Hexbyte Glen Cove Studying our solar system’s protective bubble

Hexbyte Glen Cove

Is this what the heliosphere looks like? BU-led research suggests so. The size and shape of the magnetic “force field” that protects our solar system from deadly cosmic rays has long been debated by astrophysicists. Credit: Merav Opher, et. al

A multi-institutional team of astrophysicists headquartered at Boston University, led by BU astrophysicist Merav Opher, has made a breakthrough discovery in our understanding of the cosmic forces that shape the protective bubble surrounding our solar system—a bubble that shelters life on Earth and is known by space researchers as the heliosphere.

Astrophysicists believe the heliosphere protects the planets within our solar system from powerful radiation emanating from supernovas, the final explosions of dying stars throughout the universe. They believe the heliosphere extends far beyond our solar system, but despite the massive buffer against cosmic radiation that the heliosphere provides Earth’s life-forms, no one really knows the shape of the heliosphere—or, for that matter, the size of it. 

“How is this relevant for society? The bubble that surrounds us, produced by the sun, offers protection from galactic cosmic rays, and the shape of it can affect how those rays get into the heliosphere,” says James Drake, an astrophysicist at University of Maryland who collaborates with Opher. “There’s lots of theories but, of course, the way that galactic cosmic rays can get in can be impacted by the structure of the heliosphere—does it have wrinkles and folds and that sort of thing?”

Opher’s team has constructed some of the most compelling computer simulations of the heliosphere, based on models built on observable data and theoretical astrophysics. At BU, in the Center for Space Physics, Opher, a College of Arts & Sciences professor of astronomy, leads a NASA DRIVE (Diversity, Realize, Integrate, Venture, Educate) Science Center that’s supported by $1.3 million in NASA funding. That team, made up of experts Opher recruited from 11 other universities and research institutes, develops predictive models of the heliosphere in an effort the team calls SHIELD (Solar-wind with Hydrogen Ion Exchange and Large-scale Dynamics). 

Since BU’S NASA DRIVE Science Center first received funding in 2019, Opher’s SHIELD team has hunted for answers to several puzzling questions: What is the overall structure of the heliosphere? How do its ionized particles evolve and affect heliospheric processes? How does the heliosphere interact and influence the interstellar medium, the matter and radiation that exists between stars? And how do cosmic rays get filtered by, or transported through, the heliosphere? 

“SHIELD combines theory, modeling, and observations to build comprehensive models,” Opher says. “All these different components work together to help understand the puzzles of the heliosphere.”

And now a paper published by Opher and collaborators in Astrophysical Journal reveals that neutral hydrogen particles streaming from outside our solar system most likely play a crucial role in the way our heliosphere takes shape.

In their latest study, Opher’s team wanted to understand why heliospheric jets—blooming columns of energy and matter that are similar to other types of cosmic jets found throughout the universe—become unstable. “Why do stars and black holes—and our own sun—eject unstable jets?” Opher says. “We see these jets projecting as irregular columns, and [astrophysicists] have been wondering for years why these shapes present instabilities.”

New research led by BU astrophysicist Merav Opher could explain why the heliosphere, a protective magnetic “force field” emanating from our sun and encompassing our solar system, is likely unstable and irregularly shaped. “The universe is not quiet,” Opher says. “Our BU model doesn’t try to cut out the chaos.” Credit: Merav Opher, et. al

Similarly, SHIELD models predict that the heliosphere, traveling in tandem with our sun and encompassing our solar system, doesn’t appear to be stable. Other models of the heliosphere developed by other astrophysicists tend to depict the heliosphere as having a comet-like shape, with a jet—or a “tail”—streaming behind in its wake. In contrast, Opher’s model suggests the heliosphere is shaped more like a croissant or even a donut.

The reason for that? Neutral hydrogen particles, so-called because they have equal amounts of positive and negative charge that net no charge at all.

“They come streaming through the solar system,” Opher says. Using a computational model like a recipe to test the effect of ‘neutrals’ on the shape of the heliosphere, she “took one ingredient out of the cake—the neutrals—and noticed that the jets coming from the sun, shaping the heliosphere, become super stable. When I put them back in, things start bending, the center axis starts wiggling, and that means that something inside the heliospheric jets is becoming very unstable.”

