SPACE
Scientists report ‘benchmarks’ for extreme space weather
High-energy ‘relativistic’ electrons - so-called “killer” electrons - are a major source of radiation damage to satellites and so understanding their patterns of activity is crucial. Bursts of charged particles and magnetic fields from the Sun can tear open the Earth’s magnetic field, giving rise to geomagnetic storms. During these events the number of killer electrons in the outer radiation belt can increase by orders of magnitude and become a significant space weather hazard.
Dr Nigel Meredith of BAS led an international team who analysed 20 years of data from a US GPS satellite to determine the 1 in 10, 1 in 50, and 1 in 100-year event levels. A 1 in 100-year event is an event of a size that will be equalled or exceeded on average once every 100 years.
Satellite operators, manufacturers, insurers, and governments need to prepare and mitigate against the risks posed by these electrons. Society is increasingly reliant on satellites for a variety of applications including communication, navigation, Earth observation and defence. As of April 2022, there were 5,465 operational satellites in Earth orbit, and most are exposed to energetic electrons for at least some of their orbit. In 2021, the overall global space economy generated revenues of $386 billion, an increase of four percent compared to the previous year.
Dr Nigel Meredith, space weather scientist and lead author of the study says:
“The 1 in 100 year event levels reported in this study are important for industry and government. They serve as benchmarks against which to compare other extreme space weather events and to assess the potential impact of an extreme event.”
These findings are vitally important to the satellite industry as engineers and operators require realistic estimates of the largest electron fluxes encountered in GPS orbit to prepare for the impacts of these extreme events and to improve the resilience of future satellites. The findings are essential for satellite insurers to help them ensure satellite operators are doing all they can to reduce risk and to evaluate realistic disaster scenarios
The difference between the 1 in 10 year and 1 in 100-year event varies depending on the energy of the electrons and the distance from Earth. These differences are largest at the highest energies furthest from the planet, varying between a factor of 3 and 10 for some of the highest electron energies over 35,000 km from the Earth’s surface. Such substantial increases could pose a significant additional risk to satellites operating in this region.
Like weather on our planet, space weather can vary greatly over minutes, days, seasons and the 11-year solar cycle. The researchers found that the majority of these killer electron events occurred during the solar cycle’s declining phases — seen twice during the 20-year period they studied — but the largest event was elsewhere, showing that extreme events can happen at any time.
Professor Richard Horne, FRS, from BAS and a co-author on the study, says:
"The space sector is part of our Critical National Infrastructure. This research will help us assess the resilience of satellites to a severe space weather event."
Severe space weather was added to the UK National Risk Register of Civil Emergencies in 2011. The impacts of space weather on satellites can range from momentary interruptions of service to total loss of capabilities. In 2003 a major storm caused 47 satellites to experience anomalies, over 10 to be out of action for more than a day and one was a complete loss.
Extreme Relativistic Electron Fluxes in GPS Orbit: Analysis of NS41 BDD-IIR Data by Nigel P. Meredith, Thomas E. Cayton, Michael D. Cayton, Richard B. Horne is published in the journal Space Weather
JOURNAL
Space Weather
ARTICLE TITLE
Extreme Relativistic Electron Fluxes in GPS Orbit: Analysis of NS41 BDD-IIR Data
Researchers demystify the unusual origin of the Geminids meteor shower
Princeton researchers used data from NASA's Parker Solar Probe to deduce that a catastrophic event likely created the prolific Geminids meteoroid stream.
VIDEO: PRINCETON RESEARCHERS USED OBSERVATIONS FROM NASA’S PARKER SOLAR PROBE MISSION TO DEDUCE THAT IT WAS LIKELY A VIOLENT, CATASTROPHIC EVENT – SUCH AS A HIGH-SPEED COLLISION WITH ANOTHER BODY OR A GASEOUS EXPLOSION – THAT CREATED THE GEMINIDS METEOROID STREAM. view more
CREDIT: NASA/JOHNS HOPKINS APL/BEN SMITH
The Geminids meteoroids light up the sky as they race past Earth each winter, producing one of the most intense meteor showers in our night sky.
