Have you ever been hit by a beam of high energy particles from
above? Surely you have since it happens all of the time. And the cosmic
ray situation is WORSENING. Cosmic rays hitting Earth are bad and are
getting worse. That’s the conclusion of a new paper just published in
the research journal Space Weather, showing that radiation from deep
space is dangerous and intensifying faster than previously predicted.
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| Cosmic rays were discovered unexpectedly in 1912. It is now known that
most cosmic rays are atomic nuclei. Most are hydrogen nuclei, some are
helium nuclei, and the rest heavier elements. The relative abundance
changes with cosmic ray energy, with the highest energy cosmic rays tend
to be heavier nuclei. Although many of the low energy cosmic rays come
from our Sun, the origins of the highest energy cosmic rays remains
unknown and a topic of much research. This drawing illustrates air
showers from very high energy cosmic rays. Cosmic rays may even be
important to Earth’s weather, as common lightning may be triggered by
passing cosmic rays. via APOD |
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:
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| Cosmic rays in the Earth-Moon system were peaking at levels never before seen in the Space Age and the trend is worsening. |
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:
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| Previous work suggested a ~ 20% increase of dose rates from one solar
minimum to the next. In fact, the actual dose rates in the last 4 years
exceed the predictions by ~ 10%, showing that the radiation environment
is worsening even more rapidly than we expected. |
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
Spaceweather.com and 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 our planet’s atmosphere:
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| Even on Earth the increase in cosmic rays intensity is being felt. Space
weather balloon sensors show a 13% increase in radiation (X-rays and
gamma-rays) penetrating our planet’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
lightning, potentially altering weather and climate. Furthermore, there
are studies linking cosmic rays with
cardiac arrhythmias in the general population.
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| This plot displays radiation measurements not only in the stratosphere,
but also at aviation altitudes. Dose rates are expessed as multiples of
sea level. For instance, we see that boarding a plane that flies at
25,000 feet exposes passengers to dose rates ~10x higher than sea level.
At 40,000 feet, the multiplier is closer to 50x. These measurements are
made by our usual cosmic ray payload as it passes through aviation
altitudes en route to the stratosphere over California. via Spaceweather |
Why are cosmic rays intensifying?
The main reason is the sun. Solar storm clouds such as coronal mass
ejections (CMEs) sweep aside cosmic rays when they pass by Earth. During
Solar Maximum, CMEs are abundant and cosmic rays are held at bay. Now,
however, the solar cycle is swinging toward Solar Minimum, allowing
cosmic rays to return. Another reason could be the weakening of Earth’s magnetic field, which helps protect us from deep-space radiation.
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.
