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Thursday, 13 January 2022

SpaceX Tests its Starship-Catching Launch Tower


If you thought landing a used rocket booster on a barge or a landing pad was crazy idea, take a look at how SpaceX plans to land the big Starship rocket.

The same tower that will be used to launch the rocket will also attempt “catching” the spent booster when it comes back to Earth.

Elon Musk shared a video on Twitter today, revealing the large structure, which is under construction at SpaceX’s Starbase facility in Boca Chica, Texas. The tower, nicknamed “Mechazilla” features mechanical arms, dubbed “chopsticks,” that will be used to catch and hold the rocket’s booster. The arms will then set down the booster after it delivers the second-stage into orbit.



The testing process began last week. According to the site Teslarati, on January 4th, SpaceX lifted, opened, and swung the tower’s building-sized arms for the first time. Four days later, SpaceX performed a variation on the first round of tests, again slowly lifting the assembly up the side of the launch tower and opening and closing the arms. The second test also tested the swinging motion of the arms.

SpaceX also performed some basic tests on a fueling arm located higher up on the tower, swinging it slowly towards where Starship would be positioned for launch.

Below is an animation created by @HoppAR on Twitter of how the arms will work:



We’ve been keeping an eye on the construction of the Mechazilla tower, which stands about 122 meters (400 feet) tall. When will it be used for its first official launch?

Last November, Musk hinted at a launch as early as this month (January 2022), but now it seems sometime during March is more likely. During an online meeting of the National Academies’ Space Studies Board and Board on Physics and Astronomy in November, Musk said that Starship could go through “a dozen launches, maybe more,” in 2022 and be ready to send valuable payloads to the Moon, Mars and even the Solar System’s outer planets by 2023.

Some sources say, however, that it unlikely the arms will be used in the first attempt at an orbital Starship flight, as there is not time to test all of its mechanisms sufficiently.

The tower will also prepare missions by stacking first stage boosters with Starships and refueling these elements for the next launch. This means Mechazilla is a crucial piece of the Orbital Launch Site (OLS) architecture that Elon Musk has planned for Boca Chica. Once the Starship completes its Orbital Flight Test, Starbase could become a spaceflight hub where launches and retrievals are conducted regularly.

Back in August, Musk said on Twitter, “We’re going to try to catch the Super Heavy Booster with the launch tower arm, using the grid fins to take the load… Saves mass & cost of legs & enables immediate repositioning of booster on to launch mount—ready to refly in under an hour.”

In 2021, SpaceX broke its own record by launching more than 30 rockets into orbit in a single calendar year. They also broke their own record for back-to-back launches after two separate missions using reusable Falcon 9 rockets took place within 15 hours of each other.

Earliest human remains in eastern Africa dated to more than 230,000 years ago


The age of the oldest fossils in eastern Africa widely recognized as representing our species, Homo sapiens, has long been uncertain. Now, dating of a massive volcanic eruption in Ethiopia reveals they are much older than previously thought.

The remains—known as Omo I—were found in Ethiopia in the late 1960s, and scientists have been attempting to date them precisely ever since, by using the chemical fingerprints of volcanic ash layers found above and below the sediments in which the fossils were found.

An international team of scientists, led by the University of Cambridge, has reassessed the age of the Omo I remains—and Homo sapiens as a species. Earlier attempts to date the fossils suggested they were less than 200,000 years old, but the new research shows they must be older than a colossal volcanic eruption that took place 230,000 years ago. The results are reported in the journal Nature.

The Omo I remains were found in the Omo Kibish Formation in southwestern Ethiopia, within the East African Rift valley. The region is an area of high volcanic activity, and a rich source of early human remains and artifacts such as stone tools. By dating the layers of volcanic ash above and below where archaeological and fossil materials are found, scientists identified Omo I as the earliest evidence of our species, Homo sapiens.

"Using these methods, the generally accepted age of the Omo fossils is under 200,000 years, but there's been a lot of uncertainty around this date," said Dr. Céline Vidal from Cambridge's Department of Geography, the paper's lead author. "The fossils were found in a sequence, below a thick layer of volcanic ash that nobody had managed to date with radiometric techniques because the ash is too fine-grained."

