Fusion may have a dark side. A shadowy hypothetical process called “dark fusion” could be occurring throughout the cosmos, a new study suggests.
The standard type of fusion occurs when two atomic nuclei unite to form a new element, releasing energy in the process. “This is why the sun shines,” says physicist Sam McDermott of Fermilab in Batavia, Ill. A similar process — dark fusion — could occur with particles of dark matter, McDermott suggests in a paper published in the June 1 Physical Review Letters. If the idea is correct, the proposed phenomenon may help physicists resolve a puzzle related to dark matter — a poorly understood substance believed to bulk up the mass of galaxies. Without dark matter, scientists can’t explain how galaxies’ stars move the way they do. But some of the quirks of how dark matter is distributed within galaxy centers remain a mystery.
Dark matter is thought to be composed of reclusive particles that don’t interact much with ordinary matter — the stuff that makes up stars, planets and living creatures. That introverted nature is what makes the enigmatic particles so hard to detect. But dark matter may not be totally antisocial (SN: 3/3/18, p. 8). “Why wouldn’t the dark matter particles interact with each other? There’s really no good reason to say they wouldn’t,” says physicist Manoj Kaplinghat of the University of California, Irvine.
Scientists have suggested that dark matter particles might ricochet off one another. But the new study goes a step further, proposing that pairs of dark matter particles could fuse, forming other unknown types of dark matter particles in the process.
Such dark fusion could help explain why dark matter near the centers of galaxies is more evenly distributed than expected. In computer simulations of galaxy formation, the density of dark matter rises sharply toward a cusp in the center of a galaxy. But in reality, galaxies have a core evenly filled with dark matter. Those simulations assume dark matter particles don’t interact with one another. But dark fusion could change how the particles behave, giving them energy that would provide the oomph necessary to escape entrapment in a galaxy’s dense cusp, thereby producing an evenly filled core.
“You can kick [particles] around through this interaction, so that’s kind of cool,” says physicist Annika Peter of the Ohio State University in Columbus. But, she says, dark fusion might end up kicking the particles out of the galaxy entirely, which wouldn’t mesh with expectations: The particles could escape the halo of dark matter that scientists believe surrounds each galaxy.
For now, if fusion does have an alter ego, scientists remain in the dark.
Tropical cyclones don’t move as fast as they used to.
The fierce, swirling storms move 10 percent slower, on average, than they did nearly 70 years ago, a new study finds. Such lingering storms can potentially cause more damage by dumping even more rainfall on land beneath them.
Atmospheric scientist James Kossin examined changes in how quickly tropical cyclones, known as hurricanes in the Atlantic Ocean, moved across the planet from 1949 to 2016. Storms slowed at different rates depending on the region, with the biggest changes seen in the Northern Hemisphere, Kossin reports in the June 7 Nature. Over that same time period, the average temperature of Earth’s surface rose by about half a degree Celsius. Scientists already predict that average wind speeds will increase in tropical cyclones as ocean waters warm due to global warming (SN: 6/27/15, p. 9). The new study suggests that climate change is also altering how quickly these tropical cyclones travel across land or water.
The effect was even more pronounced as storms moved over land, with those originating in the western North Pacific, such as near Japan, slowing by 30 percent. Storms coming in from the North Atlantic – such as 2017’s Hurricane Harvey — are moving 20 percent slower over land, says Kossin, of the National Oceanic and Atmospheric Administration’s National Centers for Environmental Information in Madison, Wis. The new study makes an important link between the atmospheric effects of global warming to its effects on tropical cyclones, says atmospheric scientist Christina Patricola of the Lawrence Berkeley National Laboratory in California, who also wrote a commentary that accompanies the new paper. “Tropical cyclones tend to move along with larger-scale [atmospheric] circulation around them,” she says. “Kossin perceptively hypothesized that this overall slowdown would also affect tropical cyclones.”
It’s not clear whether the slowdown will continue into the future, or how it might vary regionally, Patricola says. Most previous work has focused on how climate change will affect the wind speeds of storms rather than how quickly they travel, known as the translation speed. “But in order to have the best information for building resilience to storms, we need to understand these other characteristics,” she says.