Instability like that would theoretically cause disturbance in the solar winds and jets emanating from our sun, causing the heliosphere to split its shape—into a croissant-like form. Although astrophysicists haven’t yet developed ways to observe the actual shape of the heliosphere, Opher’s model suggests the presence of neutrals slamming into our system would make it impossible for the heliosphere to flow uniformly like a shooting comet. And one thing is for sure—neutrals are definitely pelting their way through space.

Drake, a coauthor on the new study, says Opher’s model “offers the first clear explanation for why the shape of the heliosphere breaks up in the northern and southern areas, which could impact our understanding of how galactic cosmic rays come into Earth and the near-Earth environment.” That could affect the threat that radiation poses to life on Earth and also for astronauts in space or future pioneers attempting to travel to Mars or other planets.

“The universe is not quiet,” Opher says. “Our BU model doesn’t try to cut out the chaos, which has allowed me to pinpoint the cause [of the heliosphere’s instability]…. The neutral hydrogen particles.”

Specifically, the presence of the neutrals colliding with the heliosphere triggers a phenomenon well known by physicists, called the Rayleigh-Taylor instability, which occurs when two materials of different densities collide, with the lighter material pushing against the heavier material. It’s what happens when oil is suspended above water, and when heavier fluids or materials are suspended above lighter fluids. Gravity plays a role and gives rise to some wildly irregular shapes. In the case of the cosmic jets, the drag between the neutral hydrogen particles and charged ions creates a similar effect as gravity. The “fingers” seen in the famous Horsehead Nebula, for example, are caused by the Rayleigh-Taylor instability. 

“This finding is a really major breakthrough, it’s really set us in a direction of discovering why our model gets its distinct croissant-shaped heliosphere and why other models don’t,” Opher says.

More information:
M. Opher et al, A Turbulent Heliosheath Driven by the Rayleigh–Taylor Instability, The Astrophysical Journal (2021). DOI: 10.3847/1538-4357/ac2d2e

Studying our solar system’s protective bubble (2021, December 3)
retrieved 5 December 2021
from https://phys.org/news/2021-12-solar.html

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Hexbyte Glen Cove Solar electric propulsion makes NASA's Psyche spacecraft go thumbnail

Hexbyte Glen Cove Solar electric propulsion makes NASA’s Psyche spacecraft go

Hexbyte Glen Cove

NASA’s Psyche spacecraft is photographed in July 2021 during the mission’s assembly, test, and launch operations phase at JPL. Hall thrusters will propel the spececraft to its target in the main asteroid belt. Credit: NASA/JPL-Caltech

When it comes time for NASA’s Psyche spacecraft to power itself through deep space, it’ll be more brain than brawn that does the work. Once the stuff of science fiction, the efficient and quiet power of electric propulsion will provide the force that propels the Psyche spacecraft all the way to the main asteroid belt between Mars and Jupiter. The orbiter’s target: A metal-rich asteroid also called Psyche.

The will launch in August 2022 and travel about 1.5 billion miles (2.4 billion kilometers) over three and a half years to get to the asteroid, which scientists believe may be part of the core of a planetesimal, the building block of an early rocky planet. Once in orbit, the mission team will use the payload of science instruments to investigate what this unique target can reveal about the formation of rocky planets like Earth.

The spacecraft will rely on the large chemical rocket engines of the Falcon Heavy launch vehicle to blast off the launchpad and to escape Earth’s gravity. But the rest of the journey, once Psyche separates from the launch vehicle, will rely on solar electric propulsion. This form of propulsion starts with large solar arrays that convert sunlight into electricity, providing the power source for the spacecraft’s thrusters. They’re known as Hall thrusters, and the Psyche spacecraft will be the first to use them beyond the orbit of our moon.

At left, xenon plasma emits a blue glow from an electric Hall thruster identical to those that will propel NASA’s Psyche spacecraft to the main asteroid belt. On the right is a similar non-operating thruster. Credit: NASA/JPL-Caltech

For propellant, Psyche will carry tanks full of xenon, the same neutral gas used in car headlights and plasma TVs. The spacecraft’s four thrusters will use electromagnetic fields to accelerate and expel charged atoms, or ions, of that xenon. As those ions are expelled, they create thrust that gently propels Psyche through space, emitting blue beams of ionized xenon.