As part of a four-year project led by Professor Clive Oppenheimer, Vidal and her colleagues have been attempting to date all the major volcanic eruptions in the Ethiopian Rift around the time of the emergence of Homo sapiens, a period known as the late Middle Pleistocene.

The researchers collected pumice rock samples from the volcanic deposits and ground them down to sub-millimeter size. "Each eruption has its own fingerprint—its own evolutionary story below the surface, which is determined by the pathway the magma followed," said Vidal. "Once you've crushed the rock, you free the minerals within, and then you can date them, and identify the chemical signature of the volcanic glass that holds the minerals together."

The researchers carried out new geochemical analysis to link the fingerprint of the thick volcanic ash layer from the Kamoya Hominin Site (KHS ash) with an eruption of Shala volcano, more than 400 kilometers away. The team then dated pumice samples from the volcano to 230,000 years ago. Since the Omo I fossils were found deeper than this particular ash layer, they must be more than 230,000 years old.

"First I found there was a geochemical match, but we didn't have the age of the Shala eruption," said Vidal. "I immediately sent the samples of Shala volcano to our colleagues in Glasgow so they could measure the age of the rocks. When I received the results and found out that the oldest Homo sapiens from the region was older than previously assumed, I was really excited."

"The Omo Kibish Formation is an extensive sedimentary deposit which has been barely accessed and investigated in the past," said co-author and co-leader of the field investigation Professor Asfawossen Asrat from Addis Ababa University in Ethiopia, who is currently at BIUST in Botswana. "Our closer look into the stratigraphy of the Omo Kibish Formation, particularly the ash layers, allowed us to push the age of the oldest Homo sapiens in the region to at least 230,000 years."

"Unlike other Middle Pleistocene fossils which are thought to belong to the early stages of the Homo sapiens lineage, Omo I possesses unequivocal modern human characteristics, such as a tall and globular cranial vault and a chin," said co-author Dr. Aurélien Mounier from the Musée de l'Homme in Paris. "The new date estimate, de facto, makes it the oldest unchallenged Homo sapiens in Africa."

The researchers say that while this study shows a new minimum age for Homo sapiens in eastern Africa, it's possible that new finds and new studies may extend the age of our species even further back in time.

"We can only date humanity based on the fossils that we have, so it's impossible to say that this is the definitive age of our species," said Vidal. "The study of human evolution is always in motion: boundaries and timelines change as our understanding improves. But these fossils show just how resilient humans are: that we survived, thrived and migrated in an area that was so prone to natural disasters."

"It's probably no coincidence that our earliest ancestors lived in such a geologically active rift valley—it collected rainfall in lakes, providing fresh water and attracting animals, and served as a natural migration corridor stretching thousands of kilometers," said Oppenheimer. "The volcanoes provided fantastic materials to make stone tools and from time to time we had to develop our cognitive skills when large eruptions transformed the landscape."

"Our forensic approach provides a new minimum age for Homo sapiens in eastern Africa, but the challenge still remains to provide a cap, a maximum age, for their emergence, which is widely believed to have taken place in this region," said co-author Professor Christine Lane, head of the Cambridge Tephra Laboratory where much of the work was carried out. "It's possible that new finds and new studies may extend the age of our species even further back in time."

"There are many other ash layers we are trying to correlate with eruptions of the Ethiopian Rift and ash deposits from other sedimentary formations," said Vidal. "In time, we hope to better constrain the age of other fossils in the region."

Reference: 

Céline Vidal, Age of the oldest known Homo sapiens from eastern Africa, Nature (2022). DOI: 10.1038/s41586-021-04275-8.

Wednesday, 12 January 2022

Newly discovered type of 'strange metal' could lead to deep insights


Scientists understand quite well how temperature affects electrical conductance in most everyday metals like copper or silver. But in recent years, researchers have turned their attention to a class of materials that do not seem to follow the traditional electrical rules. Understanding these so-called "strange metals" could provide fundamental insights into the quantum world, and potentially help scientists understand strange phenomena like high-temperature superconductivity.

Now, a research team co-led by a Brown University physicist has added a new discovery to the strange metal mix. In research published in the journal Nature, the team found strange metal behavior in a material in which electrical charge is carried not by electrons, but by more "wave-like" entities called Cooper pairs.