The cyclone slowdown is consistent with a weakening in atmospheric circulation in the tropical parts of the planet, a result of global warming, Kossin found. Global warming is also expected to increase how much water vapor the atmosphere can hold, which means storms could accumulate more moisture before releasing it in rainfall.
Slow-moving Hurricane Harvey, which dumped record levels of rain while lingering for days over southern Texas, could be a harbinger of things to come.
Suicide research is undergoing a timing shift, and not a moment too soon. A new breed of studies that track daily — and even hourly — changes in suicidal thinking is providing intriguing, although still preliminary, insights into how to identify those on the verge of trying to kill themselves.
Monitoring ways in which suicidal thoughts wax and wane over brief time periods, it turns out, can potentially strengthen suicide prevention strategies.
Digital technology has made these investigations possible. Smartphone applications alert people to report on suicidal thoughts as they arise in real-world settings. Scientists have traditionally been limited to tracking suicidal thinking over intervals of weeks, months and years, often in research labs and hospitals.
But risk factors that do a decent job of predicting the emergence of suicidal thoughts and acts over the long haul, such as persistent feelings of hopelessness, provide little help in tagging those who will become suicidal in the coming hours and days. Depression, often cited as a main driver of suicide, displays a strong link to suicidal thoughts but not to attempting or completing suicide in the near future.
Despite increasing efforts to combat suicide, U.S. suicide rates steadily rose from 1999 to 2016 (SN Online: 6/7/18). After declining during the 1990s, U.S. suicide rates now roughly equal those of 100 years ago. In recent weeks, the surprising high-profile suicides of designer Kate Spade and chef and television star Anthony Bourdain have attracted more attention to this problem.
“The field of suicide research needs to move away from its obsession with long-term risk studies,” says psychologist David Klonsky of the University of British Columbia in Vancouver. A better understanding of how particular suicidal thoughts play out in daily life will lead to the identification of the most telling warning signs of impending suicide attempts, Klonsky predicts. Current theories focus on a range of potential factors that transform suicidal thoughts into life-ending actions, including feeling like a burden to others and suffering from unrelenting pain and hopelessness (SN: 1/9/16, p. 22).
Researchers can’t yet pinpoint suicide alarms for specific groups of people. That makes it even more vital for people contemplating suicide to contact suicide hotlines, psychotherapists and friends for help, Klonsky says. (To reach the National Suicide Prevention Lifeline, call 1-800-273-TALK (8255).)
The rise of real-time, digital monitoring holds promise for giving clinicians a heads-up as to who is in the most immediate danger of acting on suicidal thoughts. A handful of studies published since 2009 have found that thoughts of suicide often appear rapidly in individuals with past suicide attempts, and can vary dramatically from hour to hour.
A team led by psychologist Evan Kleiman of Harvard University has taken digital monitoring a step further. The researchers recruited 51 adults from online forums related to suicide and self-harm and 32 adults hospitalized at a Boston psychiatric facility for recent suicide attempts or severe suicidal thoughts. Volunteers carried smartphones that prompted them four times daily, between four and eight hours apart, to rate the intensity of their current desire to kill themselves, their intention to carry out the act and their ability to resist suicidal urges. Those in the online group provided responses for 28 consecutive days. Hospitalized participants provided responses until they were discharged, a period that typically lasted one to two weeks.
The same five patterns of suicidal thinking appeared in both groups, Kleiman’s team reports in a paper scheduled for publication later this year in Depression and Anxiety. One of those profiles may be associated with the greatest risk for trying to kill oneself in the future, the researchers say. Some individuals reported, on average, low levels of suicidal thoughts that either stayed constant, varied moderately or fluctuated greatly throughout the day. Others reported severe suicidal thoughts that varied either a little or a lot from one report to the next.
