Cosmic rays threaten future deep-space astronaut missions

Artist's rendition of the Lunar Reconnaissance Orbiter (LRO) at the moon. 

The CRaTER telescope is seen pointing out at the bottom right center of the LRO spacecraft.

Credit: Illustration by Chris Meaney/NASA

Crewed missions to Mars remain an essential goal for NASA, but scientists are only now beginning to understand and characterise the radiation hazards that could make such ventures risky, concludes a new paper by University of New Hampshire (UNH) scientists.

In a paper published online in the journal Space Weather, associate professor Nathan Schwadron of the UNH Institute for the Study of Earth, Oceans, and Space (EOS) and the department of physics says that due to a highly abnormal and extended lack of solar activity, the solar wind is exhibiting extremely low densities and magnetic field strengths, which causes dangerous levels of hazardous radiation to pervade the space environment.

"The behaviour of the sun has recently changed and is now in a state not observed for almost 100 years," says Schwadron, lead author of the paper and principal investigator for the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) on NASA's Lunar Reconnaissance Orbiter (LRO).

He notes that throughout most of the space age, the sun's activity has shown a clockwork 11-year cycle, with approximately six- to eight-year lulls in activity (solar minimum) followed by two- to three-year periods when the sun is more active.

"However, starting in about 2006, we observed the longest solar minimum and weakest solar activity observed in the space age."

These conditions brought about the highest intensities of galactic cosmic rays seen since the beginning of the space age, which have created worsening radiation hazards that potentially threaten future deep-space astronaut missions.

"While these conditions are not necessarily a showstopper for long-duration missions to the moon, an asteroid, or even Mars, galactic cosmic ray radiation in particular remains a significant and worsening factor that limits mission durations," says Schwadron.

The study is the capstone article in the Space Weather CRaTER Special Issue, which provides comprehensive findings on space-based radiation as measured by the UNH-led detector.

The data provide critical information on the radiation hazards that will be faced by astronauts on extended missions to deep space such as those to Mars.

"These data are a fundamental reference for the radiation hazards in near Earth 'geospace' out to Mars and other regions of our sun's vast heliosphere," says Schwadron.

At the heart of CRaTER is material called "tissue equivalent plastic," a stand-in for human muscle capable of gauging radiation dosage. Ionizing radiation from galactic cosmic rays and solar energetic particles remains a significant challenge to long-duration crewed missions to deep space.

Human beings face a variety of consequences ranging from acute effects (radiation sickness) to long-term effects including cancer induction and damage to organs including the heart and brain.

The high radiation levels seen during the sun's last minimum cycle limits the allowable days for typical astronauts behind spacecraft shielding.

Given the trend of reducing solar output, the allowable days in space for astronauts is dropping and estimated to be 20 percent lower in the coming solar minimum cycle as compared to the last minimum cycle.

Journal Reference:
N. A. Schwadron, J. B. Blake, A. W. Case, C. J. Joyce, J. Kasper, J. Mazur, N. Petro, M. Quinn, J. A. Porter, C. W. Smith, S. Smith, H. E. Spence, L. W. Townsend, R. Turner, J. K. Wilson, C. Zeitlin. Does the worsening galactic cosmic radiation environment observed by CRaTER preclude future manned deep-space exploration? Space Weather, 2014; DOI: 10.1002/2014SW001084

NASA AMS-2 Particle Detector on ISS Finds Dark matter in Cosmic Rays - Update

The Alpha Magnetic Spectrometer attached to the International Space Station.

Credit: NASA

New research published Thursday in the journal Physical Review Letters shows researchers are making important progress in the hunt for dark matter, using the Alpha Magnetic Spectrometer (AMS), a state-of-the-art cosmic ray particle physics detector located on the exterior of the International Space Station.

The results include new detections of anti-matter particles that could provide new clues in the search for dark matter, invisible matter that can't be directly detected but can be inferred. An overview of the latest findings can be found here.

Computer-generated drawing of the Alpha 
Magnetic Spectrometer (AMS). Credit: NASA

The MIT group leads an international collaboration of scientists that analyzed two and a half years' worth of data taken by the Alpha Magnetic Spectrometer (AMS), a large particle detector mounted on the exterior of the International Space Station, that captures incoming cosmic rays from all over the galaxy.

Among 41 billion cosmic ray events, instances of cosmic particles entering the detector, the researchers identified 10 million electrons and positrons, stable antiparticles of electrons.

Positrons can exist in relatively small numbers within the cosmic ray flux.

An excess of these particles has been observed by previous experiments, suggesting that they may not originate from cosmic rays, but come instead from a new source.

In 2013, the AMS collaboration, for the first time, accurately measured the onset of this excess.