While electrons belong to a class of particles called fermions, Cooper pairs act as bosons, which follow very different rules from fermions. This is the first time strange metal behavior has been seen in a bosonic system, and researchers are hopeful that the discovery might be helpful in finding an explanation for how strange metals work—something that has eluded scientists for decades.

"We have these two fundamentally different types of particles whose behaviors converge around a mystery," said Jim Valles, a professor of physics at Brown and the study's corresponding author. "What this says is that any theory to explain strange metal behavior can't be specific to either type of particle. It needs to be more fundamental than that."

Strange metals


Strange metal behavior was first discovered around 30 years ago in a class of materials called cuprates. These copper-oxide materials are most famous for being high-temperature superconductors, meaning they conduct electricity with zero resistance at temperatures far above that of normal superconductors. But even at temperatures above the critical temperature for superconductivity, cuprates act strangely compared to other metals.

As their temperature increases, cuprates' resistance increases in a strictly linear fashion. In normal metals, the resistance increases only so far, becoming constant at high temperatures in accord with what's known as Fermi liquid theory. Resistance arises when electrons flowing in a metal bang into the metal's vibrating atomic structure, causing them to scatter. Fermi-liquid theory sets a maximum rate at which electron scattering can occur. But strange metals don't follow the Fermi-liquid rules, and no one is sure how they work. What scientists do know is that the temperature-resistance relationship in strange metals appears to be related to two fundamental constants of nature: Boltzmann's constant, which represents the energy produced by random thermal motion, and Planck's constant, which relates to the energy of a photon (a particle of light).

"To try to understand what's happening in these strange metals, people have applied mathematical approaches similar to those used to understand black holes," Valles said. "So there's some very fundamental physics happening in these materials."

Of bosons and fermions


In recent years, Valles and his colleagues have been studying electrical activity in which the charge carriers are not electrons. In 1952, Nobel Laureate Leon Cooper, now a Brown professor emeritus of physics, discovered that in normal superconductors (not the high-temperature kind discovered later), electrons team up to form Cooper pairs, which can glide through an atomic lattice with no resistance. Despite being formed by two electrons, which are fermions, Cooper pairs can act as bosons.

"Fermion and boson systems usually behave very differently," Valles said. "Unlike individual fermions, bosons are allowed to share the same quantum state, which means they can move collectively like water molecules in the ripples of a wave."

In 2019, Valles and his colleagues showed that Cooper pair bosons can produce metallic behavior, meaning they can conduct electricity with some amount of resistance. That in itself was a surprising finding, the researchers say, because elements of quantum theory suggested that the phenomenon shouldn't be possible. For this latest research, the team wanted to see if bosonic Cooper-pair metals were also strange metals.

The team used a cuprate material called yttrium barium copper oxide patterned with tiny holes that induce the Cooper-pair metallic state. The team cooled the material down to just above its superconducting temperature to observe changes in its conductance. They found, like fermionic strange metals, a Cooper-pair metal conductance that is linear with temperature.

The researchers say this new discovery will give theorists something new to chew on as they try to understand strange metal behavior.

"It's been a challenge for theoreticians to come up with an explanation for what we see in strange metals," Valles said. "Our work shows that if you're going to model charge transport in strange metals, that model must apply to both fermions and bosons—even though these types of particles follow fundamentally different rules."

Ultimately, a theory of strange metals could have massive implications. Strange metal behavior could hold the key to understanding high-temperature superconductivity, which has vast potential for things like lossless power grids and quantum computers. And because strange metal behavior seems to be related to fundamental constants of the universe, understanding their behavior could shed light on basic truths of how the physical world works.

Reference: 

Jie Xiong, Signatures of a strange metal in a bosonic system, Nature (2022). DOI: 10.1038/s41586-021-04239-y

The lightning triggering event has finally been identified


Lightning and the magnificent luminous events it generates are still poorly understood phenomena. Because lightning begins in the midst of towering black opaque thunderstorm clouds, it is particularly difficult to get a clear glimpse of the moment before it is triggered. Using data from the Low Frequency Interferometer Network (LOFAR), however, an international team has managed to unravel part of the mystery surrounding lightning.