Among past-year attempters, suicide tries in the month before the study clustered among those reporting severe suicidal thoughts with few fluctuations. No such association appeared in the hospitalized group, probably because most of those with each profile had been admitted shortly after suicide attempts. Following these people for a longer period, after hospital discharge, might yield a link between a specific profile of suicidal thinking and previous or new suicide attempts.
Kleiman is now participating in a similar study, directed by Harvard psychologist Matthew Nock, of 300 adults and 300 adolescents with histories of suicide attempts who will be monitored for six months after discharge from psychiatric facilities. Participants will respond to smartphone questions and wear sensors that monitor sleep and activity cycles. “Some people have difficulty recognizing how distressed they are in the moment, so we need to capture distress with nonverbal measures,” Kleiman says. By identifying these individuals, clinicians could help them to recognize physical signs of distress in themselves and devise a plan to get help when such signs occur, Klonsky adds.
A related proposal holds that at least two forms of suicidal thinking, one related to spikes in distress, exist and demand closer study in smartphone studies. Psychiatrist Maria Oquendo of the University of Pennsylvania’s Perelman School of Medicine and colleagues suspect that the first consists of sudden bursts of suicidal thoughts following stressful experiences, possibly rooted in stress sensitivity due to child abuse or other early traumas. The second is linked to a consistently depressed mood that likely leads to carefully planned suicide attempts. Oquendo and her colleagues have found evidence for these two types of suicidal thinking in surveys of more than 6,700 U.S. college students.
Stress, or the lack of it, might play a role in some or all of the patterns of suicidal thinking identified by Kleiman’s group. Sleep and activity data in the team’s upcoming study may provide an indirect look at how stress affects suicidal thoughts.
Another digital-monitoring study in the works is that of psychologist Catherine Glenn of the University of Rochester in New York. She is currently assembling a smartphone-and-sensor study that will track 50 teenagers hospitalized following suicide attempts for one month after discharge. “It’s still unclear how much suicidal thoughts fluctuate over short periods of time, especially in youth,” Glenn says.
Despite its promise, digital monitoring of people at risk for suicide only works if people respond to repeated surveys. Consider that U.S. Army soldiers who refused to answer a survey question about the duration of their suicidal thoughts were especially likely to try later to kill themselves. A team led by Harvard psychologist Matthew Nock reported that finding in the February Journal of Abnormal Psychology. Rochester’s Glenn adds that some teens recently released from psychiatric facilities go offline for a couple of days before being hospitalized again for a suicide attempt.
“Suicide is such a complicated area of study,” Glenn says.
Time is out of joint on Venus. The planet’s thick air, which spins much faster than the solid globe, may push against the flanks of mountains and change Venus’ rotation rate.
Computer simulations show that the thick Venusian atmosphere, whipping around the planet at 100 meters per second, exerts enough push against a mountain on one side and suction on the other side to speed the planet’s rotation rate by about two minutes each Venus day, according to a study in Nature Geoscience June 18. That’s not much, considering that the planet rotates just once every 243 Earth days. By comparison, Venus’ atmosphere rotates about once every four Earth days. Precise measurements of the planet’s rotation rate have varied by about seven minutes, however. The push and pull of the air over the mountains could help explain the mismatch, with some other force — possibly the gravitational influence of the sun — slowing the planet’s spin back down. The simulations by UCLA planetary scientist Thomas Navarro and colleagues are the first to account for a 10,000-kilometer-long wave in Venus’ cloud tops , spotted in 2015 by the Japanese space agency’s Akatsuki spacecraft (SN: 2/18/17, p. 5) . Similar waves are launched into the atmosphere on Earth when air flows over a mountain, but they normally dissipate quickly as opposing winds break them up. Venus’ atmosphere rotates so much faster than the planet and in such a uniform direction that the waves could persist for a long time. “This work is very interesting,” says planetary scientist Tetsuya Fukuhara of Rikkyo University in Tokyo, one of the researchers who discovered the atmosphere wave. The work helps explain where the wave comes from and addresses how Venus’ surface features affect the atmosphere, “which is the most important issue in the Venus atmospheric science.”
