The giant outer planets haven’t always been in their current position. Uranus and Neptune for example are thought to have wandered through the outer Solar System to their current orbital position. On the way, they accumulated icy, comet-like objects. A new piece of research suggests as many as three kilomerer-sized objects crashed into them every hour increasing their mass. Not only would it increase the mass but it would enrich their atmospheres.
The discovery image of the new Uranian moon S/2023 U1 using the Magellan telescope on November 4, 2023. Uranus is just off the field of view in the upper left, as seen by the increased scattered light. S/2023 U1 is the faint point of light in the center of the image with the yellow arrow. The trails are from background stars. Credit: Scott Sheppard.
Astronomers have found three new moons orbiting our Solar System’s ice giants. One is orbiting Uranus, and two are orbiting Neptune. It took hard work to find them, including dozens of time exposures by some of our most powerful telescopes over several years. All three are captured objects, and there are likely more moons around both planets waiting to be discovered.
The unique atmospheric compositions of ‘ice giant’ planets Uranus and Neptune were recreated to simulate a plunge deep within them. These simulations are part of preparation for eventual atmospheric probes the ESA intends to send. Image Credit:
University of Stuttgart’s High Enthalpy Flow Diagnostics Group
Our Solar System’s ice giants, Uranus and Neptune, have been largely left out of the planetary probe game. While all of the other planets—including even the demoted Pluto—have been the subjects of dedicated missions, the ice giants have not. In fact, the only spacecraft to ever even fly by Uranus and Neptune was Voyager 2 in the late 1980s.
An experiment conducted by an international team of scientists recreated the "diamond rain" believed to exist in the interiors of ice giants like Uranus and Neptune. Credit: Greg Stewart/SLAC National Accelerator Laboratory
The ice giant planets of Neptune and Uranus might have just the right conditions to rain diamonds. Unfortunately we can’t go and check ourselves, so we have to rely on laboratory recreations of their atmospheres to find out. And so that’s exactly what a team of physicist did: they used a vaporized form of common plastics to find out how quickly and how easily diamonds could grow in those kinds of conditions.
NASA’s Voyager 2 spacecraft captured these views of Uranus (on the left) and Neptune (on the right) during its flybys of the planets in the 1980s.
Way back in the late 1980s, the Voyager 2 spacecraft visited Uranus and Neptune. During the flybys, we got to see the first close-up views of those ice giants. Even then, planetary scientists noticed a marked color difference between the two. Yes, they both sport shades of blue. But, if you look closely at Uranus, you see a featureless pale blue planet. Neptune, on the other hand, boasts interesting clouds, dark banding, and dark spots that come and go. They’re all set against a darker blue backdrop.
So, why the difference? Planetary scientists have long suspected aerosols (droplets of gas that have liquids or dust suspended in them) in each atmosphere. But, according to a team of scientists studying the layers of the planets, the hazes those aerosols create may only be part of the story.
These composite images show Uranian auroras, which scientists caught glimpses of through the Hubble in 2011. In the left image, you can clearly see how the aurora stands high above the planet's denser atmosphere. These photos combine Hubble pictures made in UV and visible light by Hubble with photos of Uranus' disk from the Voyager 2 and a third image of the rings from the Gemini Observatory in Hawaii and Chile. The auroras are located close to the planet's north magnetic pole, making these northern lights.
Credit: NASA, ESA, and L. Lamy (Observatory of Paris, CNRS, CNES)
The magnetic fields of Uranus and Neptune are really, seriously messed up. And we don’t know why.
Hubble Reveals Dynamic Atmospheres of Uranus and Neptune. Credit: NASA/ESA/A. Simon (NASA Goddard Space Flight Center), and M.H. Wong and A. Hsu (University of California, Berkeley)
Like Earth, Uranus and Neptune have season and experience changes in weather patterns as a result. But unlike Earth, the seasons on these planets last for years rather than months, and weather patterns occur on a scale that is unimaginable by Earth standards. A good example is the storms that have been observed in Neptune and Uranus’ atmosphere, which include Neptune’s famous Great Dark Spot.
During its yearly routine of monitoring Uranus and Neptune, NASA’s Hubble Space Telescope (HST) recently provided updated observations of both planets’ weather patterns. In addition to spotting a new and mysterious storm on Neptune, Hubble provided a fresh look at a long-lived storm around Uranus’ north pole. These observations are part of Hubble‘s long-term mission to improve our understanding of the outer planets.
An experiment conducted by an international team of scientists recreated the "diamond rain" believed to exist in the interiors of ice giants like Uranus and Neptune. Credit: Greg Stewart/SLAC National Accelerator Laboratory
For more than three decades, the internal structure and evolution of Uranus and Neptune has been a subject of debate among scientists. Given their distance from Earth and the fact that only a few robotic spacecraft have studied them directly, what goes on inside these ice giants is still something of a mystery. In lieu of direct evidence, scientists have relied on models and experiments to replicate the conditions in their interiors.