Lightning is a strong electrostatic discharge that occurs between two regions of the atmosphere of opposite charge; it can occur within the same cloud, between several different clouds, or between a cloud and the earth's soil. The discharge begins with the ionization of a small area of ​​air, which develops into a channel of tree plasma extending for several kilometers. Lightning produces a large amount of very high frequency radio pulses at the ends of the negative channels; positive channels only show broadcasts along the channel (not at its end).

The LOw Frequency Array (LOFAR) - a network of interferometers spread across Europe - can detect these signals in the very high frequency radio band. It is therefore able to detect and track the spread of lightning on an unprecedented scale, allowing scientists to "observe" the entire process. "The LOFAR measurements give us the first really clear picture of what's going on inside the storm," Joseph Dwyer, a physicist at the University of New Hampshire and co-author of the new study published in Geophysical Research Letters, told Quanta Magazine.

An event caused by electrically charged ice crystals

The study is based on data collected by LOFAR in 2018, when an intense lightning strike initiated at an altitude of approximately 6 kilometers streaked the sky above the observation instruments in the Netherlands. This is not the first time that radio detectors have been used to observe lightning, but LOFAR is much more efficient than the instruments used before - its imaging frequency is 200 times faster - and can even generate a 3D map of the phenomenon.

Analysis of the data showed that the radio pulses all originated from a single area about 70 meters wide in the heart of the storm cloud, confirming one of the hypotheses previously made to explain the conditions of lightning initiation. In 2019, researchers had already solved part of the mystery surrounding the phenomenon thanks to data from LOFAR; they notably mentioned needle-shaped structures to explain why lightning was likely to fall several times in the same place (contrary to popular belief).

The hypothesis is this: when ice crystals are gathered and collide in the storm cloud, they become electrically charged (the impacts eject some of their electrons and each crystal becomes a dipole). Therefore, the positive ends of crystals attract electrons from surrounding molecules; these attractive forces generate channels of ionized air (plasma), which extend and branch out several times. Each branch will heat the surrounding air, attracting more and more electrons from the air molecules and intensifying the current flowing to the ice crystals. When a plasma channel becomes hot enough and conductive, lightning propagates all the way.

Extremely rapid ramp-up

LOFAR data shows that the event intensifies exponentially: in 15 microseconds, the first lightning signal detected increases by two orders of magnitude! In total, the signal source traveled about 88 meters. "Initiation is probably caused by branched channels with an overall constant propagation velocity of 4.8 ± 0.1 × 106 m/s during the exponential ramp-up phase," summarize the study authors.

Another study confirms the role of ice crystals in the initiation of lightning: Another team of researchers recently highlighted a link between lightning and the COVID-19 pandemic . They noticed that lightning was less frequent at the start of the pandemic: lightning would have dropped from 10% to 20% in the first three months, their study concludes . This drop would be mainly due to a decrease in the concentration of aerosols in the atmosphere, inherent in containment measures, explain the researchers. When the population was confined to home, fewer pollutants were released into the atmosphere and as a result, ice crystals had fewer nucleation sites.

If this new study sheds light on the events that are at the origin of lightning, it does not however explain what happens when the ice crystals ionize the surrounding air, underlines Ute Ebert, physicist at Eindhoven University of Technology, which did not participate in the research. "Where does the first electron come from? How does the discharge start near an ice particle?", She wonders, according to her comments reported by Quanta Magazine.

On this point, cosmic rays - on which the other theory that can explain the origin of lightning is based - could ultimately play a role as well, by creating the first electrons triggering the plasma channels. Future LOFAR data could help lift the veil on these very first moments. The team also intends to be able to retrace the entire process, from the first spark leading to its initiation, to the impact of lightning on the ground, a series of stages whose unfolding remains poorly understood.

Reference:

The Spontaneous Nature of Lightning Initiation Revealed by C. Sterpka, J. Dwyer, N. Liu, B. M. Hare, O. Scholten, S. Buitink, S. ter Veen, A. Nelles

Black hole at center of Milky Way unpredictable and chaotic


An international team of researchers, led by postgraduate student Alexis Andrés, has found that the black hole at the center of our galaxy, Sagittarius A*, not only flares irregularly from day to day but also in the long term. The team analyzed 15 years' worth of data to come to this conclusion. The research was initiated by Andres in 2019 when he was a summer student at the University of Amsterdam. In the years that followed, he continued his research, which is now to be published in Monthly Notices of the Royal Astronomical Society.

