The Worsening Cosmic Ray Situation

March 5, 2018: Cosmic rays are bad–and they’re getting worse.

That’s the conclusion of a new paper just published in the research journal Space Weather. The authors, led by Prof. Nathan Schwadron of the University of New Hampshire, show that radiation from deep space is dangerous and intensifying faster than previously expected.


The story begins four years ago when Schwadron and colleagues first sounded the alarm about cosmic rays. Analyzing data from the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) instrument onboard NASA’s Lunar Reconnaissance Orbiter (LRO), they found that cosmic rays in the Earth-Moon system were peaking at levels never before seen in the Space Age. The worsening radiation environment, they pointed out, was a potential peril to astronauts, curtailing how long they could safely travel through space.

This figure from their original 2014 paper shows the number of days a 30-year old male astronaut flying in a spaceship with 10 g/cm2 of aluminum shielding could go before hitting NASA-mandated radiation limits:


In the 1990s, the astronaut could spend 1000 days in interplanetary space. In 2014 … only 700 days. “That’s a huge change,” says Schwadron.

Galactic cosmic rays come from outside the solar system. They are a mixture of high-energy photons and sub-atomic particles accelerated toward Earth by supernova explosions and other violent events in the cosmos. Our first line of defense is the sun:  The sun’s magnetic field and solar wind combine to create a porous ‘shield’ that fends off cosmic rays attempting to enter the solar system. The shielding action of the sun is strongest during Solar Maximum and weakest during Solar Minimum–hence the 11-year rhythm of the mission duration plot above.

The problem is, as the authors note in their new paper, the shield is weakening: “Over the last decade, the solar wind has exhibited low densities and magnetic field strengths, representing anomalous states that have never been observed during the Space Age. As a result of this remarkably weak solar activity, we have also observed the highest fluxes of cosmic rays.”

Back in 2014, Schwadron et al used a leading model of solar activity to predict how bad cosmic rays would become during the next Solar Minimum, now expected in 2019-2020.  “Our previous work suggested a ∼ 20% increase of dose rates from one solar minimum to the next,” says Schwadron. “In fact, we now see that actual dose rates observed by CRaTER in the last 4 years exceed the predictions by ∼ 10%, showing that the radiation environment is worsening even more rapidly than we expected.” In this plot bright green data points show the recent excess:


The data Schwadron et al have been analyzing come from CRaTER on the LRO spacecraft in orbit around the Moon, which is point-blank exposed to any cosmic radiation the sun allows to pass. Here on Earth, we have two additional lines of defense: the magnetic field and atmosphere of our planet. Both mitigate cosmic rays.

But even on Earth the increase is being felt. The students of Earth to Sky Calculus have been launching space weather balloons to the stratosphere almost weekly since 2015. Sensors onboard those balloons show a 13% increase in radiation (X-rays and gamma-rays) penetrating Earth’s atmosphere:


X-rays and gamma-rays detected by these balloons are “secondary cosmic rays,” produced by the crash of primary cosmic rays into Earth’s upper atmosphere. They trace radiation percolating down toward our planet’s surface. The energy range of the sensors, 10 keV to 20 MeV, is similar to that of medical X-ray machines and airport security scanners.

How does this affect us? Cosmic rays penetrate commercial airlines, dosing passengers and flight crews so much that pilots are classified by the International Commission on Radiological Protection as occupational radiation workers. Some research shows that cosmic rays can seed clouds and trigger, potentially altering weather and climate. Furthermore, there are studies ( #1, #2, #3, #4) linking cosmic rays with cardiac arrhythmias in the general population.

Cosmic rays will intensify even more in the years ahead as the sun plunges toward what may be the deepest Solar Minimum in more than a century. Stay tuned for updates.


Schwadron, N. A., et al (2014), Does the worsening galactic cosmic radiation environment observed by CRaTER preclude future manned deep space exploration?, Space Weather, 12, 622–632, doi:10.1002/2014SW001084.

Schwadron, N. A., et al (2018), Update on the worsening particle radiation environment observed by CRaTER and implications for future human deep-space exploration, Space Weather, doi: 10.1002/2017SW001803.


Rads on a Plane: The Data

Feb. 21, 2018: Many people think that only astronauts have to worry about cosmic radiation. Not so. Ordinary air travelers are exposed to cosmic rays, too. On a typical flight over the continental USA, radiation dose rates in economy class are more than 40 times higher than on the ground below. Cosmic rays penetrate the walls of aircraft with ease. This has  prompted the International Commission on Radiological Protection (ICRP) to classify pilots as occupational radiation workers–just like nuclear power plant engineers.