Mysteries surrounding the origin of this meteoroid stream have long fascinated scientists because, while most meteor showers are created when a comet emits a tail of ice and dust, the Geminids stem from an asteroid — a chunk of rock that normally does not produce a tail. Until recently, the Geminids had only been studied from Earth.
Now, Princeton researchers used observations from NASA’s Parker Solar Probe mission to deduce that it was likely a violent, catastrophic event — such as a high-speed collision with another body or a gaseous explosion — that created the Geminids. The findings, which were published in the Planetary Science Journal on June 15, narrow down hypotheses about this asteroid’s composition and history that would explain its unconventional behavior.
“Asteroids are like little time capsules for the formation of our solar system,” said Jamey Szalay, research scholar at the Princeton University space physics laboratory and co-author on the paper. “They were formed when our solar system was formed, and understanding their composition gives us another piece of the story.”
An unusual asteroid
Unlike most known meteor showers that come from comets, which are made of ice and dust, the Geminids stream seems to originate from an asteroid — a chunk of rock and metal — called 3200 Phaethon.
“Most meteoroid streams are formed via a cometary mechanism, it’s unusual that this one seems to be from an asteroid,” said Wolf Cukier, undergraduate class of 2024 at Princeton and lead author on the paper.
“Additionally, the stream is orbiting slightly outside of its parent body when it’s closest to the sun, which isn’t obvious to explain just by looking at it,” he added, referring to a recent study with Parker Solar Probe images of the Geminids led by Karl Battams of the Naval Research Laboratory.
When a comet travels close to the Sun it gets hotter, causing the ice on the surface to release a tail of gas, which in turn drags with it little pieces of ice and dust. This material continues to trail behind the comet as it stays within the Sun’s gravitational pull. Over time, this repeated process fills the orbit of the parent body with material to form a meteoroid stream.
But because asteroids like 3200 Phaethon are made of rock and metal, they are not typically affected by the Sun’s heat the way comets are, leaving scientists to wonder what causes the formation of 3200 Phaethon’s stream across the night sky.
“What’s really weird is that we know that 3200 Phaethon is an asteroid, but as it flies by the Sun, it seems to have some kind of temperature-driven activity,” Szalay said. “Most asteroids don’t do that.”
Some researchers have suggested that 3200 Phaethon may actually be a comet that lost all of its snow, leaving only a rocky core resembling an asteroid. But the new Parker Solar Probe data show that although some of 3200 Phaethon’s activity is related to temperature, the creation of the Geminids stream was likely not caused by a cometary mechanism, but by something much more catastrophic.
Opening the time capsule
To learn about the origin of the Geminids stream, Cukier and Szalay used the new Parker Solar Probe data to model three possible formation scenarios, then compared these models to existing models created from Earth-based observations.
“There are what’s called the ‘basic’ model of formation of a meteoroid stream, and the ‘violent’ creation model,” Cukier said. “It’s called ‘basic’ because it’s the most straight-forward thing to model, but really these processes are both violent, just different degrees of violence.”
These different models reflect the chain of events that would transpire according to the laws of physics based on different scenarios. For example, Cukier used the basic model to simulate all of the chunks of material releasing from the asteroid with zero relative velocity — or with no speed or direction relative to 3200 Phaethon — to see what the resulting orbit would look like and compare it to the orbit shown by the Parker Solar Probe probe data.
He then used the violent creation model to simulate the material releasing from the asteroid with a relative velocity of up to one kilometer per hour, as if the pieces were knocked loose by a sudden, violent event.
He also simulated the cometary model — the mechanism behind the formation of most meteoroid streams. The resulting simulated orbit matched the least with the way the Geminids orbit actually appears according to the Parker Solar Probe data, so they ruled out this scenario.