More detailed measurements of Venus’ rotation, possibly taken with a future lander (SN: 3/3/18, p. 14), could eventually help reveal details of Venus’ interior, such as the size of its core.
“Venus is the closest thing to Earth that we know of,” Navarro says, and yet its hot, thick, toxic atmosphere makes it utterly alien. “We’d like to know what’s inside.”
MADISON, Wis. — Giving children with autism a healthier mix of gut bacteria as a way to improve behavioral symptoms continued to work even two years after treatment ended.
The finding may solidify the connection between tummy troubles and autism, and provide more evidence that the gut microbiome — the collection of bacteria and other microbes that live in the intestines — can influence behavior.
“It’s a long way from saying there’s a cure for autism,” says Michael Hylin, a neuroscientist at Southern Illinois University in Carbondale who was not involved in the work. “But I think it’s a promising approach. It’s one that’s worthwhile.”
Children with autism spectrum disorders often have gastrointestinal problems. In previous studies, environmental engineer Rosa Krajmalnik-Brown of Arizona State University in Tempe and colleagues discovered that children with autism had fewer types of bacteria living in their guts than typically developing children did. And many of the kids were missing Prevotella bacteria, which may help regulate immune system actions. The researchers wondered whether altering the children’s cocktail of gut microbes to get a more diverse and healthier mix might help fix both the digestive issues and the behavioral symptoms associated with autism. In a small study of 18 children and teenagers with autism, the scientists gave kids fecal transplants from healthy donors over eight weeks. During and two months after the treatment, the kids had fewer gastrointestinal problems, including diarrhea, constipation, abdominal pain and indigestion, than before the therapy. Autism symptoms, such as hyperactivity, repetitive actions and irritability, also improved and seemed to be getting even better at the end of the trial than immediately after treatment ended, the team reported last year in Microbiome. But no one knew whether the improvements would last.
Krajmalnik-Brown announced the results of a two-year, follow-up study July 10 at the Beneficial Microbes Conference. The children had kept many of the Prevotella and other beneficial bacteria gained during treatment. And the diversity of bacteria in the children’s guts was even greater two years later than it was two months after the therapy ended, Krajmalnik-Brown said.
Some of the children’s stomach troubles had worsened slightly. But on average, scores on a gastrointestinal-symptoms scale were still more than 60 percent better than before kids received the transplants. The real surprise was that the kids’ autism symptoms continued to lessen two years after the therapy ended. Still, the study was small. “Don’t try this at home,” Krajmalnik-Brown cautioned.
The children were ages 7 to 16 when the study started. Ideally, treatment would begin at younger ages, Krajmalnik-Brown said, but the researchers have not gotten approval to conduct the research in younger children.
Next, the scientists need to make sure that the improved behavioral symptoms are really due to fecal transplants. The team will put the idea to the test in a study of the therapy in adults with autism.
The definite detection of nonterrestrial neutrinos, whether from the sun or from beyond the solar system, will yield a far deeper understanding of stellar interiors and, therefore, of how today’s universe came to be. — Science News, July 20, 1968.
Update In May 1968, researchers reported that a particle detector in South Dakota spotted ghostly subatomic particles called neutrinos from the sun, but only about a third as many as theories predicted. The shortage vexed physicists for decades, until the 2001 discovery that many of the sun’s electron neutrinos — the only kind the South Dakota detector was designed to find — switch flavors on their way to Earth, becoming muon and tau neutrinos (SN: 6/23/01, p. 388). That switch accounted for the sun’s missing neutrinos. Detectors have also glimpsed neutrinos spawned by supernova 1987A (SN: 3/7/87, p. 148) and even a supermassive black hole (SN Online: 7/12/18).
Using tiny 2-D materials, researchers have built microscopic chemical sensors that can be sprayed in an aerosol mist. Spritzes of such minuscule electronic chips, described online July 23 in Nature Nanotechnology, could one day help monitor environmental pollution or diagnose diseases.