Since Jan. 2015, and the students of Earth to Sky Calculus have been monitoring cosmic rays in airplanes. Our method is simple: We board planes carrying the same cosmic ray payload we routinely fly to the stratosphere on space weather balloons. Inside the airplane we measure X-ray, gamma-ray and neutron dose rates along with GPS altitude, latitude and longitude

Above: Flight paths forming the basis of our aviation radiation study. 2015-2017

Three years after our first flight, our data set is impressive. We have 14,183 GPS-tagged radiation measurements collected during 67 flights over 2 oceans and 5 continents. We have spent 236.4 hours onboard planes taking data. If you accumulated that into a single flight, it would amount to 9.8 uninterrupted days on a plane.

This substantial data set is allowing us to explore how radiation varies with altitude around the globe. It’s not the same everywhere. The Arctic, for example, differs sharply from the equator, and there are interesting departures from “normal” near the South Atlantic Anomaly. We’re also discovering how Earth’s natural magnetism shields travelers from radiation: there’s a strong correlation in our data between dose rate and the geomagnetic field around the airplane.

Best of all, we can now predict dose rates for flights that haven’t even taken off yet. Using the data from 2015-2017, we’re building an empirical predictive model and actively testing it against new flights in 2018. Early results show that it works well over the continental USA, and we are beginning to check international flights, too.

Stay tuned for updates!

The Pacific Radiation Bowl

Jan. 22, 2018: For years, and the students of Earth to Sky Calculus have been flying balloons to the stratosphere to monitor cosmic rays penetrating Earth’s atmosphere. Lately, we’ve been flying the same payloads onboard airplanes. We want to map Earth’s radiation environment at aviation altitudes where millions of people are routinely exposed to elevated levels of cosmic rays.

Recently we encountered an interesting feature in data taken over the Pacific Ocean: a “radiation bowl.” On Nov. 30th, 2017, Hervey Allen, a computer scientist at the University of Oregon, carried our radiation sensors onboard a commercial flight from San Francisco, California, to Auckland, New Zealand: map. As his plane cruised at a nearly constant altitude (35,000 ft) across the equator, radiation levels gracefully dipped, then recovered, in a bowl-shaped pattern:



In one way, this beautiful curve is no surprise. We expect dose rates to reach a low point near the equator, because that is where Earth’s magnetic field provides the greatest shielding against cosmic rays. Interestingly, however, the low point is not directly above the equator. A parabolic curve fit to the data shows that the actual minimum occurred at 5.5 degrees N latitude.

Is Earth’s “radiation equator” offset from the geographic equator? Very likely it is. Earth’s magnetic field is tilted with respect to Earth’s spin axis and, moreover, there are many inhomogeneities in our planetary magnetic field that may create radiation zones of interest in unexpected places.

We are now planning additional trips across the equator to map the band of least radiation girdling our planet. In fact, we are working on a dataset now that includes an equator-crossing between the USA and Chile. Stay tuned for updates.

Neutrons on a Plane

March 18, 2017: Among researchers, it is well known that air travelers are exposed to cosmic rays. High-energy particles and photons from deep space penetrate Earth’s atmosphere and go right through the hulls of commercial aircraft. This has prompted the International Commission on Radiological Protection (ICRP) to classify pilots and flight attendants as occupational radiation workers.

Many studies of this problem focus on ionizing radiation such as x-rays and gamma-rays. On March 16th we turned the tables and measured neutrons instead. During a 12-hour flight from Stockholm to Los Angeles, and the students of Earth to Sky Calculus used bubble chambers to monitor neutron activity inside a Scandinavian Airlines jetliner.

In the photo above, taken 35,000 feet above Greenland, each bubble shows where a neutron passed through the chamber and vaporized a superheated droplet. By the time the long flight was over, we measured almost 20 uSv (microsieverts) of radiation from neutrons–similar to the dose from a panoramic X-ray at your dentist’s office. This confirms that neutrons are an important form of aviation radiation relevant to both air travelers and future space tourists.

Where do these neutrons come from? Mainly, they are secondary cosmic rays. When primary cosmic rays from deep space hit Earth’s atmosphere, they produce a spray of secondary particles including neutrons, protons, alpha particles, and other species. Cosmic ray neutrons can reach the ground; indeed, researchers routinely use neutron counters on Earth’s surface to monitor cosmic ray activity above the atmosphere. Now we’re doing the same thing onboard airplanes.