The new AMS results may ultimately help scientists narrow in on the origin and features of dark matter, whose collisions may give rise to positrons.

"The AMS results announced today are tremendously provocative, and will drive scientists around the world to continue pursuing one of the biggest mysteries in the cosmos: dark matter," NASA chief scientist Ellen Stofan said at the agency’s headquarters in Washington.

"The clear and definitive data from AMS represent the caliber of scientific discovery enabled by our unique laboratory in space, the International Space Station."

"Today we are one step closer to answering the fundamental questions about how our universe works, and we look forward to many more exciting twists in this developing story."

AMS was constructed, tested and operated by an international team of 56 institutes from 16 countries and organized under the sponsorship of the U.S. Department of Energy's Office of Science.

NASA's Johnson Space Center in Houston manages the AMS Integration Project Office. AMS was launched on space shuttle Endeavour on May 16, 2011.

Operations on the space station began three days later. AMS continues operations aboard the station today.

More Information
"Electron and Positron Fluxes in Primary Cosmic Rays Measured with the Alpha Magnetic Spectrometer on the International Space Station" Phys. Rev. Lett. 113, 121102 – Published 18 September 2014 - 10.1103/PhysRevLett.113.121102

Cosmic rays Hotspot: Physicists closer to finding the mysterious sources

This map of the northern sky shows cosmic ray concentrations, with a "hotspot" with a disproportionate number of cosmic rays shown as the bright red and yellow spot, upper right. 

An international team of physicists using the University of Utah-operated Telescope Array near Delta, Utah, say their discovery of the hotspot should narrow the search for the mysterious source or sources of ultrahigh-energy cosmic rays, which carry more energy than any other known particle in the universe. 

Credit: Kazumasa Kawata, University of Tokyo Institute for Cosmic Ray Research.

An observatory run by the University of Utah found a "hotspot" beneath the Big Dipper emitting a disproportionate number of the highest-energy cosmic rays.

The discovery moves physics another step toward identifying the mysterious sources of the most energetic particles in the universe.

Gordon Thomson

"This puts us closer to finding out the sources, but no cigar yet," says University of Utah physicist Gordon Thomson, spokesman and co-principal investigator for the $25 million Telescope Array cosmic ray observatory west of Delta, Utah; the Northern Hemisphere's largest cosmic ray detector.

"All we see is a blob in the sky, and inside this blob there is all sorts of stuff – various types of objects, that could be the source" of the powerful cosmic rays, he adds. "Now we know where to look."

A new study identifying a hotspot in the northern sky for ultrahigh-energy cosmic rays has been accepted for publication by Astrophysical Journal Letters.

Thomson says many astrophysicists suspect ultrahigh-energy cosmic rays are generated by active galactic nuclei (AGNs), in which material is sucked into a supermassive black hole at the center of galaxy, while other material is spewed away in a beam-like jet known as a blazar.

Another popular possibility is that the highest-energy cosmic rays come from some supernovas (exploding stars) that emit gamma rays bursts.

Lower-energy cosmic rays come from the sun, other stars and exploding stars, but the source or sources of the most energetic cosmic rays has been a decades-long mystery.

The study was conducted by 125 researchers in the Telescope Array project, including Thomson and 31 other University of Utah physicists, plus 94 other scientists from the University of Tokyo (ICRR) and 28 other research institutions in Japan, the United States, South Korea, Russia and Belgium.

Read the full article here

More Information: Indications of Intermediate-Scale Anisotropy of Cosmic Rays with Energy Greater Than 57 EeV in the Northern Sky Measured with the Surface Detector of the Telescope Array Experiment - Authors: K. Kawata, et al.

KASCADE Experiment: Detects Extragalactic component of cosmic rays

The KASCADE-Grande measurement field on the premises of KIT was used by scientists to study particle showers produced by cosmic rays. 

Credit: KIT

It is obvious from the data of the KASCADE-Grande experiment at the Karlsruhe Institute of Technology (KIT) that the so-called "knee" of the cosmic rays, a bend in the energy spectrum at high energies, is located at different energies for light and heavy particles.

As regards light particles, the scientists have now found that the energy spectrum flattens again beyond the knee and forms a type of "ankle".

This structure indicates that cosmic radiation particles with energies beyond the knee are accelerated in galaxies other than the Milky Way.

KIT's KASCADE-Grande experiment has yielded the important result that a characteristic bend in the energy spectrum of high-energy cosmic rays, also called "knee", is located at different energies for light and heavy primary particles.

The position of the knee appears to vary with the charge of atomic nuclei: KASCADE-Grande detected the "iron knee" at an energy that was 26 times higher than the knee in the spectrum of hydrogen nuclei.