Each sensor comprises a polymer chip about 1 micrometer thick and 100 micrometers across (about as wide as a human hair) overlaid with a circuit made with atomically thin semiconducting materials (SN Online: 2/13/18). This superflat circuit includes a photodiode, which converts ambient light into electric current, and a chemical detector. This chemical detector is composed of a 2-D material that conducts electric current more easily if the material binds with a specific chemical in its environment. Researchers can choose from a vast menu of 2-D materials to fashion detectors that are sensitive to different chemicals, says study coauthor Volodymyr Koman, a chemical engineer at MIT (SN Online: 1/17/18). In lab experiments, Koman and colleagues created a sensor spray that detected toxic ammonia vapor inside a sealed section of piping, as well as a spray that ID’d soot particles sprinkled across a flat surface.
Right now, researchers can determine whether their sensors have come in contact with certain particles only after the fact — by collecting the chips and hooking them up to electrodes. These electrodes test how easily electric current flows through a chip’s chemical detector, which reveals whether it touched a particular chemical after it was sprayed. But future sensors could emit light signals when in contact with target particles, says study coauthor Michael Strano, a chemical engineer at MIT.
The team is also investigating ways to power the circuits without ambient light and to integrate multiple chemical detectors onto a single chip. The simpler, single-chemical detection systems tested so far are “only the beginning,” Koman says. “It’s very exciting,” says Kourosh Kalantar-Zadeh, an electrical and chemical engineer at the University of New South Wales in Sydney whose commentary on the study appears in the same issue of Nature Nanotechnology. Sprayable sensors could someday detect gas leaks, pollution from power plants, volatile organic compounds and other air and water contaminants (SN: 3/17/18, p. 12).
Being so tiny, the devices could also be injected into a person’s bloodstream to monitor its chemical composition for medical purposes — like a blood test that wouldn’t require drawing any blood, Kalantar-Zadeh says. Or chemical sensors could be taken as nasal spray or swallowed to track digestive health (SN Online: 1/8/18). Unlike silicon-based devices that might pose environmental or health hazards, the polymers and the minute amounts of 2-D materials used to make the new devices are expected to be more biofriendly, he says.
The American Academy of Pediatrics is cautioning parents and pediatricians to avoid exposing children to eight chemicals found in food and in plastic packaging. The chemicals may be especially harmful to kids due to their small size, says the report published July 23 in Pediatrics. Pregnant women should also avoid the chemicals. And lower-income families who eat a lot of prepackaged foods could be at greater risk for exposure.
The chemicals include nitrates and nitrites, often added to processed meats as a preservative, as well as bisphenol A, or BPA, which is used to make durable plastics and has been linked to cancer, obesity and cardiovascular disease (SN: 10/3/15, p. 12). Also listed are phthalates, which help make plastic flexible, and perfluoroalkyl chemicals, or PFCs, which are resistant to stains, grease and water. These and other compounds have also been associated with endocrine disruption, obesity and insulin resistance, when cells don’t respond properly to insulin leading to an overproduction of the hormone (SN Online: 2/9/12). Some of these chemicals may also have neurocognitive effects, such as increased hyperactivity in children, says study coauthor Sheela Sathyanarayana, a physician and epidemiologist at the University of Washington in Seattle.
Scientists are unable to test the effects of these chemicals directly in humans, so evidence shows only that there is correlation, not causation, between exposure and disease.
To avoid these chemicals, the report suggests that parents buy fresh or frozen produce and skip processed meats packaged in plastic or food in metal cans, which can be lined with BPA. People should also avoid putting plastic containers in the dishwasher or microwave, the team says, where heat can draw chemicals out of plastic.
The researchers say that they hope the report prompts more strict regulation of these additives. “All parents should be able to know what they are feeding their children,” Sathyanarayana says.
NASA has a mantra for preparing spacecraft to launch: “Test as you fly.” The idea is to test the entire spacecraft, fully assembled, in the same environment and configuration that it will see in orbit.