Sagittarius A* is a strong source of radio, X-rays and gamma rays (visible light is blocked by intervening gas and dust). Astronomers have known for decades that Sagittarius A* flashes every day, emitting bursts of radiation that are ten to a hundred times brighter than normal signals observed from the black hole.

To find out more about these mysterious flares, the team of astronomers, led by Andrés, searched for patterns in 15 years of data made available by NASA's Neil Gehrels Swift Observatory, an Earth-orbiting satellite dedicated to the detection of gamma-ray bursts. The Swift Observatory has been observing gamma rays from black hole since 2006. Analysis of the data showed high levels of activity from 2006 to 2008, with a sharp decline in activity for the next four years. After 2012, the frequency of flares increased again—the researchers had a difficult time distinguishing a pattern.

In the next few years, the team of astronomers expect to gather enough data to be able to rule out whether the variations in the flares from Sagittarius A* are due to passing gaseous clouds or stars, or whether something else can explain the irregular activity observed from our galaxy's central black hole.

"The long dataset of the Swift observatory did not just happen by accident," says co-author and previous supervisor to Andrés, Dr. Nathalie Degenaar, also at the University of Amsterdam. Her request for these specific measurements from the Swift satellite was granted while she was a Ph.D. student. "Since then, I've been applying for more observing time regularly. It's a very special observing program that allows us to conduct a lot of research."

Co-author Dr. Jakob van den Eijnden, of the University of Oxford, comments on the team's findings: "How the flares occur exactly remains unclear. It was previously thought that more flares follow after gaseous clouds or stars pass by the black hole, but there is no evidence for that yet. And we cannot yet confirm the hypothesis that the magnetic properties of the surrounding gas play a role either."

Reference: 

A Andrés et al, A Swift study of long-term changes in the X-ray flaring properties of Sagittarius A*, Monthly Notices of the Royal Astronomical Society (2021). DOI: 10.1093/mnras/stab3407

Semiconductor demonstrates elusive quantum physics model


With a little twist and the turn of a voltage knob, Cornell researchers have shown that a single material system can toggle between two of the wildest states in condensed matter physics: The quantum anomalous Hall insulator and the two-dimensional topological insulator.

By doing so, they realized an elusive model that was first proposed more than a decade ago, but which scientists have never been able to demonstrate because a suitable material didn't seem to exist. Now that the researchers have created the right platform, their breakthrough could lead to advances in quantum devices.

The team's paper, "Quantum Anomalous Hall Effect from Intertwined Moiré Bands," published Dec. 22 in Nature. The co-lead authors are former postdoctoral researchers Tingxin Li and Shengwei Jiang, doctoral student Bowen Shen and Massachusetts Institute of Technology researcher Yang Zhang.

The project is the latest discovery from the shared lab of Kin Fai Mak, associate professor of physics in the College of Arts and Sciences, and Jie Shan, professor of applied and engineering physics in the College of Engineering, the paper's co-senior authors. Both researchers are members of the Kavli Institute at Cornell for Nanoscale Science; they came to Cornell through the provost's Nanoscale Science and Microsystems Engineering (NEXT Nano) initiative.

Their lab specializes in exploring the electronic properties of 2D quantum materials, often by stacking ultrathin monolayers of semiconductors so their slightly mismatched overlap creates a moiré lattice pattern. There, electrons can be deposited and interact with each other to exhibit a range of quantum behavior.

For the new project, the researchers paired molybdenum ditelluride (MoTe2) with tungsten diselenide (WSe2), twisting them at a 180-degree angle for a configuration that is known as an AB stack.

After applying a voltage, they observed what's known as a quantum anomalous Hall effect. This has its roots in a phenomenon called the Hall effect, first observed in the late 19th century, in which electrical current is flowed through a sample and then bent by a magnetic field that is applied at a perpendicular angle.