Latest findings of the KASCADE-Grande experiment reveal a flattening (also called "anti-knee" or "ankle") of the spectrum of light primary particles above an energy of 1017 electron volts.

This structure indicates the existence of a new, now extragalactic component of cosmic rays. This important result in high-energy astrophysics was published recently by the scientists in the Physical Review D journal.

KASCADE-Grande was a measurement field for cosmic rays on the premises of KIT Campus North.

The KASCADE experiment was extended by another 37 detector stations and measured particle showers produced by high-energy primary cosmic rays for more than a decade.

Andreas Haungs

"With KASCADE-Grande, we measured showers of secondary particles produced by primary particles of cosmic origin at energies of 1014 to 1018 electron volts," explains Dr. Andreas Haungs who coordinates the KASCADE-Grande project at KIT.

1018 electron volts: This exceeds the energy reached by the largest particle accelerators on Earth by several orders of magnitude.

The worldwide known and acknowledged experiment was shut down last year but current analysis of the full data set again yielded a scientific highlight.

This is the spectrum of cosmic rays with knee and ankle. 

While the knee is measured at different energies for light and heavy primary particles, KASCADE-Grande has now for the first time revealed an ankle-like structure for light primary particles. 

Credit: KIT

The flux of cosmic rays, i.e. of primary particles that can probably be found anywhere in the universe, decreases strongly with increasing particle energy. Slightly above an energy of 1015 electron volts, the "slope" of energy decrease changes: This leads in a bend in the spectrum, the "knee" of cosmic radiation.

KASCADE-Grande demonstrated that the knee occurs at different energies for light and heavy elements and that this difference is related to charge.

But where does the knee come from and why does its cause depend on the charge of the cosmic particle?

This might be explained by magnetic fields in the vicinity of cosmic accelerators. Towards higher energies, they work more effectively for particles of higher charge.

Moreover, our galaxy possesses a magnetic halo that prevents most of the particles from leaving our Milky Way.

It was concluded from the results of KASCADE-Grande that the primary particles of cosmic rays can be generated and stored in our Milky Way up to energies around 1017 electron volts only.

Particles of higher energy have their origin outside of the Milky Way. The transition from galactic to extragalactic cosmic radiation is assumed to lie in the energy range slightly above 1018 electron volts, at the so-called "ankle" of the spectrum.

According to the above theory relating to the formation of the knee, the transition to mainly extragalactic cosmic radiation is supposed to become visible in the energy spectrum of light primary particles first, as these are the first to leave their home galaxy.

More information: The recent results are published in the scientific journal "Physical Review D", D 87, No. 081101 (R), 2013.

Russian researchers find more evidence that lightning is caused by cosmic rays

Russian physicists Alex Gurevich and Anatoly Karashtin claim, in a paper published in the journal Physical Review Letters, they have found more evidence to support their idea that lightning is caused by cosmic rays.

The notion was first proposed by Gurevich back in 1992, and has been a source of debate ever since.

No one really knows what causes lightning to form and strike—the prevailing view is that it comes about as a result of collisions between ice crystals in clouds and hail stones. But because clouds and the lightning they produce are unpredictable and hard to pin down, no one has been able to prove this theory.

Another theory, proposed by Gurevich twenty years ago, says that lightning is formed from the collisions between cosmic rays and water droplets present in thunderclouds. Now he and a colleague claim to have found evidence to support this idea.

Gurevich suggests that cosmic rays entering thunder clouds cause the air in them to be ionized, resulting in a lot of free electrons floating around. The electronic field already present in the cloud, he continues, leads to the free electrons being boosted to higher energies.

When the electrons present in the air collide with water atoms, more electrons are released, setting off what he describes as an avalanche of high-energy particles that eventually give way to a "runaway breakdown"—a discharge that is witnessed as a lightning strike.

As with other theories regarding the origins of lightning, Gurevich's ideas haven't been proved. But he hasn't been sitting still.

In this new effort, he along with Karashtin have been measuring and analyzing radio waves in storm clouds as lightning occurs. The idea is that if such strikes are due to interactions with cosmic rays, there should be measurable amounts of radio waves given off.

Gurevich and Karashtin set up equipment to monitor storm clouds over Russia and Kazakhstan—recording radio waves emitted during 3,800 lightning strikes. In analyzing the data, they found that hundreds, and perhaps even thousands of short radio wave pulses occurred just as a bolt of lightning was about to form.

Perhaps more importantly, they matched the models Gurevich had built years before. There was on hitch however, the amount of energy delivered by the cosmic rays in the model don't happen often enough in the real world to cause lightning strikes in most every thunderstorm.

