Listen to Jupiter's strange voice as the robotic explorer moves into the magnetic field and enters into a polar orbit around the gas giant. "We have over five years of spaceflight experience and only 10 days to Jupiter orbit insertion," said Rick Nybakken, Juno project manager from NASA's Jet Propulsion Laboratory in Pasadena, California. "It is a great feeling to put all the interplanetary space in the rearview mirror and have the biggest planet in the solar system in our windshield."

In three days, July 4th, the spacecraft Juno will arrive at Jupiter, the culmination of a five-year, billion-dollar journey. It's mission: to peer deep inside the gas giant and unravel its origin and evolution. One of the biggest mysteries surrounding Jupiter is how it generates its powerful magnetic field, the strongest in the solar system.

One theory is that about halfway to Jupiter's core, the pressures and temperatures become so intense that the hydrogen that makes up 90 percent of the planet -- molecular gas on Earth -- looses hold of its electrons and begins behaving like a liquid metal. Oceans of liquid metallic hydrogen surrounding Jupiter's core would explain its powerful magnetic field.

But how and when does this transition from gas to liquid metal occur? How does it behave? Researchers hope that Juno will shed some light on this exotic state of hydrogen -- but one doesn't need to travel all the way to Jupiter to study it.

Four hundred million miles away, in a small, windowless room in the basement of Lyman Laboratory on Oxford Street in Cambridge, Massachusetts, there was, for a fraction of a fraction of a second, a small piece of Jupiter.

Earlier this year, in an experiment about five-feet long, Harvard University researchers say they observed evidence of the abrupt transition of hydrogen from liquid insulator to liquid metal. It is one of the first times such a transition has ever been observed in any experiment.

"This is planetary science on the bench," said Mohamed Zaghoo, the NASA Earth & Space Science Fellow at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS). "The question of how hydrogen transitions into a metallic state -- whether that is an abrupt transition or not -- has huge implications for planetary science. How hydrogen transitions inside Jupiter, for example, says a lot about the evolution, the temperature and the structure of these gas giants interiors."

In the experiment, Zaghoo, Ashkan Salamat, and senior author Isaac Silvera, the Thomas D. Cabot Professor of the Natural Sciences, recreated the extreme pressures and temperatures of Jupiter by squeezing a sample of hydrogen between two diamond tips, about 100 microns wide, and firing short bursts of lasers of increasing intensity to raise the temperature.

This experimental setup is significantly smaller and cheaper than other current techniques to generate metallic hydrogen, most of which rely on huge guns or lasers that generate shock waves to heat and pressurize hydrogen.

The transition of the liquid to metallic hydrogen happens too quickly for human eyes to observe and the sample lasts only a fraction of a second before it deteriorates. So, instead of watching the sample itself for evidence of the transition, the team watched lasers pointed at the sample. When the phase transition occurred, the lasers abruptly reflected.

"At some point, the hydrogen abruptly transitioned from an insulating, transparent state, like glass, to a shiny metallic state that reflected light, like copper, gold or any other metal," Zaghoo said. "Because this experiment, unlike shock wave experiments, isn't destructive, we could run the experiment continuously, doing measurements and monitoring for weeks and months to learn about the transition."

"This is the simplest and most fundamental atomic system, yet modern theory has large variances in predictions for the transition pressure," Silvera said. "Our observation serves as a crucial guide to modern theory."

The results represent a culmination of decades of research by the Silvera group. The data collected could begin to answer some of the fundamental questions about the origins of solar systems.

Metallic hydrogen also has important ramifications here on Earth, especially in energy and materials science. "A lot of people are talking about the hydrogen economy because hydrogen is combustibly clean and it's very abundant," said Zaghoo. "If you can compress hydrogen into high density, it has a lot of energy compacted into it."

"As a rocket fuel, metallic hydrogen would revolutionize rocketry as propellant an order of magnitude more powerful than any known chemical," said Silvera. "This could cut down the time it takes to get to Mars from nine months to about two months, transforming prospects of human space endeavors."

Metallic hydrogen could be used to make room temperature or even higher than room temperature super-conductors. The Juno mission goes hand-in-hand with laboratory experiments into metallic hydrogen, Zaghoo said."The measurements of Jupiter's magnetic field that Juno will be collecting is directly related to our data," he said. "We're not in competition with NASA but, in some ways, we got to Jupiter first."

In the Gemini Observatory image at the top of the page, white indicates cloud features at relatively high altitudes; blue indicates lower cloud structures; and red represents still deeper cloud features. The two red spots appear more white than red, because their tops hover high above the surrounding clouds. Also prominent is the polar stratospheric haze, which makes Jupiter bright near the pole. Other tiny white spots are regions of high clouds, like towering thunderheads. In visible light Jupiter looks orangish, but in the near-infrared the blue color is due to strong absorption features. The blue mid-level clouds are also closest to what one would see in a visual light image.

The Daily Galaxy via NASA and Harvard University

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"The most exciting possibility is that the missing photons are coming from some exotic new source, not galaxies or quasars at all," said Neal Katz of the University of Massachusetts at Amherst. "For example, the mysterious dark matter, which holds galaxies together but has never been seen directly, could itself decay and ultimately be responsible for this extra light. You know it's a crisis when you start seriously talking about decaying dark matter!"

"It's as if you're in a big, brightly-lit room, but you look around and see only a few 40-watt light bulbs," says Carnegie Institute's Juna Kollmeier. "Where is all that light coming from? It's missing from our census."

The vast reaches of empty space between galaxies are bridged by tendrils of hydrogen and helium, which can be used as a precise "light meter." In a recent study published in The Astrophysical Journal Letters, a team of scientists finds that the light from known populations of galaxies and quasars is not nearly enough to explain observations of intergalactic hydrogen. The difference is a stunning 400 percent.

"The great thing about a 400% discrepancy is that you know something is really wrong," commented co-author David Weinberg of The Ohio State University. "We still don't know for sure what it is, but at least one thing we thought we knew about the present day universe isn't true."

Strangely, this mismatch only appears in the nearby, relatively well-studied cosmos. When telescopes focus on galaxies billions of light years away (and therefore are viewing the universe billions of years in its past), everything seems to add up. The fact that this accounting works in the early universe but falls apart locally has scientists puzzled.

The light in question consists of highly energetic ultraviolet photons that are able to convert electrically neutral hydrogen atoms into electrically charged ions. The two known sources for such ionizing photons are quasars—powered by hot gas falling onto supermassive black holes over a million times the mass of the sun—and the hottest young stars.

Observations indicate that the ionizing photons from young stars are almost always absorbed by gas in their host galaxy, so they never escape to affect intergalactic hydrogen. But the number of known quasars is far lower than needed to produce the required light.

"Either our accounting of the light from galaxies and quasars is very far off, or there's some other major source of ionizing photons that we've never recognized," Kollmeier said. "We are calling this missing light the photon underproduction crisis. But it's the astronomers who are in crisis—somehow or other, the universe is getting along just fine."

The mismatch emerged from comparing supercomputer simulations of intergalactic gas to the most recent analysis of observations from Hubble Space Telescope's Cosmic Origins Spectrograph. "The simulations fit the data beautifully in the early universe, and they fit the local data beautifully if we're allowed to assume that this extra light is really there," explained Ben Oppenheimer a co-author from the University of Colorado. "It's possible the simulations do not reflect reality, which by itself would be a surprise, because intergalactic hydrogen is the component of the Universe that we think we understand the best."

The Daily Galaxy via the Carnegie Institution.