In fact, the thrust is so gentle, it exerts about the same amount of pressure you’d feel holding three quarters in your hand. But it’s enough to accelerate Psyche through deep space. With no atmospheric drag to hold it back, the spacecraft eventually will accelerate to speeds of up to 200,000 miles per hour (320,000 kilometers per hour).

Because they’re so efficient, Psyche’s Hall thrusters could operate nearly nonstop for years without running out of fuel. Psyche will carry 2,030 pounds (922 kilograms) of xenon in its tanks; engineers estimate that the mission would burn through about five times that amount of propellant if it had to use traditional chemical thrusters.

“Even in the beginning, when we were first designing the mission in 2012, we were talking about solar electric propulsion as part of the plan. Without it, we wouldn’t have the Psyche mission,” said Arizona State University’s Lindy Elkins-Tanton, who as principal investigator leads the mission. “And it’s become part of the character of the mission. It takes a specialized team to calculate trajectories and orbits using solar electric propulsion.”

A gentle maneuver

Psyche will launch from the historic Pad 39A at NASA’s Kennedy Space Center. The Falcon Heavy will place the spacecraft on a trajectory to fly by Mars for a gravity assist seven months later, in May 2023. In early 2026, the thrusters will do the delicate work of getting the spacecraft into orbit around asteroid Psyche, using a bit of ballet to back into orbit around its target.

That task will be especially tricky because of how little scientists know about the asteroid, which appears as only a tiny dot of light in telescopes. Ground-based radar suggests it’s about 140 miles (226 kilometers) wide and potato-shaped, which means that scientists won’t know until they get there how exactly its gravity field works. As the mission conducts its science investigation over 21 months, navigation engineers will use the electric propulsion thrusters to fly the spacecraft through a progression of orbits that gradually bring the spacecraft closer and closer to Psyche.

NASA’s Jet Propulsion Laboratory in Southern California, which manages the mission, used a similar propulsion system with the agency’s Deep Space 1, which launched in 1998 and flew by an asteroid and a comet before the mission ended in 2001. Next came Dawn, which used solar electric propulsion to travel to and orbit the Vesta and then the protoplanet Ceres. The first spacecraft ever to orbit two extraterrestrial targets, the Dawn mission lasted 11 years, ending in 2018 when it used up the last of the hydrazine propellant used to maintain its orientation.

Partners in propulsion

Maxar Technologies has been using solar electric propulsion to power commercial communications satellites for decades. But for Psyche, they needed to adapt the superefficient Hall thrusters to fly in deep space, and that’s where JPL engineers came in. Both teams hope that Psyche, by using Hall thrusters for the first time beyond lunar orbit, will help push the limits of solar electric propulsion.

“Solar technology delivers the right mix of cost savings, efficiency, and power and could play an important role in supporting future science missions to Mars and beyond,” said Steven Scott, Maxar’s Psyche program manager.

Along with supplying the thrusters, Maxar’s team in Palo Alto, California, was responsible for building the spacecraft’s van-size chassis, which houses the electrical system, the propulsion systems, the thermal system, and the guidance and navigation system. When fully assembled, Psyche will move into JPL’s huge thermal vacuum chamber for testing that simulates the environment of deep space. By next spring, the spacecraft will ship from JPL to Cape Canaveral for launch.

More information:
For more information about NASA’s Psyche mission, go to:



Solar electric propulsion makes NASA’s Psyche spacecraft go (2021, September 20)
retrieved 21 September 2021
from https://phys.org/news/2021-09-solar-electric-propulsion-nasa-psyche.html

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Hexbyte Glen Cove Solar development: Super bloom or super bust for desert species? thumbnail

Hexbyte Glen Cove Solar development: Super bloom or super bust for desert species?

Hexbyte Glen Cove

The rare Barstow woolly sunflower was more sensitive to solar development impacts than its common relative, the woolly daisy in a study by UC Davis and UC Santa. Credit: Karen Tanner

Throughout the history of the West, human actions have often rushed the desert—and their actions backfired. In the 1920s, the Colorado River Compact notoriously overallocated water still used today by several western states because water measurements were taken during a wet period.