For instance, it has been theorized that within Uranus and Neptune, the extreme pressure conditions squeeze hydrogen and carbon into diamonds, which then sink down into the interior. Thanks to an experiment conducted by an international team of scientists, this “diamond rain” was recreated under laboratory conditions for the first time, giving us the first glimpse into what things could be like inside ice giants.
Uranus and Neptune, the Solar System’s ice giant planets. Credit: Wikipedia Commons
For decades, scientists have held that the interiors of planets like Uranus and Neptune consist of solid cores surrounded by a dense concentrations of “ices”. In this case, ice refers to hydrogen molecules connected to lighter elements (i.e. as carbon, oxygen and/or nitrogen) to create compounds like water and ammonia. Under extreme pressure conditions, these compounds become semi-solid, forming “slush”.
And at roughly 10,000 kilometers (6214 mi) beneath the surface of these planets, the compression of hydrocarbons is thought to create diamonds. To recreate these conditions, the international team subjected a sample of polystyrene plastic to two shock waves using an intense optical laser at the Matter in Extreme Conditions (MEC) instrument, which they then paired with x-ray pulses from the SLAC’s Linac Coherent Light Source (LCLS).
“So far, no one has been able to directly observe these sparkling showers in an experimental setting. In our experiment, we exposed a special kind of plastic – polystyrene, which also consists of a mix of carbon and hydrogen – to conditions similar to those inside Neptune or Uranus.”
The plastic in this experiment simulated compounds formed from methane, a molecule that consists of one carbon atom bound to four hydrogen atoms. It is the presence of this compound that gives both Uranus and Neptune their distinct blue coloring. In the intermediate layers of these planets, it also forms hydrocarbon chains that are compressed into diamonds that could be millions of karats in weight.
The MEC hutch of SLAC’s LCLS Far Experiement Hall. Credit: SLAC National Accelerator Laboratory
The optical laser the team employed created two shock waves which accurately simulated the temperature and pressure conditions at the intermediate layers of Uranus and Neptune. The first shock was smaller and slower, and was then overtaken by the stronger second shock. When they overlapped, the pressure peaked and tiny diamonds began to form. At this point, the team probed the reactions with x-ray pulses from the LCLS.
This technique, known as x-ray diffraction, allowed the team to see the small diamonds form in real-time, which was necessary since a reaction of this kind can only last for fractions of a second. As Siegfried Glenzer, a professor of photon science at SLAC and a co-author of the paper, explained:
“For this experiment, we had LCLS, the brightest X-ray source in the world. You need these intense, fast pulses of X-rays to unambiguously see the structure of these diamonds, because they are only formed in the laboratory for such a very short time.”
In the end, the research team found that nearly every carbon atom in the original plastic sample was incorporated into small diamond structures. While they measured just a few nanometers in diameter, the team predicts that on Uranus and Neptune, the diamonds would be much larger. Over time, they speculate that these could sink into the planets’ atmospheres and form a layer of diamond around the core.
The interior structure of Neptune. Credit: Moscow Institute of Physics and Technology
In previous studies, attempts to recreate the conditions in Uranus and Neptune’s interior met with limited success. While they showed results that indicated the formation of graphite and diamonds, the teams conducting them could not capture the measurements in real-time. As noted, the extreme temperatures and pressures that exist within gas/ice giants can only be simulated in a laboratory for very short periods of time.
However, thanks to LCLS – which creates X-ray pulses a billion times brighter than previous instruments and fires them at a rate of about 120 pulses per second (each one lasting just quadrillionths of a second) – the science team was able to directly measure the chemical reaction for the first time. In the end, these results are of particular significance to planetary scientists who specialize in the study of how planets form and evolve.
As Kraus explained, it could cause to rethink the relationship between a planet’s mass and its radius, and lead to new models of planet classification:
“With planets, the relationship between mass and radius can tell scientists quite a bit about the chemistry. And the chemistry that happens in the interior can provide additional information about some of the defining features of the planet… We can’t go inside the planets and look at them, so these laboratory experiments complement satellite and telescope observations.”
This experiment also opens new possibilities for matter compression and the creation of synthetic materials. Nanodiamonds currently have many commercial applications – i.e. medicine, electronics, scientific equipment, etc, – and creating them with lasers would be far more cost-effective and safe than current methods (which involve explosives).
Fusion research, which also relies on creating extreme pressure and temperature conditions to generate abundant energy, could also benefit from this experiment. On top of that, the results of this study offer a tantalizing hint at what the cores of massive planets look like. In addition to being composed of silicate rock and metals, ice giants may also have a diamond layer at their core-mantle boundary.
Assuming we can create probes of sufficiently strong super-materials someday, wouldn’t that be worth looking into?
