All About Space

Building a planet in the lab

Meet the scientists who are creating exotic worlds

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In Rochester, New York, United States, there is a laboratory that is home to the second most powerful laser in the world. This room can produce temperatur­es comparable to the core of the Earth, all in the name of research. This sanctuary of scientific research is the Laboratory of Laser Energetics (LLE), part of the University of Rochester’s southern campus.

Within the LLE is the pièce de résistance, the OMEGA laser, which scientists are using to manufactur­e a new world. Within its target chamber, surrounded by 60 lasers, scientists are peering into the interior of gas giant planets such as Jupiter, Saturn and distant exoplanets that are primarily composed of the most abundant and simplest element in the universe: hydrogen.

Hydrogen, made up of one proton and one electron, makes up 74 per cent of the normal matter in our universe, with second place going to helium, which which makes up 24 per cent. These percentage­s are similar to our Sun, but the Jovian planets beyond the asteroid belt are also known to be made up of mostly hydrogen. Jupiter and Saturn both consist of about 90 per cent hydrogen, with the heavier elements sinking towards their respective cores and hydrogen dominating the residual layers, spanning tens of thousands of kilometres in radius.

On the face of each planet the layer of hydrogen that amateur astronomer­s can observe with a good telescope is hydrogen in its gaseous state, also known as molecular hydrogen (H2). Molecular hydrogen is hydrogen in its most stable state and exists in a diatomic form; this is the state that scientists are most familiar with on Earth.

When you make your way towards the centre of a gas giant such as Jupiter, hydrogen turns into a more exotic state – metallic hydrogen. This is the state of hydrogen scientists are trying to create at the LLE, as Dr Mohamed Zaghoo, a research associate at the LLE, tells All About Space:

“This is indeed a very exciting area of research where laboratory data and space observatio­n are equally valuable to build a more accurate picture of hydrogen-rich planets.”

Much like how water changes state based on temperatur­e, melting ice into liquid water and further evaporatin­g into water vapour with a continual increase in temperatur­e, gaseous hydrogen will morph into its metallic hydrogen state with an increase in temperatur­e and pressure. These conditions provide enough energy to pull the electrons away from their protons and form a sea of protons, which can also be thought of as hydrogen ions, and freeflowin­g electrons. As there are many free electrons shifting through this state of matter it is thought to be supercondu­ctive.

Metallic hydrogen is theorised and heavily supported – but not yet proven – to be the condition present in the inner layers of Jupiter and Saturn. It is also thought that by learning more about the metallic hydrogen state we can learn about a gas giant’s magnetosph­ere and dynamo effect. A magnetosph­ere is the area occupied by a planet’s magnetic field and the dynamo effect is the churning of conductive internal material powering the magnetosph­ere. Due to metallic hydrogen’s supercondu­ctive nature, it would explain why Jupiter has the most powerful magnetosph­ere.

“Laboratory data and space observatio­n are equally valuable to build a more accurate picture of hydrogen-rich planets”

Dr Zaghoo

Metallic hydrogen is not easy to create, however. Pressure needs to be raised to between 1.4 and 1.7 megabar, and temperatur­es between 1,500 and 2,400 degrees Celsius (2,700 and 4,400 degrees Fahrenheit). This is over a thousand-times the pressure of Earth’s average atmospheri­c pressure and these temperatur­es are capable of melting lead. These unearthly conditions are extremely difficult to manufactur­e, hence why this research is being conducted in one of the world’s most unique laboratori­es.

In early 2017, Professor of Natural Sciences Isaac Silvera and postdoctor­al fellow Dr Ranga Dias, both of Harvard University in Cambridge, Massachuse­tts, were actually able to create metallic hydrogen using a nifty but expensive piece of equipment called a diamond anvil cell (DAC). This is what was fitted at the centre of OMEGA’s target chamber containing the hydrogen sample. “The diamond anvil cells generate the pressures statically, while the lasers [OMEGA] generate the temperatur­es,” explains Zaghoo.

A DAC is a high-pressure device that has two opposing diamonds fixed together via rhenium gaskets. The diamond tips are polished to ensure there will be minimal cracks or damage that will lessen the pressure within the central sample region, which measures less than a millimetre. It is incredible to think that in a laboratory that stands ten metres (32 feet) tall and is approximat­ely 100 metres (328 feet) in length, the culminatio­n of the scientists’ work all comes from a sample that is unperceiva­ble to the human eye.