Earlier in the week, we flew these bubble chambers to the Arctic stratosphere using a space weather balloon. Interestingly, the 12-hour plane flight yielded ~6 times more neutrons than the shorter (2 hour) but far higher (97,000 ft) balloon flight to the stratosphere. What does it mean? We’re still analyzing the data and will have more insights to share in the days ahead. Stay tuned!

Radiation Clouds at Aviation Altitudes

Jan. 20, 2017: A new study published in the peer-reviewed journal Space Weather reports the discovery of radiation “clouds” at aviation altitudes. When airplanes fly through these clouds, dose rates of cosmic radiation normally absorbed by air travelers can double or more.

“We have flown radiation sensors onboard 264 research flights at altitudes as high as 17.3 km (56,700 ft) from 2013 to 2017,” says Kent Tobiska, lead author of the paper and PI of the NASA-supported program Automated Radiation Measurements for Aerospace Safety (ARMAS). “On at least six occasions, our sensors have recorded surges in ionizing radiation that we interpret as analogous to localized clouds.”

The fact that air travelers absorb radiation is not news.  Researchers have long known that cosmic rays crashing into Earth’s atmosphere create a spray of secondary particles such as neutrons, protons, electrons, X-rays and gamma-rays that penetrate aircraft.  100,000 mile frequent flyers absorb as much radiation as 20 chest X-rays—and even a single flight across the USA can expose a traveler to more radiation than a dental X-ray.

Conventional wisdom says that dose rates should vary smoothly with latitude and longitude and the height of the aircraft.  Any changes as a plane navigates airspace should be gradual.  Tobiska and colleagues have found something quite different, however: Sometimes dose rates skyrocket for no apparent reason.

“We were quite surprised to see this,” says Tobiska.

All of the surges they observed occurred at relatively high latitudes, well above 50 degrees in both hemispheres. One example offered in their paper is typical: On Oct 3, 2015, an NSF/NCAR research aircraft took off from southern Chile and flew south to measure the thickness of the Antarctic ice shelf.  Onboard, the ARMAS flight module recorded a 2x increase in ionizing radiation for about 30 minutes while the plane flew 11 km (36,000 feet) over the Antarctic Peninsula.  No solar storm was in progress.  The plane did not abruptly change direction or altitude.  Nevertheless, the ambient radiation environment changed sharply. Similar episodes have occurred off the coast of Washington state.

Above: Radiation measurements made by ARMAS while flying over Antarctica. The colored points are from ARMAS. The black points are from a NASA computer model (NAIRAS) predicting radiation dose rates. Throughout the flight, ARMAS observed higher dose rates than predicted by the model, including a surge highlighted in pink.

What’s going on?

“We’re not sure,” says Tobiska, “but we have an idea.”

Earth’s magnetic field, he explains, traps many cosmic rays and solar energetic particles in structures called “magnetic bottles.”  These bottles can be leaky.  Even minor gusts of solar wind can cause the trapped particles to squirt out the ends of the bottle, sending beams of particles down toward the Earth below.

“Basically, we think we might be flying through some of these leaky particle beams,” says Tobiska.

Tobiska notes that a team of South Korean researchers has observed similar variations in radiation while flying sensors onboard a military aircraft near the border between the two Koreas (Lee et al 2015).  If the phenomena are the same, the Korean measurements would suggest that “radiation clouds” may exist at middle latitudes, too.

The ARMAS program has a busy flight schedule in 2017. “We’ll be looking carefully for more ‘clouds’ as we continue to characterize the radiation environment at aviation altitudes,” says Tobiska.

Stay tuned for updates and, meanwhile, read Tobiska et al’s original research at this URL:

Intercontinental Space Weather Balloon Network

For the past 2 years, and the students of Earth to Sky Calculus have been launching “space weather balloons” to measure cosmic rays in the atmosphere.  Regular flights over California show that atmospheric radiation is intensifying in response to changes in the solar cycle.  Now, our monitoring program is going global.  In recent months we have been developing launch sites in multiple US states as well as South America and Europe. This is what the International Space Weather Ballooning Network looks like in October 2016:

Recent additions expand our coverage north of the Arctic Circle (Sweden) and closer to the core of the South Atlantic Anomaly (Argentina).  We also hope to add a site in Antarctica in 2018.

The purpose of launching balloons from so many places is to map out the distribution of cosmic rays around our planet. A single launch site is simply not enough to reveal the nonuniform shielding of our planet’s magnetic field and the complicated response of our atmosphere to changes in solar activity.

