosphere that only the cores remain. One exoplanet HD 149026b is thought to have a core 35 to perhaps 110 times the Earths mass (1).

But let’s take a look at something a bit closer to home. Does Jupiter have a solid core, can we use it as a yard stick to measure exoplanets against?
Using observations from a number of probes that have made their way to and beyond Jupiter, computer models have been developed to predict what the interior of the planet might consist of.
    Jupiter has an atmosphere that consists of mostly hydrogen and helium that is roughly 1,000 km thick. As you go deeper into the atmosphere the pressure becomes great enough to condense the molecular hydrogen and form a liquid hydrogen layer nearly 21,000 km thick. The pressure under this has increased so much that the electrons are forced away from the hydrogen nucleus creating a soup of liquid metallic hydrogen which is over 37,000 km thick. Now nearly 60,000 km into the planet’s atmosphere we are only 85% of the way to the center and the pressure is already far greater than that at the very center of the Earth. Gravitational measurements have shown that Jupiter has a central mass 5 -10 times the mass of the Earth (2) in a volume only twice the size.

According to current planetary formation theories, “core-accretion” model or “top-down” theory, Jupiter would have needed a massive rocky core to accrete (capture) enough gas, in the early stages of the solar systems evolution, to become the giant we observe today. However, it is now theorised that this original core may have become mixed with the other interior layers of the planet due to the intense heat and pressure along with the fast rotation of the planet. 

As you can see the core at the center of Jupiter is still in the forefront of planetary science. On August 5th 2011 NASA launched a mission to Jupiter to as part of the New Frontiers Program, Juno. Juno will aim to “Improve our understanding of the solar system’s beginnings by revealing the orign and evolution of Jupiter”. It will arrive at Jupiter in July 2016 and hopefully shed some light on planetary formation theories.
Through a combination of observations we are able to determine a lot about a planet and with an understanding of planetary structure from our own solar system and gouverning physics we can deduce their structure. However, if we do not have a clear understanding of our own planets, so close to home, then what can we truely extrapolate out to others. It is exciting that those answers are within our grasp thanks to missions like Juno and hopefully this will then mean that we can answer this question for the vast array of alien worlds that have been discovered thus far.

More ...?
Here are some links with great information for furthur reading

(1) A Precise Estimate of the Radius of the Exoplanet HD 149026b from Spitzer Photometry, P. Nutzman, et al. ApJ, 692:229-235, 2009
(2) Accretion of the Gaseous Envelope of Jupiter around a 5-10 Earth-mass Core, O. Hubickyj, et al. Icarus, V179, I2, P415-431

Monday, June 25, 2012

The Greatest Tool

One thing we are asked to do as scientists, and rightly so, is to explain what it is we are doing. And explain it in a number of different ways depending on the audience, be it another scientist working in the same or a different field of study, or a politician someone in authority who is perhaps in charge of the funding for your work. Or, what I find most interesting and the most rewarding,  explaining it to everyone else, those who want to learn but are unable to burden themselves with the painstaking task of investigating it on their own (and don’t worry this includes myself most of the time).

The thing I always find through these explanations is that I am able to give myself a deeper and more thorough understanding of what it is I am doing, and in doing so open up other questions that need to be answered. As is often the way in the process of answering one question we are posed with new ones, and it is through this process of enquiry that we have formed the world around us today.
      I recently asked my father and sister, both of whom are historians, what do you think this era will be named, will it be Elizabethan once again, or have we passed the point of naming periods of time according to monastic rule?

I think that we will look back at this time as being the age of information, where everything we know around us is the product of advancements in science and information that is within people’s lifetimes. The age of science where we moved from knowing very little about the world around us, to knowing a great deal more than any individual could possible process.

Our lives are romanticised by philosophy; why are we here, what is our purpose, are we alone in the universe? These are all questions that may get brushed aside by scientists, and yet if you break down what it is that we are actually doing, what it is that we are investigating with scientific rigour these sorts of questions form the foundations of our pursuits.

Science is a tool, perhaps the best tool we will ever have, to answer these questions. It breaks things down into their most fundamental and builds them back up again. Theorists generate simulations, built on simulations, built on simulations, each time increasing the complexity and conforming to the physical principles we know; while experimentalists and observers interpret what we can see and physically show to be around us. It is the combination of these two techniques in a trial and error loop that are continuously improving our understanding of not only the universe around us, but ourselves too.
Science is not dictated by politics or individuals, sure they may have an impact on the topic of investigation, but what I am referring to is scientific laws, truth, and evidence, not only looking for answers but questions as well. The beauty of it all is that it is also not infallible, truths we know about the world around us are built on understanding, and they are extrapolations of what we see or can show to be true. It is therefore logical to assume that with more understanding, brought about by asking more questions, that these truths might change these extrapolations and assumptions might cease to hold true. And that is by no means a bad thing!

What I hope I have been able to convey here is not that anything that is unscientific is wrong, but that perhaps to answer some of those philosophical questions or even seemingly trivial ones, maybe a little science wouldn’t hurt.


  • I urge you to read the written version of three lectures Richard Feynman gave in 1963 on “The meaning of it all”. In his own fascinatingly unique way Feynman attempts to answer some questions on the true value of science in the real world and how it perhaps does not answer all of the questions it poses. 

  • There are also a number of books by Malcolm Gladwell (The Tipping Point, Outliers, What the Dog Saw, and Blink) which investigate our own minds and scientifically evaluate our relation to the world around us and the choices that shape it. 

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