In comparing the simulated orbits from each of the models, the team found that the violent models were most consistent with the Parker Solar Probe data, meaning it’s likely that a sudden, violent event — such as a high-speed collision with another body or a gaseous explosion, among other possibilities — created the Geminids stream.
The research builds on the work of Szalay and several colleagues of the Parker Solar Probe mission, built and assembled at the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland, to assemble a picture of the structure and behavior of the large cloud of dust that swirls through the innermost solar system.
They took advantage of Parker’s flight path — an orbit that swings it just millions of miles from the Sun, closer than any spacecraft in history — to get the best direct look at the dusty cloud of grains shed from passing comets and asteroids.
Although the probe doesn’t measure dust particles directly, it can track dust grains in a clever way: as dust grains pelt the spacecraft along its path, the high-velocity impacts create plasma clouds. These impact clouds produce unique signals in electric potential that are picked up by several sensors on the probe's FIELDS instrument, which is designed to measure the electric and magnetic fields near the Sun.
“The first-of-its-kind data our spacecraft is gathering now will be analyzed for decades to come,” said Nour Raouafi, Parker Solar Probe project scientist at APL. “And it’s exciting to see scientists of all levels and skills digging into it to shed light on the Sun, the solar system and the universe beyond.”
Reaching for the stars
Cukier said his passion for learning about outer space combined with departmental support are what motivated him to pursue this project.
After taking a hands-on lab class offered by the Princeton space physics laboratory — where he gained practical experience building space instruments, like those currently sampling the Sun’s environment aboard Parker Solar Probe — and serving as treasurer for the undergraduate astronomy club, he decided he wanted to pursue extracurricular research.
He was met with enthusiasm when he reached out to scientists in the Princeton Space Physics group. “Everyone is very supportive of undergraduate research, especially in astrophysics, because it’s really part of the departmental culture,” he said.
“It’s always wonderful when our students like Wolf can contribute so strongly to this sort of space research,” said David McComas, head of the Space Physics group and vice president for the Princeton Plasma Physics Laboratory (PPPL). “Many of us have been in awe of the Geminids meteor displays for years and it is awesome to finally have the data and research to show how they likely formed.”
Cukier said that he’s been drawn to watching the sky since he was a kid. “Planetary science is surprisingly accessible,” he said. “For the Geminids, for instance, anyone can go outside on December 14 this year at night and look up. It’s visible from Princeton, and some of the meteors are really bright. I’d highly recommend seeing it.”
“Formation, Structure, and Detectability of the Geminids Meteoroid Stream” by W.Z. Cukier and J.R. Szalay was published June 15, 2023 by Planetary Science Journal (DOI 10.3847/PSJ/acd538). The research was supported by the Parker Solar Probe Guest Investigator Program (80NSSC21K1764). Parker Solar Probe is part of NASA's Living with a Star program to explore aspects of the Sun-Earth system that directly affect life and society. The program is managed by NASA's Goddard Space Flight Center for the Heliophysics Division of NASA's Science Mission Directorate. APL manages the Parker Solar Probe mission for NASA.
Artist’s concept of the Parker Solar Probe spacecraft approaching the sun. Launched in 2018, the probe is increasing our ability to forecast major space-weather events that impact life on Earth.
CREDIT
NASA/Johns Hopkins APL/Steve Gribben
JOURNAL
Planetary Science
METHOD OF RESEARCH
Computational simulation/modeling
ARTICLE TITLE
Formation, Structure, and Detectability of the Geminids Meteoroid Stream
ARTICLE PUBLICATION DATE
15-Jun-2023
Discovery of white dwarf pulsar sheds light on star evolution
The discovery of a rare type of white dwarf star system provides new understanding into stellar evolution
Peer-Reviewed PublicationIMAGE: CREDIT DR MARK GARLICK//UNIVERSITY OF WARWICK view more
CREDIT: CREDIT DR MARK GARLICK//UNIVERSITY OF WARWICK
The discovery of a rare type of white dwarf star system provides new understanding into stellar evolution.