Our first test of the network validated these ideas. During a 48 hour period from August 20th-22nd we launched 4 balloons in quick succession from southern Chile, California, Oregon, and Washington. The ascending payloads sampled atmospheric radiation (X-rays and gamma-rays) from ground level to the stratosphere over a geographical range of more than 10,000 km. Here are the results:

The curves show radiation levels vs. altitude for each of the four sites. Numbers in parentheses are magnetic latitude–a measure of distance from Earth’s magnetic equator.

At a glance we can see that atmospheric radiation is a strong function of magnetic latitude. Washington State at +53o has more than twice the amount of radiation as southern Chile at -29o–despite the fact that the Chilean balloon flew into the outskirts of the South Atlantic Anomaly. Clearly, Earth’s magnetic field provides very uneven protection against cosmic rays.

To explore these findings further, we are planning additional network launches every month from now on, adding new sites as often as possible. A launch from inside the Arctic Circle in January 2017 is highly anticipated. Stay tuned for updates from the Intercontinental SWx Balloon Network.

Yeast Survive and Mutate at the Edge of Space

Yeast and people have a lot in common. About 1/3rd of our DNA is the same. Indeed, the DNA of yeast is so similar to that of humans, yeast can actually live with human genes spliced into their genetic code. This is why and the students of Earth to Sky Calculus have been flying yeast to the edge of space. Understanding how the microbes respond to cosmic rays could tell us how human cells respond as well. Here are three strains of yeast (one per test tube) flying 113,936 feet above Earth’s surface on August 15th:

The student in the picture is Joey, a high school senior, hitching a ride to the stratosphere along with the yeast. Joey and other members of the student research team are busy measuring growth curves and mutation rates for the space-traveling yeast.

One result is already clear: Yeast are incredibly tough. En route to the stratosphere they were frozen solid at temperatures as low as -63C, and they experienced dose rates of ionizing radiation 100x Earth normal. Survival rates in some of the returning samples were close to 100%.

Photo-micrographs show that yeast mutates in the stratosphere. This image, for instance, shows a colony of white mutants alongside the normal red colonies of Saccharomyces cerevisiae (HA2):

In addition to the white mutation shown above, the students have also observed petite mutants, which are a sign of changes in the cells’ mitochondrial genome. These changes are of interest to space biologists because the DNA repair mechanisms of yeast are remarkably similar to those of human beings. In particular, proteins encoded by yeast RAD genes are closely related to proteins used by human cells to undo radiation damage.

Flying at Night Doesn’t Protect You from Cosmic Rays

On the evening of Sept. 27th, and the students of Earth to Sky Calculus conducted a routine flight of their cosmic ray payload to the stratosphere. Routine, that is, except for one thing: the balloon flew at night during a lunar eclipse. One of the goals of the flight was to compare radiation levels at night to those recorded during the day. Here are the data they recorded:

Compare this plot of radiation vs. altitude to a similar plot recorded in broad daylight only a few days earlier. They are almost identical. Radiation levels in the stratosphere matched at the 1% level. Radiation levels at aviation altitudes (where planes fly) agreed within about 3%. Night and day were the same.

This simple experiment highlights something that is already well known to researchers. Cosmic rays in Earth’s atmosphere come mainly from deep space. They are accelerated toward Earth by supernovas, colliding neutron stars, and other violent events in the Milky Way. Flying at night is no safeguard against these energetic particles because they are ever-present, coming at us from all directions, day and night.

HEY THANKS (and Happy Birthday): The lunar eclipse flight was sponsored by reader JR Biggs, whose donation of $500 paid for the supplies neccesary to get the balloon off the ground. To say “thank you” for his contribution, we flew a birthday card for his daughter to the edge of space:

Happy Birthday to Autumn! She enjoyed watching a complete video of the flight when she turned 4 on Oct. 10th.

Readers, if you would like to support a research flight and send your birthday card, business logo, or other photo along for the ride, it only costs $500. Contact Dr. Tony Phillips to make arrangements.

Did Radiation Kill the Martian?

by Dr. Tony Phillips (This article originally appeared on

Spoiler alert: Stop reading now if you haven’t yet seen The Martian.

The #1 movie in theaters right now is The Martian, a film adaptation of Andy Weir’s eponymous book. It tells the heart-pounding story of fictional astronaut Mark Watney, who is stranded on Mars and ultimately rescued by the crewmates who had inadvertently left him behind. To survive long enough to be rescued, Watney has to “science the hell out of” a very tricky situation: he grows food in alien soil, extracts water from rocket fuel, dodges Martian dust storms, and sends signals to NASA using an old Mars rover that had been buried in red sand for some 30 years.