But the Parker Solar Probe, set to launch August 11, is no ordinary spacecraft (SN Online: 7/5/18). And it’s headed to no ordinary environment. Parker will sweep through the sun’s scorching hot atmosphere for humankind’s first close encounter with the star at the center of the solar system. “Solar Probe is a little bit special,” says space plasma physicist Stuart Bale of the University of California, Berkeley. Getting the whole kit and caboodle into a setting that simulated the sun’s energetic particles, intense light and searing heat “was deemed impossible.” Scientists had to get creative to test the technology that will touch the sun, using everything from huge mirrors to dust tunnels to reams of paper.
Taking the heat The first order of business was to find materials that can stand the heat. The sun’s outer atmosphere, or corona, sizzles at millions of degrees Celsius — but it is so diffuse that it doesn’t pose much threat to the spacecraft (SN Online: 8/20/17). Direct sunlight, however, can heat exposed components to around 1370° Celsius. Two of the spacecraft’s scientific instruments, plus parts of its solar panels and its revolutionary heat shield, will be exposed to that searing sunlight at all times.
“Normal things … would melt,” says solar physicist Kelly Korreck of the Smithsonian Astrophysical Observatory in Cambridge, Mass. Korreck works on the Solar Wind Electrons Alphas and Protons instrument, known by its acronym SWEAP, which will catch the charged particles of the solar wind with a sensor called a Faraday cup (SN Online: 8/18/17). “It actually sticks around the heat shield and will be able to touch the sun,” Korreck says. “That cup is special.” To build the cup and other instruments that will see the sun directly, engineers settled on three main materials — a niobium alloy called C103 that is used in rocket engines, an alloy of titanium, zirconium and molybdenum called TZM, and tungsten. Some cables carrying power to the SWEAP cup are also lined with sapphire, a good insulator at high temperatures. And the probe’s heat shield is made of two kinds of carbon-based materials.
Figuring out how each of these materials would behave in space was tricky. Engineers couldn’t just use an oven to test the metals, which in heat can react with oxygen to rust or corrode. Carbon also can react with oxygen to combust. So the team had to test pieces of the instruments in airless vacuum chambers.
“Getting things hot on Earth is easier than you would think it is,” says Elizabeth Congdon of Johns Hopkins Applied Physics Laboratory in Laurel, Md., the lead engineer for the heat shield. “Getting things hot on Earth in vacuum is difficult.”
One way the Parker team mimicked the sun’s heat was using actual sunlight. Engineers took material samples to the world’s largest solar furnace, the PROMES facility in Odeillo, France. A series of 63 mirrors built on a hillside redirect sunlight onto an enormous concave mirror on the side of an eight-story building. That mirror then focuses the sunlight into a beam no more than 80 centimeters wide that heats materials to 3000° C inside a small vacuum chamber in a laboratory on stilts.
The beam is so hot, “you can take a two-by-four and swing it through the beam, and it burns right off,” Bale says. “Just a flash of smoke and it’s gone.” Bale leads another of the probe’s experiments called FIELDS that also needed heat testing. FIELDS is comprised of five long antennas, four of which will be exposed to the sun, that will measure electric and magnetic fields in the corona.
The SWEAP team needed an even more realistic simulator, one that would deliver intense sunlight at the angles that Parker will experience. They found an unlikely solution in IMAX film projectors, which emit light in a similar range of wavelengths to the sun.
“It took a completely custom test facility to do it,” says astrophysicist Anthony Case of the Smithsonian Astrophysical Observatory, who also works on the SWEAP instrument. He and his colleagues turned four IMAX projectors around so the lamps focused light into a small vacuum chamber, rather than spreading it across a huge screen. That gave the team the right light intensity and angles to test their instrument. Biting the dust Solar heat isn’t the only threat to the Parker Solar Probe. The region around the sun is also expected to be full of dust, left over from the formation of the planets. Scientists don’t know exactly how much dust to expect, but it’s likely to be moving almost as fast as the spacecraft, about 170 kilometers per second.