White dwarfs are small, dense stars typically the size of a planet. They are formed when a star of low mass has burnt all its fuel, losing its outer layers. Sometimes referred to as “stellar fossils”, they offer insight into different aspects of star formation and evolution.
A rare type of white dwarf pulsar has been discovered for the second time only, in research led by the University of Warwick. White dwarf pulsars include a rapidly spinning, burnt-out stellar remnant called a white dwarf, which lashes its neighbour – a red dwarf – with powerful beams of electrical particles and radiation, causing the entire system to brighten and fade dramatically over regular intervals. This is owing to strong magnetic fields, but scientists are unsure what causes them.
A key theory which explains the strong magnetic fields is the “dynamo model” – that white dwarfs have dynamos (electrical generators) in their core, as does the Earth, but much more powerful. But for this theory to be tested, scientists needed to search for other white dwarf pulsars to see if their predictions held true.
Published today in Nature Astronomy, scientists funded by the UK Science and Technology Facilities Council (STFC) describe the newly detected white dwarf pulsar, J191213.72-441045.1 (J1912-4410 for short). It is only the second time such a star system has been found, following the discovery of AR Scorpii (AR Sco) in 2016.
773 light years away from Earth and spinning 300 times faster than our planet, the white dwarf pulsar has a size similar to the Earth, but a mass at least as large as the Sun. This means that a teaspoon of white dwarf material would weigh around 15 tons. White dwarfs begin their lives at extremely hot temperatures before cooling down over billions of years, and the low temperature of J1912−4410 points to an advanced age.
Dr Ingrid Pelisoli, STFC Ernest Rutherford Research Fellow at the University of Warwick’s Department of Physics, said: “The origin of magnetic fields is a big open question in many fields of astronomy, and this is particularly true for white dwarf stars. The magnetic fields in white dwarfs can be more than a million times stronger than the magnetic field of the Sun, and the dynamo model helps to explain why. The discovery of J1912−4410 provided a critical step forward in this field.
“We used data from a few different surveys to find candidates, focusing on systems that had similar characteristics to AR Sco. We followed up any candidates with ULTRACAM, which detects the very fast light variations expected of white dwarf pulsars. After observing a couple dozen candidates, we found one that showed very similar light variations to AR Sco. Our follow-up campaign with other telescopes revealed that every five minutes or so, this system sent a radio and X-ray signal in our direction.
“This confirmed that there are more white dwarf pulsars out there, as predicted by previous models. There were other predictions made by the dynamo model, which were confirmed by the discovery of J1912−4410. Due to their old age, the white dwarfs in the pulsar system should be cool. Their companions should be close enough that the gravitational pull of the white dwarf was in the past strong enough to capture mass from the companion, and this causes them to be fast spinning. All of those predictions hold for the new pulsar found: the white dwarf is cooler than 13,000K, spins on its axis once every five minutes, and the gravitational pull of the white dwarf has a strong effect in the companion.
“This research is an excellent demonstration that science works – we can make predictions and put them to test, and that is how any science progresses.”
Dr Pelisoli is one of the first group of research fellows and PhD students supported by a £3.5 million private philanthropic donation from a Warwick alumnus. One of the largest gifts towards the study of astronomy and astrophysics in the UK, the donation is enabling the next generation of astronomers to explore the furthest reaches of our universe.
Axel Schwope, Leibniz Institute for Astrophysics Potsdam (AIP), who is leading a complementary study published as a letter in Astronomy and Astrophysics, added: "We are excited to have independently found the object in the X-ray all-sky survey performed with SRG/eROSITA. The follow-up investigation with the ESA satellite XMM-Newton revealed the pulsations in the high-energy X-ray regime, thus confirming the unusual nature of the new object and firmly establishing the white dwarf pulsars as a new class.”
Read the paper here https://www.nature.com/articles/s41550-023-01995-x
University of Warwick press office contact:
Annie Slinn
Communications Officer | Press & Media Relations | University of Warwick
Email: annie.slinn@warwick.ac.uk
JOURNAL
Nature Astronomy
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