More currently, operators of the massive Ivanpah Solar Electric Generating System in the Mojave Desert are spending around $45 million on desert tortoise mitigation after initial numbers of the endangered animals were undercounted before its construction.

A study published in the journal Ecological Applications from the University of California, Davis, and UC Santa Cruz warns against another potential desert timing mismatch amid the race against and toward rapid renewable energy development.

“Our study suggests that and conservation goals may come into conflict in California’s Mojave Desert, which supports nearly 500 rare plant species as well as a rapidly expanding solar industry,” said lead author Karen Tanner, who conducted the work as a Ph.D. student at UC Santa Cruz under a grant led by UC Davis assistant professor Rebecca R. Hernandez.

Tanner spent seven years teasing out the demography of two native desert flowers—the rare Barstow woolly sunflower (E. mohavense) and the common Wallace’s woolly daisy (E. wallacei), comparing their performance both in the open and under experimental solar panels. The authors wondered, how would desert-adapted plants respond to panels that block light and rainfall? Would rare species respond differently than to these changes?

These aren’t easy questions to unearth. At one point, Tanner glued tiny seeds to individual toothpicks to gather emergence data. At another, she scoured the desert floor on hands and knees to count emerging seedlings of the rare sunflower—about the size of a thumbnail at maturity.

A common Wallace’s woolly daisy grows in the Mojave Desert. Common wildflowers appear to be less vulnerable than rare wildflowers to desert solar developments, a study from UC Davis and UC Santa Cruz found. Credit: Karen Tanner

Super bloom surprises

Such painstaking commitment is one reason no previous studies have modeled species’ responses to photovoltaics at the population level. It takes time and overcoming tricky logistical and mathematical challenges to model little-known species interactions in the evasive desert. What is nowhere in sight one year, may thrive the next.

That element of surprise is what makes “super blooms” so special and so captivating. Those bursts of wildflowers blanket expanses of desert landscapes after especially wet years and are believed to be critical to the long-term persistence of desert annual populations.

The study found that solar panel effects on plant response were strongly influenced by weather and physical features of the landscape. During the 2017 super bloom, panel shade negatively affected population growth of the rare species, but had little effect on its common relative.

The study suggests that may be more sensitive to solar development impacts than common species. It highlights the potential for solar panel effects to vary among species, as well as over space and time.

Widflowers blanket the desert near the study site in the Mojave Desert. Credit: Karen Tanner

A question of time

The study provides an example of the importance of taking the necessary time to understand an ecosystem before irrevocably changing it.

“The —and many other biomes—don’t respond on our timescales,” said Hernandez, co-director of the Wild Energy Initiative through the UC Davis John Muir Institute. “If we want to understand them, we need to study them on the timescales they operate. Otherwise, it is like taking a photo of a moving train and calling it a shipping container. Racing to build renewable energy in places that have already been skinned of their biology makes sense—let’s not wait to put solar on existing rooftops. But in natural environments, we need to listen and observe first.”

More information:
Karen E. Tanner et al, Microhabitats associated with solar energy development alter demography of two desert annuals, Ecological Applications (2021). DOI: 10.1002/eap.2349

Solar development: Super bloom or super bust for desert species? (2021, May 3)
retrieved 4 May 2021
from https://phys.org/news/2021-05-solar-super-bloom-species.html

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Hexbyte Glen Cove Parker Solar Probe sees Venus orbital dust ring in first complete view thumbnail

Hexbyte Glen Cove Parker Solar Probe sees Venus orbital dust ring in first complete view

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Images from the WISPR instrument — short for Wide-field Imager for Solar Probe — on board NASA’s Parker Solar Probe spacecraft have provided the first complete view of the ring of dust along Venus’ orbit. The dust ring stretches diagonally from the lower left to the upper right of the image. The bright objects are planets: from left to right, Earth, Venus, and Mercury. Part of the Milky Way galaxy is visible on the left side. The four frames of this composite image were captured on Aug. 25, 2019. Credits: NASA/Johns Hopkins APL/Naval Research Laboratory/Guillermo Stenborg and Brendan Gallagher

NASA’s Parker Solar Probe mission has given scientists the first complete look at Venus’ orbital dust ring, a collection of microscopic dust particles that circulates around the Sun along Venus’ orbit. Though earlier missions have made some observations of Venus’ orbital dust ring, Parker Solar Probe’s images are the first to show the planet’s dust ring for nearly its entire 360-degree span around the Sun.