Gurevich and Karashtin say the discrepancy can be explained by the addition of energy into the system by free electrons passing near hydrometeors (bits of hail or water droplets).

When that happens, very small discharges result, adding to the total charge. Taken together they say, enough energy is added to cause the cascade that leads to lightning formation.

More information: Runaway Breakdown and Hydrometeors in Lightning Initiation, Phys. Rev. Lett. 110, 185005 (2013). prl.aps.org/abstract/PRL/v110/i18/e185005

Space 'Superbubbles' Could Spawn Energetic Cosmic Rays

An artist's concept of the heliosphere, a magnetic bubble that partially protects the solar system from cosmic rays.

CREDIT: Richard Mewaldt/Caltech

Enigmatic cosmic rays that strike Earth with giant amounts of energy might come from hot gaseous "superbubbles" in space, a new study reveals.

Cosmic rays have perplexed scientists for a century. These electrically charged particles bombard Earth with energies dwarfing anything we are capable of, but their origins remain a mystery.

Since cosmic rays are electrically charged, they can get pushed and pulled around by interstellar magnetic fields in the gas between the stars as they zip through space, obscuring where they come from.

One suspected fountain of cosmic rays are star-forming regions. The massive stars within these stellar nurseries can spew out massive amounts of energy and explode as supernovas.

IceCube Spies Unexplained Pattern Of Cosmic Rays

Photo: courtesy IceCube collaboration

This "skymap," generated in 2009 from data collected by the IceCube Neutrino Observatory, shows the relative intensity of cosmic rays directed toward the Earth's Southern Hemisphere.

Researchers from UW-Madison and elsewhere identified an unusual pattern of cosmic rays, with an excess (warmer colors) detected in one part of the sky and a deficit (cooler colors) in another.


Though still under construction, the IceCube Neutrino Observatory at the South Pole is already delivering scientific results - including an early finding about a phenomenon the telescope was not even designed to study.

IceCube captures signals of notoriously elusive but scientifically fascinating subatomic particles called neutrinos. The telescope focuses on high-energy neutrinos that travel through the Earth, providing information about faraway cosmic events such as supernovas and black holes in the part of space visible from the Northern Hemisphere.

However, one of the challenges of detecting these relatively rare particles is that the telescope is constantly bombarded by other particles, including many generated by cosmic rays interacting with the Earth's atmosphere over the southern half of the sky.

For most IceCube neutrino physicists these particles are simply background noise, but University of Wisconsin-Madison researchers Rasha Abbasi and Paolo Desiati, with collaborator Juan Carlos Diaz-Velez, recognized an opportunity in the cosmic ray data.

"IceCube was not built to look at cosmic rays. Cosmic rays are considered background," Abbasi says. "However, we have billions of events of background downward cosmic rays that ended up being very exciting."

Abbasi saw an unusual pattern when she looked at a "skymap" of the relative intensity of cosmic rays directed toward the Earth's Southern Hemisphere, with an excess of cosmic rays detected in one part of the sky and a deficit in another. A similar lopsidedness, called "anisotropy," has been seen from the Northern Hemisphere by previous experiments, she says, but its source is still a mystery.

"At the beginning, we didn't know what to expect. To see this anisotropy extending to the Southern Hemisphere sky is an additional piece of the puzzle around this enigmatic effect - whether it's due to the magnetic field surrounding us or to the effect of a nearby supernova remnant, we don't know," Abbasi says.

Our Cruel Sun: Exposed Earth to Cosmic Rays

The sun protects the earth from cosmic rays and dust from the solar system but squeezing of various stars could leave us unprotected (Image: NASA/HST collection)

THE sun provides ideal conditions for life to thrive, right? In fact, it periodically leaves Earth open to assaults from interstellar nasties in a way that most stars do not.

The sun protects us from cosmic rays and dust from beyond the solar system by enveloping us in the heliosphere - a bubble of solar wind that extends past Pluto. These cosmic rays would damage the ozone layer, and interstellar dust could dim sunlight and trigger an ice age. However, when the solar system passes through very dense gas and dust clouds, the heliosphere can shrink until its edge is inside Earth's orbit.

In a paper to appear in Astrobiology, David Smith at the University of Arizona in Tucson and John Scalo at the University of Texas, Austin, calculated the squeezing of various stars' protective "astrospheres". They found Earth is exposed to between one and 10 interstellar assaults every billion years. Habitable planets around a red dwarf, which account for three of every four stars, are never exposed. That's because they need to be close to these dim stars to be warm enough to be habitable. "The bottom line is that habitable planets around red dwarfs are better protected from climate catastrophes than Earth is," says Smith.