The quantum Hall effect, discovered in 1980, is the supersized version, in which a far greater magnetic field is applied, triggering even stranger phenomena: The interior of the bulk sample becomes an insulator, while an electrical current moves in a single direction along the outer edge, with resistances quantized to a value defined by the fundamental constants in the universe, regardless of the details of the material.

The quantum anomalous Hall insulator, first discovered in 2013, achieves the same effect but without the intervention of any magnetic field, the electrons speeding along the edge as if on a highway, without dissipating energy, somewhat like a superconductor.

"For a long time people thought that a magnetic field is needed for the quantum Hall effect, but you actually don't need one," Mak said. "So what replaces the role of a magnetic field? It turns out that it is magnetism. You have to make the material magnetic."

The MoTe2/WSe2 stack now joins the ranks of only handful of materials that are known to be quantum anomalous Hall insulators. But that is only half of its appeal.

The researchers found that by simply tweaking the voltage, they could turn their semiconductor stack into a 2D topological insulator, which is a cousin of sorts to the quantum anomalous Hall insulator, except that it exists in duplicate. In one "copy," the electron highway flows clockwise around the edge, and in the other, it flows counterclockwise.

The two states of matter have never before been demonstrated in the same system.

After consulting with collaborators led by co-author Liang Fu at MIT, the Cornell team learned its experiment had realized a toy model for graphene first proposed by physics professors Charles Kane and Eugene Mele at the University of Pennsylvania in 2005. The Kane-Mele model was the first theoretical model for 2D topological insulators.

"That was a surprise to us," Mak said. "We just made this material and did the measurements. We saw the quantum anomalous Hall effect and the 2D topological insulator and said 'Oh, wow. That's great.' Then we talked to our theory friend, Liang Fu, at MIT. They did the calculations and figured out the material actually realized a long sought-after model in condensed matter. We never expected this."

Like graphene moiré materials, MoTe2/WSe2 can switch between a range of quantum states, including a transition from a metal to a Mott insulator, a discovery the team reported in Nature in September.

Now Mak and Shan's lab is investigating the full potential of the material by coupling it with superconductors and using it to build quantum anomalous Hall interferometers, both of which in turn could generate qubits, the basic element for quantum computing. Mak is also hopeful they may find a way to significantly raise the temperature at which the quantum anomalous Hall effect occurs—which is at about 2 kelvin—resulting in a high-temperature dissipationless conductor.

Co-authors include doctoral students Lizhong Li and Zui Tao; and researchers from MIT and the National Institute for Materials Science in Tsukuba, Japan.

Reference: 

Tingxin Li et al, Quantum anomalous Hall effect from intertwined moiré bands, Nature (2021). DOI: 10.1038/s41586-021-04171-1 

Tingxin Li et al, Continuous Mott transition in semiconductor moiré superlattices, Nature (2021). DOI: 10.1038/s41586-021-03853-0

Tuesday, 11 January 2022

Astronomers identify potential clue to reinonization of universe


About 400,000 years after the universe was created began a period called “The Epoch of Reionization.”

During this time, the once hotter universe began to cool and matter clumped together, forming the first stars and galaxies. As these stars and galaxies emerged, their energy heated the surrounding environment, reionizing some of the remaining hydrogen in the universe.

The universe’s reionization is well known, but determining how it happened has been tricky. To learn more, astronomers have peered beyond our Milky Way galaxy for clues. In a new study, astronomers at the University of Iowa identified a source in a suite of galaxies called Lyman continuum galaxies that may hold clues about how the universe was reionized.

In the study, the Iowa astronomers identified a black hole, a million times as bright as our sun, that may have been similar to the sources that powered the universe’s reionization. That black hole, the astronomers report from observations made in February 2021 with NASA’s flagship Chandra X-ray observatory, is powerful enough to punch channels in its respective galaxy, allowing ultraviolet photons to escape and be observed.

“The implication is that outflows from black holes may be important to enable escape of the ultraviolet radiation from galaxies that reionized the intergalactic medium,” says Phil Kaaret, professor and chair in the Department of Physics and Astronomy and the study’s corresponding author.

