Sunday, March 24, 2013

Planetary Outreach Part 2: Giants

Some more planetary insights from the top of my head to fill in a potential NASA gap in education and outreach*.

Random Thoughts on Jupiter
Jupiter the planet is the best high-pressure experiment on hydrogen, and Jupiter’s huge magnetic field tells us of the metallization of hydrogen at high pressures and—a prediction made by Wigner & Huntington in 1935 and so far not confirmed by experiment. Not for lack of trying. Many diamonds and a more than a few careers have perished in the attempt to demonstrate electrically conducting hydrogen at high pressures. I’ll put this on my list of blog-post ideas, because there is so much to write about the combination science/sociology of this field.

Jupiter could have several Earth-sized objects in the center, and we cannot tell with our current observations. Jupiter is actually quite simple. A very simple first-order polytrope defining the density-pressure behavior of Jupiter’s interior does a superb job of explaining the mass, volume, and observed moments of inertia. In the graduate “Build-A-Planet” course that I teach at UCLA, we find that the size of Jupiter is quite stable. Add more mass and the gravity shrinks it in. Take away some mass and it expands out a bit. Saturn is a different story.

 Saturn is an important second experiment on the high pressure behavior of hydrogen, and just like in the lab where occasionally additional data points just mess up the beautiful story, Saturn complicates matters. Saturn is a little less dense than Jupiter, but planetary formation intuition suggests that Saturn and Jupiter have similar interior compositions. Yet Saturn has some funky gravitational behavior, that suggests a more complicated interior model than is required for Jupiter. [For a deeper and better description see the paper of Helled et al., 2009 paper in Icarus]

On the Difficulties of Lecturing About Uranus
The gas giant Uranus is perhaps the most difficult to handle in the context of a classroom. See? When I taught UCLA’s ESS9 Introduction to the Solar System course, each night I practiced my lectures for my ~6-7 yr old son. We’d nestle in his bed and I would talk through the slides, and he would offer helpful commentary mostly consisting of single word reactions: either “boring” or “cool.” When it came time for the Uranus lecture, he thought it was the funniest thing he had ever heard. Every time I said the word Uranus in any context he exploded. “Uranus is a gas-giant.” “Uranus has rings.” “There might be diamonds in the interior of Uranus.” “Scientists are studying hot gas emissions from Uranus.” My son would roll around on his bed laughing. 

Diamonds in Neptune and Uranus
Like the sunspot cycle, every decade or so a scientific article detailing the diamonds in Uranus (excuse me) goes viral, and the science-media is temporarily flooded with imaginations of Neptune and Uranus and now exoplanets as giant-diamond planets. My advice to the scientist(s) who are enjoying the media spotlight on your new paper entitled something like “High pressure-laboratory investigations of a solar-subtracted-chondritic composition and potential implications for giant carbon planet interiors”: enjoy the publicity when it happens, but don’t stare straight at the sun. My advice for the rest of us: also enjoy our colleagues’ publicity and public exposure for the usual subterranean high pressure research, but remember that like many planetary phenomena, these media events are cyclical.

Here are some diamond-planet highlights from the last few cycles.
From ABC news: Artist's conception of 55 Cancri e. Haven Giguere/Yale University

*Yesterday’s fact-check on this revealed two NASA tweets suggesting EPO cuts are not necessarily happening but there is additional reporting that suggests otherwise:

Note: My research program is not supported by NASA currently, but I have had some NASA support in the past. My salary and research program is supported by a combination of the State of California, NSF, and DOE.

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