Parker Solar Probe’s WISPR instrument—short for Wide-field Imager for Solar Probe—is designed to study the solar wind, the Sun’s constantly outflowing material. Space is teeming with , which reflects so much light that it typically shines at least a hundred times brighter than the solar wind. (The light reflected from space dust is what creates the zodiacal light, sometimes visible from Earth as a faint column of light rising upward from the horizon.)

In order to see the solar wind with WISPR, scientists use image processing to remove the dust background and stars from the images. This process worked so well that Venus’ orbital dust ring—which appears as a bright band stretching across the images—was subtracted as well. It wasn’t until Parker Solar Probe performed rolling maneuvers to manage its momentum on its way to its next solar flyby, which changed the orientation of its cameras, that the static dust ring was noticed by scientists. Based on the relative brightness, scientists estimate that the dust along Venus’ orbit is about 10% more dense than in neighboring regions. The results were published on April 7, 2021, in The Astrophysical Journal.

This animation shows the geometry of the dust rings along the orbits of Mercury, Venus, and Earth, along with Parker Solar Probe’s trajectory. Only the dust along these planets’ orbital paths is shown — the dust near the Sun and between the planets’ orbits is omitted for clarity. Credit: NASA/Johns Hopkins APL/Ben Smith

The German-American Helios spacecraft and NASA’s STEREO mission—short for Solar Terrestrial Relations Observatory—have both made earlier observations of the dust ring along Venus’ orbit. Those measurements have allowed scientists to develop new models of the origins of dust along Venus’ orbit. Parker Solar Probe’s sensitive imagers and unique orbit have given scientists an unprecedented peek at Venus’ —something the science team aimed for since the mission’s early days.

As Parker Solar Probe flies ever-closer to the Sun over the course of its mission, the science team also expects to make the first observations of a long-hypothesized dust-free zone, a region close to the Sun where dust has been heated and vaporized by the intense sunlight. If there is a dust-free zone near the Sun—an idea supported by regions of thinning dust that Parker Solar Probe has already observed from afar—this would not only confirm theories about the interaction between our star and its nearby dust, but could also help astrophysicists who study more distant objects: Just as can interfere with seeing the , it can also muddle measurements of stars and galaxies.

However, for many scientists, the dust itself is what’s interesting. For example, the exact origins of the dust that fills the solar system isn’t settled science. For decades, scientists have largely thought the dust is debris from comets and asteroids—but new research using data from NASA’s Juno mission to Jupiter suggests that on Mars could be the source of much of the solar system’s dust.

Space dust may also form the building blocks of stars and planets, carry gases between star systems, and provide a nurturing environment for young planets. These were some of the questions in mind for scientists on the DUST sounding rocket mission—short for Determining Unknown yet Significant Traits—which launched in 2019 to investigate how dust grains coagulate in the microgravity of space.

More information:
Guillermo Stenborg et al. Pristine PSP/WISPR Observations of the Circumsolar Dust Ring near Venus’s Orbit, The Astrophysical Journal (2021). DOI: 10.3847/1538-4357/abe623

Parker Solar Probe sees Venus orbital dust ring in first complete view (2021, April 18)
retrieved 19 April 2021
from https://phys.org/news/2021-04-parker-solar-probe-venus-orbital.html

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Hexbyte Glen Cove The solar system follows the galactic standard—but it is a rare breed thumbnail

Hexbyte Glen Cove The solar system follows the galactic standard—but it is a rare breed

Hexbyte Glen Cove

Illustration showing an artist’s interpretation of what the TRAPPIST-1 solar system could look like. The seven planets of TRAPPIST-1 are all Earth-sized and terrestrial, and could potentially harbor liquid water, depending on their compositions. Credit: NASA/JPL-Caltech

Researchers at the Niels Bohr Institute, University of Copenhagen, have investigated more than 1000 planetary systems orbiting stars in our own galaxy, the Milky Way, and have discovered a series of connections between planetary orbits, number of planets, occurrence and the distance to their stars. It turns out that our own solar system in some ways is very rare, and in others very ordinary.