That’s a big worry for Parker’s twin telescopes, together called the Wide-field Imager for Solar Probe, or WISPR. One of the telescopes will be facing the direction that Parker is traveling, so it will be heading directly into the dust storm. “It can’t be protected,” says astrophysicist Russell Howard of the U.S. Naval Research Laboratory in Washington, D.C.
Dust particles hitting the telescope’s lens leave it pocked with little craters. Only 0.6 percent of the lens should be pitted by the end of Parker’s seven-year mission, according to computer models of dust in the inner solar system. But even a few pits can skew the data, so the team wanted to minimize the damage by choosing the right glass.
Howard and colleagues tested three possible materials for the lens in a dust acceleration tunnel at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. The tunnel accelerated charged iron particles, ranging from half a micrometer to 3 micrometers wide, to speeds between half a kilometer per second to 8 kilometers per second — fast enough for the scientists to extrapolate up to the dust speeds Parker might experience.
Sapphire withstood the barrage best, but it was unclear how it would behave as a lens. The team also rejected diamond-coated BK7 glass, commonly used for space telescopes, after the coating separated from the glass and left an extra ring around the impact spot. Regular, uncoated BK7 was the winner.
What’s what The Parker Solar Probe will use four sets of scientific instruments plus innovative self-protective measures to explore the environment near the sun. Take a tour of the spacecraft’s tech.
Tap or click to explore the tech. Swinging the temperatures Most of the spacecraft won’t have to worry about the dust or the sun’s extreme heat. Aside from SWEAP and FIELDS, almost everything is tucked behind the all-important heat shield.
That 2.5-meter-wide heat shield is made of carbon foam sandwiched between two carbon sheets. The whole thing is just 11.5 centimeters thick, and is coated on the sun-facing side with white ceramic paint to reflect as much sunlight as possible. Even then, that side could get as hot as 1370° C. But behind it, the bulk of the spacecraft will chill at an average of just 30° C (about 85° Fahrenheit).
“We hide in the shadows,” says solar physicist Eric Christian of NASA’s Goddard Space Flight Center in Greenbelt, Md. He’s the deputy principal investigator of the Integrated Science Investigation of the Sun experiment, which will measure solar particles across a wide range of energies. His team was able to build with ordinary materials and skip the rigorous heat testing. “We’re the lucky ones.” But Parker won’t always be near the sun. The spacecraft’s orbit will bring it as far from the sun as Venus, where temperatures are around –270° C. At that distance, the spacecraft that will touch the sun needs onboard heaters to keep it at 20° C. So Parker needed to be tested for cold and extreme temperature changes, too. “We’re not just worried about hot cycles, we’re worried about hot then cold then hot then cold,” says Congdon.
In January 2018, the entire spacecraft was lowered into a thermal vacuum chamber at NASA Goddard for two months of testing. The chamber, a cylinder standing 12 meters tall and 8 meters wide, was cooled to –190° C. A radiator glowing at about 315° C represented the heat coming from the back of the heat shield — but most of that heat never reached the scientific instruments since a titanium truss holds the heat shield at a safe distance from the spacecraft’s main body. The team cycled through hot and cold several times to simulate what Parker will experience.
Another challenge was keeping the probe’s solar panels cool. “You think, obviously, you’re going to the sun, solar power makes the most sense,” Congdon says. “But solar panels don’t like to get hot.” So the panels are threaded with veins that carry water to cool them off. The water absorbs heat from the panels and carries it to radiators that release the heat into space.
The solar panels are also on a shoulder joint, so they can tuck behind the heat shield at Parker’s closest approaches to the sun. Only the last row of cells will see the sun then. “That single row of cells can produce the same amount of power as the full wing can when we’re by the Earth,” says solar physicist Nicola Fox of Johns Hopkins Applied Physics Laboratory, the probe’s project scientist.But Parker won’t always be near the sun. The spacecraft’s orbit will bring it as far from the sun as Venus, where temperatures are around –270° C. At that distance, the spacecraft that will touch the sun needs onboard heaters to keep it at 20° C. So Parker needed to be tested for cold and extreme temperature changes, too. “We’re not just worried about hot cycles, we’re worried about hot then cold then hot then cold,” says Congdon.