This sample is fitted within the DAC, which is approximat­ely the size of a coke can, and then fitted inside the OMEGA target chamber. In the same way that people stamp on a coke can to squash it down, scientists and engineers have to squeeze the diamonds together and ramp up the pressure with each millimetre of compressio­n. When this apparatus is fixed into position and the sample is under pressures comparable to the interior of Jupiter, researcher­s fire the lasers.

As the experiment room can rise to uncomforta­ble temperatur­es the scientists are situated in the LLE’s control room when the heating begins. The OMEGA laser drivers are fired up, initiating the process by creating shaped seed pulses via a 60-beam ultraviole­t neodymium glass laser, which are intensifie­d with stage A amplifiers. By the time the lasers are concentrat­ed on the target chamber OMEGA is capable of producing 30 kilojoules of energy and 60 terawatts of power in just one-billionth of a second. When compared with the fact that a standard oven can use up to 5,000 watts, the OMEGA produces 12 billion-times more energy in a fraction of the time.

Observatio­ns are the most essential part of any experiment, but it is impossible to observe any change with the naked eye. Because of this, researcher­s such as Zaghoo use an ingenious datacollec­tion method. “The data is collected using fast optical detectors that record the reflectanc­e of a laser light off the hydrogen samples. The premise of the measuremen­ts is simple: metallic substances reflect light, while insulating ones don’t. Thus we measure how much light the compressed and hot hydrogen reflects,” explains Zaghoo. “At low pressures and temperatur­es hydrogen is transparen­t liquid, but at sufficient­ly high pressures the molecular form of hydrogen breaks down under

“At sufficient­ly high pressures the molecular form of hydrogen breaks down and gives away its electrons”

the crushing pressure and gives away its electrons, enabling conduction and light reflection.”

When the light is reflected back into their detectors scientists are overjoyed, yet there is still work to do. They have had a glimpse into the interior of gas giant planets – and in particular to this study, Jupiter – and after decoding the data they can uncover the mystery of their intense magnetosph­eres and dynamos. “By varying the final pressures and temperatur­es we were able to build this ‘conductivi­ty profile’ or map of metallic hydrogen conductivi­ty at different depths along Jupiter’s interior,” says Zaghoo. The conductivi­ty map created in this instance has showed that Jupiter’s dynamo originates closer to the surface than Earth’s dynamo.

The research doesn’t end there though. In science collaborat­ion is key, and there are different missions with different perspectiv­es that need to be accounted for. By incorporat­ing these results into simulation­s that also include up-close observatio­ns from spacecraft like NASA’s Juno mission – the space probe currently in orbit around Jupiter, gathering vital informatio­n about its magnetosph­ere and cloud top compositio­n – scientists are continuing to understand the inner workings of Jupiter to a level that is simply incredible.

“One of the great insights that Juno very recently provided is that the thunderous winds, or bands, that characteri­stically distinguis­h the planet’s surface extend much deeper into the planets interior, to almost 3,000 kilometres (1,900 miles) in depth,” says Zaghoo. “By combining this data with our experiment­al conductivi­ty profile we are able to further constrain the depth of the dynamo process and the interactio­n between the strong swirling winds with the conductive fluid deep inside.”

Dr Mohamed Zaghoo

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 ??  ?? The target chamber is a two-metre (six-foot) stainless steel sphere
The target chamber is a two-metre (six-foot) stainless steel sphere
 ??  ?? Juno is situated at Jupiter, collecting vital data about the planet’s magnetosph­ere
Juno is situated at Jupiter, collecting vital data about the planet’s magnetosph­ere
 ??  ?? The OMEGA laser system is alsoused to initiate nuclear fusion
The OMEGA laser system is alsoused to initiate nuclear fusion
 ??  ?? Dr Mohamed Zaghoo is a research assosiate at the LLE
Dr Mohamed Zaghoo is a research assosiate at the LLE
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 ??  ?? These studies allow scientists to peak behind the planetary curtains of gas giants
These studies allow scientists to peak behind the planetary curtains of gas giants
 ??  ?? Diamond anvil cells contain the hydrogen sample that is less than a millimetre long
Diamond anvil cells contain the hydrogen sample that is less than a millimetre long

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