“We can’t yet see the sources that actually powered the universe’s reionization because they are too far away,” Kaaret says. “We looked at a nearby galaxy with properties similar to the galaxies that formed in the early universe. One of the primary reasons that the James Webb Space Telescope was built was to try to see the galaxies hosting the sources that actually powered the universe’s reionization.”

The paper is titled, “Rapid turn-on of a luminous X-ray source in the candidate Lyman continuum emitting galaxy Tol 0440-381.” It was published online on Dec. 14, 2021, in the journal Monthly Notices of the Royal Astronomical Society.

Reference:

P Kaaret, J Bluem, A H Prestwich. Rapid turn-on of a luminous X-ray source in the candidate Lyman continuum emitting galaxy Tol 0440-381. Monthly Notices of the Royal Astronomical Society: Letters, 2021; DOI: 10.1093/mnrasl/slab127

Ocean physics explain cyclones on Jupiter


Hurtling around Jupiter and its 79 moons is the Juno spacecraft, a NASA-funded satellite that sends images from the largest planet in our solar system back to researchers on Earth. These photographs have given oceanographers the raw materials for a new study published today in Nature Physics that describes the rich turbulence at Jupiter's poles and the physical forces that drive the large cyclones.

Lead author Lia Siegelman, a physical oceanographer and postdoctoral scholar at Scripps Institution of Oceanography at the University of California San Diego, decided to pursue the research after noticing that the cyclones at Jupiter's pole seem to share similarities with ocean vortices she studied during her time as a Ph.D. student. Using an array of these images and principles used in geophysical fluid dynamics, Siegelman and colleagues provided evidence for a longtime hypothesis that moist convection—when hotter, less dense air rises—drives these cyclones.

"When I saw the richness of the turbulence around the Jovian cyclones with all the filaments and smaller eddies, it reminded me of the turbulence you see in the ocean around eddies," said Siegelman. "These are especially evident on high-resolution satellite images of plankton blooms for example."

Siegelman says that understanding Jupiter's energy system, a scale much larger than Earth's one, could also help us understand the physical mechanisms at play on our own planet by highlighting some energy routes that could also exist on Earth.

"To be able to study a planet that is so far away and find physics that apply there is fascinating," she said. "It begs the question, do these processes also hold true for our own blue dot?"

Juno is the first spacecraft to capture images of Jupiter's poles; previous satellites orbited the equatorial region of the planet, providing views of the planet's famed Red Spot. Juno is equipped with two camera systems, one for visible light images and another that captures heat signatures using the Jovian Infrared Auroral Mapper (JIRAM), an instrument on the Juno spacecraft supported by the Italian Space Agency.

Siegelman and colleagues analyzed an array of infrared images capturing Jupiter's north polar region, and in particular the polar vortex cluster. From the images, the researchers could calculate wind speed and direction by tracking the movement of the clouds between images. Next, the team interpreted infrared images in terms of cloud thickness. Hot regions correspond to thin clouds, where it is possible to see deeper into Jupiter's atmosphere. Cold regions represent thick cloud cover, blanketing Jupiter's atmosphere.

These findings gave the researchers clues on the energy of the system. Since Jovian clouds are formed when hotter, less dense air rises, the researchers found that the rapidly rising air within clouds acts as an energy source that feeds larger scales up to the large circumpolar and polar cyclones.

Juno first arrived at the Jovian system in 2016, providing scientists with the first look at these large polar cyclones, which have a radius of about 1,000 kilometers or 620 miles. There are eight of these cyclones occurring at Jupiter's north pole, and five at its south pole. These storms have been present since that first view five years ago. Researchers are unsure how they originated or for how long they have been circulating, but they now know that moist convection is what sustains them. Researchers first hypothesized this energy transfer after observing lightning in storms on Jupiter.

Juno will continue orbiting Jupiter until 2025, providing researchers and the public alike with novel images of the planet and its extensive lunar system.

Reference: 

Lia Siegelman, Moist convection drives an upscale energy transfer at Jovian high latitudes, Nature Physics (2022). DOI: 10.1038/s41567-021-01458-y.

Sánchez-Lavega, A, From storms to cyclones at Jupiter's poles. Nat. Phys. (2022). DOI: 10.1038/s41567-021-01481-z