Darkening a lecture room after a full day of sessions seems like a dangerous prospect. But Wednesday’s Town Hall meeting on ultra-high pressures was actually pretty lively.

The basic idea? Squeeze hard on any element, ratchet up the temperature, and you end up with some unexpected new phases. At high enough pressures and temperatures, ordinary, transparent water becomes opaque. Push even further, and it becomes transparent. Dive down into Jupiter’s atmosphere, and the pressures quickly become so high that even hydrogen becomes metallic.

This relatively small field of physics is expected to get bigger as the National Ignition Facility comes online, which might happen as early as next year. So the talks came with a request — a call to arms for fellow physicists who might contribute.

“If as a result of this talk I infuriate you because I have overlooked some result or some phenomenon, then I have succeeded,” said Raymond Jeanloz of the University of California, Berkeley, adding that his goal is to engage as many people to think about the subject as possible. But aside from the sheer excitement of mapping new phases of matter, what’s the draw?

For one, it might help resolve some open questions in planetary formation. David Stevenson of Caltech told attendeees that when he was a grad student in the 70’s, the picture of Jupiter’s interior was clear. It had dense core of rock and ice, weighing in at roughly five Earth masses.

Then everyone wasn’t so sure. Later experiments squeezing and heating hydrogen, the primary element in Jupiter’s composition, increased the error bars on what hydrogen might look like in the planet. Jupiter might not have a core after all.

Stevenson says NASA’s Juno mission, which is set to launch in 2011 and reach Jupiter by 2016, could help answer that question — improving our picture of the planet’s gravity field as well as its magentosphere (which the metallic hydrogen helps sustain).

But interpreting Juno’s data will depend on a precise understanding of how hydrogen depends on temperature and pressure. “I would like to see a community effort to really understand the equation of state of hydrogen,” Stevenson said. Even a small uncertainty, Stevenson said, could make the difference between core and no core.

Darkening a lecture room after a full day of sessions seems like a dangerous prospect. But Wednesday’s Town Hall meeting on ultra-high pressures was actually pretty lively.

The basic idea? Squeeze hard on any element, ratchet up the temperature, and you end up with some unexpected new phases. At high enough pressures and temperatures, ordinary, transparent water becomes opaque. Push even further, and it becomes transparent. Dive down into Jupiter’s atmosphere, and the pressures quickly become so high that even hydrogen becomes metallic.

This relatively small field of physics is expected to get bigger as the National Ignition Facility comes online, which might happen as early as next year. So the talks came with a request — a call to arms for fellow physicists who might contribute.

“If as a result of this talk I infuriate you because I have overlooked some result or some phenomenon, then I have succeeded,” said Raymond Jeanloz of the University of California, Berkeley, adding that his goal is to engage as many people to think about the subject as possible. But aside from the sheer excitement of mapping new phases of matter, what’s the draw?

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