It is rare to have eight planets, but the study shows that the solar system follows exactly the same, very basic rules for the formation of planets around a star that they all do. The question about what exactly makes it so special that it harbors life is still a good question. The study is now published in MNRAS

Eccentric planet orbits are the key to determining the number of planets

There is a very clear correlation between the eccentricity of the orbits and the number of planets in any given solar system. When the planets form, they begin in circular orbits in a cloud of gas and dust. But they are still relatively small in size, up to sizes comparable to the moon. On a slightly longer they interact via gravitation and acquire more and more eccentric or elliptic orbits. This means they start colliding because elliptical orbits cross one another—and so the planets grow in size due to the collisions. If the end result of the collisions is that all the pieces become just one or a few planets, then they stay in elliptical orbits. But if they end up becoming many planets, the gravitational pull between them makes them lose energy—and so they form more and more circular orbits.

The researchers have found a very clear correlation between the number of planets and how circular the orbits are. “Actually, this is not really a surprise,” professor Uffe Gråe Jørgensen explains. “But our solar system is unique in the sense that no other solar systems with as many planets as ours are known. So perhaps it could be expected that our solar system doesn’t fit into the correlation. But it does—as a matter of fact, it is right on.”

The only solar systems that don’t fit into this rule are systems with only one planet. In some cases, the reason is that in these single-planet systems, the planet is orbiting the star in very close proximity, but in others, the reason is that the systems may actually hold more planets that initially assumed. “In these cases, we believe that the deviation from the rule can help us reveal more planets that were hidden up until now,” Nanna Bach-Møller, first author of the scientific article, explains. If we are able to see the extent of eccentricity of the planet , then we know how many other planets must be in the system—and vice versa, if we have the number of planets, we now know their orbits. “This would be a very important tool for detecting like our own solar system, because many exoplanets similar to the planets in our solar system would be difficult to detect directly, if we don’t know where to look for them.”

The Earth is among the lucky 1%

No matter which method is used in the search for exoplanets, one reaches the same result. So, there is basic, universal physics at play. The researchers can use this to say: How many systems possess the same eccentricity as our solar system? – which we can then use to assess how many systems have the same number of planets as our solar system. The answer is that there are only 1% of all solar systems with the same number of planets as our solar system or more. If there are approximately 100 billion stars in the Milky Way, this is, however, still no less than one billion solar systems. There are approximately 10 billion Earth-like planets in the , i.e. in a distance from their star allowing for the existence of liquid water. But there is a huge difference between being in the habitable zone and being habitable or having developed a technological civilization, Uffe Gråe Jørgensen stresses. “Something is the cause of the fact that there aren’t a huge amount of UFOs out there. When the conquest of the planets in a solar system has begun, it goes pretty quickly. We can see that in our own civilization. We have been to the moon and on Mars we have several robots already. But there aren’t a whole lot of UFOs from the billions of Earth-like exo-planets in the habitable zones of the stars, so life and technological civilizations in particular are probably still fairly scarce.”

The Earth is not particularly special—the number of planets in the system is what it is all about

What more does it take to harbor life than being an Earth-size planet in the habitable zone? What is really special here on Earth and in our solar system? Earth is not special—there are plenty of Earth-like planets out there. But perhaps it could be the number of planets and the nature of them. There are many large gas planets in our solar system, half of all of them. Could it be that the existence of the large gas planets are the cause of our existence here on Earth? A part of that debate entails the question of whether the large gas planets, Saturn and Jupiter, redirected water-bearing comets to Earth when the planet was a half-billion years old, enabling the forming of life here.

This is the first time a study has shown how unique it is for a solar system to be home to eight planets, but at the same time, shows that our solar system is not entirely unique. Our solar system follows the same physical rules for forming as any other , we just happen to be in the unusual end of the scale. And we are still left with the question of why, exactly, we are here to be able to wonder about it.

More information:
Nanna Bach-Møller et al. Orbital eccentricity–multiplicity correlation for planetary systems and comparison to the Solar system, Monthly Notices of the Royal Astronomical Society (2020). DOI: 10.1093/mnras/staa3321

The solar system follows the galactic standard—but it is a rare breed (2020, November 30)

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