It’s a thrilling adventure told with considerable accuracy—except, perhaps, for one thing. “While Andy Weir does a good job of representing the risks faced by Mark Watney stranded on Mars, he is silent on the threat of radiation, not just to Mark but particularly to the crew of the Hermes as they execute a daring rescue mission that more than doubles their time in deep space,” says Dr. Ron Turner, Distinguished Analyst at ANSER, a public-service research institute in Virginia.

Space radiation comes from two main sources: solar storms and galactic cosmic rays. Solar storms are intense, short-lived, and infrequent. Fortunately for Mark, there weren’t any during his mission. He dodged that bullet. However, he and his crewmates could not have avoided cosmic rays. These are high-energy particles that arise from supernovas, colliding neutron stars, and other violent events happening all the time in the Milky Way. They are ever-present, 24/7, and there is no way to avoid them. So far, NASA has developed no effective shield against these sub-atomic cannon balls from deep space. “Doubling a nominal spacecraft shielding thickness only reduces the GCR [galactic cosmic rays] exposure by a few percent,” notes Turner.

In the movie, Watney is actually safer than the crew of the Hermes. Turner explains: “The radiation exposure is significantly less on the surface of Mars. For one thing, the planet beneath your feet reduces your exposure by half. The atmosphere, while thin, further reduces the dose. The dose rate on Mars, while high, is only about 1/3rd of that on the Hermes.”

The biggest threat from cosmic radiation exposure is the possibility of dying from radiation-induced cancer sometime after a safe return to Earth. NASA’s radiation limits today are set to limit this life-shortening risk to less than three percent. Taking into account many factors, such as the phase of the solar cycle and the number of days the crew spent in deep space and on the surface of Mars, Turner has calculated the total dose of cosmic rays absorbed by Watney (41 cSv) and the crew (72 cSv). “cSV” is a centi-Seivert, a unit of radiation commonly used in discussion of human dose rates.

There is considerable uncertainty in how these doses translate into an increased risk of cancer. Turner estimates the added risk to Watney as somewhere between 0.25% and 3.25%. For members of the crew, the added risk ranges from 0.48% to 7.6%. The high end of these ranges are well outside NASA safety limits. The crew especially could be facing medical problems after their homecoming.

Post-flight cancer is not the only problem, however. “There is some additional concern that sustained radiation exposure could lead to other problems that manifest during the mission, instead of years afterward. Possible examples include heart disease, reduced immune system effectiveness, and neurological effects mimicking the symptoms of Alzheimer disease.”

As far as we can tell, none of these things happened to the crew of the Hermes. It’s just as well. They had enough trouble without cosmic rays. For the complete details of Turner’s analysis CLICK HERE (pdf).

Rads on a Plane

by Dr. Tony Phillips (This article originally appeared on

05 Nov. 2015: and the students of Earth to Sky Calculus regularly fly helium balloons to the stratosphere to measure cosmic rays. For the past six months, May through Oct. 2015, they have been taking their radiation sensors onboard commercial airplanes, too. The chart below summarizes their measurements on 18 different airplanes flying back and forth across the continental United States.

The points on the graph indicate the dose rate of cosmic rays inside the airplanes compared to sea level. For instance, the dose rate for flights that cruised at 40,000+ feet was more than 50 times higher than the dose rate on the ground below. No wonder the International Commission on Radiological Protection (ICRP) classifies pilots as occupational radiation workers.

Cosmic rays come from deep space. They are high energy particles accelerated toward Earth by distant explosions such as supernovas and colliding neutron stars. Astronauts aren’t the only ones who have to think about them; flyers do, too. Cosmic rays penetrate deep inside Earth’s atmosphere where airplanes travel every day.

Our radiation sensors detect X-rays and gamma-rays in the energy range 10 keV to 20 MeV. These energies span the range of medical X-ray machines and airport security scanners.

Cosmic Rays are modulated by solar activity. Solar storms and CMEs tend to sweep aside cosmic rays, making it more difficult for cosmic rays to reach Earth. Low solar activity, on the other hand, allows an extra dose of cosmic rays to reach our planet. This is important because forecasters expect solar activity to drop sharply in the years ahead as we approach a new Solar Minimum. Cosmic rays are poised to increase accordingly.

The plot, above, tells us what is “normal” in 2015. How will it change as the solar cycle wanes? Stay tuned for regular updates.