In January 2018, the entire spacecraft was lowered into a thermal vacuum chamber at NASA Goddard for two months of testing. The chamber, a cylinder standing 12 meters tall and 8 meters wide, was cooled to –190° C. A radiator glowing at about 315° C represented the heat coming from the back of the heat shield — but most of that heat never reached the scientific instruments since a titanium truss holds the heat shield at a safe distance from the spacecraft’s main body. The team cycled through hot and cold several times to simulate what Parker will experience.
Another challenge was keeping the probe’s solar panels cool. “You think, obviously, you’re going to the sun, solar power makes the most sense,” Congdon says. “But solar panels don’t like to get hot.” So the panels are threaded with veins that carry water to cool them off. The water absorbs heat from the panels and carries it to radiators that release the heat into space.
The solar panels are also on a shoulder joint, so they can tuck behind the heat shield at Parker’s closest approaches to the sun. Only the last row of cells will see the sun then. “That single row of cells can produce the same amount of power as the full wing can when we’re by the Earth,” says solar physicist Nicola Fox of Johns Hopkins Applied Physics Laboratory, the probe’s project scientist. Up and away Before Parker can peer into the sun’s secrets, though, it must survive the trip to space.
The violent shaking during a spacecraft’s launch make it a tense time for scientists, even if they’ve tested all of the parts in an acoustic vibration chamber. Watching SWEAP’s vibration test “made me swear,” Korreck says. “It’s very scary to watch this thing you’ve spent 10 years on flop around as it keeps shaking more and more.”
Her team faced an unusual challenge in making Parker ready to rattle. It could not glue screws in place to prevent them from shaking loose, because epoxies would melt in the sunlight. So the SWEAP team twisted thin niobium wire by hand to tie hundreds of screws together in such a way that, if one comes loose, the others hold it in.
Launch can be a high-pressure time for the spacecraft, too — literally. Engineers initially thought Parker’s launch aboard a powerful Delta IV Heavy rocket, would subject the heat shield to a force 20 times that of Earth’s gravity, although later the team realized the launch force wouldn’t be so severe. To make sure the 72.5-kilogram shield wouldn’t bend or break, the team stacked 1,360 kilograms of paper on top of it.
Once it’s passed the final test of launching and deploying, Parker’s first scientific data should start trickling back to Earth in December. These missives will let scientists take the first step to unlocking the secrets of the sun’s superheated atmosphere and its energetic winds.
“It’s like being a proud parent. I worry that something could happen, but I don’t worry that we didn’t prepare or test her well,” Fox says. “I just hope she writes home every day with beautiful data.”
Editor’s note: This story was updated on August 27, 2018 to correct the cooling temperature in the thermal vacuum testing chamber at NASA Goddard.
Not content with protons and atomic nuclei, physicists took a new kind of particle for a spin around the world’s most powerful particle accelerator.
On July 25, the Large Hadron Collider, located at the laboratory CERN in Geneva, accelerated ionized lead atoms, each containing a single electron buddied up with a lead nucleus. Each lead atom normally has 82 electrons, but researchers stripped away all but one in the experiment, giving the particles an electric charge. Previously, the LHC had accelerated only protons and the nuclei of atoms, without any electron hangers-on.
Scientists hope the successful test means that the LHC could one day be used as a gamma-ray factory. Gamma rays, a type of high-energy light, could be produced by zapping beams of ionized atoms with laser light. That light would jostle the atoms’ electrons into higher energy states, and the accelerated atoms would emit gamma rays when the electrons later returned to lower energy states. Existing facilities make gamma rays from beams of electrons, but the LHC might be able to produce gamma rays at greater intensities.
More powerful beams of gamma rays would be useful for various scientific purposes, including searching for certain types of dark matter — mysterious particles that scientists believe exist in the universe but have yet to detect (SN: 11/12/16, p. 14). The gamma rays could also be used to produce beams of other particles, such as heavy, electron-like particles called muons, for use in new kinds of experiments.
