Cosmic radiation is a form of energetic radiation that originates from sources beyond Earth. It consists of high-energy particles continuously streaming through space. This natural background radiation reaches Earth, with the amount varying due to factors like elevation, atmospheric conditions, and the planet’s magnetic field.
Where Cosmic Radiation Comes From
Cosmic radiation primarily originates from two sources: Galactic Cosmic Rays (GCRs) and Solar Energetic Particles (SEPs). GCRs are high-energy particles that travel from outside our solar system. Supernovae, the explosive remnants of massive stars, are thought to be a significant source of GCRs within our Milky Way galaxy.
GCRs are composed mostly of atomic nuclei, traveling at nearly the speed of light. Approximately 90% of GCRs are protons (hydrogen nuclei), about 9% are alpha particles (helium nuclei), and the remaining 1% are nuclei of heavier elements, including those up to uranium. These charged particles are influenced by magnetic fields as they traverse interstellar space, making it difficult to trace their exact origins.
Solar Energetic Particles (SEPs) originate from the Sun, primarily during explosive events such as solar flares and coronal mass ejections (CMEs). SEPs are composed of high-energy protons, electrons, and heavy ions, with energies ranging from tens of keV to several GeV.
These particles can reach Earth in a matter of minutes, though SEP events can last for days. Researchers have traced the origin of some SEPs to plasma in the Sun’s corona, which is then accelerated by these powerful solar eruptions.
How Cosmic Radiation Interacts
Earth’s natural defenses, its magnetic field and atmosphere, play a role in mitigating cosmic radiation. The Earth’s magnetic field, generated by the movement of molten iron in the planet’s outer core, creates a protective bubble called the magnetosphere. This magnetic shield deflects most charged cosmic ray particles, preventing them from directly reaching the atmosphere.
The magnetosphere’s protective capacity varies, being strongest at the equator and weakest near the poles, where some particles can enter and create auroras. The magnetic field generally repels harmful solar and cosmic particle radiation.
The Earth’s atmosphere provides a second layer of defense, absorbing and scattering much of the remaining radiation. When primary cosmic ray particles collide with atoms in the upper atmosphere, they produce showers of secondary particles. Very few of these secondary particles reach ground level, and those that do have significantly less energy than the original cosmic rays, making them generally safe.
In environments without such natural shielding, like deep space or on the Moon and Mars, exposure to cosmic radiation increases substantially. Astronauts in deep space are constantly bombarded by a complex field of high-energy protons and atomic nuclei. On the lunar surface or Mars, without a substantial atmosphere or strong magnetic field, radiation levels are much higher than on Earth.
Effects on Biological Systems and Technology
Cosmic radiation poses health risks to biological systems, particularly for astronauts on extended space missions. Space radiation, composed of various charged particles, can penetrate the human body at near-light speeds, causing damage at the cellular level. This damage primarily affects DNA, leading to breaks in strands or alterations to DNA bases.
While cells attempt to repair this damage, misrepairs can lead to mutations, and the accumulation of these mutations over time can increase the risk of cancer. Beyond cancer, cosmic radiation exposure can also affect the central nervous system, potentially leading to cognitive impairment and memory deficits. The cardiovascular system is also susceptible, with possible damage to the heart, hardening of arteries, and loss of blood vessel lining cells, which can contribute to cardiovascular disease.
For technology, cosmic radiation can cause single-event upsets (SEUs) in electronic devices. An SEU is a temporary change in the logic state of a circuit, often caused by a high-energy particle, like a cosmic ray, striking a sensitive area within a microcircuit. This impact deposits enough charge to flip a bit from one state to another (e.g., 0 to 1 or vice versa).
SEUs can lead to a range of malfunctions, from minor glitches to system-wide failures in spacecraft and satellites. As electronic components become smaller and more energy-efficient, they become increasingly susceptible to SEUs. These events can corrupt data in memory, disrupt software, or cause central processing units to halt, potentially impacting mission operations.
Protecting Against Cosmic Radiation
Protecting against cosmic radiation involves a combination of passive shielding, active shielding concepts, and careful mission planning. Passive shielding utilizes materials placed between the radiation source and the target to absorb radiation. Hydrogen-rich materials, such as polyethylene, water, and even liquid methane, are favored due to their effectiveness in attenuating charged particles and neutrons.
For example, a protective layer of water approximately 20 to 30 cm thick could reduce an astronaut’s radiation dose by 40% to 50%. While aluminum is also used, materials with lighter atoms like hydrogen and carbon are generally more effective because they produce fewer harmful secondary particles upon interaction.
Active shielding concepts, still largely in developmental stages, aim to deflect charged particles using electric or magnetic fields before they interact with spacecraft materials. These methods theoretically offer superior protection by preventing the generation of secondary particles. However, the engineering challenges of generating and maintaining the extremely strong electric or magnetic fields required in space are substantial.
Operational measures are also integrated into mission planning to minimize exposure. This includes timing missions to avoid periods of peak solar activity, as increased solar activity can intensify radiation levels. Selecting mission trajectories that reduce travel time and choosing landing sites on celestial bodies with natural shielding are also considered.